Actinobacteria From Desert: Diversity and Biotechnological Applications

Genome Mining Reveals Rifamycin Biosynthesis in a Taklamakan Desert Actinomycete

Actinomycetes are recognized for producing diverse bioactive natural products, yet most biosynthetic gene clusters (BGCs) remain inactive under laboratory conditions. Rare actinomycetes from extreme environments represent underexplored reservoirs of metabolic potential. This study investigates Actinomadura sp. TRM71106, a rare actinomycete isolated from the Taklamakan Desert, through integrated genomic and metabolomic approaches. Genome sequencing revealed 45 secondary metabolic BGCs, including BGC38 showing 65% nucleotide similarity to the rifamycin BGC. Gene cluster networking and linear comparisons predicted its capacity to encode novel rifamycin analogs. Targeted activation strategies-overexpression of the pathway-specific regulator LuxR combined with metabolite isolation-mark the first activation of a rifamycin-like BGC in desert actinomycetes. This study highlights the untapped biosynthetic potential of rare actinomycetes in extreme environments and establishes Actinomadura sp. TRM71106 as a novel source for rifamycin production. These results provide a promising avenue for expanding the clinical pipeline of rifamycin-derived antibiotics.

Natural products as drug leads: exploring their potential in drug discovery and development

Natural products have been pivotal in drug discovery, offering a wealth of bioactive compounds that significantly contribute to therapeutic developments. Despite the rise of synthetic chemistry, natural products continue to play a crucial role due to their unique chemical structures and diverse biological activities. This study reviews and evaluates the potential of natural products in drug discovery and development, emphasizing the integration of traditional knowledge with modern drug discovery methodologies and addressing the associated challenges. A comprehensive literature search was conducted across PubMed/MedLine, Scopus, Web of Science, Google Scholar, and Cochrane Library, covering publications from 2000 to 2023. Inclusion criteria focused on studies related to natural products, bioactive compounds, medicinal plants, phytochemistry, and AI applications in drug discovery. Data were categorized into source, extraction methods, bioactivity assays, and technological advances. The current review underscores the historical and ongoing importance of natural products in drug discovery. Technological advancements in chromatographic and spectroscopic techniques have improved the isolation and structural elucidation of bioactive compounds. AI and machine learning have streamlined the identification and optimization of natural product leads. Challenges such as biodiversity sustainability and development complexities are discussed, alongside innovative approaches like biosynthetic engineering and metagenomics. Natural products remain a vital source of novel therapeutic agents, providing unique chemical diversity and specific biological activities. Integrating traditional knowledge with modern scientific methods is essential for maximizing the potential of natural products in drug discovery. Despite existing challenges, ongoing research and technological advancements are expected to enhance the efficiency and success of natural product-based drug development.

Strategies for Actinobacteria Isolation, Cultivation, and Metabolite Production that Are Biologically Important

Novel antimicrobial agents are urgently needed to combat antimicrobial resistance from multidrug-resistant organisms. Actinobacteria are key sources of bioactive metabolites with diverse biological activities. Despite their contributions to drug discovery, the process from strain identification to drug manufacturing faces many challenges, especially the rediscovery of known compounds. Recent technological and scientific advancements have accelerated drug development. Efforts to isolate and screen rare actinobacterial species could yield novel bioactive compounds. This review summarizes techniques for selectively isolating rare actinobacteria, improving bioactive metabolite production, and discovering potential strains. Notably, new genomic strategies and new discoveries regarding spectroscopic signature-based bioactive natural products containing specific structural motifs are also discussed. Furthermore, this review updates the compounds derived from rare actinobacteria and their biological applications.

2-Amino-3-Chlorobenzoic Acid from Streptomyces coelicolor: A Cancer Antagonist Targeting PI3K/AKT Markers via miRNA Modulation

Background/Objectives: Actinomycetes, particularly species within the Streptomyces genus, are renowned for their ability to produce a wide array of bioactive molecules with therapeutic potential. This study aimed to comprehensively investigate the antimicrobial and anticancer properties of Streptomyces coelicolor ERI-15, with a particular focus on a purified compound, 2-amino-3-chlorobenzoic acid (2A3CB), and its efficacy against microbial pathogens and breast cancer cell lines. Methods: Antimicrobial compounds were produced through fermentation techniques and isolated via column chromatography. Bioassay-guided fractionation was conducted against Staphylococcus aureus (ATCC 25923), methicillin-resistant Staphylococcus aureus (MRSA), Escherichia coli (ATCC 25922), and Bacillus subtilis (ATCC 441). Major fractions were further purified using preparative thin-layer chromatography (TLC). The structures of active compounds were elucidated using spectral analyses including IR, mass spectrometry, and 1H/13C NMR. The compound 2A3CB (m/z 171) was tested against MDA-MB-231 and 3T3 cell lines. Cytotoxicity was assessed by the MTT assay, and apoptotic mechanisms were explored via cell proliferation assays, dual fluorescent staining, migration and invasion assays, and analysis of apoptotic markers at mRNA and protein levels. Results: 2A3CB exhibited strong cytotoxic effects on MDA-MB-231 cells, with IC50 values of 26 µM, 5 µM, and 7.2 µM at 24, 48, and 72 h, respectively. It significantly inhibited cell proliferation and migration, and induced apoptosis via caspase-mediated pathways. Expression levels of PTEN, PCNA, BAX, and STAT3 were downregulated, suggesting inhibition of metastasis through the suppression of invasion and migration. Conclusions: The results demonstrate that 2A3CB, derived from S. coelicolor ERI-15, possesses potent antimicrobial and anticancer properties. Its ability to inhibit growth and induce apoptosis in MDA-MB-231 breast cancer cells highlights its potential as a natural therapeutic candidate for targeted cancer treatment, particularly in breast cancer progression.

A Review on Rare and Symbiotic Actinobacteria: Emerging Biotechnological Tools Against Antimicrobial Resistance

Antimicrobial resistance (AMR) poses a global threat to public health, with projections estimating 10 million deaths annually by 2050 if current trends persist. Actinobacteria, renowned for their biosynthetic capacity, are a key source of bioactive compounds, producing over 75% of known antibiotics. The adaptability of these microorganisms allows them to thrive in diverse habitats, including extreme ones, through the production of secondary metabolites that are of paramount importance for industry. Furthermore, actinobacteria are capable of living in symbiosis with several organisms, producing metabolites to protect and promote the growth of the host in exchange for nutrients and shelter. Some of these metabolites, such as antibiotics, play a key role in combating host pathogens and can be biotechnologically exploited to combat human resistant pathogens. This review presents the origins of AMR, the unique biology of actinobacteria, as well as their diverse biosynthetic pathways and their role in mitigating the AMR crisis. It also highlights the need for innovative biotechnological strategies for the isolation of rare and understudied actinobacteria, as symbiotic actinobacteria, to avoid rediscovery of molecules while finding new potential natural products and scaffolds for synthetic drugs. By providing a better understanding of their ecological, genomic, and metabolic diversity, this review provides valuable insights into the exploration of rare and symbiotic actinobacteria for developing antimicrobial solutions.

Actinomycetes studies in Tunisia

Tunisia, located in North Africa, has a diverse topography along the Mediterranean Sea to the Sahara Desert. These environments encompass oases, rhizosphere soils, desert deposits, saline wetlands, offshore oilrigs, and ancient monument rocks. The country's varied environments have led to the isolation of a multitude of actinomycetes. A phylogenetic analysis based on the 16S rRNA sequences of one hundred isolated actinomycetes strains revealed that the majority belong to the genus Streptomyces. Secondary metabolite studies from these actinomycetes yielded 33 natural products. Notably, compound 12, 3-O-methylviridicatin, exhibited antitumor activity and suppressed HIV expression. This showcases Tunisia's potential for natural product research.

PPtase-activated production of borrelidin from extremophilic actinobacteria against multidrug-resistant cotton pathogen Verticillium dahliae

As the most devastating disease in cotton crops, Verticillium wilt caused by Verticillium dahliae led to fiber quality reduction and extensive yield loss. In recent years, Verticillium wilt has been increasingly serious in Xinjiang, China, the world's largest cotton production area. In this study, 52 actinobacterial strains were selected for the discovery of NPs with anti-V. dahliae activity, from our strain collection isolated from three types of extreme habitats (high salinity, high temperature or plant endophytes) in Xinjiang. In the culture broth extracts of phosphopantetheinyl transferase (PPtase)-activated actinobacterial strains, four showed good anti-V. dahliae activities. By isolation, purification and spectral analysis of the antifungal metabolite, its structure was elucidated as borrelidin from Streptomyces rochei TRM46813. This is the first report that borrelidin shows anti-V. dahliae activity. Notably, borrelidin could effectively inhibit different commercial fungicides-resistant V. dahliae pathogens with MICs of 0.125 to 2 μg/mL. The growth-inhibitory effect was antagonized by L-threonine in a dose-dependent manner, suggesting that threonyl-tRNA synthetase (ThrRS) may be the target of borrelidin in V. dahliae. Interestingly, although borrelidin was previously reported to bind to ThrRS and thus inhibit protein translation in Gram-positive pathogens, our mode-of-action analysis indicates that borrelidin led to the accumulation of cell wall precursor, which may be due to the inhibited effects on protein translation. Our findings suggest that borrelidin is a promising candidate for the development of novel antifungal agents to overcome the growing problem of Verticillium wilt.

Enhancing environmental decontamination and sustainable production through synergistic and complementary interactions of actinobacteria and fungi

Actinobacteria and fungi are renowned for their metabolic diversity and adaptability to various environments, thus exhibiting significant potential for environmental decontamination and sustainable production. Both actinobacteria and fungi excel in producing diverse secondary metabolites and enzymes, offering valuable tools for industrial and environmental applications. Their ability to detoxify metals and degrade a wide range of organic pollutants, such as pesticides, hydrocarbons, and dyes, positions them as promising candidates for bioremediation. Recent shifts in microbiological sciences emphasize research on mixed microbial populations. Microbial interactions in mixed communities emulate natural processes and yield emergent properties such as stability, robustness, and enhanced metabolism. Co-cultures of actinobacteria and fungi harness a broader range of genes and metabolic capabilities through their distinctive interactions, opening new avenues for developing novel products and/or technologies. This review provides a critical analysis of the present status of knowledge regarding the potential of actinobacteria-fungi co-cultures with a particular focus on novel functionalities and heightened production efficiency. These consortia are promising in several fields, from environmental applications to the biosynthesis of industrially relevant metabolites and enzymes, and enhancements in agricultural production. Although challenges still exist, their potential to address complex problems has been demonstrated and deserves further investigation.

Metabolites Discovery from Streptomyces xanthus: Exploring the Potential of Desert Microorganisms

The Taklamakan Desert is an extreme environment supporting a unique and diverse microbial community with significant potential for exploration. Strain TRM70308T, isolated from desert soil, shares 98.43% 16S rRNA gene sequence similarity with Streptomyces alkaliterrae OF1T. Polyphasic taxonomy confirmed TRM70308T as a novel species, named Streptomyces xanthus. Genomic analysis revealed that only one of the strain's 25 biosynthetic gene clusters (BGCs) formed a cluster of gene families (CGFs) within the MIBiG database, emphasizing its genomics uniqueness. LC-MS/MS and Feature-Based Molecular Networking (FBMN) identified 33 metabolites across various categories, including alkaloids, saponins, benzoic acids, and benzofurans, most of which remain uncharacterized. Further chemical investigation led to the isolation of one novel compound, aconicarpyrazine C, and four known compounds: thiolutin, dibutyl phthalate, bis(2-ethylhexyl) phthalate, and N-acetyltryptamine. Thiolutin exhibited strong activity against five local fungal pathogens that cause plant diseases, with a production yield of 270 mg/L. These results establish a foundation for pilot-scale thiolutin production and its potential development as an antifungal agent for agricultural applications. Our findings highlight deserts as a valuable source of novel actinomycetes and bioactive natural products with immense potential for future research and development.

Persistent Desert Microbiota in the Southern European Sky

Long-range atmospheric processes facilitate global microbial dispersal, with a pivotal role in Earth's ecosystem functioning and global health. Aerobiological studies have traditionally focused on low troposphere aerosols, leading to the assumption that airborne communities are primarily controlled by neighbouring ecosystems. We show a temporal sampling of aerosols from the free troposphere extending a period of almost three decades, coupled with the study of both high troposphere air masses provenances and genetic data of topsoils from North Africa and from a global public bacterial database. The results unveil a long-lasting influence of airborne North African desert microorganisms in Southern Europe. Although sea spray dominates global aerosol emissions, the predominance of desert microorganisms was widespread even in rain traced back to the Atlantic Ocean. The frequency of dust outbreaks, altitude reached, and long residence times are postulated as critical factors that significantly shape the long-range and persistence of aerial assemblages, with air mass provenance playing a secondary role. This study advances the current understanding of atmospheric microorganisms, underscoring their close and long-lasting relationship with terrestrial ecosystems. Further research is needed to fully understand intercontinental aerial connections with deserts and drylands elsewhere, and the influence of desert immigrants on worldwide ecosystems.

Metabarcoding expands knowledge on diversity and ecology of rare actinobacteria in the Brazilian Cerrado

Rare and unknown actinobacteria from unexplored environments have the potential to produce new bioactive molecules. This study aimed to use 16 s rRNA metabarcoding to determine the composition of the actinobacterial community, particularly focusing on rare and undescribed species, in a nature reserve within the Brazilian Cerrado called Sete Cidades National Park. Since this is an inaccessible area without due legal authorization, it is understudied, and, therefore, its diversity and biotechnological potential are not yet fully understood, and it may harbor species with groundbreaking genetic potential. In total, 543 operational taxonomic units (OTUs) across 14 phyla were detected, with Actinobacteria (41.2%), Proteobacteria (26.5%), and Acidobacteria (14.3%) being the most abundant. Within Actinobacteria, 107 OTUs were found, primarily from the families Mycobacteriaceae, Pseudonocardiaceae, and Streptomycetaceae. Mycobacterium and Streptomyces were the predominant genera across all samples. Seventeen rare OTUs with relative abundance < 0.1% were identified, with 82.3% found in only one sample yet 25.5% detected in all units. Notable rare and transient genera included Salinibacterium, Nocardia, Actinomycetospora_01, Saccharopolyspora, Sporichthya, and Nonomuraea. The high diversity and distribution of Actinobacteria OTUs indicate the area's potential for discovering new rare species. Intensified prospection on underexplored environments and characterization of their actinobacterial diversity could lead to the discovery of new species capable of generating innovative natural products.

Nuclear Magnetic Resonance Fingerprinting and Principal Component Analysis Strategies Lead to Anti-Tuberculosis Natural Product Discovery from Actinomycetes

BACKGROUND

The increasing prevalence of drug-resistant tuberculosis (TB) underscores the urgent need for novel antimicrobial agents.

METHODS

This study integrates cultivation optimization, nuclear magnetic resonance (NMR) fingerprinting, and principal component analysis (PCA) to explore microbial secondary metabolites as potential anti-TB agents.

RESULTS

Using the combined approach, 11 bioactive compounds were isolated and identified, all exhibiting anti-Mycobacterium bovis BCG activity. Notable findings include borrelidin, a potent threonyl-tRNA synthetase inhibitor with broad biological activities, and L-O-Lac-L-Val-D-O-Hiv-D-Val, a peptide isolated for the first time from a plant endophyte, demonstrating broad-spectrum antimicrobial activity. Additionally, elaiophylin and polycyclic tetramate macrolactams (PTMs) displayed significant bactericidal effects, with elaiophylin achieving complete BCG inhibition at 72 h and PTMs marking their first reported anti-TB activity. The study also identified bafilomycins as potent scaffolds for anti-TB drug development, showcasing rapid bactericidal activity at low MIC values.

CONCLUSIONS

These findings emphasize the value of microbial metabolites as a reservoir of bioactive compounds and provide new avenues for developing next-generation anti-TB therapies.

Genomic and Phenotypic Characterization of Streptomyces sirii sp. nov., Amicetin-Producing Actinobacteria Isolated from Bamboo Rhizospheric Soil

In our large-scale search for antimicrobial-producing bacteria, we isolated an actinomycete strain from rhizospheric soil of Bambusa vulgaris. The strain designated BP-8 showed noticeable antibacterial activity. BP-8 was subjected to a whole-genome analysis via a polyphasic taxonomy approach, and its antibacterial metabolite was identified by HRLS-MS. The results of the physiological and morphological analyses indicated that BP-8 is an aerobic, neutrophilic, mesophilic organism that is tolerant to 8% NaCl and can use a wide range of carbohydrates. It forms curly sporophores with a warty surface. The results of the phylogenetic and average nucleotide identity analyses and in silico DNA-DNA hybridization calculation indicated that BP-8 represents the type strain of a novel Streptomyces species. A comparative in silico analysis of the genome sequences of BP-8 and its closest related strains revealed the presence of genes encoding chemotaxonomic markers characteristic of Streptomyces. The antibacterial compound was identified as amicetin. Genomic mining also revealed more than 10 biosynthetic gene clusters that have not been described previously and may lead to the discovery of new valuable compounds. On the basis of these results, strain BP-8T (=VKM Ac-3066T = CCTCC AA 2024094T) is proposed as the type strain of the novel species Streptomyces sirii sp. nov.

Human limits in machine learning: prediction of potato yield and disease using soil microbiome data

BACKGROUND

The preservation of soil health is a critical challenge in the 21st century due to its significant impact on agriculture, human health, and biodiversity. We provide one of the first comprehensive investigations into the predictive potential of machine learning models for understanding the connections between soil and biological phenotypes. We investigate an integrative framework performing accurate machine learning-based prediction of plant performance from biological, chemical, and physical properties of the soil via two models: random forest and Bayesian neural network.

RESULTS

Prediction improves when we add environmental features, such as soil properties and microbial density, along with microbiome data. Different preprocessing strategies show that human decisions significantly impact predictive performance. We show that the naive total sum scaling normalization that is commonly used in microbiome research is one of the optimal strategies to maximize predictive power. Also, we find that accurately defined labels are more important than normalization, taxonomic level, or model characteristics. ML performance is limited when humans can't classify samples accurately. Lastly, we provide domain scientists via a full model selection decision tree to identify the human choices that optimize model prediction power.

CONCLUSIONS

Our study highlights the importance of incorporating diverse environmental features and careful data preprocessing in enhancing the predictive power of machine learning models for soil and biological phenotype connections. This approach can significantly contribute to advancing agricultural practices and soil health management.

Metagenomic approaches and opportunities in arid soil research

Arid soils present unique challenges and opportunities for studying microbial diversity and bioactive potential due to the extreme environmental conditions they bear. This review article investigates soil metagenomics as an emerging tool to explore complex microbial dynamics and unexplored bioactive potential in harsh environments. Utilizing advanced metagenomic techniques, diverse microbial populations that grow under extreme conditions such as high temperatures, salinity, high pH levels, and exposure to metals and radiation can be studied. The use of extremophiles to discover novel natural products and biocatalysts emphasizes the role of functional metagenomics in identifying enzymes and secondary metabolites for industrial and pharmaceutical purposes. Metagenomic sequencing uncovers a complex network of microbial diversity, offering significant potential for discovering new bioactive compounds. Functional metagenomics, connecting taxonomic diversity to genetic capabilities, provides a pathway to identify microbes' mechanisms to synthesize valuable secondary metabolites and other bioactive substances. Contrary to the common perception of desert soil as barren land, the metagenomic analysis reveals a rich diversity of life forms adept at extreme survival. It provides valuable findings into their resilience and potential applications in biotechnology. Moreover, the challenges associated with metagenomics in arid soils, such as low microbial biomass, high DNA degradation rates, and DNA extraction inhibitors and strategies to overcome these issues, outline the latest advancements in extraction methods, high-throughput sequencing, and bioinformatics. The importance of metagenomics for investigating diverse environments opens the way for future research to develop sustainable solutions in agriculture, industry, and medicine. Extensive studies are necessary to utilize the full potential of these powerful microbial communities. This research will significantly improve our understanding of microbial ecology and biotechnology in arid environments.

Biosynthetic gene clusters from uncultivated soil bacteria of the Atacama Desert

Soil microorganisms mediate several biological processes through the secretion of natural products synthesized in specialized metabolic pathways, yet functional characterization in ecological contexts remains challenging. Using culture-independent metagenomic analyses of microbial DNA derived directly from soil samples, we examined the potential of biosynthetic gene clusters (BGCs) from six bacterial communities distributed along an altitudinal gradient of the Andes Mountains in the Atacama Desert. We mined 38 metagenome-assembled genomes (MAGs) and identified 168 BGCs. Results indicated that most predicted BGCs were classified as non-ribosomal-peptides (NRP), post-translational modified peptides (RiPP), and terpenes, which were mainly identified in genomes of species from Acidobacteriota and Proteobacteria phyla. Based on BGC composition according to types of core biosynthetic genes, six clusters of MAGs were observed, three of them with predominance for a single phylum, of which two also showed specificity to a single sampling site. Comparative analyses of accessory genes in BGCs showed associations between membrane transporters and other protein domains involved in specialized metabolism with classes of biosynthetic cores, such as resistance-nodulation-cell division (RND) multidrug efflux pumps with RiPPs and the iron-dependent transporter TonB with terpenes. Our findings increase knowledge regarding the biosynthetic potential of uncultured bacteria inhabiting pristine locations from one of the oldest and driest nonpolar deserts on Earth.IMPORTANCEMuch of what we know about specialized metabolites in the Atacama Desert, including Andean ecosystems, comes from isolated microorganisms intended for drug development and natural product discovery. To complement research on the metabolic potential of microbes in extreme environments, comparative analyses on functional annotations of biosynthetic gene clusters (BGCs) from uncultivated bacterial genomes were carried out. Results indicated that in general, BGCs encode for structurally unique metabolites and that metagenome-assembled genomes did not show an obvious relationship between the composition of their core biosynthetic potential and taxonomy or geographic distribution. Nevertheless, some members of Acidobacteriota showed a phylogenetic relationship with specific metabolic traits and a few members of Proteobacteria and Desulfobacterota exhibited niche adaptations. Our results emphasize that studying specialized metabolism in environmental samples may significantly contribute to the elucidation of structures, activities, and ecological roles of microbial molecules.

Looking for Pathogens in Dust from North Africa Arriving in the French West Indies Using Metabarcoding and Cultivable Analysis

Periodically, the French West Indies receive dust originating from North Africa (NA). Microorganisms associated with desert dust can be transported over long distances through the atmosphere and could represent a means for the remote colonization of new habitats by putatively pathogenic microorganisms. The aim of this study was to determine the diversity and frequency of microbial agents (bacteria, eukaryotes) in NA dusts and the potential threat toward human and/or animal health by comparing microbial air composition during dust events and in control samples. In 2017 and 2018, 16 samples were collected during seven NA dust episodes and there were 9 controls. The microbial composition of the samples was characterized using a cultivable approach and by metabarcoding analyses (16S and 18S). A greater bacterial load and greater diversity were observed during the dust events, and some genera were significantly associated with the events. Some, such as Geodermatophilus, can be considered signature species of NA dust. No pathogenic species were found with the cultivable approach, whereas the metabarcoding analyses highlighted the presence of several potentially pathogenic species or known human pathogens such as Naegleria fowleri.

Biotechnological and pharmaceutical potential of twenty-eight novel type strains of Actinomycetes from different environments worldwide

Actinomycetes are a prolific source of bioactive natural compounds many of which are used as antibiotics or other drugs. In this study we investigated the genomic and biochemical diversity of 32 actinobacterial strains that had been deposited at the DSMZ-German Collection of Microorganisms and Cell Cultures decades ago. Genome-based phylogeny and in silico DNA-DNA hybridization supported the assignment of these strains to 26 novel species and two novel subspecies and a reclassification of a Streptomyces species. These results were consistent with the biochemical, enzymatic, and chemotaxonomic features of the strains. Most of the strains showed antimicrobial activities against a range of Gram-positive and Gram-negative bacteria, and against yeast. Genomic analysis revealed the presence of numerous unique biosynthetic gene clusters (BGCs) encoding for potential novel antibiotic and anti-cancer compounds. Strains DSM 41636T and DSM 61640T produced the antibiotic compounds A33853 and SF2768, respectively. Overall, this reflects the significant pharmaceutical and biotechnological potential of the proposed novel type strains and underlines the role of prokaryotic systematics for drug discovery. In order to compensate for the gender gap in naming prokaryotic species, we propose the eponyms for all newly described species to honour female scientists.

Secondary metabolites with antimicrobial activity produced by thermophilic bacteria from a high-altitude hydrothermal system

Thermophilic microorganisms possess several adaptations to thrive in high temperature, which is reflected as biosynthesis of proteins and thermostable molecules, isolation and culture represent a great methodological challenge, therefore High throughput sequencing enables screening of the whole bacterial genome for functional potential, providing rapid and cost-effective information to guide targeted cultures for the identification and characterization of novel natural products. In this study, we isolated two thermophilic bacterial strains corresponding to Bacillus LB7 and Streptomyces LB8, from the microbial mats in the Atacama Desert. By combining genome mining, targeted cultures and biochemical characterization, we aimed to identify their capacity to synthesize bioactive compounds with antimicrobial properties. Additionally, we determined the capability to produce bioactive compounds under controlled in vitro assays and detected by determining their masses by Thin-Layer Chromatography/Mass Spectrometry (TLC/MS). Overall, both isolates can produce antimicrobial (e.g., Myxalamide C by-product) and antioxidants (e.g. Dihydroxymandelic Acid, Amide biotine and Flavone by-products) compounds. Bacillus LB7 strain possesses a more diverse repertoire with 51.95% of total metabolites unmatched, while Streptomyces LB8 favors mainly antioxidants, but has over 70% of unclassified compounds, highlighting the necessity to study and elucidate the structure of novel compounds. Based on these results, we postulate that the uncultured or rare cultured thermophiles inhabiting high-altitude hydrothermal ecosystems in the Atacama Desert offer a promising opportunity to the study of novel microbial bioactive compounds.

Atacama desert actinomycetes: taxonomic analysis, drought tolerance and plant growth promoting potential

This study was designed to recover representative culturable actinomycetes from the Atacama Desert, and to detect their ability to promote plant growth under drought conditions. Environmental samples were taken from three Atacama Desert habitats, namely, from the Aguas Calientes, Lomas Bayas and Yungay core regions. With one exception higher actinomycete counts were obtained when isolation media were inoculated with mineral particles than with corresponding aliquots of serial dilution. Comparative 16S rRNA gene sequencing showed that representative isolates belonged to thirteen genera including putative novel Blastococcus, Kocuria, Micromonospora, Pseudonocardia, Rhodococcus and Streptomyces species. Representative isolates produced indole-3-acetic acid, siderophore and solubilized phosphate as well as displaying an ability to grow under drought conditions. In conclusion, the current findings open up exciting prospects for the promising potential of actinomycetes from the Atacama Desert to be used as bioinoculants to promote plant growth in arid and semi-arid biomes.

Purification and Characterization of a Novel Fibrinolytic Enzyme from Marine Bacterium Bacillus sp. S-3685 Isolated from the South China Sea

A novel fibrinolytic enzyme, BSFE1, was isolated from the marine bacterium Bacillus sp. S-3685 (GenBank No.: KJ023685) found in the South China Sea. This enzyme, with a molecular weight of approximately 42 kDa and a specific activity of 736.4 U/mg, exhibited its highest activity at 37 °C in a phosphate buffer at pH 8.0. The fibrinolytic enzyme remained stable over a pH range of 7.5 to 10.0 and retained about 76% of its activity after being incubated at 37 °C for 2 h. The Km and Vmax values of the enzyme at 37 °C were determined to be 2.1 μM and 49.0 μmol min-1 mg-1, respectively. The fibrinolytic activity of BSFE1 was enhanced by Na+, Ba2+, K+, Co2+, Mn2+, Al3+, and Cu2+, while it was inhibited by Fe3+, Ca2+, Mg2+, Zn2+, and Fe2+. These findings indicate that the fibrinolytic enzyme isolated in this study exhibits a strong affinity for fibrin. Moreover, the enzyme we have purified demonstrates thrombolytic enzymatic activity. These characteristics make BSFE1 a promising candidate for thrombolytic therapy. In conclusion, the results obtained from this study suggest that our work holds potential in the development of agents for thrombolytic treatment.

Integrative Genomics and Bioactivity-Guided Isolation of Novel Antimicrobial Compounds from Streptomyces sp. KN37 in Agricultural Applications

Actinomycetes have long been recognized as an important source of antibacterial natural products. In recent years, actinomycetes in extreme environments have become one of the main research directions. Streptomyces sp. KN37 was isolated from the cold region of Kanas in Xinjiang. It demonstrated potent antimicrobial activity, but the primary active compounds remained unclear. Therefore, we aimed to combine genomics with traditional isolation methods to obtain bioactive compounds from the strain KN37. Whole-genome sequencing and KEGG enrichment analysis indicated that KN37 possesses the potential for synthesizing secondary metabolites, and 41 biosynthetic gene clusters were predicted, some of which showed high similarity to known gene clusters responsible for the biosynthesis of antimicrobial antibiotics. The traditional isolation methods and activity-guided fractionation were employed to isolate and purify seven compounds with strong bioactivity from the fermentation broth of the strain KN37. These compounds were identified as 4-(Diethylamino)salicylaldehyde (1), 4-Nitrosodiphenylamine (2), N-(2,4-Dimethylphenyl)formamide (3), 4-Nitrocatechol (4), Methylsuccinic acid (5), Phenyllactic acid (6) and 5,6-Dimethylbenzimidazole (7). Moreover, 4-(Diethylamino)salicylaldehyde exhibited the most potent inhibitory effect against Rhizoctonia solani, with an EC50 value of 14.487 mg/L, while 4-Nitrosodiphenylamine showed great antibacterial activity against Erwinia amylovora, with an EC50 value of 5.715 mg/L. This study successfully isolated several highly active antimicrobial compounds from the metabolites of the strain KN37, which could contribute as scaffolds for subsequent chemical synthesis. On the other hand, the newly predicted antibiotic-like substances have not yet been isolated, but they still hold significant research value. They are instructive in the study of active natural product biosynthetic pathways, activation of silent gene clusters, and engineering bacteria construction.

Going to extremes: progress in exploring new environments for novel antibiotics

The discoveries of penicillin and streptomycin were pivotal for infection control with the knowledge subsequently being used to enable the discovery of many other antibiotics currently used in clinical practice. These valuable compounds are generally derived from mesophilic soil microorganisms, predominantly Streptomyces species. Unfortunately, problems with the replication of results suggested that this discovery strategy was no longer viable, motivating a switch to combinatorial chemistry in conjunction with existing screening programmes to derive new antimicrobials. However, the chemical space occupied by these synthetic products is vastly reduced compared to those of natural products. More recent approaches such as using artificial intelligence to 'design' synthetic ligands to dock with molecular targets suggest that chemical synthesis is still a promising option for discovery. It is important to employ diverse discovery strategies to combat the worrying increase in antimicrobial resistance (AMR). Here, we reconsider whether nature can supply innovative solutions to recalcitrant infections. Specifically, we assess progress in identifying novel antibiotic-producing organisms from extreme and unusual environments. Many of these organisms have adapted physiologies which often means they produce different repertoires of bioactive metabolites compared to their mesophilic counterparts, including antibiotics. In addition, we examine insights into the regulation of extremotolerant bacterial physiologies that can be harnessed to increase the production of clinically important antibiotics and stimulate the synthesis of new antibiotics in mesophilic microorganisms. Finally, we comment on the insights provided by combinatorial approaches to the treatment of infectious diseases that might enhance the efficacy of antibiotics and reduce the development of AMR.

Isolation of Bacteriophages on Actinobacteria Hosts

Bacteriophages are ubiquitous biological entities which can be found in a variety of habitats. Here, we describe protocols for the isolation of bacteriophages on a variety of Actinobacterial genera. Two approaches to phage isolation, direct isolation and enriched isolation, are described, which can be performed individually or in parallel. The protocols described can be adapted to isolate a wide array of bacteriophages.

Comparative genomics reveals environmental adaptability and antimicrobial activity of a novel Streptomyces isolated from soil under black Gobi rocks

A novel Streptomyces strain, designated 3_2T, was isolated from soil under the black Gobi rock sample of Northwest China. The taxonomic position of this strain was revealed by a polyphasic approach. Comparative analysis of the 16S rRNA gene sequences indicated that 3_2T was closely related to the members of the genus Streptomyces, with the highest similarity to Streptomyces rimosus subsp. rimosus CGMCC 4.1438 (99.17%), Streptomyces sioyaensis DSM 40032 (98.97%). Strain 3_2T can grow in media up to 13% NaCl. The genomic DNA G + C content of strain 3_2T was 69.9%. We obtained the genomes of 22 Streptomyces strains similar to strain 3_2T, compared the average nucleotide similarity, dDDH and average amino acid identity, and found that the genomic similarity of the new isolate 3_2T to all strains was below the threshold for interspecies classification. Chemotaxonomic data revealed that strain 3_2T possessed MK-9 (H6) and MK-9 (H8) as the major menaquinones. The cell wall contained LL-diaminopimelic acid (LL-DAP) and the whole-cell sugars were ribose and glucose. The major fatty acid methyl esters were iso-C16:0 (23.6%) and anteiso-C15:0 (10.4%). The fermentation products of strain 3_2T were inhibitory to Staphylococcus aureus and Bacillus thuringiensi. The genome of 3_2T was further predicted using anti-smash and the strain was found to encode the production of 41 secondary metabolites, and these gene clusters may be key to the good inhibitory activity exhibited by the strain. Genomic analysis revealed that strain 3_2T can encode genes that produce a variety of genes in response to environmental stresses, including cold shock, detoxification, heat shock, osmotic stress, oxidative stress, and these genes may play a key role in the harsh environment in which the strain can survive. Therefore, this strain represents a novel Streptomyces species, for which the name Streptomyces halobius sp. nov. is proposed. The type strain is 3_2T (= JCM 34935T = GDMCC 4.217T).

Glacier as a source of novel polyethylene terephthalate hydrolases

Polyethylene terephthalate (PET) is a major component of microplastic contamination globally, which is now detected in pristine environments including Polar and mountain glaciers. As a carbon-rich molecule, PET could be a carbon source for microorganisms dwelling in glacier habitats. Thus, glacial microorganisms may be potential PET degraders with novel PET hydrolases. Here, we obtained 414 putative PET hydrolase sequences by searching a global glacier metagenome dataset. Metagenomes from the Alps and Tibetan glaciers exhibited a higher relative abundance of putative PET hydrolases than those from the Arctic and Antarctic. Twelve putative PET hydrolase sequences were cloned and expressed, with one sequence (designated as GlacPETase) proven to degrade amorphous PET film with a similar performance as IsPETase, but with a higher thermostability. GlacPETase exhibited only 30% sequence identity to known active PET hydrolases with a novel disulphide bridge location and, therefore may represent a novel PET hydrolases class. The present work suggests that extreme carbon-poor environments may harbour a diverse range of known and novel PET hydrolases for carbon acquisition as an environmental adaptation mechanism.

Tillandsia landbeckii phyllosphere and laimosphere as refugia for bacterial life in a hyperarid desert environment

BACKGROUND

The lack of water is a major constraint for microbial life in hyperarid deserts. Consequently, the abundance and diversity of microorganisms in common habitats such as soil are strongly reduced, and colonization occurs primarily by specifically adapted microorganisms that thrive in particular refugia to escape the harsh conditions that prevail in these deserts. We suggest that plants provide another refugium for microbial life in hyperarid deserts. We studied the bacterial colonization of Tillandsia landbeckii (Bromeliaceae) plants, which occur in the hyperarid regions of the Atacama Desert in Chile, one of the driest and oldest deserts on Earth.

RESULTS

We detected clear differences between the bacterial communities being plant associated to those of the bare soil surface (PERMANOVA, R2 = 0.187, p = 0.001), indicating that Tillandsia plants host a specific bacterial community, not only dust-deposited cells. Moreover, the bacterial communities in the phyllosphere were distinct from those in the laimosphere, i.e., on buried shoots (R2 = 0.108, p = 0.001), indicating further habitat differentiation within plant individuals. The bacterial taxa detected in the phyllosphere are partly well-known phyllosphere colonizers, but in addition, some rather unusual taxa (subgroup2 Acidobacteriae, Acidiphilum) and insect endosymbionts (Wolbachia, "Candidatus Uzinura") were found. The laimosphere hosted phyllosphere-associated as well as soil-derived taxa. The phyllosphere bacterial communities showed biogeographic patterns across the desert (R2 = 0.331, p = 0.001). These patterns were different and even more pronounced in the laimosphere (R2 = 0.467, p = 0.001), indicating that different factors determine community assembly in the two plant compartments. Furthermore, the phyllosphere microbiota underwent temporal changes (R2 = 0.064, p = 0.001).

CONCLUSIONS

Our data demonstrate that T. landbeckii plants host specific bacterial communities in the phyllosphere as well as in the laimosphere. Therewith, these plants provide compartment-specific refugia for microbial life in hyperarid desert environments. The bacterial communities show biogeographic patterns and temporal variation, as known from other plant microbiomes, demonstrating environmental responsiveness and suggesting that bacteria inhabit these plants as viable microorganisms. Video Abstract.

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.

Systematic bioprospection for cellulolytic actinomycetes in the Chihuahuan Desert: isolation and enzymatic profiling

The quest for microbial cellulases has intensified as a response to global challenges in biofuel production. The efficient deconstruction of lignocellulosic biomass holds promise for generating valuable products in various industries such as food, textile, and detergents. This article presents a systematic bioprospection aimed at isolating actinomycetes with exceptional cellulose deconstruction capabilities. Our methodology explored the biodiverse oligotrophic region of Cuatro Cienegas, Coahuila, within the Chihuahuan Desert. Among the evaluated actinomycetes collection, 78% exhibited cellulolytic activity. Through a meticulous screening process based on enzymatic index evaluation, we identified a highly cellulolytic Streptomyces strain for further investigation. Submerged fermentation of this strain revealed an endoglucanase enzymatic activity of 149 U/mg. Genomic analysis of strain Streptomyces sp. STCH565-A revealed unique configurations of carbohydrate-active enzyme (CAZyme) genes, underscoring its potential for lignocellulosic bioconversion applications. These findings not only highlight the significance of the Chihuahuan Desert as a rich source of cellulolytic microorganisms but also offer insights into the systematic exploration and selection of high-performing cellulolytic microorganisms for application in diverse environmental contexts. In conclusion, our bioprospecting study lays a foundation for harnessing the cellulolytic potential of actinomycetes from the Chihuahuan Desert, with implications for advancing cellulose deconstruction processes in various industries. The findings can serve as a blueprint for future bioprospecting efforts in different regions, facilitating the targeted discovery of microorganisms with exceptional cellulosic deconstruction capabilities.

Taxonomic and ecophysiological characteristics of actinobacteria in soils of the dry steppe zone of the Selenga Highlands (Western Transbaikalia)

Arid habitats have recently attracted increasing attention in terms of biodiversity research and the discovery of new bacterial species. These habitats are among the target ecosystems suitable for isolating new strains of actinobacteria that are likely to produce new metabolites. This paper presents the results on the isolation of actinobacteria from soils of the dry steppe zone of the Selenga Highlands, the characterization of their taxonomic diversity, as well as ecological and trophic properties. The bacterial counts on ISP 4 medium ranged from 6.6 × 105 to 7.1 × 106 CFU/g. The highest bacterial counts were observed in the subsurface and middle horizons of the studied soils. 28 strains of Gram-positive bacteria represented by thin-branched mycelium, coccoid and bacilliform forms were isolated. According to the results of 16S rRNA gene analysis, the isolated strains were representatives of Streptomyces, Arthrobacter, Glycomyces, Kocuria, Microbacterium, Micromonospora, Nocardioides, Pseudarthrobacter, and Rhodococcus (Actinomycetota). One isolate that showed low 16S rRNA gene sequence similarity with previously isolated and validly described species was a new species of the genus Glycomyces. It was shown that all tested strains are mesophilic, prefer neutral or slightly alkaline conditions, have growth limits in the temperature range of 5-45 °C and pH 6-9. The optimal NaCl concentration for growth of most strains was 0-1 %. The strains under study were capable of utilizing a wide range of mono- and disaccharides and polyatomic alcohols as a carbon source. The isolated strains were capable of using both organic (proteins and amino acids) and inorganic (ammonium salts and nitrates) compounds as nitrogen sources. The examinations of extracellular enzymes showed that all isolates were capable of producing catalase and amylase; 78.6 % of the total number of isolates produced protease and lipase; 53.6 %, cellulase; and 28.6 %, urease. The data obtained expand current knowledge about the diversity of microbial communities in soils of the Selenga Highlands and also confirm the potential of searching for new actinobacteria species in these soils.

Inoculation with Actinobacteria spp. Isolated from a Hyper-Arid Environment Enhances Tolerance to Salinity in Lettuce Plants (Lactuca sativa L.)

Irrigated agriculture is responsible for a third of global agricultural production, but the overuse of water resources and intensification of farming practices threaten its sustainability. The use of saline water in irrigation has become an alternative in areas subjected to frequent drought, but this practice affects plant growth due to osmotic impact and excess of ions. Plant-growth-promoting rhizobacteria (PGPR) can mitigate the negative impacts of salinity and other abiotic factors on crop yields. Actinobacteria from the hyper-arid Atacama Desert could increase the plant tolerance to salinity, allowing their use as biofertilizers for lettuce crops using waters with high salt contents. In this work, rhizosphere samples of halophytic Metharme lanata were obtained from Atacama Desert, and actinobacteria were isolated and identified by 16S gene sequencing. The PGPR activities of phosphate solubilization, nitrogen fixation, and the production of siderophore and auxin were assessed at increasing concentrations of NaCl, as well as the enhancement of salt tolerance in lettuce plants irrigated with 100 mM of NaCl. Photosynthesis activity and chlorophyll content, proline content, lipid peroxidation, cation and P concentration, and the identification and quantification of phenolic compounds were assessed. The strains S. niveoruber ATMLC132021 and S. lienomycini ATMLC122021 were positive for nitrogen fixation and P solubilization activities and produced auxin up to 200 mM NaCl. In lettuce plants, both strains were able to improve salt stress tolerance by increasing proline contents, carotenoids, chlorophyll, water use efficiency (WUE), stomatal conductance (gs), and net photosynthesis (A), concomitantly with the overproduction of the phenolic compound dicaffeoylquinic acid. All these traits were positively correlated with the biomass production under saltwater irrigation, suggesting its possible use as bioinoculants for the agriculture in areas where the water resources are scarce and usually with high salt concentrations.

Culturing the desert microbiota

Over the last 30 years, the description of microbial diversity has been mainly based on culture-independent approaches (metabarcoding and metagenomics) allowing an in-depth analysis of microbial diversity that no other approach allows. Bearing in mind that culture-dependent approaches cannot replace culture-independent approaches, we have improved an original method for isolating strains consisting of "culturing" grains of sand directly on Petri dishes (grain-by-grain method). This method allowed to cultivate up to 10% of the bacteria counted on the surface of grains of the three sites studied in the Great Western Erg in Algeria (Timoudi, Béni Abbès, and Taghit), knowing that on average about 10 bacterial cells colonize each grain. The diversity of culturable bacteria (collection of 290 strains) predicted by 16S rRNA gene sequencing revealed that Arthrobacter subterraneus, Arthrobacter tecti, Pseudarthrobacter phenanthrenivorans, Pseudarthrobacter psychrotolerans, and Massilia agri are the dominant species. The comparison of the culture-dependent and -independent (16S rRNA gene metabarcoding) approaches at the Timoudi site revealed 18 bacterial genera common to both approaches with a relative overestimation of the genera Arthrobacter/Pseudarthrobacter and Kocuria, and a relative underestimation of the genera Blastococcus and Domibacillus by the bacterial culturing approach. The bacterial isolates will allow further study on the mechanisms of tolerance to desiccation, especially in Pseudomonadota (Proteobacteria).

Evaluation of Mangrove Soil Streptomyces spp. Exhibiting Culture and Biochemical Variation for Determination of Antibacterial Activity

Among actinobacteria, the genus Streptomyces are found in abundance in specific soil environments. Streptomyces are cultivable using Streptomyces-specific media, including starch casein, yeast extract, or ISP 2 media. Streptomyces isolates can be identified based on their macroscopic culture morphology and microscopic observations, and can be taxonomically placed within the Streptomyces genus. In the present study, mangrove soil samples collected from the coast of Mangalore harboring a multitude of microorganisms were enriched with calcium carbonate and pre-heated to isolate Streptomyces organisms. Cultures were quantified in colony forming units and their diversity was evaluated based on phenotypic features, enzyme hydrolysis, biochemical testing, and antibiotic sensitivity tests. The cross streaking method was used to select Streptomyces isolates, which were then further subjected to intracellular buffer extraction and evaluated against test organisms to determine their antibacterial efficacy. This study highlights the occurrence of prominent Streptomyces species with effective antibacterial activity in a unique environmental habitat of mangrove soil on the Mangalore coast.

The 1-aminocyclopropane-1-carboxylic acid deaminase-producing Streptomyces violaceoruber UAE1 can provide protection from sudden decline syndrome on date palm

In the United Arab Emirates (UAE), sudden decline syndrome (SDS) is one of the major fungal diseases caused by Fusarium solani affecting date palm plantations. To minimize the impact of the causal agent of SDS on date palm, native actinobacterial strains isolated from rhizosphere soils of healthy date palm plants were characterized according to their antifungal activities against F. solani DSM 106836 (Fs). Based on their in vitro abilities, two promising biocontrol agents (BCAs), namely Streptomyces tendae UAE1 (St) andStreptomyces violaceoruber UAE1 (Sv), were selected for the production of antifungal compounds and cell wall degrading enzymes (CWDEs), albeit their variations in synthesizing 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase (ACCD). Although both isolates showed antagonism when applied 7 days before the pathogen in the greenhouse experiments, the ACCD-producing Sv was relatively superior in its efficacy against SDS over the non-ACCD-producing St. This was evident from the symptoms of SDS in diseased date palm seedlings which were greatly reduced by Sv compared to St. On a scale of 5.0, the estimated disease severity indices in Fs-diseased seedlings were significantly (P < 0.05) reduced from 4.8 to 1.5 and 0.5 by St and Sv, respectively. Thus, the number of conidia of Fs recovered from plants pre-treated with both BCAs was comparable, but significantly (P < 0.05) reduced compared to plants without any BCA treatment. In addition, a significant (P < 0.05) decrease in ACC levels of both the root and shoot tissues was detected inSv + Fs seedlings to almost similar levels of healthy seedlings. However, in planta ACC levels highly increased in seedlings grown in soils infested with the pathogen alone or amended with St prior to F. solani infestation (St + Fs). This suggests a major role of ACCD production in relieving the stress of date palm seedlings infected with F. solani, thus supporting the integrated preventive disease management programs against this pathogen. This is the first report of effective rhizosphere actinobacterial BCAs to provide protection against SDS on date palm, and to help increase agricultural productivity in a more sustainable manner in the UAE and the other arid regions.

Actinobacteria Community and Their Antibacterial and Cytotoxic Activity on the Weizhou and Xieyang Volcanic Islands in the Beibu Gulf of China

Weizhou Island and Xieyang Island are two large and young volcanic sea islands in the northern part of the South China Sea. In this study, high-throughput sequencing (HTS) of 16S rRNA genes was used to explore the diversity of Actinobacteria in the Weizhou and Xieyang Islands. Moreover, a traditional culture-dependent method was utilized to isolate Actinobacteria, and their antibacterial and cytotoxic activities were detected. The alpha diversity indices (ACE metric) of the overall bacterial communities for the larger island (Weizhou) were higher than those for the smaller island (Xieyang). A beta diversity analysis showed a more dispersive pattern of overall bacterial and actinobacterial communities on a larger island (Weizhou). At the order level, Frankiales, Propionibacteriales, Streptomycetales, Micrococcales, Pseudonocardiales, Micromonosporales, Glycomycetales, Corynebacteriales, and Streptosporangiales were the predominant Actinobacteria. A total of 22.7% of the OTUs shared 88%-95% similarity with some known groups. More interestingly, 15 OTUs formed a distinct and most predominant clade, and shared identities of less than 95% with any known families. This is the first report about this unknown group and their 16S rRNA sequences obtained from volcanic soils. A total of 268 actinobacterial strains were isolated by the culture-dependent method. Among them, 55 Streptomyces species were isolated, representing that 76.6% of the total. S. variabilis and S. flavogriseus were the most abundant. Moreover, some rare Actinobacteria were isolated. These included Micromonospora spp., Nocardia spp., Amycolatopsis spp., Tsukamurella spp., Mycobacterium spp., and Nonomuraea spp. Among them, eight Streptomyces spp. exhibited antibacterial activity against Bacillus cereus. Only three strains inhibited the growth of Escherichia coli. Four strains showed good activity against aquatic pathogenic bacterial strains of Streptococcus iniae. The cytotoxicity assay results showed that 27 strains (10.07%) exhibited cytotoxic activity against HeLa and A549 cell lines. Many actinobacterial strains with cytotoxic activity were identified as rare Actinobacteria, which illustrated that volcanic islands are vast reservoirs for Actinobacteria with promising antibacterial and cytotoxic activity. This study may significantly improve our understanding of actinobacterial communities on volcanic islands. The isolated Actinobacteria showed promising prospects for future use.