Environmental adaptation: genomic analysis of the piezotolerant and psychrotolerant deep-sea iron reducing bacterium Shewanella piezotolerans WP3

Cold-active enzymes from deep marine psychrophiles: harnessing their potential in enhanced food production and sustainability

Exploring the untapped potential of deep-sea microorganisms, particularly their cold-active enzymes, or psychrozymes, offers exciting possibilities for revolutionizing various aspects of the food processing industry. This review focuses on these enzymes, derived from the largely unexplored depths of the deep ocean, where microorganisms have developed unique adaptations to extreme conditions. Psychrozymes, as bioactive molecules, hold significant promise for food industry applications. However, despite their potential, the understanding and industrial utilization of psychrozymes remains limited. This review provides an in-depth analysis of how psychrozymes can: improve processing efficiency, enhance sensory qualities, extend product shelf life, and reduce energy consumption across the food production chain. We explore the cryodefense strategies and cold-adaptation mechanisms that support these enzymes, shedding light on the most extensively studied psychrozymes and assessing their journey from theoretical applications to practical use in food production. The key properties, such as stability, substrate specificity, and catalytic efficiency in cold environments, are also discussed. Although psychrozymes show considerable promise, their large-scale application in the food industry remains largely unexplored. This review emphasizes the need for further research to unlock the full potential of psychrozymes, encouraging their broader integration into the food sector to contribute to more sustainable food production processes.

Biological and Chemical Processes of Nitrate Reduction and Ferrous Oxidation Mediated by Shewanella oneidensis MR-1

Iron, Earth's most abundant redox-active metal, undergoes both abiotic and microbial redox reactions that regulate the formation, transformation, and dissolution of iron minerals. The electron transfer between ferrous iron (Fe(II)) and ferric iron (Fe(III)) is critical for mineral dynamics, pollutant remediation, and global biogeochemical cycling. Bacteria play a significant role, especially in anaerobic Fe(II) oxidation, contributing to Fe(III) mineral formation in oxygen-depleted environments. In iron-rich, neutral anaerobic settings, microbial nitrate-reducing Fe(II) oxidation (NRFO) and iron reduction processes happen simultaneously. This study used Shewanella oneidensis MR-1 to create an anaerobic NRFO system between Fe(II) and nitrate, revealing concurrent Fe(II) oxidation and nitrate reduction. Both gene-mediated biological Fe(II) oxidation and chemical Fe(II) oxidation, facilitated by nitrite (a byproduct of nitrate reduction), were observed. The MtrABC gene cluster was linked to this process. At low Fe(II) concentrations, toxicity and mineral precipitation inhibited nitrate reduction by Shewanella oneidensis MR-1, whereas high Fe(II) levels led to Fe(II) oxidation, resulting in cell encrustation, which further constrained nitrate reduction.

Comparative genomic analysis of Stenotrophomonas maltophilia unravels their genetic variations and versatility trait

Stenotrophomonas maltophilia is a species with immensely broad phenotypic and genotypic diversity that could widely distribute in natural and clinical environments. However, little attention has been paid to reveal their genome plasticity to diverse environments. In the present study, a comparative genomic analysis of S. maltophilia isolated from clinical and natural sources was systematically explored its genetic diversity of 42 sequenced genomes. The results showed that S. maltophilia owned an open pan-genome and had strong adaptability to different environments. A total of 1612 core genes were existed with an average of 39.43% of each genome, and the shared core genes might be necessary to maintain the basic characteristics of those S. maltophilia strains. Based on the results of the phylogenetic tree, the ANI value, and the distribution of accessory genes, genes associated with the fundamental process of those strains from the same habitat were found to be mostly conserved in evolution. Isolates from the same habitat had a high degree of similarity in COG category, and the most significant KEGG pathways were mainly involved in carbohydrate and amino acid metabolism, indicating that genes related to essential processes were mostly conserved in evolution for the clinical and environmental settings. Meanwhile, the number of resistance and efflux pump gene was significantly higher in the clinical setting than that of in the environmental setting. Collectively, this study highlights the evolutionary relationships of S. maltophilia isolated from clinical and environmental sources, shedding new light on its genomic diversity.

The methanogen core and pangenome: conservation and variability across biology's growth temperature extremes

Temperature is a key variable in biological processes. However, a complete understanding of biological temperature adaptation is lacking, in part because of the unique constraints among different evolutionary lineages and physiological groups. Here we compared the genomes of cultivated psychrotolerant and thermotolerant methanogens, which are physiologically related and span growth temperatures from -2.5°C to 122°C. Despite being phylogenetically distributed amongst three phyla in the archaea, the genomic core of cultivated methanogens comprises about one-third of a given genome, while the genome fraction shared by any two organisms decreases with increasing phylogenetic distance between them. Increased methanogenic growth temperature is associated with reduced genome size, and thermotolerant organisms-which are distributed across the archaeal tree-have larger core genome fractions, suggesting that genome size is governed by temperature rather than phylogeny. Thermotolerant methanogens are enriched in metal and other transporters, and psychrotolerant methanogens are enriched in proteins related to structure and motility. Observed amino acid compositional differences between temperature groups include proteome charge, polarity and unfolding entropy. Our results suggest that in the methanogens, shared physiology maintains a large, conserved genomic core even across large phylogenetic distances and biology's temperature extremes.

Characterization of the pathogenicity of a Bacillus cereus isolate from the Mariana Trench

Bacillus cereus is an important opportunistic pathogen widely distributed in the environment. In this study, we reported the isolation and characterization of a B. cereus isolate, MB1, from the Challenger Deep of the Mariana Trench. MB1 is aerobic, motile, and able to form endospores. It possesses 5966 genes distributed on a circular chromosome and two plasmids. The MB1 genome contains 14 sets of 23S, 5S, and 16S ribosomal RNA operons, 106 tRNA genes, 4 sRNA genes, 12 genomic islands, 13 prophages, and 302 putative virulence genes, including enterotoxins and cytolysins. Infection studies showed that MB1 was able to cause acute and lethal infection in fish and mice, and was highly toxic to mammalian cells. MB1 induced, in a dose-dependent manner, pyroptotic cell death, characterized by activation of caspase-1, cleavage of gasdermin D, and release of IL-1β and IL-18. MB1 spores exhibited swimming and haemolytic capacity, but were severely attenuated in pathogenicity, which, however, was regained to the full extent when the spores germinated under suitable conditions. Taken together, these results provide new insights into the biological and pathogenic mechanism of deep sea B. cereus.

Global occurrence of the bacteria with capability for extracellular reduction of iodate

The γ-proteobacterium Shewanella oneidensis MR-1 reduces iodate to iodide extracellularly. Both dmsEFAB and mtrCAB gene clusters are involved in extracellular reduction of iodate by S. oneidensis MR-1. DmsEFAB reduces iodate to hypoiodous acid and hydrogen peroxide (H₂O₂). Subsequently, H₂O₂ is reduced by MtrCAB to facilitate DmsEFAB-mediated extracellular reduction of iodate. To investigate the distribution of bacteria with the capability for extracellular reduction of iodate, bacterial genomes were systematically searched for both dmsEFAB and mtrCAB gene clusters. The dmsEFAB and mtrCAB gene clusters were found in three Ferrimonas and 26 Shewanella species. Coexistence of both dmsEFAB and mtrCAB gene clusters in these bacteria suggests their potentials for extracellular reduction of iodate. Further analyses demonstrated that these bacteria were isolated from a variety of ecosystems, including the lakes, rivers, and subsurface rocks in East and Southeast Asia, North Africa, and North America. Importantly, most of the bacteria with both dmsEFAB and mtrCAB gene clusters were found in different marine environments, which ranged from the Arctic Ocean to Antarctic coastal marine environments as well as from the Atlantic Ocean to the Indian and Pacific Oceans. Widespread distribution of the bacteria with capability for extracellular reduction of iodate around the world suggests their significant importance in global biogeochemical cycling of iodine. The genetic organization of dmsEFAB and mtrCAB gene clusters also varied substantially. The identified mtrCAB gene clusters often contained additional genes for multiheme c-type cytochromes. The numbers of dmsEFAB gene cluster detected in a given bacterial genome ranged from one to six. In latter, duplications of dmsEFAB gene clusters occurred. These results suggest different paths for these bacteria to acquire their capability for extracellular reduction of iodate.

The Roles of DmsEFAB and MtrCAB in Extracellular Reduction of Iodate by Shewanella oneidensis MR-1 with Lactate as the Sole Electron Donor

To investigate their roles in extracellular reduction of iodate (IO₃ ^- ) with lactate as an electron donor, the gene clusters of dmsEFAB, mtrCAB, mtrDEF, and so4360-4357 in Shewanella oneidensis MR-1were systematically deleted. Deletions of dmsEFAB and/or mtrCAB gene clusters diminished the bacterial ability to reduce IO₃ ^- . Furthermore, DmsEFAB and MtrCAB worked collaboratively to reduce IO₃ ^- of which DmsEFAB played a more dominant role than MtrCAB. MtrCAB was involved in detoxifying the reaction intermediate hydrogen peroxide (H₂ O₂ ). The reaction intermediate hypoiodous acid (HIO) was also found to inhibit microbial IO₃ ^- reduction. SO4360-4357 and MtrDEF, however, were not involved in IO₃ ^- reduction. Collectively, these results suggest a novel mechanism of extracellular reduction of IO₃ ^- at molecular level, in which DmsEFAB reduces IO₃ ^- to HIO and H₂ O₂ . The latter is further reduced to H₂ O by MtrCAB to facilitate the DmsEFAB-mediated IO₃ ^- reduction. The extracellular electron transfer pathway of S. oneidensis MR-1is believed to mediate electron transfer from bacterial cytoplasmic membrane, across the cell envelope to the DmsEFAB and MtrCAB on the bacterial outer membrane.

Significance of Shewanella Species for the Phytoavailability and Toxicity of Arsenic-A Review

Simple Summary

The availability of some toxic heavy metals, such as arsenic (As), is related to increased human and natural activities. This type of metal availability in the environment is associated with various health and environmental issues. Such problems may arise due to direct contact with or consumption of plant products containing this metal in some of their parts. A microbial approach that employs a group of bacteria (Shewanella species) is proposed to reduce the negative consequences of the availability of this metal (As) in the environment. This innovative strategy can reduce As mobility, its spread, and uptake by plants in the environment. The benefits of this approach include its low cost and the possibility of not exposing other components of the environment to unfavourable consequences.

Abstract

The distribution of arsenic continues due to natural and anthropogenic activities, with varying degrees of impact on plants, animals, and the entire ecosystem. Interactions between iron (Fe) oxides, bacteria, and arsenic are significantly linked to changes in the mobility, toxicity, and availability of arsenic species in aquatic and terrestrial habitats. As a result of these changes, toxic As species become available, posing a range of threats to the entire ecosystem. This review elaborates on arsenic toxicity, the mechanisms of its bioavailability, and selected remediation strategies. The article further describes how the detoxification and methylation mechanisms used by Shewanella species could serve as a potential tool for decreasing phytoavailable As and lessening its contamination in the environment. If taken into account, this approach will provide a globally sustainable and cost-effective strategy for As remediation and more information to the literature on the unique role of this bacterial species in As remediation as opposed to conventional perception of its role as a mobiliser of As.

The origin and impeded dissemination of the DNA phosphorothioation system in prokaryotes

Phosphorothioate (PT) modification by the dnd gene cluster is the first identified DNA backbone modification and constitute an epigenetic system with multiple functions, including antioxidant ability, restriction modification, and virus resistance. Despite these advantages for hosting dnd systems, they are surprisingly distributed sporadically among contemporary prokaryotic genomes. To address this ecological paradox, we systematically investigate the occurrence and phylogeny of dnd systems, and they are suggested to have originated in ancient Cyanobacteria after the Great Oxygenation Event. Interestingly, the occurrence of dnd systems and prophages is significantly negatively correlated. Further, we experimentally confirm that PT modification activates the filamentous phage SW1 by altering the binding affinity of repressor and the transcription level of its encoding gene. Competition assays, concurrent epigenomic and transcriptomic sequencing subsequently show that PT modification affects the expression of a variety of metabolic genes, which reduces the competitive fitness of the marine bacterium Shewanella piezotolerans WP3. Our findings strongly suggest that a series of negative effects on microorganisms caused by dnd systems limit horizontal gene transfer, thus leading to their sporadic distribution. Overall, our study reveals putative evolutionary scenario of the dnd system and provides novel insights into the physiological and ecological influences of PT modification.

Response of Bacteria to Mechanical Stimuli

Abstract—

Bacteria adapt rapidly to changes in ambient conditions, constantly inspecting their surroundings by means of their sensor systems. These systems are often thought to respond only to signals of a chemical nature. Yet, bacteria are often affected by mechanical forces, e.g., during transition from planktonic to sessile state. Mechanical stimuli, however, have seldom been considered as the signals bacteria can sense and respond to. Nonetheless, bacteria perceive mechanical stimuli, generate signals, and develop responses. This review analyzes the information on the way bacteria respond to mechanical stimuli and outlines how bacteria convert incoming signals into appropriate responses.

A deep-sea bacterium related to coastal marine pathogens

Evolution of virulence traits from adaptation to environmental niches other than the host is probably a common feature of marine microbial pathogens, whose knowledge might be crucial to understand their emergence and pathogenetic potential. Here, we report genome sequence analysis of a novel marine bacterial species, Vibrio bathopelagicus sp. nov., isolated from warm bathypelagic waters (3309 m depth) of the Mediterranean Sea. Interestingly, V. bathopelagicus sp. nov. is closely related to coastal Vibrio strains pathogenic to marine bivalves. V. bathopelagicus sp. nov. genome encodes genes involved in environmental adaptation to the deep-sea but also in virulence, such as the R5.7 element, MARTX toxin cluster, Type VI secretion system and zinc-metalloprotease, previously associated with Vibrio infections in farmed oysters. The results of functional in vitro assays on immunocytes (haemocytes) of the Mediterranean mussel Mytilus galloprovincialis and the Pacific oyster Crassostrea gigas, and of the early larval development assay in Mytilus support strong toxicity of V. bathopelagicus sp. nov. towards bivalves. V. bathopelagicus sp. nov., isolated from a remote Mediterranean bathypelagic site, is an example of a planktonic marine bacterium with genotypic and phenotypic traits associated with animal pathogenicity, which might have played an evolutionary role in the origin of coastal marine pathogens.

Condition-Specific Molecular Network Analysis Revealed That Flagellar Proteins Are Involved in Electron Transfer Processes of Shewanella piezotolerans WP3

Because of the ability to metabolize a large number of electron acceptors such as nitrate, nitrite, fumarate, and metal oxides, Shewanella species have attracted much attention in recent years. Generally, the use of these electron acceptors is mainly achieved through electron transfer proteins and their interactions which will dynamically change across different environmental conditions in cells. Therefore, functional analysis of condition-specific molecular networks can reveal biological information on electron transfer processes. By integrating expression data and molecular networks, we constructed condition-specific molecular networks for Shewanella piezotolerans WP3. We then identified condition-specific key genes and studied their potential functions with an emphasis on their roles in electron transfer processes. Functional module analysis showed that different flagellar assembly modules appeared under these conditions and suggested that flagellar proteins are important for these conditions. We also identified the electron transfer modules underlying these various environmental conditions. The present results could help with screening electron transfer genes and understanding electron transfer processes under various environmental conditions for the Shewanella species.

Thermococcus aciditolerans sp. nov., a piezotolerant, hyperthermophilic archaeon isolated from a deep-sea hydrothermal vent chimney in the Southwest Indian Ridge

A hyperthermophilic, strictly anaerobic archaeon, designated strain SY113^T, was isolated from a deep-sea hydrothermal vent chimney on the Southwest Indian Ridge at a water depth of 2770 m. Enrichment and isolation of strain SY113^T were performed at 85 °C at 0.1 MPa. Cells of strain SY113^T were irregular motile cocci with peritrichous flagella and generally 0.8-2.4 µm in diameter. Growth was observed at temperatures between 50 and 90 °C (optimum at 85 °C) and under hydrostatic pressures of 0.1-60 MPa (optimum, 27 MPa). Cells of SY113^T grew at pH 4.0-9.0 (optimum, pH 5.5) and a NaCl concentration of 0.5-5.5 % (w/v; optimum concentration, 3.0 % NaCl). Strain SY113^T was an anaerobic chemoorganoheterotroph and grew on complex proteinaceous substrates such as yeast extract and tryptone, as well as on maltose and starch. Elemental sulphur stimulated growth, but not obligatory for its growth. The G+C content of the genomic DNA was 55.0 mol%. Phylogenetic analysis of the 16S rRNA sequence of strain SY113^T showed that the novel isolate belonged to the genus Thermococcus. On the basis of physiological characteristics, average nucleotide identity values and in silico DNA-DNA hybridization results, we propose a novel species, named Thermococcus aciditolerans sp. nov. The type strain is SY113^T (=MCCC 1K04190^T=JCM 39083^T).

Genome sequence analysis of deep sea Aspergillus sydowii BOBA1 and effect of high pressure on biodegradation of spent engine oil

A deep-sea fungus Aspergillus sydowii BOBA1 isolated from marine sediment at a depth of 3000 m was capable of degrading spent engine (SE) oil. The response of immobilized fungi towards degradation at elevated pressure was studied in customized high pressure reactors without any deviation in simulating in situ deep-sea conditions. The growth rate of A. sydowii BOBA1 in 0.1 MPa was significantly different from the growth at 10 MPa pressure. The degradation percentage reached 71.2 and 82.5% at atmospheric and high pressure conditions, respectively, within a retention period of 21 days. The complete genome sequence of BOBA1 consists of 38,795,664 bp in size, comprises 2582 scaffolds with predicted total coding genes of 18,932. A total of 16,247 genes were assigned with known functions and many families found to have a potential role in PAHs and xenobiotic compound metabolism. Functional genes controlling the pathways of hydrocarbon and xenobiotics compound degrading enzymes such as dioxygenase, decarboxylase, hydrolase, reductase and peroxidase were identified. The spectroscopic and genomic analysis revealed the presence of combined catechol, gentisate and phthalic acid degradation pathway. These results of degradation and genomic studies evidenced that this deep-sea fungus could be employed to develop an eco-friendly mycoremediation technology to combat the oil polluted marine environment. This study expands our knowledge on piezophilic fungi and offer insight into possibilities about the fate of SE oil in deep-sea.

A glimpse of deep-sea adaptation in chemosynthetic holobionts: Depressurization causes DNA fragmentation and cell death of methanotrophic endosymbionts rather than their deep-sea Bathymodiolinae host

Bathymodiolinae mussels are typical species in deep-sea cold seeps and hydrothermal vents and an ideal model for investigating chemosynthetic symbiosis and the influence of high hydrostatic pressure on deep-sea organisms. Herein, the potential influence of depressurization on DNA fragmentation and cell death in Bathymodiolinae hosts and their methanotrophic symbionts were surveyed using isobaric and unpressurized samples. As a hallmark of cell death, massive DNA fragmentation was observed in methanotrophic symbionts from unpressurized Bathymodiolinae while several endonucleases and restriction enzymes were upregulated. Additionally, genes involved in DNA repair, glucose/methane metabolism as well as two-component regulatory system were also differentially expressed in depressurized symbionts. DNA fragmentation and programmed cell death, however, were rarely detected in the host bacteriocytes owing to the orchestrated upregulation of inhibitor of apoptosis genes and downregulation of caspase genes. Meanwhile, diverse host immune recognition receptors were promoted during depressurization, probably enabling the regain of symbionts. When the holobionts were subjected to a prolonged acclimation at atmospheric pressure, alternations in both the DNA fragmentation and the expression atlas of aforesaid genes were continuously observed in symbionts, demonstrating the persistent influence of depressurization. Contrarily, the host cells demonstrated certain tolerance against depressurization stress as expression level of some immune-related genes returned to the basal level in isobaric samples. Altogether, the present study illustrates the distinct stress responses of Bathymodiolinae hosts and their methanotrophic symbionts against depressurization, which could provide further insight into the deep-sea adaptation of Bathymodiolinae holobionts while highlighting the necessity of using isobaric sampling methods in deep-sea research.

Transcriptomic Analysis Reveals Common Adaptation Mechanisms Under Different Stresses for Moderately Piezophilic Bacteria

Piezophiles, by the commonly accepted definition, grow faster under high hydrostatic pressure (HHP) than under ambient pressure and are believed to exist only in pressurized environments where life has adapted to HHP during evolution. However, recent findings suggest that piezophiles have developed a common adaptation strategy to cope with multiple types of stresses including HHP. These results raise a question on the ecological niches of piezophiles: are piezophiles restricted to habitats with HHP? In this study, we observed that the bacterial strains Sporosarcina psychrophila DSM 6497 and Lysinibacillus sphaericus LMG 22257, which were isolated from surface environments and then transferred under ambient pressure for half a century, possess moderately piezophilic characteristics with optimal growth pressures of 7 and 20 MPa, respectively. Their tolerance to HHP was further enhanced by MgCl₂ supplementation under the highest tested pressure of 50 MPa. Transcriptomic analysis was performed to compare gene expression with and without MgCl₂ supplementation under 50 MPa for S. psychrophila DSM 6497. Among 4390 genes or transcripts obtained, 915 differentially expressed genes (DEGs) were identified. These DEGs are primarily associated with the antioxidant defense system, intracellular compatible solute accumulation, and membrane lipid biosynthesis, which have been reported to be essential for cells to cope with HHP. These findings indicate no in situ pressure barrier for piezophile isolation, and cells may adopt a common adaptation strategy to cope with different stresses.

Distinctive gene and protein characteristics of extremely piezophilic Colwellia

Background

The deep ocean is characterized by low temperatures, high hydrostatic pressures, and low concentrations of organic matter. While these conditions likely select for distinct genomic characteristics within prokaryotes, the attributes facilitating adaptation to the deep ocean are relatively unexplored. In this study, we compared the genomes of seven strains within the genus Colwellia, including some of the most piezophilic microbes known, to identify genomic features that enable life in the deep sea.

Results

Significant differences were found to exist between piezophilic and non-piezophilic strains of Colwellia. Piezophilic Colwellia have a more basic and hydrophobic proteome. The piezophilic abyssal and hadal isolates have more genes involved in replication/recombination/repair, cell wall/membrane biogenesis, and cell motility. The characteristics of respiration, pilus generation, and membrane fluidity adjustment vary between the strains, with operons for a nuo dehydrogenase and a tad pilus only present in the piezophiles. In contrast, the piezosensitive members are unique in having the capacity for dissimilatory nitrite and TMAO reduction. A number of genes exist only within deep-sea adapted species, such as those encoding d-alanine-d-alanine ligase for peptidoglycan formation, alanine dehydrogenase for NADH/NAD⁺ homeostasis, and a SAM methyltransferase for tRNA modification. Many of these piezophile-specific genes are in variable regions of the genome near genomic islands, transposases, and toxin-antitoxin systems.

Conclusions

We identified a number of adaptations that may facilitate deep-sea radiation in members of the genus Colwellia, as well as in other piezophilic bacteria. An enrichment in more basic and hydrophobic amino acids could help piezophiles stabilize and limit water intrusion into proteins as a result of high pressure. Variations in genes associated with the membrane, including those involved in unsaturated fatty acid production and respiration, indicate that membrane-based adaptations are critical for coping with high pressure. The presence of many piezophile-specific genes near genomic islands highlights that adaptation to the deep ocean may be facilitated by horizontal gene transfer through transposases or other mobile elements. Some of these genes are amenable to further study in genetically tractable piezophilic and piezotolerant deep-sea microorganisms.

Porin from Marine Bacterium Marinomonas primoryensis KMM 3633T: Isolation, Physico-Chemical Properties, and Functional Activity

Marinomonas primoryensis KMM 3633^T, extreme living marine bacterium was isolated from a sample of coastal sea ice in the Amursky Bay near Vladivostok, Russia. The goal of our investigation is to study outer membrane channels determining cell permeability. Porin from M. primoryensis KMM 3633^T (MpOmp) has been isolated and characterized. Amino acid analysis and whole genome sequencing were the sources of amino acid data of porin, identified as Porin_4 according to the conservative domain searching. The amino acid composition of MpOmp distinguished by high content of acidic amino acids and low content of sulfur-containing amino acids, but there are no tryptophan residues in its molecule. The native MpOmp existed as a trimer. The reconstitution of MpOmp into black lipid membranes demonstrated its ability to form ion channels whose conductivity depends on the electrolyte concentration. The spatial structure of MpOmp had features typical for the classical gram-negative porins. However, the oligomeric structure of isolated MpOmp was distinguished by very low stability: heat-modified monomer was already observed at 30 °C. The data obtained suggest the stabilizing role of lipids in the natural membrane of marine bacteria in the formation of the oligomeric structure of porin.

The thermo-regulated genetic switch of deep-sea filamentous phage SW1 and its distribution in the Pacific Ocean

Viruses, especially bacteriophages, are thought to have important functions in the deep-sea ecosystem, but little is known about the induction mechanism of benthic phages in response to environmental change. Our prior work characterized a cold-active filamentous phage SW1 that infects the deep-sea bacterium Shewanella piezotolerans WP3; however, the underlying mechanism of the putative thermo-regulated genetic switch of SW1 is still unclear. In this study, the DNA copy number and mRNA abundance of the deep-sea phage SW1 were quantified in the whole life cycle of its host S. piezotolerans WP3 at different temperatures. Our results demonstrated that the induction of SW1 is dependent on a threshold temperature (4°C), but this dependency is not proportional to temperature gradient. RNA-Seq analyses revealed two highly transcribed regions at 4°C and verified the presence of a long 3' untranslated region (UTR) in the SW1 genome. Interestingly, recruitment analysis showed that SW1-like inoviruses prevail in deep sea (depth >1000 m) and photic epipelagic and mesopelagic zones (depth <1000 m), which suggested that the thermo-regulated genetic switch revealed in SW1 may be widely distributed in the ocean.

Flagellation of Shewanella oneidensis Impacts Bacterial Fitness in Different Environments

Flagella occur on many prokaryotes, which primarily propel cells to move from detrimental to favorable environments. A variety of species-specific flagellation patterns have been identified. Although it is presumed that for each of these flagellated microorganisms, an evolutionarily fixed flagellation pattern is favored under the normal living conditions, direct evidence is lacking. Here, we use Shewanella oneidensis, a rod-shaped Gram-negative bacterium with a monotrichous polar flagellum (MR-1, the wild-type), as a research model. The investigation has been enabled by multiple mutants with diverse flagellation patterns that had been generated by removing FlhF and FlhG proteins that control flagellar location and number, respectively. Growth assays, as a measure of fitness, revealed that the wild-type strain predominated in spreading on swim plates and in pellicles which form at the air-liquid interface. However, under the pellicles where oxygen is limited, both aflagellated and monotrichous lateral strains showed similar increase in fitness, whereas strains with multiple flagella were less competitive. Moreover, under shaking culturing conditions, the aflagellated strain outcompeted all other strains, including the wild-type, suggesting that cells devoid of flagella would be more likely enriched upon agitation. Overall, these data support the presumption that the monotrichous polar flagellum, as evolutionarily fixed in the wild-type strain, is optimal for the growth fitness of S. oneidensis over any other mutants under most test conditions. However, upon specific changes of environmental conditions, another form could come to predominate. These findings provide insight into the impacts of flagellation patterns and function on bacterial adaptation to differing environments.

Isolation of Gram-positive Firmibacteria as major eicosapentaenoic acid producers from subtropical marine sediments

In this study, a total of 172 putative omega-3 producers were isolated from 28 sediment samples from the Arabian Gulf employing a selective isolation procedure using marine agar containing 0·1% triphenyl tetrazolium chloride (TTC). Out of these 172 isolates, 19 isolates produced eicosapentaenoic acid (EPA) as confirmed by Gas Chromatography-Mass Spectrometry (GC-MS). The EPA content of the isolated bacterial strain varied from 1·76 to 6·52% of total fatty acids. Among the 19 isolates of EPA producers, while 17 isolates harboured both pfaA gene and Δ6 desaturase gene, only five isolates harboured Δ5 desaturase gene. Two of the EPA positive strains harbour none of the three genes tested. The 16s RNA identification of these isolates revealed that except one, all the EPA producers were Gram-positive marine bacteria belonging to the phylum Firmicutes, family Bacillacea, genera Bacillus and Oceanobacillus. Halomonas pacifica was the only Gram-negative Gamma-Proteobacteria detected to produce EPA from this region. SIGNIFICANCE AND IMPACT OF THE STUDY: Recently, marine bacteria are considered as a promising source of polyunsaturated fatty acid (PUFA) over marine fishes and microalgae. PUFA producers reported from polar and deep-sea sources were restricted to five well-known marine genera under two distinct domains of bacteria such as proteobacteria (Shewanella, Colwellia, and Moritella) and cytophaga group (Flexibacter, Psychroflexus). This study revealed that subtropical marine environment could also be the source of PUFA producing bacteria, and they predominantly belonged to the class of Firmibacteria. This finding opens up new avenue for research to study the inherent mechanism and physiology of such organisms from this unique environment.

A First Study of the Virulence Potential of a Bacillus subtilis Isolate From Deep-Sea Hydrothermal Vent

Bacillus subtilis is the best studied Gram-positive bacterium, primarily as a model of cell differentiation and industrial exploitation. To date, little is known about the virulence of B. subtilis. In this study, we examined the virulence potential of a B. subtilis strain (G7) isolated from the Iheya North hydrothermal field of Okinawa Trough. G7 is aerobic, motile, endospore-forming, and requires NaCl for growth. The genome of G7 is composed of one circular chromosome of 4,216,133 base pairs with an average GC content of 43.72%. G7 contains 4,416 coding genes, 27.5% of which could not be annotated, and the remaining 72.5% were annotated with known or predicted functions in 25 different COG categories. Ten sets of 23S, 5S, and 16S ribosomal RNA operons, 86 tRNA and 14 sRNA genes, 50 tandem repeats, 41 mini-satellites, one microsatellite, and 42 transposons were identified in G7. Comparing to the genome of the B. subtilis wild type strain NCIB 3610^T, G7 genome contains many genomic translocations, inversions, and insertions, and twice the amount of genomic Islands (GIs), with 42.5% of GI genes encoding hypothetical proteins. G7 possesses abundant putative virulence genes associated with adhesion, invasion, dissemination, anti-phagocytosis, and intracellular survival. Experimental studies showed that G7 was able to cause mortality in fish and mice following intramuscular/intraperitoneal injection, resist the killing effect of serum complement, and replicate in mouse macrophages and fish peripheral blood leukocytes. Taken together, our study indicates that G7 is a B. subtilis isolate with unique genetic features and can be lethal to vertebrate animals once being introduced into the animals by artificial means. These results provide the first insight into the potential harmfulness of deep-sea B. subtilis.

Microevolution and Adaptive Strategy of Psychrophilic Species Flavobacterium bomense sp. nov. Isolated From Glaciers

Numerous mountain glaciers located on the Tibetan Plateau are inhabited by abundant microorganisms. The microorganisms on the glacier surface are exposed to the cold, barren, and high-ultraviolet radiation environments. Although the microbial community composition on glaciers has been revealed by high-throughput sequencing, little is known about the microevolution and adaptive strategy of certain bacterial populations. In this study, we used a polyphasic approach to determine the taxonomic status of 11 psychrophilic Flavobacterium strains isolated from glaciers on the Tibetan Plateau and performed a comparative genomic analysis. The phylogenetic tree based on the concatenated single-copy gene sequences showed the 11 strains clustered together, forming a distinct and novel clade in the genus Flavobacterium. The average nucleotide identity (ANI) values among these strains were higher than 96%. However, the values much lower than 90% between them and related species indicated that they represent a novel species and the name Flavobacterium bomense sp. nov. is proposed. The core and accessory genomes of strains in this new Flavobacterium species showed diverse distinct patterns of gene content and metabolism pathway. In order to infer the driving evolutionary forces of the core genomes, homologous recombination was found to contribute twice as much to nucleotide substitutions as mutations. A series of genes encoding proteins with known or predicted roles in cold adaptation were found in their genomes, for example, cold-shock protein, proteorhodopsin, osmoprotection, and membrane-related proteins. A comparative analysis of the group with optimal growth temperature (OGT) ≤ 20°C and the group with OGT > 20°C of the 32 Flavobacterium type strains and 11 new strains revealed multiple amino acid substitutions, including the decrease of the proline and glutamine content and the increase of the methionine and isoleucine content in the group with OGT ≤ 20°C, which may contribute to increased protein flexibility at low temperatures. Thus, this study discovered a novel Flavobacterium species in glaciers, which has high intraspecific diversity and multiple adaptation mechanisms that enable them to cope and thrive in extreme habitats.

Exploring the piezotolerant/piezophilic microbial community and genomic basis of piezotolerance within the deep subsurface Deccan traps

The deep biosphere is often characterized by multiple extreme physical-chemical conditions, of which pressure is an important parameter that influences life but remains less studied. This geomicrobiology study was designed to understand the response of a subterranean microbial community of the Deccan traps to high-pressure conditions and to elucidate their genomic properties. Groundwater from a deep basaltic aquifer of the Deccan traps was used to ascertain the community response to 25 MPa and 50 MPa pressure following enrichment in high-salt and low-salt organic media. Quantitative PCR data indicated a decrease in bacterial and archaeal cell numbers with increasing pressure. 16S rRNA gene sequencing displayed substantial changes in the microbial community in which Acidovorax appeared to be the most dominant genus in the low-salt medium and Microbacteriaceae emerged as the major family in the high-salt medium under both pressure conditions. Genes present in metagenome-associated genomes which have previously been associated with piezotolerance include those related to nutrient uptake and extracytoplasmic stress (omp, rseC), protein folding and unfolding (dnaK, groEL and others), and DNA repair mechanisms (mutT, uvr and others). We hypothesize that these genes facilitate tolerance to high pressure by certain groups of microbes residing in subsurface Deccan traps.

Genome analysis of Rubritalea profundi SAORIC-165T, the first deep-sea verrucomicrobial isolate, from the northwestern Pacific Ocean

Although culture-independent studies have shown the presence of Verrucomicrobia in the deep sea, verrucomicrobial strains from deep-sea environments have been rarely cultured and characterized. Recently, Rubritalea profundi SAORIC-165^T, a psychrophilic bacterium of the phylum Verrucomicrobia, was isolated from a depth of 2,000 m in the northwestern Pacific Ocean. In this study, the genome sequence of R. profundi SAORIC-165^T, the first deep-sea verrucomicrobial isolate, is reported with description of the genome properties and comparison to surface-borne Rubritalea genomes. The draft genome consisted of four contigs with an entire size of 4,167,407 bp and G+C content of 47.5%. The SAORIC-165^T genome was predicted to have 3,844 proteincoding genes and 45 non-coding RNA genes. The genome contained a repertoire of metabolic pathways, including the Embden-Meyerhof-Parnas pathway, pentose phosphate pathway, tricarboxylic acid cycle, assimilatory sulfate reduction, and biosynthesis of nicotinate/nicotinamide, pantothenate/coenzyme A, folate, and lycopene. The comparative genomic analyses with two surface-derived Rubritalea genomes showed that the SAORIC-165^T genome was enriched in genes involved in transposition of mobile elements, signal transduction, and carbohydrate metabolism, some of which might be related to bacterial enhancement of ecological fitness in the deep-sea environment. Amplicon sequencing of 16S rRNA genes from the water column revealed that R. profundi-related phylotypes were relatively abundant at 2,000 m and preferred a particle-associated life style in the deep sea. These findings suggest that R. profundi represents a genetically unique and ecologically relevant verrucomicrobial group well adapted to the deep-sea environment.

Anaerobic ammonium oxidation coupled to iron reduction in constructed wetland mesocosms

Acidimicrobiaceae sp. A6 (referred to as A6) was recently identified as playing a key role in the Feammox process (ammonium oxidation coupled to iron reduction). Two constructed wetlands (CW) were built and bioaugmented with A6 to determine if, under the right conditions, Feammox can be enhanced in CWs by having strata with higher iron content. Hence, the solid stratum in the CWs was sand, and one CW was augmented with ferrihydrite. Vertical ammonium (NH₄⁺) concentration profiles in the CW mesocosms were monitored regularly. After four months of operation, when reducing conditions were established in the CWs, they were inoculated with an enrichment culture containing A6 and monitored for an additional four months, after which they were dismantled and analyzed. During the four-month period after the A6 enrichment culture injection, 25.0 ± 7.3% of NH₄⁺ was removed from the CW with the high iron substrate whereas 11.0 ± 9.7% was removed from the CW with the low iron substrate on average. Since the CW with high NH₄⁺ removal had the same plant density, same bacterial biomass, same fraction of ammonium oxidizing bacteria (AOB), a higher biomass of A6, and a higher pH (NH₄⁺ oxidation by Feammox raises pH, whereas NH₄⁺ oxidation by aerobic AOB decreases pH), this difference in NH₄⁺ removal is attributed to the Feammox process, indicating that wetlands can be constructed to take advantage of the Feammox process for increased NH₄⁺ removal.

Pressure-Regulated Gene Expression and Enzymatic Activity of the Two Periplasmic Nitrate Reductases in the Deep-Sea Bacterium Shewanella piezotolerans WP3

Shewanella species are widely distributed in marine environments, from the shallow coasts to the deepest sea bottom. Most Shewanella species possess two isoforms of periplasmic nitrate reductases (NAP-α and NAP-β) and are able to generate energy through nitrate reduction. However, the contributions of the two NAP systems to bacterial deep-sea adaptation remain unclear. In this study, we found that the deep-sea denitrifier Shewanella piezotolerans WP3 was capable of performing nitrate respiration under high hydrostatic pressure (HHP) conditions. In the wild-type strain, NAP-β played a dominant role and was induced by both the substrate and an elevated pressure, whereas NAP-α was constitutively expressed at a relatively lower level. Genetic studies showed that each NAP system alone was sufficient to fully sustain nitrate-dependent growth and that both NAP systems exhibited substrate and pressure inducible expression patterns when the other set was absent. Biochemical assays further demonstrated that NAP-α had a higher tolerance to elevated pressure. Collectively, we report for the first time the distinct properties and contributions of the two NAP systems to nitrate reduction under different pressure conditions. The results will shed light on the mechanisms of bacterial HHP adaptation and nitrogen cycling in the deep-sea environment.

Genome guided investigation of antibiotics producing actinomycetales strain isolated from a Macau mangrove ecosystem

Actinomycetes are a heterogeneous group of gram positive filamentous bacteria that have been found to produce a wide range of valuable bioactive secondary metabolites, particularly antibiotics. Moreover, actinomycetes isolated from unexplored environments show an unprecedented potential to generate novel active compounds. Hence, in order to search for novel antibiotics, we isolated and characterized actinomycetes strains from plant samples collected from a mangrove in Macau. Within the class of actinobacteria, fourteen actinomycetes isolates have been isolated and identified belonging to the genus of Streptomyces, Micromonospora, Mycobacterium, Brevibacterium, Curtobacterium and Kineococcus based on their 16S rRNA sequences. Further whole genome sequencing analysis of one of the isolated Streptomyces sp., which presented 99.13% sequence similarity with Streptomyces parvulus strain 2297, showed that it consisted of 118 scaffolds, 8,348,559 base pairs and had a 72.28% G + C content. In addition, genome-mining revealed that the isolated Streptomyces sp. contains 109 gene clusters responsible for the biosynthesis of known and/or novel secondary metabolites, including different types of terpene, T1pks, T2pks, T3pks, Nrps, indole, siderophore, bacteriocin, thiopeptide, phosphonate, lanthipeptide, ectoine, butyrolactone, T3pks-Nrps, and T1pks-Nrps. Meanwhile, the small molecules present in ethyl acetate extract of the fermentation broth of this strain were analyzed by LC-MS. Predicted secondary metabolites of melanin and desferrioxamine B were identified and both of them were firstly found to be produced by the Streptomyces parvulus strain. Our study highlights that combining genome mining is an efficient method to detect potentially promising natural products from mangrove-derived actinomycetes.

Genomic insights into the Acidobacteria reveal strategies for their success in terrestrial environments

Members of the phylum Acidobacteria are abundant and ubiquitous across soils. We performed a large-scale comparative genome analysis spanning subdivisions 1, 3, 4, 6, 8 and 23 (n = 24) with the goal to identify features to help explain their prevalence in soils and understand their ecophysiology. Our analysis revealed that bacteriophage integration events along with transposable and mobile elements influenced the structure and plasticity of these genomes. Low- and high-affinity respiratory oxygen reductases were detected in multiple genomes, suggesting the capacity for growing across different oxygen gradients. Among many genomes, the capacity to use a diverse collection of carbohydrates, as well as inorganic and organic nitrogen sources (such as via extracellular peptidases), was detected - both advantageous traits in environments with fluctuating nutrient environments. We also identified multiple soil acidobacteria with the potential to scavenge atmospheric concentrations of H2 , now encompassing mesophilic soil strains within the subdivision 1 and 3, in addition to a previously identified thermophilic strain in subdivision 4. This large-scale acidobacteria genome analysis reveal traits that provide genomic, physiological and metabolic versatility, presumably allowing flexibility and versatility in the challenging and fluctuating soil environment.

Enhancing the Adaptability of the Deep-Sea Bacterium Shewanella piezotolerans WP3 to High Pressure and Low Temperature by Experimental Evolution under H2O2 Stress

Oxidative stresses commonly exist in natural environments, and microbes have developed a variety of defensive systems to counteract such events. Although increasing evidence has shown that high hydrostatic pressure (HHP) and low temperature (LT) induce antioxidant defense responses in cells, there is no direct evidence to prove the connection between antioxidant defense mechanisms and the adaptation of bacteria to HHP and LT. In this study, using the wild-type (WT) strain of a deep-sea bacterium, Shewanella piezotolerans WP3, as an ancestor, we obtained a mutant, OE100, with an enhanced antioxidant defense capacity by experimental evolution under H₂O₂ stress. Notably, OE100 exhibited better tolerance not only to H₂O₂ stress but also to HHP and LT (20 MPa and 4°C, respectively). Whole-genome sequencing identified a deletion mutation in the oxyR gene, which encodes the transcription factor that controls the oxidative stress response. Comparative transcriptome analysis showed that the genes associated with oxidative stress defense, anaerobic respiration, DNA repair, and the synthesis of flagella and bacteriophage were differentially expressed in OE100 compared with the WT at 20 MPa and 4°C. Genetic analysis of oxyR and ccpA2 indicated that the OxyR-regulated cytochrome c peroxidase CcpA2 significantly contributed to the adaptation of WP3 to HHP and LT. Taken together, these results confirmed the inherent relationship between antioxidant defense mechanisms and the adaptation of a benthic microorganism to HHP and LT.IMPORTANCE Oxidative stress exists in various niches, including the deep-sea ecosystem, which is an extreme environment with conditions of HHP and predominantly LT. Although previous studies have shown that HHP and LT induce antioxidant defense responses in cells, direct evidence to prove the connection between antioxidant defense mechanisms and the adaptation of bacteria to HHP and LT is lacking. In this work, using the deep-sea bacterium Shewanella piezotolerans WP3 as a model, we proved that enhancement of the adaptability of WP3 to HHP and LT can benefit from its antioxidant defense mechanism, which provided useful insight into the ecological roles of antioxidant genes in a benthic microorganism and contributed to an improved understanding of microbial adaptation strategies in deep-sea environments.

High Hydrostatic Pressure Inducible Trimethylamine N-Oxide Reductase Improves the Pressure Tolerance of Piezosensitive Bacteria Vibrio fluvialis

High hydrostatic pressure (HHP) exerts severe effects on cellular processes including impaired cell division, abolished motility and affected enzymatic activities. Transcriptomic and proteomic analyses showed that bacteria switch the expression of genes involved in multiple energy metabolism pathways to cope with HHP. We sought evidence of a changing bacterial metabolism by supplying appropriate substrates that might have beneficial effects on the bacterial lifestyle at elevated pressure. We isolated a piezosensitive marine bacterium Vibrio fluvialis strain QY27 from the South China Sea. When trimethylamine N-oxide (TMAO) was used as an electron acceptor for energy metabolism, QY27 exhibited a piezophilic-like phenotype with an optimal growth at 30 MPa. Raman spectrometry and biochemistry analyses revealed that both the efficiency of the TMAO metabolism and the activity of the TMAO reductase increased under high pressure conditions. Among the two genes coding for TMAO reductase catalytic subunits, the expression level and enzymatic activity of TorA was up-regulated by elevated pressure. Furthermore, a genetic interference assay with the CRISPR-dCas9 system demonstrated that TorA is essential for underpinning the improved pressure tolerance of QY27. We extended the study to Vibrio fluvialis type strain ATCC33809 and observed the same phenotype of TMAO-metabolism improved the pressure tolerance. These results provide compelling evidence for the determinant role of metabolism in the adaption of bacteria to the deep-sea ecosystems with HHP.

Pan-genome analyses of 24 Shewanella strains re-emphasize the diversification of their functions yet evolutionary dynamics of metal-reducing pathway

BACKGROUND

Shewanella strains are important dissimilatory metal-reducing bacteria which are widely distributed in diverse habitats. Despite efforts to genomically characterize Shewanella, knowledge of the molecular components, functional information and evolutionary patterns remain lacking, especially for their compatibility in the metal-reducing pathway. The increasing number of genome sequences of Shewanella strains offers a basis for pan-genome studies.

RESULTS

A comparative pan-genome analysis was conducted to study genomic diversity and evolutionary relationships among 24 Shewanella strains. Results revealed an open pan-genome of 13,406 non-redundant genes and a core-genome of 1878 non-redundant genes. Selective pressure acted on the invariant members of core genome, in which purifying selection drove evolution in the housekeeping mechanisms. Shewanella strains exhibited extensive genome variability, with high levels of gene gain and loss during the evolution, which affected variable gene sets and facilitated the rapid evolution. Additionally, genes related to metal reduction were diversely distributed in Shewanella strains and evolved under purifying selection, which highlighted the basic conserved functionality and specificity of respiratory systems.

CONCLUSIONS

The diversity of genes present in the accessory and specific genomes of Shewanella strains indicates that each strain uses different strategies to adapt to diverse environments. Horizontal gene transfer is an important evolutionary force in shaping Shewanella genomes. Purifying selection plays an important role in the stability of the core-genome and also drives evolution in mtr-omc cluster of different Shewanella strains.

Deep-Sea Bacterium Shewanella piezotolerans WP3 Has Two Dimethyl Sulfoxide Reductases in Distinct Subcellular Locations

Dimethyl sulfoxide (DMSO) acts as a substantial sink for dimethyl sulfide (DMS) in deep waters and is therefore considered a potential electron acceptor supporting abyssal ecosystems. Shewanella piezotolerans WP3 was isolated from west Pacific deep-sea sediments, and two functional DMSO respiratory subsystems are essential for maximum growth of WP3 under in situ conditions (4°C/20 MPa). However, the relationship between these two subsystems and the electron transport pathway underlying DMSO reduction by WP3 remain unknown. In this study, both DMSO reductases (type I and type VI) in WP3 were found to be functionally independent despite their close evolutionary relationship. Moreover, immunogold labeling of DMSO reductase subunits revealed that the type I DMSO reductase was localized on the outer leaflet of the outer membrane, whereas the type VI DMSO reductase was located within the periplasmic space. CymA, a cytoplasmic membrane-bound tetraheme c-type cytochrome, served as a preferential electron transport protein for the type I and type VI DMSO reductases, in which type VI accepted electrons from CymA in a DmsE- and DmsF-independent manner. Based on these results, we proposed a core electron transport model of DMSO reduction in the deep-sea bacterium S. piezotolerans WP3. These results collectively suggest that the possession of two sets of DMSO reductases with distinct subcellular localizations may be an adaptive strategy for WP3 to achieve maximum DMSO utilization in deep-sea environments.IMPORTANCE As the dominant methylated sulfur compound in deep oceanic water, dimethyl sulfoxide (DMSO) has been suggested to play an important role in the marine biogeochemical cycle of the volatile anti-greenhouse gas dimethyl sulfide (DMS). Two sets of DMSO respiratory systems in the deep-sea bacterium Shewanella piezotolerans WP3 have previously been identified to mediate DMSO reduction under in situ conditions (4°C/20 MPa). Here, we report that the two DMSO reductases (type I and type VI) in WP3 have distinct subcellular localizations, in which type I DMSO reductase is localized to the exterior surface of the outer membrane and type VI DMSO reductase resides in the periplasmic space. A core electron transport model of DMSO reduction in WP3 was constructed based on genetic and physiological data. These results will contribute to a comprehensive understanding of the adaptation mechanisms of anaerobic respiratory systems in benthic microorganisms.

Genome-Wide Detection of Small Regulatory RNAs in Deep-Sea Bacterium Shewanella piezotolerans WP3

Shewanella are one of the most abundant Proteobacteria in the deep-sea and are renowned for their versatile electron accepting capacities. The molecular mechanisms involved in their adaptation to diverse and extreme environments are not well understood. Small non-coding RNAs (sRNAs) are known for modulating the gene expression at transcriptional and posttranscriptional levels, subsequently playing a key role in microbial adaptation. To understand the potential roles of sRNAs in the adaptation of Shewanella toward deep-sea environments, here an in silico approach was utilized to detect the sRNAs in the genome of Shewanella piezotolerans WP3, a piezotolerant and psychrotolerant deep-sea iron reducing bacterium. After scanning 3673 sets of 5' and 3' UTRs of orthologous genes, 209 sRNA candidates were identified with high confidence in S. piezotolerans WP3. About 92% (193 out of 209) of these putative sRNAs belong to the class trans-encoded RNAs, suggesting that trans-regulatory RNAs are the dominant class of sRNAs in S. piezotolerans WP3. The remaining 16 cis-regulatory RNAs were validated through quantitative polymerase chain reaction. Five cis-sRNAs were further shown to act as cold regulated sRNAs. Our study provided additional evidence at the transcriptional level to decipher the microbial adaptation mechanisms to extreme environmental conditions.

DNA Backbone Sulfur-Modification Expands Microbial Growth Range under Multiple Stresses by its anti-oxidation function

DNA phosphorothioate (PT) modification is a sulfur modification on the backbone of DNA introduced by the proteins DndA-E. It has been detected within many bacteria isolates and metagenomic datasets, including human pathogens, and is considered to be widely distributed in nature. However, little is known about the physiological function of this modification, and thus its evolutionary significance and application potential remains largely a mystery. In this study, we focused on the advantages of DNA PT modification to bacterial cells coping with environmental stresses. We show that the mesophile Escherichia coli and the extremophile Shewanella piezotolerans both expanded their growth ranges following exposure to extreme temperature, salinity, pH, pressure, UV, X-ray and heavy metals as a result of DNA phophorothioation. The phophorothioated DNA reacted to both H₂O₂ and hydroxyl radicals in vivo, and protected genomic DNA as well as sensitive enzymes from intracellular oxidative damage. We further demonstrate that this process has evolved separate from its associated role in DNA restriction and modification. These findings provide a physiological role for a covalent modification widespread in nature and suggest possible applications in biotechnology and biomedicine.

A Genome-Scale Model of Shewanella piezotolerans Simulates Mechanisms of Metabolic Diversity and Energy Conservation

The well-studied nature of the metabolic diversity of Shewanella bacteria makes species from this genus a promising platform for investigating the evolution of carbon metabolism and energy conservation. The Shewanella phylogeny is diverged into two major branches, referred to as group 1 and group 2. While the genotype-phenotype connections of group 2 species have been extensively studied with metabolic modeling, a genome-scale model has been missing for the group 1 species. The metabolic reconstruction of Shewanella piezotolerans strain WP3 represented the first model for Shewanella group 1 and the first model among piezotolerant and psychrotolerant deep-sea bacteria. The model brought insights into the mechanisms of energy conservation in WP3 under anaerobic conditions and highlighted its metabolic flexibility in using diverse carbon sources. Overall, the model opens up new opportunities for investigating energy conservation and metabolic adaptation, and it provides a prototype for systems-level modeling of other deep-sea microorganisms.

Shewanella piezotolerans strain WP3 belongs to the group 1 branch of the Shewanella genus and is a piezotolerant and psychrotolerant species isolated from the deep sea. In this study, a genome-scale model was constructed for WP3 using a combination of genome annotation, ortholog mapping, and physiological verification. The metabolic reconstruction contained 806 genes, 653 metabolites, and 922 reactions, including central metabolic functions that represented nonhomologous replacements between the group 1 and group 2 Shewanella species. Metabolic simulations with the WP3 model demonstrated consistency with existing knowledge about the physiology of the organism. A comparison of model simulations with experimental measurements verified the predicted growth profiles under increasing concentrations of carbon sources. The WP3 model was applied to study mechanisms of anaerobic respiration through investigating energy conservation, redox balancing, and the generation of proton motive force. Despite being an obligate respiratory organism, WP3 was predicted to use substrate-level phosphorylation as the primary source of energy conservation under anaerobic conditions, a trait previously identified in other Shewanella species. Further investigation of the ATP synthase activity revealed a positive correlation between the availability of reducing equivalents in the cell and the directionality of the ATP synthase reaction flux. Comparison of the WP3 model with an existing model of a group 2 species, Shewanella oneidensis MR-1, revealed that the WP3 model demonstrated greater flexibility in ATP production under the anaerobic conditions. Such flexibility could be advantageous to WP3 for its adaptation to fluctuating availability of organic carbon sources in the deep sea.

IMPORTANCE The well-studied nature of the metabolic diversity of Shewanella bacteria makes species from this genus a promising platform for investigating the evolution of carbon metabolism and energy conservation. The Shewanella phylogeny is diverged into two major branches, referred to as group 1 and group 2. While the genotype-phenotype connections of group 2 species have been extensively studied with metabolic modeling, a genome-scale model has been missing for the group 1 species. The metabolic reconstruction of Shewanella piezotolerans strain WP3 represented the first model for Shewanella group 1 and the first model among piezotolerant and psychrotolerant deep-sea bacteria. The model brought insights into the mechanisms of energy conservation in WP3 under anaerobic conditions and highlighted its metabolic flexibility in using diverse carbon sources. Overall, the model opens up new opportunities for investigating energy conservation and metabolic adaptation, and it provides a prototype for systems-level modeling of other deep-sea microorganisms.

Current trends of human infections and antibiotic resistance of the genus Shewanella

Shewanella spp. are commonly known as environmental bacteria and are most frequently isolated from aquatic areas. Currently, diseases syndromes and multidrug resistance have increasingly been reported in the genus Shewanella. Some species are associated with various infections, such as skin and soft tissue infections, as well as bacteremia. Generally, these bacteria are opportunistic and mostly affect people with an impaired immune system. This genus is also a probable vehicle and progenitor of antibiotic resistance genes. In fact, several resistance genes and mobile genetic elements have been identified in some resistant species isolated from environmental or clinical settings. These genes confer resistance to different antibiotic classes, including those used in therapies such as β-lactams and quinolones, and are generally located on the chromosome. Recently, a multidrug-resistant (MDR) plasmid harboring several drug resistance genes associated with transposons and integrons has been identified in Shewanella xiamenensis. These antibiotic resistance genes can circulate in the environment and contribute to the emergence of antibiotic resistance. This review describes different aspects of Shewanella, focusing on the infections caused by this genus, as well as their role in the propagation of antibiotic resistance via mobile genetic elements.

Characterization of the relationship between polar and lateral flagellar structural genes in the deep-sea bacterium Shewanella piezotolerans WP3

Bacteria with a dual flagellar system, which consists of a polar flagellum (PF) and several lateral flagella (LF), have been identified in diverse environments. Nevertheless, whether and how these two flagellar systems interact with each other is largely unknown. In the present study, the relationship between the structural genes for the PF and LF of the deep-sea bacterium Shewanella piezotolerans WP3 was investigated by genetic, phenotypic and phylogenetic analyses. The mutation of PF genes induced the expression of LF genes and the production of LF in liquid medium, while the defective LF genes led to a decrease in PF gene transcription. However, the level of PF flagellin remained unchanged in LF gene mutants. Further investigation showed that the flgH2 gene (encoding LF L-ring protein) can compensate for mutations of the flgH1 gene (encoding PF L-ring protein), but this compensation does not occur between the flagellar hook-filament junction proteins (FlgL1, FlgL2). Swarming motility was shown to specifically require LF genes, and PF genes cannot substitute for the LF genes in the lateral flagella synthesis. Considering the importance of flagella-dependent motility for bacterial survival in the abyssal sediment, our study thus provided a better understanding of the adaptation strategy of benthic bacteria.

A transcriptome resource for the deep-sea bacterium Shewanella piezotolerans WP3 under cold and high hydrostatic pressure shock stress

Low temperature and high hydrostatic pressure (HHP) are two of the most remarkable environmental factors influencing deep-sea ecosystem. The adaptive mechanisms of microorganisms which live in these extreme environments to low temperature and high pressure warrant investigation. In this study, the global gene expression patterns of the deep-sea bacterium Shewanella piezotolerans WP3 in response to cold (0 °C) and HHP (50 MPa) shock were evaluated through DNA microarray analysis. Results revealed that 22, 66, and 106 genes were differentially expressed after WP3 was respectively exposed to cold shock for 30, 60, and 90 min. Of these genes, 16 genes were identified as common differentially expressed genes (DEGs). After 30 min and 120 min of HHP shock, 5 and 10 genes were respectively identified as DEGs. The hierarchical clustering analysis of the DEG pattern indicated that WP3 may employ different adaptive strategies to cope with cold and HHP shock stress. Taken together, our study provided a transcriptome resource for deep-sea bacterial responses to cold and HHP stress. This study also established a basis for further investigations on environmental adaptive mechanisms utilized by benthic bacteria.

The Two Sets of DMSO Respiratory Systems of Shewanella piezotolerans WP3 Are Involved in Deep Sea Environmental Adaptation

Dimethyl sulfoxide (DMSO) is an abundant methylated sulfur compound in deep sea ecosystems. However, the mechanism underlying DMSO-induced reduction in benthic microorganisms is unknown. Shewanella piezotolerans WP3, which was isolated from a west Pacific deep sea sediment, can utilize DMSO as the terminal electron acceptor. In this study, two putative dms gene clusters [type I (dmsEFA1B1G1H1) and type II (dmsA2B2G2H2)] were identified in the WP3 genome. Genetic and physiological analyses demonstrated that both dms gene clusters were functional and the transcription of both gene clusters was affected by changes in pressure and temperature. Notably, the type I system is essential for WP3 to thrive under in situ conditions (4°C/20 MPa), whereas the type II system is more important under high pressure or low temperature conditions (20°C/20 MPa, 4°C/0.1 MPa). Additionally, DMSO-dependent growth conferred by the presence of both dms gene clusters was higher than growth conferred by either of the dms gene clusters alone. These data collectively suggest that the possession of two sets of DMSO respiratory systems is an adaptive strategy for WP3 survival in deep sea environments. We propose, for the first time, that deep sea microorganisms might be involved in global DMSO/DMS cycling.

Global transcriptome analysis of the heat shock response of the deep-sea bacterium Shewanella piezotolerans WP3

For microorganisms, heat shock is a major stressful condition. Heat shock is characterized by sudden temperature increases that damage important protein structures and interfere with essential cellular functions. In this study, global gene expression patterns of the deep-sea bacterium Shewanella piezotolerans WP3 in response to heat shock were studied by DNA microarray analysis. Overall, 438, 573, and 627 genes were found to be differentially expressed after heat shock for 30, 60, and 90min, respectively. Functional classification of differentially transcribed genes was performed using the Clusters of Orthologous Groups of Proteins database. Additionally, 361 genes were identified as common differentially expressed genes. These genes may comprise the core genes responsible for coping with heat shock stress of WP3. Moreover, comparative analysis of gene expression pattern in WP3 and other bacteria indicated the presence of different adaptive strategies. These data represent the first transcriptome resource for the response of this deep-sea bacterium to high-temperature stress. This study contributes to the understanding of the global adaptation mechanisms of benthic bacteria toward environmental stresses.

An overview of siderophores for iron acquisition in microorganisms living in the extreme

Siderophores are iron-chelating molecules produced by microbes when intracellular iron concentrations are low. Low iron triggers a cascade of gene activation, allowing the cell to survive due to the synthesis of important proteins involved in siderophore synthesis and transport. Generally, siderophores are classified by their functional groups as catecholates, hydroxamates and hydroxycarboxylates. Although other chemical structural modifications and functional groups can be found. The functional groups participate in the iron-chelating process when the ferri-siderophore complex is formed. Classified as acidophiles, alkaliphiles, halophiles, thermophiles, psychrophiles, piezophiles, extremophiles have particular iron requirements depending on the environmental conditions in where they grow. Most of the work done in siderophore production by extremophiles is based in siderophore concentration and/or genomic studies determining the presence of siderophore synthesis and transport genes. Siderophores produced by extremophiles are not well known and more work needs to be done to elucidate chemical structures and their role in microorganism survival and metal cycling in extreme environments.

Comparative Genomics Analysis of Streptomyces Species Reveals Their Adaptation to the Marine Environment and Their Diversity at the Genomic Level

Over 200 genomes of streptomycete strains that were isolated from various environments are available from the NCBI. However, little is known about the characteristics that are linked to marine adaptation in marine-derived streptomycetes. The particularity and complexity of the marine environment suggest that marine streptomycetes are genetically diverse. Here, we sequenced nine strains from the Streptomyces genus that were isolated from different longitudes, latitudes, and depths of the South China Sea. Then we compared these strains to 22 NCBI downloaded streptomycete strains. Thirty-one streptomycete strains are clearly grouped into a marine-derived subgroup and multiple source subgroup-based phylogenetic tree. The phylogenetic analyses have revealed the dynamic process underlying streptomycete genome evolution, and lateral gene transfer is an important driving force during the process. Pan-genomics analyses have revealed that streptomycetes have an open pan-genome, which reflects the diversity of these streptomycetes and guarantees the species a quick and economical response to diverse environments. Functional and comparative genomics analyses indicate that the marine-derived streptomycetes subgroup possesses some common characteristics of marine adaptation. Our findings have expanded our knowledge of how ocean isolates of streptomycete strains adapt to marine environments. The availability of streptomycete genomes from the South China Sea will be beneficial for further analysis on marine streptomycetes and will enrich the South China Sea's genetic data sources.

Filamentous phage SW1 is active and influences the transcriptome of the host at high-pressure and low-temperature

As the most abundant biological entities on the planet, viruses are involved in global biogeochemical cycles, and they have been shown to play an important role in the overall functioning of the deep-sea ecosystem. Nevertheless, little is known about whether and how deep-sea viruses affect the physiology of their bacterial hosts. Previously, the filamentous phage SW1 was identified in the bathypelagic bacterium Shewanella piezotolerans WP3, which was isolated from the upper sediment of West Pacific ocean. In this study, phage SW1 was shown to be active under in situ environmental conditions (20 MPa and 4°C) by transmission electron microscopy and reverse-transcription quantitative polymerase chain reaction. Further comparative analysis showed that SW1 had a significant influence on the growth and transcriptome of its host. The transcription of genes responsible for basic cellular activities, including the transcriptional/translational apparatus, arginine synthesis, purine metabolism and the flagellar motor, were down-regulated by the phage. Our results present the first characterization of a phage-host interaction under high-pressure and low-temperature conditions, which indicated that the phage adjusted the energy utilization strategy of the host for improved survival in deep-sea environments.

The Histone-Like Nucleoid Structuring Protein (H-NS) Is a Negative Regulator of the Lateral Flagellar System in the Deep-Sea Bacterium Shewanella piezotolerans WP3

Although the histone-like nucleoid structuring protein (H-NS) is well known for its involvement in the adaptation of mesophilic bacteria, such as Escherichia coli, to cold environments and high-pressure stress, an understanding of the role of H-NS in the cold-adapted benthic microorganisms that live in the deep-sea ecosystem, which covers approximately 60% of the earth's surface, is still lacking. In this study, we characterized the function of H-NS in Shewanella piezotolerans WP3, which was isolated from West Pacific sediment at a depth of 1,914 m. Anhns gene deletion mutant (WP3Δhns) was constructed, and comparative whole-genome microarray analysis was performed. H-NS had a significant influence (fold change, >2) on the expression of a variety of WP3 genes (274 and 280 genes were upregulated and downregulated, respectively), particularly genes related to energy production and conversion. Notably, WP3Δhnsexhibited higher expression levels of lateral flagellar genes than WP3 and showed enhanced swarming motility and lateral flagellar production compared to those of WP3. The DNA gel mobility shift experiment showed that H-NS bound specifically to the promoter of lateral flagellar genes. Moreover, the high-affinity binding sequences of H-NS were identified by DNase I protection footprinting, and the results support the "binding and spreading" model for H-NS functioning. To our knowledge, this is the first attempt to characterize the function of the universal regulator H-NS in a deep-sea bacterium. Our data revealed that H-NS has a novel function as a repressor of the expression of genes related to the energy-consuming secondary flagellar system and to swarming motility.

Genomic and physiological analysis reveals versatile metabolic capacity of deep-sea Photobacterium phosphoreum ANT-2200

Bacteria of the genus Photobacterium thrive worldwide in oceans and show substantial eco-physiological diversity including free-living, symbiotic and piezophilic life styles. Genomic characteristics underlying this variability across species are poorly understood. Here we carried out genomic and physiological analysis of Photobacterium phosphoreum strain ANT-2200, the first deep-sea luminous bacterium of which the genome has been sequenced. Using optical mapping we updated the genomic data and reassembled it into two chromosomes and a large plasmid. Genomic analysis revealed a versatile energy metabolic potential and physiological analysis confirmed its growth capacity by deriving energy from fermentation of glucose or maltose, by respiration with formate as electron donor and trimethlyamine N-oxide (TMAO), nitrate or fumarate as electron acceptors, or by chemo-organo-heterotrophic growth in rich media. Despite that it was isolated at a site with saturated dissolved oxygen, the ANT-2200 strain possesses four gene clusters coding for typical anaerobic enzymes, the TMAO reductases. Elevated hydrostatic pressure enhances the TMAO reductase activity, mainly due to the increase of isoenzyme TorA1. The high copy number of the TMAO reductase isoenzymes and pressure-enhanced activity might imply a strategy developed by bacteria to adapt to deep-sea habitats where the instant TMAO availability may increase with depth.

Long 5' untranslated regions regulate the RNA stability of the deep-sea filamentous phage SW1

Virus production in the deep-sea environment has been found to be high, and viruses have been suggested to play significant roles in the overall functioning of this ecosystem. Nevertheless, little is known about these viruses, including the mechanisms that control their production, which makes them one of the least understood biological entities on Earth. Previously, we isolated the filamentous phage SW1, whose virus production and gene transcription were found to be active at low temperatures, from a deep-sea bacterium, Shewanella piezotolerans WP3. In this study, the operon structure of phage SW1 is presented, which shows two operons with exceptionally long 5′ and 3′ untranslated regions (UTRs). In addition, the 5′UTR was confirmed to significantly influence the RNA stability of the SW1 transcripts. Our study revealed novel regulation of the operon and led us to propose a unique regulatory mechanism for Inoviruses. This type of RNA-based regulation may represent a mechanism for significant viral production in the cold deep biosphere.