Widespread and persistent populations of a major new marine actinomycete taxon in ocean sediments

A review on marine source as anticancer agents

This review investigates the potential of natural compounds obtained from marine sources for the treatment of cancer. The oceans are believed to contain physiologically active compounds, such as alkaloids, nucleosides, macrolides, and polyketides, which have shown promising effects in slowing human tumor cells both in vivo and in vitro. Various marine species, including algae, mollusks, actinomycetes, fungi, sponges, and soft corals, have been studied for their bioactive metabolites with diverse chemical structures. The review explores the therapeutic potential of various marine-derived substances and discusses their possible applications in cancer treatment.

Two new p-methoxyphenyl-type derivatives from a saline-lake derived Streptomyces sp. XZB32

Two new p-methoxyphenyl-type derivatives cytchloramol (1) and cytoxazinanone (2), along with six known compounds (3-8) were identified from the chemical investigations of a saline lake actinomycete, Streptomyces sp. XZB32. The structures of the new compounds were elucidated by extensive NMR spectroscopic analysis, HRESIMS data, GIAO (gauge-including atomic orbitals) NMR, specific optical rotation (SOR) and electronic circular dichroism (ECD) calculations. Cytotoxicity evaluation of the two new compounds showed that compound 1 exhibited significant activity against HCT-116 and MDA-MB-231 human cancer cell line with IC50 values of 2.7 ± 0.07 µM and 1.54 ± 0.14 µM, respectively.

Dry Stamping Coral Powder: An Effective Method for Isolating Coral Symbiotic Actinobacteria

Actinobacteria are important sources of antibiotics and have been found repeatedly in coral core microbiomes, suggesting this bacterial group plays important functional roles tied to coral survival. However, to unravel coral-actinobacteria ecological interactions and discover new antibiotics, the complex challenges that arise when isolating symbiotic actinobacteria must be overcome. Moreover, by isolating unknown actinobacteria from corals, novel biotechnological applications may be discovered. In this study, we compared actinobacteria recovery from coral samples between two widely known methods for isolating actinobacteria: dry stamping and heat shock. We found that dry stamping was at least three times better than heat shock. The assembly of isolated strains by dry stamping was unique for each species and consistent across same-species samples, highlighting that dry stamping can be reliably used to characterize coral actinobacteria communities. By analyzing the genomes of the closest related type strains, we were able to identify several functions commonly found among symbiotic organisms, such as transport and quorum sensing. This study provides a detailed methodology for isolating coral actinobacteria for ecological and biotechnological purposes.

Complete genome sequence analysis of plant growth-promoting bacterium, Isoptericola sp. AK164 isolated from the rhizosphere of Avicennia marina growing at the Red Sea coast

Isoptericola sp. AK164 is a Gram-positive, aerobic bacterial genus from the family Promicromonosporaceae, isolated from the root rhizosphere of Avicennia marina. AK164 significantly enhanced the growth of the Arabidopsis thaliana plant under normal and saline conditions. These bacteria can produce ACC deaminase and several enzymes playing a role in carbohydrate hydrolyses, such as cellulose, hemicellulose, and chitin degradation, which may contribute to plant growth, salt tolerance, and stress elevation. The genome sequence AK164 has a single circular chromosome of approximately 3.57 Mbp with a GC content of 73.53%. A whole genome sequence comparison of AK164 with type strains from the same genus, using digital DNA-DNA hybridization and average nucleotide identity calculations, revealed that AK164 might potentially belong to a new species of Isoptericola. Genome data and biochemical analyses indicate that AK164 could be a potential biostimulant for improving agriculture in submerged saline land.

Transgenic soybean of GsMYB10 shapes rhizosphere microbes to promote resistance to aluminum (Al) toxicity

Plant resistance genes could affect rhizosphere microbiota, which in turn enhanced plant resistance to stresses. Our previous study found that overexpression of the GsMYB10 gene led to enhanced tolerance of soybean plants to aluminum (Al) toxicity. However, whether GsMYB10 gene could regulate rhizosphere microbiota to mitigate Al toxicity remains unclear. Here, we analyzed the rhizosphere microbiomes of HC6 soybean (WT) and transgenic soybean (trans-GsMYB10) at three Al concentrations, and constructed three different synthetic microbial communities (SynComs), including bacterial, fungal and cross-kingdom (bacteria and fungi) SynComs to verify their role in improving Al tolerance of soybean. Trans-GsMYB10 shaped the rhizosphere microbial communities and harbored some beneficial microbes, such as Bacillus, Aspergillus and Talaromyces under Al toxicity. Fungal and cross-kingdom SynComs showed a more effective role than the bacterial one in resistance to Al stress, and these SynComs helped soybean resist Al toxicity via affecting some functional genes that involved cell wall biosynthesis and organic acid transport etc. Overall, this study reveals the mechanism of soybean functional genes regulating the synergistic resistance of rhizosphere microbiota and plants to Al toxicity, and also highlights the possibility of focusing on the rhizobial microbial community as a potential molecular breeding target to produce crops.

Ecobiology and distribution of Streptomyces species from distinctive metal polluted sediment of tropical estuary, Northwest coast of India

The present study aims to isolate diverse actinomycetes communities from the estuarine sediments of Patalganga located at Northwest coast of India. Total 40 actinomycetes were isolated from 24 sediment samples by dilution plating on six different isolation media. Among them, morphologically 18 distinct selected isolates of actinomycetes were verified by 16S rRNA gene sequencing and identified as Streptomyces spp. The relationship between diversity of total actinomycetes population (TAP) and its antagonistic behaviour with the physico-chemical characteristics of sediment samples were investigated. Multiple regression analysis revealed that the influencing physico-chemical factors comprises of sediment temperature, sediment pH, organic carbon and heavy metals. The results of statistical analysis showed that TAP is positively correlated (p < 0.01) with sediment organic carbon whereas, negatively correlated with Cr (p < 0.05) and Mn (p < 0.01). Based on Principle component Analysis (PCA) and cluster analysis results, the obtained six stations can be divided into three groups. Among them mobile fraction of metals, TAP could be the main factor reflecting the lower and middle estuary. The recovery of large number of actinomycete isolates suggests that Patalganga Estuary could be potential source of bioactive compounds with biosynthetic capabilities.

Inhibition and eradication of Pseudomonas aeruginosa biofilms by secondary metabolites of Nocardiopsis lucentensis EMB25

Millions of people worldwide have been impacted by biofilm-associated disorders, which are impregnable owing to frequent changes in surface antigens and gene expression. Globally, about 11% of nosocomial infections, including cystic fibrosis, chronic wound infections, and post-surgical infections, are caused by Pseudomonas aeruginosa, the most prevalent Gram-negative bacterial species. Moreover, biofilms are highly resistant to the host's immune system, and exhibit increased tolerance to stress factors such as starvation, dehydration, and antimicrobials. Here, we have isolated a rare halophilic actinobacteria, Nocardiopsis lucentensis EMB25, and utilized the secondary metabolites for inhibition and eradication of P. aeruginosa biofilm. For the first time, N. lucentensis EMB25 bacteria was explored to study the anti-effect of secondary metabolites on pre-established biofilm. The secondary metabolites targeted the quorum sensing pathway and were found to bind to LasR and RhlR, as confirmed via molecular docking. Also, the reduction in virulence factors, rhamnolipids and pyocyanin further supported the study as these two are regulated by LasR and RhlR. In addition, the downregulation of various QS system genes lasA, lasB, rhlA, rhlB, and pqsA confirmed that the secondary metabolites act on two main regulators of the quorum sensing pathway, LasR, and RhlR. The findings of this study support the bioprospecting of previously unknown and extreme-condition actinobacteria as a rich source of novel bioactives against infections caused by bacterial biofilms.

Bacterial microbiome in tropical lichens and the effect of the isolation method on culturable lichen-derived actinobacteria

Ten samples of tropical lichens collected from Doi Inthanon, Thailand, were explored for the diversity of their bacterial microbiomes through 16S rRNA-based metagenomics analysis. The five predominant lichen-associated bacteria belonged to the phyla Proteobacteria (31.84%), Planctomycetota (17.08%), Actinobacteriota (15.37%), Verrucomicrobiota (12.17%), and Acidobacteriota (7.87%). The diversity analysis metric showed that Heterodermia contained the highest bacterial species richness. Within the lichens, Ramalina conduplicans and Cladonia rappii showed a distinct bacterial community from the other lichen species. The community of lichen-associated actinobacteria was investigated as a potential source of synthesized biologically active compounds. From the total Operational Taxonomic Units (OTUs) found across the ten different lichen samples, 13.21% were identified as actinobacteria, including the rare actinobacterial genera that are not commonly found, such as Pseudonocardia, Kineosporia, Dactylosporangium, Amycolatopsis, Actinoplanes, and Streptosporangium. Evaluation of the pretreatment method (heat, air-drying, phenol, and flooding) and isolation media used for the culture-dependent actinobacterial isolation revealed that the different pretreatments combined with different isolation media were effective in obtaining several species of actinobacteria. However, metagenomics analyses revealed that there were still several strains, including rare actinobacterial species, that were not isolated. This research strongly suggests that lichens appear to be a promising source for obtaining actinobacteria.

Polyene Carboxylic Acids from a Streptomyces sp. Isolated from Tibet Soil

Six new polyene carboxylic acids named serpentemycins E–J (1–6), together with three known analogs (7–9), were isolated from the fermentation medium of Streptomyces sp. TB060207, which was isolated from arid soil collected from Tibet, China. The structures of the new compounds were elucidated mainly on the basis of HR-ESI-MS and NMR spectroscopic analyses. The inhibitory activities of compounds 1–9 against NO production in LPS-activated RAW264.7 cells were evaluated. Compound 9 has an inhibition rate of 87.09% to 60.53% at concentrations ranging from 5.0 to 40.0 µM.

Bioactivity of bacteria associated with Red Sea nudibranchs and whole genome sequence of Nocardiopsis dassonvillei RACA-4

Microorganisms associated with marine invertebrates consider an important source of bioactive products. This study aimed to screen for antimicrobial and anticancer activity of crude extracts of bacteria associated with Red sea nudibranchs and molecular identification of the bioactive isolates using 16Sr RNA sequencing, in addition to whole-genome sequencing of one of the most bioactive bacteria. This study showed that bacteria associated with Red sea nudibranchs are highly bioactive and 16Sr RNA sequencing results showed that two isolates belonged to Firmicutes, and two isolates belonged to Proteobacteria, and Actinobacteria. The whole genome sequence data of the isolated Nocardiopsis RACA4 isolate has an estimated genome length of 6,721,839 bp and the taxonomy showed it belongs to the bacteria Nocardiopsis dassonvillei. The De novo assembly of RACA-4 paired reads using Unicycler v0.4.8 initially yielded 97 contigs with an N50 value of 214,568 bp and L50 value of 10, The resulting assembly was further mapped to the reference genome Nocardiopsis dassonvillei strain NCTC10488 using RagTag software v.2.1.0 and a final genome assembly resulted in 39 contigs and N50 value of 6,726,007 and L50 of 1. Genome mining using anti-smash showed around 9.1% of the genome occupied with genes related to secondary metabolites biosynthesis. A wide variety of secondary metabolites belonging to Polyketides, Terpenes, and nonribosomal peptides were predicted with high degree of similarity to known compounds. Non-characterized clusters were also found which suggest new natural compounds discovered by further studies.

Microbiological analysis, antimicrobial activity, heavy-metals content and physico-chemical properties of Fijian mud pool samples

The hot springs are home to a rich bacterial diversity which could be the source of enzymes, antibiotics and many other commercially important products. Most of the hot springs present in Fiji are unexplored and their analysis of microbial diversity could be of great interest in facilitating various industrial, agricultural and medicinal applications. This study is an attempt to evaluate the heavy metal concentration and to analyze the comprehensive bacterial diversity of two Fijian thermal mud pools, namely Sabeto and Tifajek. The two hot springs have a pH of 7.28 to 7.19 and a temperature of 32.2 to 38.8 °C, respectively. Mean metal concentrations of the studied mud samples ranged from 4.758 to 6.870 mg/kg and followed a decreasing sequence as Fe > Mn > Zn > Na > Ni > Cd > Ca > Cr > Cu. Levels of Fe, Na, Mn, Zn, Ni, Cd, Ca, Cr, Cu in the mud pool samples were within World Health Organisation (WHO) limits, while Cd was above regulatory limits. The heavy metals analysis results showed that both mud pools had high values for Cd, above the WHO limit of 3 mg/kg. In addition, 8 strains of actinomycetes were successfully identified for the first time in the Sabeto mud pool, where most of them showed antibacterial activity. The genetic identification of most isolates was determined in BLASTn analyses of their 16S rRNA sequences. Isolates were identified as that of Streptomyces, Nocardia and Rhodococcus genus. Further, AntiSMASH results of the closest relatives of cultured actinobacteria have shown to produce antibiotics, natural pesticides and other compounds of various usage. This study also found no fecal coliforms and supports existing knowledge and practice of using Fijian thermal mud pools for their therapeutic properties. Overall, the presented work indicated that the studied mud pools have therapeutic properties, harboring wealth of bacteria with antibiotic profiles and were risk free from health-related issues of heavy metals and disease-causing pathogens. It provides great insight into the studied mud pools which serves as a baseline from which further heavy metal monitoring or mitigation programs and microbial researches can be conducted.

Isolation and Characterization of a Novel Actinomycete Isolated from Marine Sediments and Its Antibacterial Activity against Fish Pathogens

Marine habitats are especially complex, with a varied diversity of living organisms. Marine organisms, while living in such intense conditions, have developed great physiological and metabolic potential to survive. This has led them to produce several potent metabolites, which their terrestrial counterparts are unable to produce. Over the past few years, marine Actinomycetes have been considered one of the most abundant sources of diverse and novel metabolites. In this work, an attempt was made to isolate Actinomycetes from marine sediments in terms of their ability to produce several novel bioactive compounds. A total of 16 different Actinomycete colonies were obtained from marine sediment samples. Among the 16 Actinomycete isolates, 2 isolates demonstrated in vitro antibacterial activity against Aeromonas hydrophila and Vibrio parahemolyticus. However, among them, only one isolate was found to have potent antibacterial activity, and hence, was taken for further analysis. This isolate was designated as Beijerinickia fluminensis VIT01. The bioactive components obtained were extracted and later subjected to Fourier transform infrared spectroscopy (FTIR) and gas chromatography-mass spectroscopy (GC-MS) analyses for identification. Several novel bioactive compounds were reported from the data obtained and were found to have potent antibacterial activity. Hence, they could be used as an alternative to antibiotics for treating several fish pathogens in the aquaculture industry.

Draft Genome Sequences of Three Streptomycetes Isolated from Frobisher Bay Marine Sediments

Three Streptomyces strains (RKAG290, RKAG293, and RKAG337) were isolated from intertidal marine sediments of Frobisher Bay (Canada).

Habitat-adapted heterologous symbiont Salinispora arenicola promotes growth and alleviates salt stress in tomato crop plants

To ensure food security given the current scenario of climate change and the accompanying ecological repercussions, it is essential to search for new technologies and tools for agricultural production. Microorganism-based biostimulants are recognized as sustainable alternatives to traditional agrochemicals to enhance and protect agricultural production. Marine actinobacteria are a well-known source of novel compounds for biotechnological uses. In addition, former studies have suggested that coral symbiont actinobacteria may support co-symbiotic photosynthetic growth and tolerance and increase the probability of corals surviving abiotic stress. We have previously shown that this activity may also hold in terrestrial plants, at least for the actinobacteria Salinispora arenicola during induced heterologous symbiosis with a wild Solanaceae plant Nicotiana attenuata under in vitro conditions. Here, we further explore the heterologous symbiotic association, germination, growth promotion, and stress relieving activity of S. arenicola in tomato plants under agricultural conditions and dig into the possible associated mechanisms. Tomato plants were grown under normal and saline conditions, and germination, bacteria-root system interactions, plant growth, photosynthetic performance, and the expression of salt stress response genes were analyzed. We found an endophytic interaction between S. arenicola and tomato plants, which promotes germination and shoot and root growth under saline or non-saline conditions. Accordingly, photosynthetic and respective photoprotective performance was enhanced in line with the induced increase in photosynthetic pigments. This was further supported by the overexpression of thermal energy dissipation, which fine-tunes energy use efficiency and may prevent the formation of reactive oxygen species in the chloroplast. Furthermore, gene expression analyses suggested that a selective transport channel gene, SlHKT1,2, induced by S. arenicola may assist in relieving salt stress in tomato plants. The fine regulation of photosynthetic and photoprotective responses, as well as the inhibition of the formation of ROS molecules, seems to be related to the induced down-regulation of other salt stress response genes, such as SlDR1A-related genes or SlAOX1b. Our results demonstrate that the marine microbial symbiont S. arenicola establishes heterologous symbiosis in crop plants, promotes growth, and confers saline stress tolerance. Thus, these results open opportunities to further explore the vast array of marine microbes to enhance crop tolerance and food production under the current climate change scenario.

Tromethamine and dodecanol appear to be the major secondary metabolites of Streptomyces decoyicus M

An isolate of Streptomyces decoyicus M* (code of the isolate) was identified by the sequencing of 16S rRNA gene. It was grown on solid media and secondary metabolites were extracted with n-butanol. The extract was dried and run in a sodium dodecyl sulphate-polyacrylamide gel (SDS-PAGE, 10%). Two main bands obtained were sliced and the metabolites were regained in n-butanol. These two samples were then identified by gas-chromatography-mass spectrometry (GC-MS), and Fourier-transform infrared spectroscopy (FT-IR). The results demonstrated that tromethamine- and 1-dodecanol were the main constituents (band 1: 61% and 17.7%; band 2: 41% and 54%, respectively). This finding maintained that the isolate of Streptomyces decoyicus produced high amounts tromethamine- and 1-dodecanol under the conditions investigated.

Marine Actinomycetes Associated with Stony Corals: A Potential Hotspot for Specialized Metabolites

Microbial secondary metabolites are an important source of antibiotics currently available for combating drug-resistant pathogens. These important secondary metabolites are produced by various microorganisms, including Actinobacteria. Actinobacteria have a colossal genome with a wide array of genes that code for several bioactive metabolites and enzymes. Numerous studies have reported the isolation and screening of millions of strains of actinomycetes from various habitats for specialized metabolites worldwide. Looking at the extent of the importance of actinomycetes in various fields, corals are highlighted as a potential hotspot for untapped secondary metabolites and new bioactive metabolites. Unfortunately, knowledge about the diversity, distribution and biochemistry of marine actinomycetes compared to hard corals is limited. In this review, we aim to summarize the recent knowledge on the isolation, diversity, distribution and discovery of natural compounds from marine actinomycetes associated with hard corals. A total of 11 new species of actinomycetes, representing nine different families of actinomycetes, were recovered from hard corals during the period from 2007 to 2022. In addition, this study examined a total of 13 new compounds produced by five genera of actinomycetes reported from 2017 to 2022 with antibacterial, antifungal and cytotoxic activities. Coral-derived actinomycetes have different mechanisms of action against their competitors.

Antimicrobial Potential of Extract from a Pseudomonas aeruginosa Isolate

Microorganisms are one of the main sources of antimicrobial agents and over 50% of antibiotics currently used in hospitals are metabolites from microbes. This study aimed to isolate microorganisms from the Dompoase landfill site, Kwame Nkrumah University Physics Garden, Kosiko River, and Ada Foah seashore of Ghana and screen their metabolites for antimicrobial activity. Forty-eight (48) microorganisms were isolated and their metabolites were screened against Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, Klebsiella pneumoniae, Vibrio cholerae, Salmonella typhi, Pseudomonas aeruginosa, Streptococcus pyogenes, Proteus mirabilis, and Candida albicans using the agar well diffusion method. Ten (10) of the isolates exhibited antimicrobial activity. Isolate DO5, identified as P. aeruginosa isolate, from the Dompoase landfill site was selected for fermentation because it exhibited the highest activity against all the test organisms. DO5 produced optimum antimicrobial activity when fermented for 11 days at 30°C. In the agar diffusion method, the extract of isolate DO5 recorded zones of inhibition ranging between 11.67 ± 0.23 and 21.50 ± 0.71 mm. The MIC and MBC recorded for the DO5 extract ranged from 3.13-25.0 mg/mL and from 6.25-50.0 mg/mL, respectively. Column chromatography analysis yielded eight (8) subfractions from the DO5 extract. IR analysis revealed the presence of functional groups such as alcohols, esters, and hydrocarbons in the fractions. GC-MS analysis identified nine compounds that have been reported to have antimicrobial agents. The DO5 metabolites stand the chance to be developed into potent antibiotics for infection treatment.

Characterization of a Deep-Sea Actinobacterium Strain Uncovers Its Prominent Capability of Utilizing Taurine and Polyvinyl Alcohol

Actinobacteria represent a large group of important prokaryotes with great application potentials and widely distribute in diverse natural environments including the ocean. However, compared to their terrestrial cultured members, there are much less available marine Actinobacteria, especially deep-sea counterparts. Here, we cultured a bacterial strain of deep-sea actinobacterium, Marmoricola sp. TYQ2, by using a basal medium supplemented with taurine. Consistently, the growth of strain TYQ2 was significantly promoted by the supplement of taurine. Transcriptomic analysis showed that the expressions of genes encoding proteins associated with taurine metabolization and utilization as well as energy generation were evidently up-regulated when taurine was added. Moreover, strain TYQ2 was demonstrated to degrade polyvinyl alcohol (PVA) with the involvement of the redox cycle of extracellular quinol and quinone and the reduction of iron to ferrous, and strain TYQ2 could utilize the degradation products for energy production, thereby supporting bacterial growth. Overall, our experimental results demonstrate the prominent degradation capabilities of Marmoricola sp. TYQ2 toward the organics taurine and PVA.

Structure and Candidate Biosynthetic Gene Cluster of a Manumycin-Type Metabolite from Salinispora pacifica

A new manumycin-type natural product named pacificamide (1) and its candidate biosynthetic gene cluster (pac) were discovered from the marine actinobacterium Salinispora pacifica CNT-855. The structure of the compound was determined using NMR, electronic circular dichroism, and bioinformatic predictions. The pac gene cluster is unique to S. pacifica and found in only two of the 119 Salinispora genomes analyzed across nine species. Comparative analyses of biosynthetic gene clusters encoding the production of related manumycin-type compounds revealed genetic differences in accordance with the unique pacificamide structure. Further queries of manumycin-type gene clusters from public databases revealed their limited distribution across the phylum Actinobacteria and orphan diversity that suggests additional products remain to be discovered in this compound class. Production of the known metabolite triacsin D is also reported for the first time from the genus Salinispora. This study adds two classes of compounds to the natural product collective isolated from the genus Salinispora, which has proven to be a useful model for natural product research.

Rare actinobacteria isolated from the hypersaline Ojo de Liebre Lagoon as a source of novel bioactive compounds with biotechnological potential

The Ojo de Liebre Lagoon is a Marine Protected Area that lies within a UNESCO World Heritage Site and is a critical habitat for important migratory species such as the grey whale and bird species. Unique hypersaline environments, such as the Ojo de Liebre Lagoon, are underexplored in terms of their bacterial and chemical diversity, representing a potential source for new bioactive compounds with pharmacological properties. Actinobacteria are one of the most diverse and prolific taxonomic bacterial groups in terms of marine bioactive compounds. This study aimed to identify the culturable actinobacterial community inhabiting the Lagoon, as well as to test their potential as new sources of anticancer compounds with pharmacological potential. A selective isolation approach focused on spore-forming bacteria from 40 sediment samples generated a culture collection of 64 strains. The 16S rRNA gene analyses identified three phyla in this study, the Actinobacteria, Firmicutes and Proteobacteria, where the phylum Actinobacteria dominated (57%) the microbial community profiles. Within the Actinobacteria, nine different genera were isolated including the Actinomadura, Micromonospora, Nocardiopsis, Plantactinospora and Streptomyces sp. We observed seasonal differences on actinobacteria recovery. For instance, Micromonospora strains were recovered during the four sampling seasons, while Arthrobacter and Pseudokineococcus were only isolated in February 2018, and Blastococcus, Rhodococcus and Streptomyces were uniquely isolated in June 2018. Ethyl acetate crude extracts derived from actinobacterial cultures were generated and screened for cytotoxic activity against six cancer cell lines. Strains showed promising low percentages of viability on lung (H1299), cervical (SiHa), colon (Caco-2) and liver (HepG2) cancer lines. Molecular networking results suggest many of the metabolites produced by these strains are unknown and they might harbour novel chemistry. Our results showed the Ojo de Liebre Lagoon is a novel source for isolating diverse marine actinobacteria which produce promising bioactive compounds for potential biotechnological use as anticancer agents.

Salsipaludibacter albus gen. nov., sp. nov., a novel actinobacterial strain isolate from a Portuguese solar saltern and proposal of Salsipaludibacteraceae fam. nov. and Salsipaludibacterales ord. nov

A novel micro-organism designated AS10T was isolated from dry salt collected from Aveiro saltern in the north of Portugal. Cells were Gram-stain-positive, non-motile, non-endospore-forming, rod-shaped and aerobic. Strain AS10T was characterized by long filaments of rod-shaped cells, presenting also coccoid cellular forms at the end of the filaments, unveiling some pleomorphism. Rod-shaped cells varied from 0.3 to 0.6 µm wide and from 0.6 to 2 µm long. Growth of AS10T occurred at 15–40 °C (optimum, 20–30 °C), 0–10% (w/v) NaCl (optimum, 2%) and pH 4.5–11.0 (optimum, pH 8.0–11.0). The peptidoglycan type was A1ϒ-type with 3-hydroxy-diaminopimelic acid. The major fatty acids were C16:0, iso-C14:0, C17:0 and C14:0. The major respiratory quinone was MK-9(H4). Phylogenetic analysis based on 16S rRNA gene sequences showed that strain AS10T was similar to actinobacterial members of the class Nitriliruptoria , with Nitriliruptor alkaliphilus ANL-iso2T being the closest relative the species with a sequence pairwise similarity of 91.21%. Average nucleotide identity, average amino acid identity and in silico DNA–DNA hybridization values between strain AS10T and N. alkaliphilus ANL-iso2T were 71.34, 53.57 and 18.90%, respectively. The genome DNA G+C content of AS10T was 71.8 mol%. Based on genomic, phylogenetic, phenotypic and chemotaxonomic studies, we describe a new species of a novel genus represented by strain AS10T (=LMG 31937T=CECT 30148T) for which we propose the name Salsipaludibacter albus gen. nov., sp. nov. We also propose that this organism represents a new family named Salsipaludibacteraceae fam. nov. of a novel order named Salsipaludibacterales ord. nov.

Metataxanomic, bioactivity and microbiome analysis of Red Sea marine sponges from Egypt

Red Sea marine sponges (phylum Porifera) and associated microorganisms harbor a wide range of microorganisms, which are considered an essential source of bioactive products. In this study, we screened both the crude extracts of Red Sea marine sponges and their associated bacterial extract for antimicrobial activity and antiviral activity. Molecular characterization of bioactive producers was performed using16S rRNA sequencing, in addition to metagenomic analysis of three representative sponges utilizing the 16S rRNA gene V3-V4 region sequencing in two different seasons. Twelve samples were collected from five different sponge species by scuba diving, and all the crude extracts of sponges showed antimicrobial activity except Negombata corticata. Moreover, 84 out of 110 bacterial isolates extracts demonstrated antimicrobial activity against at least one tested microorganism. These results revealed the bioactivity and biodiversity of the Red Sea marine invertebrates-associated bacteria. It was found that the bioactive isolates belong to several bacterial groups. The bacterial communities of Negombata magnifica, Negombata corticata, and Siphonochalina siphonella were shown with great diversity and differences in the bacterial percentage, diversity, and unique community composition at different seasons in each sponge species. Unique microenvironment for each sponge species may be linked to the production of specific bioactive product.

The Diversity, Metabolomics Profiling, and the Pharmacological Potential of Actinomycetes Isolated from the Estremadura Spur Pockmarks (Portugal)

The Estremadura Spur pockmarks are a unique and unexplored ecosystem located in the North Atlantic, off the coast of Portugal. A total of 85 marine-derived actinomycetes were isolated and cultured from sediments collected from this ecosystem at a depth of 200 to 350 m. Nine genera, Streptomyces, Micromonospora, Saccharopolyspora, Actinomadura, Actinopolymorpha, Nocardiopsis, Saccharomonospora, Stackebrandtia, and Verrucosispora were identified by 16S rRNA gene sequencing analyses, from which the first two were the most predominant. Non-targeted LC-MS/MS, in combination with molecular networking, revealed high metabolite diversity, including several known metabolites, such as surugamide, antimycin, etamycin, physostigmine, desferrioxamine, ikarugamycin, piericidine, and rakicidin derivatives, as well as numerous unidentified metabolites. Taxonomy was the strongest parameter influencing the metabolite production, highlighting the different biosynthetic potentials of phylogenetically related actinomycetes; the majority of the chemical classes can be used as chemotaxonomic markers, as the metabolite distribution was mostly genera-specific. The EtOAc extracts of the actinomycete isolates demonstrated antimicrobial and antioxidant activity. Altogether, this study demonstrates that the Estremadura Spur is a source of actinomycetes with potential applications for biotechnology. It highlights the importance of investigating actinomycetes from unique ecosystems, such as pockmarks, as the metabolite production reflects their adaptation to this habitat.

Vertical Inheritance Facilitates Interspecies Diversification in Biosynthetic Gene Clusters and Specialized Metabolites

While specialized metabolites are thought to mediate ecological interactions, the evolutionary processes driving chemical diversification, particularly among closely related lineages, remain poorly understood. Here, we examine the evolutionary dynamics governing the distribution of natural product biosynthetic gene clusters (BGCs) among 118 strains representing all nine currently named species of the marine actinobacterial genus Salinispora. While much attention has been given to the role of horizontal gene transfer (HGT) in structuring BGC distributions, we find that vertical descent facilitates interspecies BGC diversification over evolutionary timescales. Moreover, we identified a distinct phylogenetic signal among Salinispora species at both the BGC and metabolite level, indicating that specialized metabolism represents a conserved phylogenetic trait. Using a combination of genomic analyses and liquid chromatography–high-resolution tandem mass spectrometry (LC-MS/MS) targeting nine experimentally characterized BGCs and their small molecule products, we identified gene gain/loss events, constrained interspecies recombination, and other evolutionary processes associated with vertical inheritance as major contributors to BGC diversification. These evolutionary dynamics had direct consequences for the compounds produced, as exemplified by species-level differences in salinosporamide production. Together, our results support the concept that specialized metabolites, and their cognate BGCs, can represent phylogenetically conserved functional traits with chemical diversification proceeding in species-specific patterns over evolutionary time frames.

A Meta-Omics Analysis Unveils the Shift in Microbial Community Structures and Metabolomics Profiles in Mangrove Sediments Treated with a Selective Actinobacterial Isolation Procedure

Mangrove sediment ecosystems in the coastal areas of the Yucatan peninsula are unique environments, influenced by their karstic origin and connection with the world’s largest underground river. The microbial communities residing in these sediments are influenced by the presence of mangrove roots and the trading chemistry for communication between sediment bacteria and plant roots can be targeted for secondary metabolite research. To explore the secondary metabolite production potential of microbial community members in mangrove sediments at the “El Palmar” natural reserve in Sisal, Yucatan, a combined meta-omics approach was applied. The effects of a cultivation medium reported to select for actinomycetes within mangrove sediments’ microbial communities was also analyzed. The metabolome of the microbial communities was analyzed by high-resolution liquid chromatography-tandem mass spectrometry, and molecular networking analysis was used to investigate if known natural products and their variants were present. Metagenomic results suggest that the sediments from “El Palmar” harbor a stable bacterial community independently of their distance from mangrove tree roots. An unexpected decrease in the observed abundance of actinomycetes present in the communities occurred when an antibiotic-amended medium considered to be actinomycete-selective was applied for a 30-day period. However, the use of this antibiotic-amended medium also enhanced production of secondary metabolites within the microbial community present relative to the water control, suggesting the treatment selected for antibiotic-resistant bacteria capable of producing a higher number of secondary metabolites. Secondary metabolite mining of “El Palmar” microbial community metagenomes identified polyketide synthase and non-ribosomal peptide synthetases’ biosynthetic genes in all analyzed metagenomes. The presence of these genes correlated with the annotation of several secondary metabolites from the Global Natural Product Social Molecular Networking database. These results highlight the biotechnological potential of the microbial communities from “El Palmar”, and show the impact selective media had on the composition of communities of actinobacteria.

Phylogenetic diversity and activity screening of cultivable Actinobacteria isolated from marine sponges and associated environments from the western coast of India

The phylogenetic diversity of cultivable actinobacteria isolated from sponges (Haliclona spp.) and associated intertidal zone environments along the northern parts of the western coast of India were studied using 16S rRNA gene sequences. A subset of randomly selected actinobacterial cultures were screened for three activities, namely predatory behaviour, antibacterial activity and enzyme inhibition. We recovered 237 isolates from the phylum Actinobacteria belonging to 19 families and 28 genera, which could be attributed to 95 putative species using maximum-likelihood partition and 100 putative species using Bayesian partition in Poisson tree processes. Although the trends in the discovery of actinobacterial genera isolated from sponges were consistent with previous studies from different study areas, we provide the first report of nine actinobacterial species from sponges. We observed widespread non-obligate epibiotic predatory behaviour in eight actinobacterial genera and we provide the first report of predatory activity in Brevibacterium, Glutamicibacter, Micromonospora, Nocardiopsis, Rhodococcus and Rothia. Sponge-associated actinobacteria showed significantly more predatory behaviour than environmental isolates. While antibacterial activity by actinobacterial isolates mainly affected Gram-positive target bacteria with little or no effect on Gram-negative bacteria, predation targeted both Gram-positive and Gram-negative prey with equal propensity. Actinobacterial isolates from both sponges and associated environments produced inhibitors of serine proteases and angiotensin-converting enzyme. Predatory behaviour was strongly associated with inhibition of trypsin and chymotrypsin. Our study suggests that the sponges and associated environments of the western coast of India are rich in actinobacterial diversity, with widespread predatory activity, antibacterial activity and production of enzyme inhibitors. Understanding the diversity and associations among various actinobacterial activities – with each other and the source of isolation – can provide new insights into marine microbial ecology and provide opportunities to isolate novel therapeutic agents.

Antagonistic Potential of Soil Streptomyces Isolates from Southern Thailand to Inhibit Foodborne Bacterial Pathogens

Streptomyces are well known for their competence to produce thousands of bioactive secondary metabolites and enzymes. This study aimed to assess the inhibitory activities of crude extracts from diverse Streptomyces collected from rice soils in Narathiwat, Thailand, against foodborne bacterial pathogens. In total, 136 Actinomycete isolates were screened using a cross-streak method for the ability to produce effective metabolites against 5 pathogenic bacteria. Out of these, 19 (13.97%) isolates had antibacterial activity against at least one tested bacterium. Most of the isolates could strongly suppress the growth of S. aureus ATCC25923 and B. cereus MTCC430 except P. aeruginosa ATCC27853. On the basis of morphological, cultural, and biochemical characteristics, all potent isolates exhibited typical features that fitted the genus Streptomyces. Two of the 7 selected ethyl acetate crude extracts had good antagonistic activity against S. aureus ATCC25923 and B. cereus MTCC430 when tested using the agar well diffusion assay. Furthermore, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values of the 2 extracts evaluated using the colorimetric broth microdilution method ranged from 256 to >1,024 μg/ml against the tested bacteria. The partial nucleotide sequences of the 16S rRNA gene led to identifying both active isolates as Streptomyces species. These active Streptomyces isolates could provide an interesting source for generating innumerable natural compounds with antibacterial activity that can presumably be developed to fight bacterial pathogens in the near future.

Multiple strain analysis of Streptomyces species from Philippine marine sediments reveals intraspecies heterogeneity in antibiotic activities

The marine ecosystem has become the hotspot for finding antibiotic-producing actinomycetes across the globe. Although marine-derived actinomycetes display strain-level genomic and chemodiversity, it is unclear whether functional traits, i.e., antibiotic activity, vary in near-identical Streptomyces species. Here, we report culture-dependent isolation, antibiotic activity, phylogeny, biodiversity, abundance, and distribution of Streptomyces isolated from marine sediments across the west-central Philippines. Out of 2212 marine sediment-derived actinomycete strains isolated from 11 geographical sites, 92 strains exhibited antibacterial activities against multidrug-resistant Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli. The 16S rRNA and rpoB gene sequence analyses confirmed that antibiotic-producing strains belong to the genus Streptomyces, highlighting Streptomyces parvulus as the most dominant species and three possible new species. Antibiotic-producing Streptomyces strains were highly diverse in Southern Antique, and species diversity increase with marine sediment depth. Multiple strains with near-identical 16S rRNA and rpoB gene sequences displayed varying strength of antibiotic activities. The genotyping of PKS and NRPS genes revealed that closely related antibiotic-producing strains have similar BGC domains supported by their close phylogenetic proximity. These findings collectively suggest Streptomyces' intraspecies adaptive characteristics in distinct ecological niches that resulted in outcompeting other bacteria through differential antibiotic production.

Pseudonocardia abyssalis sp. nov. and Pseudonocardia oceani sp. nov., two novel actinomycetes isolated from the deep Southern Ocean

The actinomycetes strains KRD168T and KRD185T were isolated from sediments collected from the deep Southern Ocean and, in this work, they are described as representing two novel species of the genus Pseudonocardia through a polyphasic approach. Despite sharing >99 % 16S rRNA gene sequence similarity with other members of the genus, comparative genomic analysis allowed species delimitation based on average nucleotide identity and digital DNA-DNA hybridization. The KRD168T genome is characterized by a size of 6.31 Mbp and a G+C content of 73.44 mol%, while the KRD185T genome has a size of 6.82 Mbp and a G+C content of 73.98 mol%. Both strains contain meso-diaminopimelic acid as the diagnostic diamino acid, glucose as the major whole-cell sugar, MK-8(H4) as a major menaquinone and iso-branched hexadecanoic acid as a major fatty acid. Biochemical and fatty acid analyses also revealed differences between these strains and their phylogenetic neighbours, supporting their status as distinct species. The names Pseudonocardia abyssalis sp. nov. (type strain KRD168T=DSM 111918T=NCIMB 15270T) and Pseudonocardia oceani (type strain KRD185T=DSM 111919T=NCIMB 15269T) are proposed.

Marine Actinomycetes, New Sources of Biotechnological Products

The Actinomycetales order is one of great genetic and functional diversity, including diversity in the production of secondary metabolites which have uses in medical, environmental rehabilitation, and industrial applications. Secondary metabolites produced by actinomycete species are an abundant source of antibiotics, antitumor agents, anthelmintics, and antifungals. These actinomycete-derived medicines are in circulation as current treatments, but actinomycetes are also being explored as potential sources of new compounds to combat multidrug resistance in pathogenic bacteria. Actinomycetes as a potential to solve environmental concerns is another area of recent investigation, particularly their utility in the bioremediation of pesticides, toxic metals, radioactive wastes, and biofouling. Other applications include biofuels, detergents, and food preservatives/additives. Exploring other unique properties of actinomycetes will allow for a deeper understanding of this interesting taxonomic group. Combined with genetic engineering, microbial experimental evolution, and other enhancement techniques, it is reasonable to assume that the use of marine actinomycetes will continue to increase. Novel products will begin to be developed for diverse applied research purposes, including zymology and enology. This paper outlines the current knowledge of actinomycete usage in applied research, focusing on marine isolates and providing direction for future research.

Diversity and Antimicrobial Activity of Vietnamese Sponge-Associated Bacteria

This study aimed to assess the diversity and antimicrobial activity of cultivable bacteria associated with Vietnamese sponges. In total, 460 bacterial isolates were obtained from 18 marine sponges. Of these, 58.3% belonged to Proteobacteria, 16.5% to Actinobacteria, 18.0% to Firmicutes, and 7.2% to Bacteroidetes. At the genus level, isolated strains belonged to 55 genera, of which several genera, such as Bacillus, Pseudovibrio, Ruegeria, Vibrio, and Streptomyces, were the most predominant. Culture media influenced the cultivable bacterial composition, whereas, from different sponge species, similar cultivable bacteria were recovered. Interestingly, there was little overlap of bacterial composition associated with sponges when the taxa isolated were compared to cultivation-independent data. Subsequent antimicrobial assays showed that 90 isolated strains exhibited antimicrobial activity against at least one of seven indicator microorganisms. From the culture broth of the isolated strain with the strongest activity (Bacillus sp. M1_CRV_171), four secondary metabolites were isolated and identified, including cyclo(L-Pro-L-Tyr) (1), macrolactin A (2), macrolactin H (3), and 15,17-epoxy-16-hydroxy macrolactin A (4). Of these, compounds 2-4 exhibited antimicrobial activity against a broad spectrum of reference microorganisms.

Complete Genome Sequence of Streptomyces sp. Strain CA-256286

Here, we report the sequencing, assembly, and annotation of the genome of Streptomyces sp. strain CA-256286. The genome consists of a linear 7,726,360-nucleotide chromosome and a linear 466,817-nucleotide putative plasmid. This strain is predicted to produce a range of novel secondary metabolites.

Functional assembly of root-associated microbial consortia improves nutrient efficiency and yield in soybean

Root-associated microbes are critical for plant growth and nutrient acquisition. However, scant information exists on optimizing communities of beneficial root-associated microbes or the mechanisms underlying their interactions with host plants. In this report, we demonstrate that root-associated microbes are critical influencers of host plant growth and nutrient acquisition. Three synthetic communities (SynComs) were constructed based on functional screening of 1,893 microbial strains isolated from root-associated compartments of soybean plants. Functional assemblage of SynComs promoted significant plant growth and nutrient acquisition under both N/P nutrient deficiency and sufficiency conditions. Field trials further revealed that application of SynComs stably and significantly promoted plant growth, facilitated N and P acquisition, and subsequently increased soybean yield. Among the tested communities, SynCom1 exhibited the greatest promotion effect, with yield increases of up to 36.1% observed in two field sites. Further RNA-seq implied that SynCom application systemically regulates N and P signaling networks at the transcriptional level, which leads to increased representation of important growth pathways, especially those related to auxin responses. Overall, this study details a promising strategy for constructing SynComs based on functional screening, which are capable of enhancing nutrient acquisition and crop yield through the activities of beneficial root-associated microbes.

Laboratory scale cultivation of Salinispora tropica in shake flasks and mechanically stirred bioreactors

OBJECTIVE

Marine actinomycetes from the genus Salinispora have an unexploited biotechnological potential. To accurately estimate their application potential however, data on their cultivation, including biomass growth kinetics, are needed but only incomplete information is currently available.

RESULTS

This work provides some insight into the effect of temperature, salinity, nitrogen source, glucose concentration and oxygen supply on growth rate, biomass productivity and yield of Salinispora tropica CBN-440^T. The experiments were carried out in unbaffled shake flasks and agitated laboratory-scale bioreactors. The results show that the optimum growth temperature lies within the range 28-30 °C, salinity is close to sea water and the initial glucose concentration is around 10 g/L. Among tested nitrogen sources, yeast extract and soy peptone proved to be the most suitable. The change from unbaffled to baffled flasks increased the volumetric oxygen transfer coefficient (k_La) as did the use of agitated bioreactors. The highest specific growth rate (0.0986 h^-1) and biomass productivity (1.11 g/L/day) were obtained at k_La = 28.3 h^-1. A further increase in k_La was achieved by increasing stirrer speed, but this led to a deterioration in kinetic parameters.

CONCLUSIONS

Improvement of S. tropica biomass growth kinetics of was achieved mainly by identifying the most suitable nitrogen sources and optimizing k_La in baffled flasks and agitated bioreactors.

Secondary metabolites and biodiversity of actinomycetes

BACKGROUND

The ability to produce microbial bioactive compounds makes actinobacteria one of the most explored microbes among prokaryotes. The secondary metabolites of actinobacteria are known for their role in various physiological, cellular, and biological processes.

MAIN BODY

Actinomycetes are widely distributed in natural ecosystem habitats such as soil, rhizosphere soil, actinmycorrhizal plants, hypersaline soil, limestone, freshwater, marine, sponges, volcanic cave-hot spot, desert, air, insects gut, earthworm castings, goat feces, and endophytic actinomycetes. The most important features of microbial bioactive compounds are that they have specific microbial producers: their diverse bioactivities and their unique chemical structures. Actinomycetes represent a source of biologically active secondary metabolites like antibiotics, biopesticide agents, plant growth hormones, antitumor compounds, antiviral agents, pharmacological compounds, pigments, enzymes, enzyme inhibitors, anti-inflammatory compounds, single-cell protein feed, and biosurfactant.

SHORT CONCLUSIONS

Further highlight that compounds derived from actinobacteria can be applied in a wide range of industrial applications in biomedicines and the ecological habitat is under-explored and yet to be investigated for unknown, rare actinomycetes diversity.

From ecophysiology to cultivation methodology: filling the knowledge gap between uncultured and cultured microbes

Earth is dominated by a myriad of microbial communities, but the majority fails to grow under in situ laboratory conditions. The basic cause of unculturability is that bacteria dominantly occur as biofilms in natural environments. Earlier improvements in the culture techniques are mostly done by optimizing media components. However, with technological advancement particularly in the field of genome sequencing and cell imagining techniques, new tools have become available to understand the ecophysiology of microbial communities. Hence, it becomes easier to mimic environmental conditions in the culture plate. Other methods include co-culturing, emendation of growth factors, and cultivation after physical cell sorting. Most recently, techniques have been proposed for bacterial cultivation by employing genomic data to understand either microbial interactions (network-directed targeted bacterial isolation) or ecosystem engineering (reverse genomics). Hopefully, these techniques may be applied to almost all environmental samples, and help fill the gaps between the cultured and uncultured microbial communities.

Phylogenetic analysis of the salinipostin γ-butyrolactone gene cluster uncovers new potential for bacterial signalling-molecule diversity

Bacteria communicate by small-molecule chemicals that facilitate intra- and inter-species interactions. These extracellular signalling molecules mediate diverse processes including virulence, bioluminescence, biofilm formation, motility and specialized metabolism. The signalling molecules produced by members of the phylum Actinobacteria generally comprise γ-butyrolactones, γ-butenolides and furans. The best-known actinomycete γ-butyrolactone is A-factor, which triggers specialized metabolism and morphological differentiation in the genus Streptomyces . Salinipostins A–K are unique γ-butyrolactone molecules with rare phosphotriester moieties that were recently characterized from the marine actinomycete genus Salinispora . The production of these compounds has been linked to the nine-gene biosynthetic gene cluster (BGC) spt . Critical to salinipostin assembly is the γ-butyrolactone synthase encoded by spt9 . Here, we report the surprising distribution of spt9 homologues across 12 bacterial phyla, the majority of which are not known to produce γ-butyrolactones. Further analyses uncovered a large group of spt -like gene clusters outside of the genus Salinispora , suggesting the production of new salinipostin-like diversity. These gene clusters show evidence of horizontal transfer and location-specific recombination among Salinispora strains. The results suggest that γ-butyrolactone production may be more widespread than previously recognized. The identification of new γ-butyrolactone BGCs is the first step towards understanding the regulatory roles of the encoded small molecules in Actinobacteria.

Characterizing the culturable surface microbiomes of diverse marine animals

Biofilm-forming bacteria have the potential to contribute to the health, physiology, behavior and ecology of the host and serve as its first line of defense against adverse conditions in the environment. While metabarcoding and metagenomic information furthers our understanding of microbiome composition, fewer studies use cultured samples to study the diverse interactions among the host and its microbiome, as cultured representatives are often lacking. This study examines the surface microbiomes cultured from three shallow-water coral species and two whale species. These unique marine animals place strong selective pressures on their microbial symbionts and contain members under similar environmental and anthropogenic stress. We developed an intense cultivation procedure, utilizing a suite of culture conditions targeting a rich assortment of biofilm-forming microorganisms. We identified 592 microbial isolates contained within 15 bacterial orders representing 50 bacterial genera, and two fungal species. Culturable bacteria from coral and whale samples paralleled taxonomic groups identified in culture-independent surveys, including 29% of all bacterial genera identified in the Megaptera novaeangliae skin microbiome through culture-independent methods. This microbial repository provides raw material and biological input for more nuanced studies which can explore how members of the microbiome both shape their micro-niche and impact host fitness.

Polyene-Producing Streptomyces spp. From the Fungus-Growing Termite Macrotermes barneyi Exhibit High Inhibitory Activity Against the Antagonistic Fungus Xylaria

Fungus-growing termites are engaged in a tripartite mutualism with intestinal microbes and a monocultivar (Termitomyces sp.) in the fungus garden. The termites are often plagued by entomopathogen (Metarhizium anisopliae) and fungus garden is always threatened by competitors (Xylaria spp.). Here, we aim to understand the defensive role of intestinal microbes, the actinomycetes which were isolated from the gut of Macrotermes barneyi. We obtained 44 antifungal isolates, which showed moderate to strong inhibition to Xylaria sp. HPLC analysis indicated that different types of polyenes (tetraene, pentene, and heptaene) existed in the metabolites of 10 strong antifungal Streptomyces strains. Two pentene macrolides (pentamycin and 1′14-dihydroxyisochainin) were firstly purified from Streptomyces strain HF10, both exhibiting higher activity against Xylaria sp. and M. anisopliae than cultivar Termitomyces. Subsequently, tetraene and heptaene related gene disruption assay showed that the mutant strains lost the ability to produce corresponding polyenes, and they also had significantly decreased activities against Xylaria sp. and M. anisopliae compared to that of wild type strains. These results indicate that polyene-producing Streptomyces from the guts of M. barneyi have strong inhibition to competitor fungus and polyenes contribute to inhibitory effects on Xylaria sp.

Streptomyces ureilyticus sp. nov. and Streptomyces mesophilus sp. nov., two novel Actinobacteria with antimicrobial activity isolated from lake sediment

Two novel Actinobacteria, designated strains YC419^T and YC504^T, were isolated from a sediment sample collected from Lake Yeniçağa, Bolu Province, Turkey. Chemotaxonomic and morphological characteristics of isolates were found to be typical of members of the genus Streptomyces. Phylogenetic analyses based on 16S rRNA gene sequences revealed that strain YC419^T was most closely related to Streptomyces vastus NBRC 13094^T (99.0 %) and 'Streptomyces xiangluensis' NEAU-LA29 (98.6 %), and strain YC504^T was to most closely related to Streptomyces caldifontis NCCP-1331^T (98.6 %) and Streptomyces indicus IH32-1^T (98.0 %). The cell walls of the two strains contained ll-diaminopimelic acid as the diagnostic diamino acid and the whole-cell hydrolysates were glucose, mannose and ribose. The predominant menaquinones were MK-9(H₈) and MK-9(H₆) in both strains. The major polar lipids of strain YC419^T were diphosphatidylglycerol, phosphatidylethanolamine and phosphatidylinositol, while strain YC504^T had a similar profile but lacking diphosphatidylglycerol. The G+C contents of the genomic DNAs were 69.6 and 70.3 mol% for strains YC419^T and YC504^T, respectively. The phenotypic and genotypic data indicated that these two strains were readily distinguished from one another and the type strains of the other species classified in the genus Streptomyces. Therefore, the strains are suggested to represent two novel species of the genus Streptomyces, for which the names Streptomyces ureilyticus sp. nov. and Streptomyces mesophilus sp. nov. are proposed. The type strains are YC419^T (=DSM 102299^T=KCTC 39757^T) and YC504^T (=DSM 102300^T=KCTC 39756^T), respectively.

Biodiversity, Bioactivity, and Metabolites of High Desert Derived Oregonian Soil Bacteria

From arid, high desert soil samples collected near Bend, Oregon, 19 unique bacteria were isolated. Each strain was identified by 16S rRNA gene sequencing, and their organic extracts were tested for antibacterial and antiproliferative activities. Noteworthy, six extracts (30 %) exhibited strong inhibition resulting in less than 50 % cell proliferation in more than one cancer cell model, tested at 10 μg/mL. Principal component analysis (PCA) of LC/MS data revealed drastic differences in the metabolic profiles found in the organic extracts of these soil bacteria. In total, fourteen potent antibacterial and/or cytotoxic metabolites were isolated via bioactivity-guided fractionation, including two new natural products: a pyrazinone containing tetrapeptide and 7-methoxy-2,3-dimethyl-4H-chromen-4-one, as well as twelve known compounds: furanonaphthoquinone I, bafilomycin C1 and D, FD-594, oligomycin A, chloramphenicol, MY12-62A, rac-sclerone, isosclerone, tunicamycin VII, tunicamycin VIII, and (6S,16S)-anthrabenzoxocinone 1.264-C.

Marine Sediment Recovered Salinispora sp. Inhibits the Growth of Emerging Bacterial Pathogens and other Multi-Drug-Resistant Bacteria

Marine obligate actinobacteria produce a wide variety of secondary metabolites with biological activity, notably those with antibiotic activity urgently needed against multi-drug-resistant bacteria. Seventy-five marine actinobacteria were isolated from a marine sediment sample collected in Punta Arena de La Ventana, Baja California Sur, Mexico. The 16S rRNA gene identification, Multi Locus Sequence Analysis, and the marine salt requirement for growth assigned seventy-one isolates as members of the genus Salinispora, grouped apart but related to the main Salinispora arenicola species clade. The ability of salinisporae to inhibit bacterial growth of Staphylococcus epidermidis, Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacer baumannii, Pseudomonas aeruginosa, and Enterobacter spp. was evaluated by cross-streaking plate and supernatant inhibition tests. Ten supernatants inhibited the growth of eight strains of S. epidermidis from patients suffering from ocular infections, two out of the eight showed growth inhibition on ten S. epidermidis strains from prosthetic joint infections. Also, it inhibited the growth of the remaining six multi-drug-resistant bacteria tested. These results showed that some Salinispora strains could produce antibacterial compounds to combat bacteria of clinical importance and prove that studying different geographical sites uncovers untapped microorganisms with metabolic potential.

Phytoplankton trigger the production of cryptic metabolites in the marine actinobacterium Salinispora tropica

Filamentous members of the phylum Actinobacteria are a remarkable source of natural products with pharmaceutical potential. The discovery of novel molecules from these organisms is, however, hindered because most of the biosynthetic gene clusters (BGCs) encoding these secondary metabolites are cryptic or silent and are referred to as orphan BGCs. While co-culture has proven to be a promising approach to unlock the biosynthetic potential of many microorganisms by activating the expression of these orphan BGCs, it still remains an underexplored technique. The marine actinobacterium Salinispora tropica, for instance, produces valuable compounds such as the anti-cancer molecule salinosporamide but half of its putative BGCs are still orphan. Although previous studies have used marine heterotrophs to induce orphan BGCs in Salinispora, its co-culture with marine phototrophs has yet to be investigated. Following the observation of an antimicrobial activity against a range of phytoplankton by S. tropica, we here report that the photosynthate released by photosynthetic primary producers influences its biosynthetic capacities with production of cryptic molecules and the activation of orphan BGCs. Our work, using an approach combining metabolomics and proteomics, pioneers the use of phototrophs as a promising strategy to accelerate the discovery of novel natural products from marine actinobacteria.

Thomas O, Barraja P, Gaudêncio SP, Bertoni F. Marine Anticancer Agents: An Overview with a Particular Focus on Their Chemical Classes

The marine environment is a rich source of biologically active molecules for the treatment of human diseases, especially cancer. The adaptation to unique environmental conditions led marine organisms to evolve different pathways than their terrestrial counterparts, thus producing unique chemicals with a broad diversity and complexity. So far, more than 36,000 compounds have been isolated from marine micro- and macro-organisms including but not limited to fungi, bacteria, microalgae, macroalgae, sponges, corals, mollusks and tunicates, with hundreds of new marine natural products (MNPs) being discovered every year. Marine-based pharmaceuticals have started to impact modern pharmacology and different anti-cancer drugs derived from marine compounds have been approved for clinical use, such as: cytarabine, vidarabine, nelarabine (prodrug of ara-G), fludarabine phosphate (pro-drug of ara-A), trabectedin, eribulin mesylate, brentuximab vedotin, polatuzumab vedotin, enfortumab vedotin, belantamab mafodotin, plitidepsin, and lurbinectedin. This review focuses on the bioactive molecules derived from the marine environment with anticancer activity, discussing their families, origin, structural features and therapeutic use.