Culturable Actinobacteria Research Articles

Bioactive Potential of Actinobacteria Strains Isolated from the Rhizosphere of Lavender, Lemon Balm, and Oregano

The objective of this study was to isolate and characterize actinobacteria from the rhizosphere of medicinal and aromatic plants, specifically lavender (Lavandula angustifolia Mill.), lemon balm (Melissa officinalis L.), and oregano (Origanum vulgare L.). Rhizospheric soil samples revealed a high abundance of culturable actinobacteria (6.97–7.23 log10 CFU/g). Six isolates were selected for their promising enzymatic activities (lignin peroxidase, carboxymethyl cellulase) and antimicrobial properties. Isolates M345 and M162 exhibited the highest cellulase activity indices (3.19 ± 0.71 and 2.54 ± 0.22, respectively), with five isolates producing lignin peroxidase. These actinobacteria also demonstrated plant growth-promoting traits such as phosphate solubilization and nitrogen fixation, along with strong antimicrobial activity against Gram-negative bacteria and phytopathogenic fungi. Additionally, they significantly enhanced maize seed germination, increasing the vigor index from 4283.33 ± 1264.37 to 6248.28 ± 1661.94 compared to that of the control. These results indicate that the isolated actinobacteria strains hold potential as microbial inoculants for sustainable agriculture, contributing to soil health, plant growth, and pathogen management.

Culturable Actinobacteria from Two Marine Sponges of the Genus Aplysina in Southwest Puerto Rico

Culturable Actinobacteria from Two Marine Sponges of the Genus Aplysina in Southwest Puerto Rico

Bioprospecting for the soil-derived actinobacteria and bioactive secondary metabolites on the Western Qinghai-Tibet Plateau.

The increase in incidence of multidrug-resistant bacteria and the inadequacy of new antimicrobial drugs have led to a widespread outbreak of bacterial antimicrobial resistance. To discover new antibiotics, biodiversity, and novelty of culturable actinobacteria dwelled in soil of the Western Qinghai-Tibet Plateau were investigated. By integrating antibacterial assay with omics tools, Amycolatopsis sp. A133, a rare actinobacterial strain and its secondary metabolites were further studied. Culture-dependent method was used to obtain actinobacterial strains from two soil samples collected from Ali region in Qinghai-Tibet Plateau. The cultural extractions of representative strains were assayed against "ESKAPE" pathogens by paper-disk diffusion method and the double fluorescent protein reporter "pDualrep2" system. An Amycolatopsis strain coded as A133 was prioritized and its secondary metabolites were further analyzed and annotated by omics tools including antiSMASH and GNPS (Global Natural Social Molecular Networking). The predicted rifamycin analogs produced by Amycolatopsis sp. A133 were isolated and identified by chromatographic separation, such as Sephadex LH-20 and HPLC, and spectral analysis, such as NMR and UPLC-HRESI-MS/MS, respectively. A total of 406 actinobacteria strains affiliated to 36 genera in 17 families of 9 orders were isolated. Out of 152 representative strains, 63 isolates exhibited antagonistic activity against at least one of the tested pathogens. Among them, 7 positive strains were identified by the "pDualrep2" system as either an inhibitor of protein translation or DNA biosynthesis. The cultural broth of Amycolatopsis sp. A133 exhibited a broader antimicrobial activity and can induce expression of TurboRFP. The secondary metabolites produced by strain A133 was annotated as rifamycins and zampanolides by antiSMASH and GNPS analysis. Five members of rifamycins, including rifamycin W, protorifamycin I, rifamycin W-M1, proansamycin B, and rifamycin S, were purified and identified. Rifamycin W-M1, was found as a new member of the naturally occurring rifamycin group of antibiotics. Assisted by omics tools, the successful and highly efficient discovery of rifamycins, a group of clinically used antibiotics from actinobacteria in Ali area encouraged us to devote more energy to explore new antibiotics from the soils on the Western Tibetan Plateau.

Bioprospecting of Actinobacterial Diversity and Antibacterial Secondary Metabolites from the Sediments of Four Saline Lakes on the Northern Tibetan Plateau.

The Tibetan Plateau, known as the "Roof of the World" and "The Third Pole", harbors numerous saline lakes primarily distributed in the Northern Tibetan Plateau. However, the challenging conditions of high altitude, low oxygen level, and harsh climate have limited investigations into the actinobacteria from these saline lakes. This study focuses on investigating the biodiversity and bioactive secondary metabolites of cultivable actinobacteria isolated from the sediments of four saline lakes on the Northern Tibetan Plateau. A total of 255 actinobacterial strains affiliated with 21 genera in 12 families of 7 orders were recovered by using the pure culture technique and 16S rRNA gene phylogenetic analysis. To facilitate a high-throughput bioactivity evaluation, 192 isolates underwent OSMAC cultivation in a miniaturized 24-well microbioreactor system (MATRIX cultivation). The antibacterial activity of crude extracts was then evaluated in a 96-well plate antibacterial assay. Forty-six strains demonstrated antagonistic effects against at least one tested pathogen, and their underlying antibacterial mechanisms were further investigated through a dual-fluorescent reporter assay (pDualrep2). Two Streptomyces strains (378 and 549) that produce compounds triggering DNA damage were prioritized for subsequent chemical investigations. Metabolomics profiling involving HPLC-UV/vis, UPLC-QTOF-MS/MS, and molecular networking identified three types of bioactive metabolites belonging to the aromatic polyketide family, i.e., cosmomycin, kidamycin, and hedamycin. In-depth analysis of the metabolomic data unveiled some potentially novel anthracycline compounds. A genome mining study based on the whole-genome sequences of strains 378 and 549 identified gene clusters potentially responsible for cosmomycin and kidamycin biosynthesis. This work highlights the effectiveness of combining metabolomic and genomic approaches to rapidly identify bioactive chemicals within microbial extracts. The saline lakes on the Northern Tibetan Plateau present prospective sources for discovering novel actinobacteria and biologically active compounds.

Natural Products and Biological Activity from Actinomycetes Associated with Marine Algae.

Marine natural products have been recognized as the most promising source of bioactive substances for drug discovery research. This review illustrates the diversity of culturable actinobacteria associated with marine algae, their bioactivity and metabolites, and approaches to their isolation and determination of their biological properties. Furthermore, actinobacteria associated with marine algae are presented as a new subject for an extensive investigation to find novel and active natural products, which make them a potentially rich and innovative source for new drug development deserving more attention and exploration.

Actinobacteria from Arctic and Atlantic deep-sea sediments-Biodiversity and bioactive potential.

The deep-sea covers over 70% of the Earth's surface and harbors predominantly uncharacterized bacterial communities. Actinobacteria are the major prokaryotic source of bioactive natural products that find their way into drug discovery programs, and the deep-sea is a promising source of biotechnologically relevant actinobacteria. Previous studies on actinobacteria in deep-sea sediments were either regionally restricted or did not combine a community characterization with the analysis of their bioactive potential. Here we characterized the actinobacterial communities of upper layers of deep-sea sediments from the Arctic and the Atlantic (Azores and Madeira) ocean basins, employing 16S rRNA metabarcoding, and studied the biosynthetic potential of cultivable actinobacteria retrieved from those samples. Metabarcoding analysis showed that the actinobacterial composition varied between the sampled regions, with higher abundance in the Arctic samples but higher diversity in the Atlantic ones. Twenty actinobacterial genera were detected using metabarcoding, as a culture-independent method, while culture-dependent methods only allowed the identification of nine genera. Isolation of actinobacteria resulted on the retrieval of 44 isolates, mainly associated with Brachybacterium, Microbacterium, and Brevibacterium genera. Some of these isolates were only identified on a specific sampled region. Chemical extracts of the actinobacterial isolates were subsequently screened for their antimicrobial, anticancer and anti-inflammatory activities. Extracts from two Streptomyces strains demonstrated activity against Candida albicans. Additionally, eight extracts (obtained from Brachybacterium, Brevibacterium, Microbacterium, Rhodococcus, and Streptomyces isolates) showed significant activity against at least one of the tested cancer cell lines (HepG2 and T-47D). Furthermore, 15 actinobacterial extracts showed anti-inflammatory potential in the RAW 264.4 cell model assay, with no concomitant cytotoxic response. Dereplication and molecular networking analysis of the bioactive actinobacterial extracts showed the presence of some metabolites associated with known natural products, but one of the analyzed clusters did not show any match with the natural products described as responsible for these bioactivities. Overall, we were able to recover taxonomically diverse actinobacteria with different bioactivities from the studied deep-sea samples. The conjugation of culture-dependent and -independent methods allows a better understanding of the actinobacterial diversity of deep-sea environments, which is important for the optimization of approaches to obtain novel chemically-rich isolates.

Diversity and adaptation properties of actinobacteria associated with Tunisian stone ruins.

Stone surface is a unique biological niche that may host a rich microbial diversity. The exploration of the biodiversity of the stone microbiome represents a major challenge and an opportunity to characterize new strains equipped with valuable biological activity. Here, we explored the diversity and adaptation strategies of total bacterial communities associated with Roman stone ruins in Tunisia by considering the effects of geo-climatic regions and stone geochemistry. Environmental 16S rRNA gene amplicon was performed on DNA extracted from stones samples collected in three different sampling sites in Tunisia, along an almost 400km aridity transect, encompassing Mediterranean, semiarid and arid climates. The library was sequenced on an Illumina MiSeq sequencing platform. The cultivable Actinobacteria were isolated from stones samples using the dilution plate technique. A total of 71 strains were isolated and identified based on 16S rRNA gene sequences. Cultivable actinobacteria were further investigated to evaluate the adaptative strategies adopted to survive in/on stones. Amplicon sequencing showed that stone ruins bacterial communities were consistently dominated by Cyanobacteria, followed by Proteobacteria and Actinobacteria along the aridity gradient. However, the relative abundance of the bacterial community components changed according to the geo-climatic origin. Stone geochemistry, particularly the availability of magnesium, chromium, and copper, also influenced the bacterial communities' diversity. Cultivable actinobacteria were further investigated to evaluate the adaptative strategies adopted to survive in/on stones. All the cultivated bacteria belonged to the Actinobacteria class, and the most abundant genera were Streptomyces, Kocuria and Arthrobacter. They were able to tolerate high temperatures (up to 45°C) and salt accumulation, and they produced enzymes involved in nutrients' solubilization, such as phosphatase, amylase, protease, chitinase, and cellulase. Actinobacteria members also had an important role in the co-occurrence interactions among bacteria, favoring the community interactome and stabilization. Our findings provide new insights into actinobacteria's diversity, adaptation, and role within the microbiome associated with stone ruins.

The Potential of Phylogenetically Diverse Culturable Actinobacteria from Litopenaeus vannamei Pond Sediment as Extracellular Proteolytic and Lipolytic Enzyme Producers.

Enzymes are catalysts that can increase the reaction time of a biochemical process. Hydrolytic enzymes have a pivotal role in degrading organic waste in both terrestrial and aquatic environments. The aims of this study were (1) to investigate the ability of actinobacteria isolated from Litopenaeus vannamei pond sediment to produce proteolytic and lipolytic enzymes, (2) to identify promising candidates using 16S rRNA gene amplification, and (3) to construct a phylogenetic tree based on the 16S rRNA genes. A skim milk agar medium was used in the preliminary experiment of the proteolytic assay, and a Tween 20/80 medium was used in the lipolytic assay. Fifteen and 20 (out of 40) actinobacterial isolates showed great potential for proteolytic and lipolytic activities, respectively. Furthermore, four actinobacteria isolates produced both enzyme types with proteolytic and lipolytic index scores of 1-6.5. The most promising candidates were SA 2.2 (IM8), SC 2.1 (IM6), SD 1.5 (IM6) and SE 1.1 (IM8). BLAST homology results showed a high similarity between the actinobacteria isolates and Streptomyces verucosisporus, S. mangrovicola, S. barkulensis and Nocardiopsis lucentensis, respectively. Therefore, actinobacteria from Litopenaeus vannamei pond sediment are high-potential proteolytic and lipolytic enzyme producers.

Antimicrobial potential of culturable actinobacteria isolated from the Pacific oyster Crassostrea gigas (Bivalvia,Ostreidae).

Explore the diversity of culturable actinobacteria isolated from the Pacific oyster Crassostrea gigas with special emphasis on their antimicrobial activity. For the characterization of the isolated actinobacteria, a polyphasic approach was adopted and thereby phenotypic descriptions, phylogenetic analysis, evaluations of antimicrobial activities and chemical analyses of crude extracts through HPLC and LC-HRESIMS were performed. Five strains were isolated from C. gigas. The 16S rRNA gene analysis revealed that three of them were taxonomically affiliated to the genus Streptomyces and the other two strains were related to Micromonospora. High inhibition was detected against different test microorganisms such as Candida albicans, Staphylococcus aureus, Bacillus subtilis and Mycobacterium smegmatis. On the basis of the chemical analysis, 11 compounds from the active fractions of the crude extracts were determined, and 8 were related putatively to previously reported compounds. Actinobacteria isolated from C. gigas represent an interesting reservoir of antimicrobial compounds, and further study to uncover the full capacity of this source is encouraged. At present, the study of actinobacteria and their antimicrobial potential from uncommon sources as C. gigas is vital to the development of new therapeutic agents to cope with the widespread resistance of human pathogens.

Exploring the Diversity and Antibacterial Potentiality of Cultivable Actinobacteria from the Soil of the Saxaul Forest in Southern Gobi Desert in Mongolia.

Saxaul (Haloxylon ammodendron) is the most widespread plant community in the Gobi Desert in Mongolia, which plays important roles in wind control, sand fixation and water conservation. Investigations of soil-derived actinobacteria inhabiting in the saxaul forest in Gobi Desert in Mongolia have been scarce. In this study, biodiversity of culturable actinobacteria isolated from soil of the saxaul forest in Southern Gobi Aimak (Southern Gobi Province) of Mongolia was characterized and their potential to produce compounds with antibacterial activities was assessed. A total of 172 actinobacterial strains were recovered by culture-based approaches and were phylogenetically affiliated into 22 genera in 13 families of seven orders. Forty-nine actinobacterial isolates were selected to evaluate the antibacterial activities and their underlying mechanism of action was screened by means of a dual-fluorescent reporter assay (pDualrep2). Twenty-three isolates exhibited antagonistic activity against at least one of the tested pathogens, of which two Streptomyces strains can attenuate protein translation by ribosome stalling. Combinational strategies based on modern metabolomics, including bioassay-guided thin-layer chromatography (TLC), UPLC-QTOF-MS/MS based structural annotation and enhanced molecular networking successfully annotated chloramphenicol, althiomycin and granaticin and their derivatives as the antibacterial compounds from extracts in three Streptomyces strains, respectively. This work demonstrates that UPLC-MS/MS-based structural identification and enhanced molecular networking are effective strategies to rapidly illuminate the bioactive chemicals in the microbial extracts. Meanwhile, our results show that the saxaul forest in Mongolia Gobi Desert is a prospective source for discovering novel actinobacteria and biologically active compounds.

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.

Fruit wrapping kraft coated paper promotes the isolation of actinobacteria using ex situ and in situ methods

Designing novel isolation methods could enhance the diversification of the available bacterial strains to biotechnology. In this study, the new ex situ and in situ cultivation methods are introduced for the isolation of actinobacteria. In the ex situ experiments, the soil suspension was spread on the isolation media located above some ordinary papers in immediate contact with the slurry of soil substrate and incubated for 16weeks. The paper was wholly immersed in the cave soil for in situ cultivations, and the containers were buried under layers of soil in Hampoeil cave for 10weeks. Fruit wrapping kraft coated paper, with 68.8% recovery of isolates, was a better choice in isolation of actinobacteria than other studied filter paper. Based on the molecular identification results, 19% of the isolates obtained from the in situ cultivation method had less than 98.5% similarity to known taxa of actinobacteria and potentially may represent new species. In contrast, in the standard cultivation method, 1.3% of the isolates had less than 98.5% similarity 16Sr RNA gene. This data shows that the introduced cultivation method is a promising technique for isolating less culturable or new actinobacteria.

The diversity and antibacterial activity of culturable actinobacteria isolated from the rhizosphere soil of Deschampsia antarctica (Galindez Island, Maritime Antarctic)

Antarctic actinobacteria, which can be isolated from both soils and marine sediments, demonstrate a wide range of antimicrobial activities as well as significant biosynthetic potential as the producers of biologically active compounds. However, the actinobacterial diversity of the Antarctic region has not yet been sufficiently studied. The present study sought to examine the diversity and antibacterial activity of culturable actinobacteria isolated from the rhizosphere soil of Deschampsia antarctica (É. Desv.), which was collected from Galindez Island, Maritime Antarctic. Among the actinobacteria isolated using a 16S rRNA gene sequence-based phylogenetic analysis process, five genera, namely Streptomyces, Micromonospora, Umezawaea, Kribbella and Micrococcus, were identified. To the best of our knowledge, this is the first report to describe the isolation and initial characterisation of members of the genus Umezawaea from the Antarctic. The isolated actinobacteria were assayed to determine their activity against Gram-positive bacteria, Gram-negative bacteria and yeast. Among the isolated strains, only 30.2% were able to inhibit the growth of at least one of the tested pathogens. The polymerase chain reaction-based screening of the biosynthetic genes revealed the presence of type I polyketide synthases (65.1%), type II polyketide synthases (25.6%) and non-ribosomal peptide synthetases (9.3%) in the actinobacteria strains. The examination of the sensitivity/resistance to antibiotics profile of the actinobacteria strains revealed their high sensitivity in relation to the tested antibiotics. Taken together, the results showed that Antarctic actinobacteria demonstrate potential as the producers of natural bioactive compounds, which means that they represent a valuable prospect for further studies.

Antimicrobial Activity and Functional Genes of Actinobacteria from Coastal Wetland.

Isolation of culturable actinobacteria from coastal wetlands and screening of their potential biological activities are important for the development of new marine natural products. We collected and isolated 109 actinobacteria from the Sanggou Bay and the Swan Lake wetlands, in the coast of Weihai, China. Of the 109 isolates, 104 had antimicrobial activity against at least one indicator strain. The 35 strains with the strongest inhibitory effects were chosen for the screening of the biosynthesis gene clusters of polyketide synthase (PKS) and non-ribosomal peptide synthetase (NRPS). Four strains with the PKS gene, six strains with the NRPS gene, and three strains with both genes were detected. Eight of the 13 strains with PKS or NRPS genes belong to the genera Streptomyces, and other strains belonged to genus Micromonospora, Nocardiopsis, Rhodococcus, Saccharomonospora, and Staphylococcus. Our results reveal that the culturable actinobacteria isolated from coastal wetlands showed broad-spectrum antimicrobial activities, and some strains with antimicrobial activities possessed PKS and NRPS genes. Thus, culturable actinobacteria from coastal wetlands may contain potential new bioactive substances.

Diversity and antimicrobial activity of culturable actinobacteria isolated from the sediment of Sarıkum Lake

In this study, actinobacteria isolated from Sarıkum Lake sediment were characterized (Sinop-Turkey). A total of 48 actinobacteria were isolated using ten selective media with the dilution-plating method. The phylogenetic analysis according to 16S rRNA gene sequencing showed that 40% of the isolated strains belong to the widely distributed genus of Streptomyces, 36% belong to genus of Micromonospora, 24% of the isolates belong to rare genera such as Rhodococcus, Plantactinospora, Nonomuraea, Actinomadura and Streptosporangium. Most of the isolated strains belong to the genus Streptomyces (40%) and two isolates may be new species. All of the isolates were tested for antimicrobial activity; only 12 isolates exhibited antimicrobial activity. Nevertheless, 11 isolates were active against gram-positive, 5 were potential against gram-negative and no isolates had any effect against pathogenic fungi. All of the 48 isolates were analysed for genes encoding nonribosomal peptide synthetases (NRPS) and polyketide synthases (PKS). In all of the 48 isolates were detected NRPS sequences, PKS-I in 28 isolates and PKS-II in 22 isolates. PKS-I – PKS-II – NRPS genes were identified ın 17 isolates.

Isolation and characterization of culturable actinobacteria associated with Polytrichum strictum (Galindez Island, the maritime Antarctic)

The main objective of the study is the evaluation of the diversity of actinobacteria associated with Polytrichum strictum — dominant species of widespread Antarctic Тall moss turf subformation and their characteristics as the producers of biologically active compounds. The actinobacterial isolates were isolated by direct inoculation, phenol pretreatment, and heated treatment. The cultural properties of the isolates were evaluated using diagnostic media. The antimicrobial activity of the isolates was determined by the point inoculations method. The phylogenetic analysis was based on sequence analysis of the 16S rRNA gene. The biosynthetic genes screening was performed using polymerase chain reaction. A total of 23 actinobacterial isolates associated with P. strictum were isolated, the four identified genera being Streptomyces (7 isolates), Micromonospora (14 isolates), Kribbella (1 isolate), and Micrococcus (1 isolate). Eight psychrotrophic strains of all identified genera were identified. The optimal pH values for all isolates were in the range 6–10. Four isolates grew on the medium with 7.5% NaCl. A significant number of the isolates showed a wide range of enzymatic activities. Antagonists of a wide range of pathogenic microorganisms were found, including against multidrug-resistant strain of Candida albicans and Methicillin-resistant Staphylococcus aureus. Some strains were active against phytopathogenic bacteria, namely three strains against Erwinia amylovora, one strain against Agrobacterium tumefaciens, and one strain against Pectobacterium carotovorum. More than half of the isolates showed antifungal activity against Fusarium oxysporum and Aspergillus niger. The biosynthetic genes involved in synthesizing a wide range of bioactive compounds were found in more than 80% of isolates. Antarctic actinobacteria isolated in this study demonstrate potential as the producers of a wide range of biologically active compounds. Further studies of these actinobacteria may lead to the identification of previously unknown biologically active compounds.

Actinobacterial Communities of Chosen Extreme Habitats in China

Actinobacteria living in frozen soils which potentially could be producers of valuable and biologically active metabolites, remain still largely unexplored. Therefore, the diversity of culturable actinobacteria in the six frozen soil samples collected from the high-latitude and the high-altitude regions in China was investigated by using the culture-dependent method and 16S rRNA gene analysis. A total of 184 culturable actinobacterial isolates (morphotypes) were obtained. The abundance of culturable actinobacteria was 6.20 × 103–3.49 × 105 colony forming units (CFU) per gram of soil (dry weight). The actinobacteria isolated from the high-latitude region in China belong to five genera: Streptacidiphilus, Kitasatospora, Streptomyces, Arthrobacter, and Rhodococcus. The strains belonging to Arthrobacter were dominant, the 19 strains were closely related to Arthrobacter globiformis in terms of evolutionary distance. The actinobacterial isolates from the high-altitude region, from 2, 813 m to 4, 775 m in elevation, in China could be grouped into six genera (Arthrobacter, Microbacterium, Streptomyces, Rhodococcus, Nocardia, and Nocardiopsis), with dominant Streptomyces and Arthrobacter strains. The 4 strains were closely related to Rhodococcus fascians and one strain was closely with Microbacterium hydrocarbonoxydans in terms of evolutionary distance. Three genera of Arthrobacter, Streptomyces, and Rhodococcus were found in both areas. Our research provides new insight into the characteristics of the distribution of actinobacteria associated with frozen soils, which help us gain a better understanding of the potential of the cryogenic environments – the potential source of actinobacterial antibiotics.

Bryophytes Harbor Cultivable Actinobacteria With Plant Growth Promoting Potential.

This study was designed to investigate the cultivable actinobacteria associated with bryophytes and their plant growth promoting ability. Thirteen actinobacteria were isolated and tested for their ability to promote growth of plant in vitro and in planta. All isolates were able to produce IAA and siderophores. Six isolates were identified as members of the genus Micromonospora. Five isolates belonged to the genus Streptomyces and one each of Microbispora and Mycobacterium. Micromonospora sp. CMU55-4 was inoculated to rare moss [Physcomitrium sphaericum (C. Ludw.) Fürnr.] and could increase the amount of carotenoid, fresh weight, and dry weight of this moss. In addition, this strain promoted capsule production, and rescued P. sphaericum’s gametophytes during acclimatization to land. Strain CMU55-4 was identified as Micromonospora chalcea based on whole genome sequence analysis. Its plant growth promoting potential was further characterized through genome mining. The draft genome size was 6.6 Mb (73% GC). The genome contained 5,933 coding sequences. Functional annotation predicted encoded genes essential for siderophore production, phosphate solubilization that enable bacteria to survive under nutrient limited environment. Glycine-betaine accumulation and trehalose biosynthesis also aid plants under drought stress. M. chalcea CMU55-4 also exhibited genes for various carbohydrate metabolic pathways indicating those for efficient utilization of carbohydrates inside plant cells. Additionally, predictive genes for heat shock proteins, cold shock proteins, and oxidative stress such as glutathione biosynthesis were identified. In conclusion, our results demonstrate that bryophytes harbor plant growth promoting actinobacteria. A representative isolate, M. chalcea CMU55-4 promotes the growth of P. sphaericum moss and contains protein coding sequences related to plant growth promoting activities in its genome.

Diversity of Culturable Actinobacteria Producing Protease Inhibitors Isolated from the Intertidal Zones of Maharashtra, India

Phylogenetic diversity of culturable actinobacteria isolated from the intertidal regions of west coast of Maharashtra, India was studied using 16S rRNA gene sequencing. Total of 140 actinobacterial isolates were obtained, which belonged to 14 genera, 10 families and 65 putative species with Streptomyces being the most dominant (63%) genus followed by Nocardiopsis and Micromonospora. Isolates were screened for production of extracellular protease inhibitors (PI) against three pure proteases viz. chymotrypsin, trypsin, subtilisin and a crude extracellular protease from Pseudomonas aeruginosa. Eighty percent of the isolates showed PI activity against at least one of the four proteases, majority of these belonged to genus Streptomyces. Actinobacterial diversity from two sites Ade (17° 52' N, 73° 04' E) and Harnai (17° 48' N, 73° 05' E) with varying anthropological pressure showed that more putative species diversity was obtained from site with lower human intervention i.e. Ade (Shannon's H 3.45) than from Harnai (Shannon's H 2.83), a site with more human intervention. However, in Ade, percentage of isolates not showing PI activity against any of the proteases was close to 21% and that in Harnai was close to 9%. In other words, percentage of PI producers was lower at a site with lesser human intervention.

Cultivable Actinobacteria First Found in Baikal Endemic Algae Is a New Source of Natural Products with Antibiotic Activity.

Inadequate use of antibiotics has led to spread of microorganisms resistant to effective antimicrobial compounds for humans and animals. This study was aimed to isolate cultivable strains of actinobacteria associated with Baikal endemic alga Draparnaldioides baicalensis and estimate their antibiotic properties. During this study, we isolated both widespread and dominant strains related to the genus Streptomyces and representatives of the genera Saccharopolyspora, Nonomuraea, Rhodococcus, and Micromonospora. For the first time, actinobacteria belonging to the genera Nonomuraea and Saccharopolyspora were isolated from Baikal ecosystem. Also, it was the first time when actinobacteria of the genus Nonomuraea were isolated from freshwater algae. Some rare strains demonstrated activity inhibiting growth of bacteria and yeasts. Also, it has been shown that the strains associated with Baikal alga D. baicalensis are active against both Gram-positive and Gram-negative bacteria. According to this study and previously published materials, diversity of cultivable actinobacteria and rare strains isolated from D. baicalensis is comparable to that of cultivable actinobacteria previously isolated from plant sources of Lake Baikal. Also, it exceeds the cultivable actinobacteria diversity previously described for macroinvertebrates, water, or sediments of Lake Baikal. The large number of rare and active strains associated with the endemic alga D. baicalensis could be the promising sources for biopharmaceutical and biotechnological developments and discovery of new natural compounds.