Exiguobacterium alkaliphilum sp. nov. isolated from alkaline wastewater drained sludge of a beverage factory

From genes to nanotubes: exploring the UV-resistome in the Andean extremophile Exiguobacterium sp. S17

Exiguobacterium sp. S17, a polyextremophile isolated from a High-Altitude Andean Lake, exhibits a multi-resistance profile against toxic arsenic concentrations, high UV radiation, and elevated salinity. Here, we characterize the mechanisms underlying the UV resistance of Exiguobacterium sp. S17 (UV-resistome) through comparative genomics within the Exiguobacterium genus and describe morphological and ultrastructural changes using Scanning (SEM) and Transmission (TEM) Electron Microscopy.UV-resistome in Exiguobacterium species ranges from 112 to 132 genes. While we anticipated Exiguobacterium sp. S17 to lead the non-HAAL UV-resistome, it ranked eleventh with 113 genes. This larger UV-resistome in Exiguobacterium spp. aligns with their known adaptation to extreme environments. With SEM/TEM analyses we observed the formation of nanotubes (NTs), a novel finding in Exiguobacterium spp., which increased with higher UV-B doses. These NTs, confirmed to be membranous structures through sensitivity studies and imaging, suggest a role in cellular communication and environmental sensing. Genomic evidence supports the presence of essential NT biogenesis genes in Exiguobacterium sp. S17, further elucidating its adaptive capabilities.Our study highlights the complex interplay of genetic and phenotypic adaptations enabling Exiguobacterium sp. S17 to thrive in extreme UV environments. The novel discovery of NTs under UV stress presents a new avenue for understanding bacterial survival strategies in harsh conditions.

Study on potential microbial community to the waste water treatment from bauxite desilication process

Discharging waste water from the bauxite desilication process will bring potential environmental risk from the residual ions and organic compounds, especially hydrolyzed polyacrylamide. Characterization of the microbial community diversity in waste water plays an important role in the biological treatment of waste water. In this study, eight waste water samples from five flotation plants in China were investigated. The microbial community and functional profiles within the waste water were analyzed by a metagenomic sequencing method and associated with geochemical properties. The results revealed that Proteobacteria and Firmicutes were the dominant bacterial phyla. Both phylogenetical and clusters of orthologous groups' analyses indicated that Tepidicella, Paracoccus, Pseudomonas, and Exiguobacterium could be the dominant bacterial genera in the waste water from bauxite desilication process for their abilities to biodegrade complex organic compounds. The results of the microbial community diversity and functional gene compositions analyses provided a beneficial orientation for the biotreatment of waste water, as well as regenerative using of water resources. Besides, this study revealed that waste water from bauxite desilication process was an ideal ecosystem to find novel microorganisms, such as efficient strains for bio-desilication and bio-desulfurization of bauxite.

Plant growth-promoting characteristics of halotolerant endophytic bacteria isolated from Sporobolus specatus (Vahr) Kunth and Cyperus laevigatus L. of Ethiopian rift valley lakes

Understanding plant microbes' intimate relationship and search for beneficial microbes is a sustainable alternative to improve plant growth and yield under a wide range of biotic and abiotic stress conditions. More than 20% of the total global agricultural land is affected by salinity. High salinity challenges crop plants by affecting several metabolic pathways and decreasing plant growth and yield. Unlike chemical fertilizers and pesticides, endophytic microbes offer an eco-friendly approach to increasing crop yield via various metabolites during salinity stress. The objective of this study was to isolate and characterize endophytic halotolerant bacterial isolates from haloalkaliphytes, investigate their plant growth-promoting (PGP) properties and tolerance for various stress conditions. Sporobolus specatus (Vahr) Kunth and Cyperus laevigatus L. grass samples were collected from the shores of two Ethiopian soda lakes (Lakes Abijata, and Chitu, respectively). A total of 167 halotolerant endophytic bacterial isolates, that clustered into 21 ARDRA (Amplified ribosomal DNA restriction analysis) groups, affiliated to members of 11 bacterial genera, namely Halomonas, Agrobacterium, Exiguobacterium, Jonesia, Stenotrophomonas, Pseudomonas, Alishewanella, Kosakonia, Bacillus, Paracoccus and Pannonibacter, were identified based on 16S rRNA sequencing. Most of the strains were able to produce IAA (indole-3-acetic acid) and hydrogen cyanide, grow on a nitrogen-free medium and solubilize phosphate. In vitro tolerance tests reveal that isolates were tolerant to: 5.0-15% NaCl, up to 40% PEG 6000, temperatures up to 50 °C, and pH 5-11. These characteristics of the isolates indicate their potential PGP application under various plant stress conditions.

Characterization and genomic analysis of Exiguobacterium alkaliphilum B-3531D, an efficient crude oil degrading strain

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B-3531D is the first E. alkaliphilum strain with fully assembled genome.

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It is the first E. alkaliphilum strain with the ability to utilize crude oil.

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Strain utilized 34.5% of crude oil for 14 days at 28 °C and a salinity of 11%.

The aim of the work was to carry out the physiological, biochemical and genetic characterization of the Exiguobacterium alkaliphilum B-3531D strain. This strain is promising for use in the field of environmental biotechnology, since it has a pronounced ability to utilize crude oil and individual hydrocarbons in a wide temperature range. The genome of the strain was sequenced and completely assembled, it consists of a 2,903,369 bp circular chromosome and two circular plasmids, namely, pE73 (73,590 bp) and pE52 (52,125 bp). When cultivated in a mineral medium containing 2% of crude oil, the strain utilized 50% within 30 days of the experiment. In simulated seawater with the same oil content, the loss of hydrocarbons was 45% over the same period. For the first time we observed in an E. alkaliphilum strain the ability to efficiently utilize crude oil, including with an increased content of sodium chloride in the cultivation medium.

Exiguobacterium algae sp. nov. and Exiguobacterium qingdaonense sp. nov., two novel moderately halotolerant bacteria isolated from the coastal algae

Two Gram-stain-positive, facultatively anaerobic, rod-shaped bacterial strains, S126^T and S82^T, were isolated from coastal algae of China. Strains S126^T and S82^T are halotolerant and could grow in the presence of 0-13% NaCl and 0-14% NaCl, respectively. The two strains shared 98.9% 16S rRNA gene sequence similarity with each other and 93.4-99.8% similarity with type strains of Exiguobacterium species. The major fatty acids (> 10%) of strains S126^T and S82^T were iso-C_17:0, iso-C_13:0, anteiso-C_13:0 and iso-C_15:0. The predominant quinones of strains S126^T and S82^T were MK-7 and MK-8. The polar lipid profiles of strain S126^T and S82^T contained diphosphatidylglycerol, phosphatidylglycerol and phosphatidylethanolamine. The cell-wall peptidoglycans of both strains S126^T and S82^T were of the A3α L-Lys-Gly type. The average nucleotide identity (ANI) and average nucleotide index (AAI) between strains S126^T and S82^T and type strains of Exiguobacterium species were all below the thresholds to discriminate bacterial species, indicating that they constitute two novel species in the genus Exiguobacterium. Based on polyphasic taxonomy characterization and genomic aspects, the names Exiguobacterium algae sp. nov. and Exiguobacterium qingdaonense sp. nov. are proposed for the two novel species, with type strains being S126^T (= CGMCC 1.17116^T = KCTC 43079 ^T) and S82^T (= CGMCC 1.17115^T = KCTC 43078^T), respectively.

Recovery of complete genomes and non-chromosomal replicons from activated sludge enrichment microbial communities with long read metagenome sequencing

New long read sequencing technologies offer huge potential for effective recovery of complete, closed genomes from complex microbial communities. Using long read data (ONT MinION) obtained from an ensemble of activated sludge enrichment bioreactors we recover 22 closed or complete genomes of community members, including several species known to play key functional roles in wastewater bioprocesses, specifically microbes known to exhibit the polyphosphate- and glycogen-accumulating organism phenotypes (namely Candidatus Accumulibacter and Dechloromonas, and Micropruina, Defluviicoccus and Candidatus Contendobacter, respectively), and filamentous bacteria (Thiothrix) associated with the formation and stability of activated sludge flocs. Additionally we demonstrate the recovery of close to 100 circularised plasmids, phages and small microbial genomes from these microbial communities using long read assembled sequence. We describe methods for validating long read assembled genomes using their counterpart short read metagenome-assembled genomes, and assess the influence of different correction procedures on genome quality and predicted gene quality. Our findings establish the feasibility of performing long read metagenome-assembled genome recovery for both chromosomal and non-chromosomal replicons, and demonstrate the value of parallel sampling of moderately complex enrichment communities to obtaining high quality reference genomes of key functional species relevant for wastewater bioprocesses.

Enhanced performance of tetracycline treatment in wastewater using aerobic granular sludge with in-situ generated biogenic manganese oxides

Wastewaters containing tetracycline (TC) are produced in many industries, and biotechnology is an economic way to treat it. In this work, aerobic granular sludge (AGS) modified with in-situ generated biogenic manganese oxides (BioMnOx), named after manganese-oxidizing AGS (Mn-AGS), was used to treat TC in wastewater. Comparisons between Mn-AGS and AGS indicated that Mn-AGS showed superior TC resistance and treatment results than AGS. The activity of Mn-AGS was not inhibited by TC content as high as 20 mg/L. Wastewater TC could be removed stably and efficiently (95.2 ± 0.8%) in the Mn-AGS reactors after 119 days' acclimation. Furthermore, TC may be first adsorbed on Mn-AGS sludge and then degraded by both microbial community and BioMnOx. TC adsorption could be greatly improved by increasing solution pH, which can be attributed to the increase in negatively charged TC species at high pHs. The microbial community changed greatly after TC exposure and some TC-resistant bacteria, such as Flavobacterium, were enriched in the final sludge. Moreover, the antibiotic resistance genes (ARGs) tetA, tetG, and tetX largely increased and the microorganisms were TC-resistant through efflux pumps and antibiotic inactivation mechanisms. This work suggests a new biological-chemical coupling strategy, Mn-AGS, to treat antibiotics in organic wastewater with high efficiency and stability.

Exiguobacterium flavidum sp. nov., isolated from the Red Maple Lake

A Gram-stain-positive, motile, facultatively anaerobic, non-sporing, and rod-shaped bacterial strain, designated HF60^T, was isolated from the Red Maple Lake of Guizhou Province, China. The DNA G+C content of the strain HF60^T was 55.0 %. The predominant isoprenoid quinones were identified as MK-7 (56.4 %) and MK-8 (35.7 %). The major polar lipids were phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol and aminophosphoglycolipid. The major fatty acids were anteiso-C_13 : 0, iso-C_15 : 0, C_16 : 0 and iso-C_13 : 0. The strain had cell wall peptidoglycan type A3α l-Lys-Gly. Phylogenetic analyses based on 16S rRNA gene sequences indicated that strain HF60^T belonged to the genus Exiguobacterium and was most closely related to Exiguobacterium sibiricum JCM 13490^T (97.2 % 16S rRNA gene sequence similarity), followed by Exiguobacterium undae DSM 14481^T (97.1 %), Exiguobacterium antarcticum DSM 14480^T (96.9 %) and Exiguobacterium aurantiacum NBRC 14763^T (94.5 %). The differential phenotypic properties, together with the phylogenetic and genetic distinctiveness indicated that strain HF60^T can be considered to represent a novel species of the genus Exiguobacterium, for which the name Exiguobacterium flavidum sp. nov. is proposed, The type strain is HF60^T (=MCCC 1H00336^T=KCTC 33987^T).

A predator-prey interaction between a marine Pseudoalteromonas sp. and Gram-positive bacteria

Predator-prey interactions play important roles in the cycling of marine organic matter. Here we show that a Gram-negative bacterium isolated from marine sediments (Pseudoalteromonas sp. strain CF6-2) can kill Gram-positive bacteria of diverse peptidoglycan (PG) chemotypes by secreting the metalloprotease pseudoalterin. Secretion of the enzyme requires a Type II secretion system. Pseudoalterin binds to the glycan strands of Gram positive bacterial PG and degrades the PG peptide chains, leading to cell death. The released nutrients, including PG-derived D-amino acids, can then be utilized by strain CF6-2 for growth. Pseudoalterin synthesis is induced by PG degradation products such as glycine and glycine-rich oligopeptides. Genes encoding putative pseudoalterin-like proteins are found in many other marine bacteria. This study reveals a new microbial interaction in the ocean.

Predator-prey interactions play important roles in the cycling of marine organic matter. Here the authors show that a Gram-negative bacterium isolated from marine sediments can kill and feed on Gram-positive bacteria by secreting a peptidoglycan-degrading enzyme.

The Complete Genome and Physiological Analysis of the Eurythermal Firmicute Exiguobacterium chiriqhucha Strain RW2 Isolated From a Freshwater Microbialite, Widely Adaptable to Broad Thermal, pH, and Salinity Ranges

Members of the genus Exiguobacterium are found in diverse environments from marine, freshwaters, permafrost to hot springs. Exiguobacterium can grow in a wide range of temperature, pH, salinity, and heavy-metal concentrations. We characterized Exiguobacterium chiriqhucha strain RW2 isolated from a permanently cold freshwater microbialite in Pavilion Lake, British Columbia using metabolic assays, genomics, comparative genomics, phylogenetics, and fatty acid composition. Strain RW2 has the most extensive growth range for temperature (4–50°C) and pH (5–11) of known Exiguobacterium isolates. Strain RW2 genome predicts pathways for wide differential thermal, cold and osmotic stress using cold and heat shock cascades (e.g., csp and dnaK), choline and betaine uptake/biosynthesis (e.g., opu and proU), antiporters (e.g., arcD and nhaC Na⁺/K⁺), membrane fatty acid unsaturation and saturation. Here, we provide the first complete genome from Exiguobacterium chiriqhucha strain RW2, which was isolated from a freshwater microbialite. Its genome consists of a single 3,019,018 bp circular chromosome encoding over 3,000 predicted proteins, with a GC% content of 52.1%, and no plasmids. In addition to growing at a wide range of temperatures and salinities, our findings indicate that RW2 is resistant to sulfisoxazole and has the genomic potential for detoxification of heavy metals (via mercuric reductases, arsenic resistance pumps, chromate transporters, and cadmium-cobalt-zinc resistance genes), which may contribute to the metabolic potential of Pavilion Lake microbialites. Strain RW2 could also contribute to microbialite formation, as it is a robust biofilm former and encodes genes involved in the deamination of amino acids to ammonia (i.e., L-asparaginase/urease), which could potentially boost carbonate precipitation by lowering the local pH and increasing alkalinity. We also used comparative genomic analysis to predict the pathway for orange pigmentation that is conserved across the entire Exiguobacterium genus, specifically, a C₃₀ carotenoid biosynthesis pathway is predicted to yield diaponeurosporene-4-oic acid as its final product. Carotenoids have been found to protect against ultraviolet radiation by quenching reactive oxygen, releasing excessive light energy, radical scavenging, and sunscreening. Together these results provide further insight into the potential of Exiguobacterium to exploit a wide range of environmental conditions, its potential roles in ecosystems (e.g., microbialites/microbial mats), and a blueprint model for diverse metabolic processes.

Characterization and Salt Response in Recurrent Halotolerant Exiguobacterium sp. SH31 Isolated From Sediments of Salar de Huasco, Chilean Altiplano

Poly-extremophiles microorganisms have the capacity to inhabit hostile environments and can survive several adverse conditions that include as variations in temperature, pH, and salinity, high levels UV light and atmospheric pressure, and even the presence of toxic compounds and the formation of reactive oxygen species (ROS). A halotolerant Exiguobacterium strain was isolated from Salar de Huasco (Chilean Altiplano), a well-known shallow lake area with variable salinity levels, little human intervention, and extreme environmental conditions, which makes it ideal for the study of resistant mechanisms and the evolution of adaptations. This bacterial genus has not been extensively studied, although its cosmopolitan location indicates that it has high levels of plasticity and adaptive capacity. However, to date, there are no studies regarding the tolerance and resistance to salinity and osmotic pressure. We set out to characterize the Exiguobacterium sp. SH31 strain and describe its phenotypical and genotypical response to osmotic stress. In this context, as a first step to characterize the response to the SH31 strain to salinity and to establish the bases for a molecular study, we proposed to compare its response under three salt conditions (0, 25, and 50 g/l NaCl). Using different physiology, genomic, and transcriptomic approaches, we determined that the bacterium is able to grow properly in a NaCl concentration of up to 50 g/l; however, the best growth rate was observed at 25 g/l. Although the presence of flagella is not affected by salinity, motility was diminished at 25 g/l NaCl and abolished at 50 g/l. Biofilm formation was induced proportionally with increases in salinity, which was expected. These phenotypic results correlated with the expression of related genes: fliG and fliS Motility); opuBA and putP (transport); glnA, proC, gltA, and gbsA (compatible solutes); ywqC, bdlA, luxS y pgaC (biofilm and stress response); and therefore, we conclude that this strain effectively modifies gene expression and physiology in a differential manner when faced with different concentrations of NaCl and these modifications aid survival.

Patterns of variation in diversity of the Mississippi river microbiome over 1,300 kilometers

We examined the downriver patterns of variation in taxonomic diversity of the Mississippi River bacterioplankton microbiome along 1,300 river kilometers, or approximately one third the total length of the river. The study section included portions of the Upper, Middle, and Lower Mississippi River, confluences with five tributaries draining distinct sub-basins, river cities, and extended stretches without major inputs to the Mississippi. The composition and proportional abundance of dominant bacterial phyla was distinct for free-living and particle-associated cells, and constant along the entire reach, except for a substantial but transient disturbance near the city of Memphis, Tennessee. At a finer scale of taxonomic resolution (operational taxonomic units, OTUs), however, there were notable patterns in downriver variation in bacterial community alpha diversity (richness within a site) and beta diversity (variation in composition among sites). There was a strong and steady increase downriver in alpha diversity of OTUs on suspended particles, suggesting an increase in particle niche heterogeneity, and/or particle colonization. Relatively large shifts in beta diversity of free-living and particle-associated communities occurred following major tributary confluences and transiently at Memphis, while in long stretches between these points diversity typically varied more gradually. We conclude that the Mississippi River possesses a bacterioplankton microbiome distinct in diversity from other large river microbiomes in the Mississippi River Basin, that at major river confluences or urban point sources its OTU diversity may shift abruptly and substantially, presumably by immigration of distinct external microbiomes, but that where environmental conditions are more stable along the downriver gradient, microbiome diversity tends to vary gradually, presumably by a process of successional change in community composition.

Exiguobacterium enclense sp. nov., isolated from sediment

A Gram-stain-positive bacterium, designated strain NIO-1109(T), was isolated from a marine sediment sample from Chorao Island, Goa, India. Phenotypic and chemotaxonomic characteristics and data from phylogenetic analysis based on 16S rRNA gene sequences indicated that strain NIO-1109(T) was related to the genus Exiguobacterium . Strain NIO-1109(T) exhibited >98.0% 16S rRNA gene sequence similarity with respect to Exiguobacterium indicum HHS 31(T) (99.5%) and Exiguobacterium acetylicum NCIMB 9889(T) (99.1%); the type strains of other species showed <98% similarity. Levels of DNA-DNA relatedness between strain NIO-1109(T) and E. acetylicum DSM 20416(T) and E. indicum LMG 23471(T) were less than 70% (33.0 ± 2.0 and 37 ± 3.2%, respectively). Strain NIO-1109(T) also differed from these two closely related species in a number of phenotypic traits. Based on phenotypic, chemotaxonomic and phylogenetic data, strain NIO-1109(T) is considered to represent a novel species of the genus Exiguobacterium , for which the name Exiguobacterium enclense sp. nov. is proposed. The type strain is NIO-1109(T) ( =NCIM 5457(T) =DSM 25128(T)  = CCTCC AB 2011124(T)).