Genomic-based classification of Catenulispora pinisilvae sp. nov., novel actinobacteria isolated from a pine forest soil in Poland and emended description of Catenulispora rubra

Generation of a high quality library of bioactive filamentous actinomycetes from extreme biomes using a culture-based bioprospecting strategy

Introduction

Filamentous actinomycetes, notably members of the genus Streptomyces, remain a rich source of new specialized metabolites, especially antibiotics. In addition, they are also a valuable source of anticancer and biocontrol agents, biofertilizers, enzymes, immunosuppressive drugs and other biologically active compounds. The new natural products needed for such purposes are now being sought from extreme habitats where harsh environmental conditions select for novel strains with distinctive features, notably an ability to produce specialized metabolites of biotechnological value.

Methods

A culture-based bioprospecting strategy was used to isolate and screen filamentous actinomycetes from three poorly studied extreme biomes. Actinomycetes representing different colony types growing on selective media inoculated with environmental suspensions prepared from high-altitude, hyper-arid Atacama Desert soils, a saline soil from India and from a Polish pine forest soil were assigned to taxonomically predictive groups based on characteristic pigments formed on oatmeal agar. One hundred and fifteen representatives of the colour-groups were identified based on 16S rRNA gene sequences to determine whether they belonged to validly named or to putatively novel species. The antimicrobial activity of these isolates was determined using a standard plate assay. They were also tested for their capacity to produce hydrolytic enzymes and compounds known to promote plant growth while representative strains from the pine forest sites were examined to determine their ability to inhibit the growth of fungal and oomycete plant pathogens.

Results

Comparative 16S rRNA gene sequencing analyses on isolates representing the colour-groups and their immediate phylogenetic neighbours showed that most belonged to either rare or novel species that belong to twelve genera. Representative isolates from the three extreme biomes showed different patterns of taxonomic diversity and characteristic bioactivity profiles. Many of the isolates produced bioactive compounds that inhibited the growth of one or more strains from a panel of nine wild strains in standard antimicrobial assays and are known to promote plant growth. Actinomycetes from the litter and mineral horizons of the pine forest, including acidotolerant and acidophilic strains belonging to the genera Actinacidiphila, Streptacidiphilus and Streptomyces, showed a remarkable ability to inhibit the growth of diverse fungal and oomycete plant pathogens.

Discussion

It can be concluded that selective isolation and characterization of dereplicated filamentous actinomyctes from several extreme biomes is a practical way of generating high quality actinomycete strain libraries for agricultural, industrial and medical biotechnology.

Novel Antibacterial, Cytotoxic and Catalytic Activities of Silver Nanoparticles Synthesized from Acidophilic Actinobacterial SL19 with Evidence for Protein as Coating Biomolecule

Silver nanoparticles (AgNPs) have potential applications in medicine, photocatalysis, agriculture, and cosmetic fields due to their unique physicochemical properties and strong antimicrobial activity. Here, AgNPs were synthesized using actinobacterial SL19 strain, isolated from acidic forest soil in Poland, and confirmed by UV-vis and FTIR spectroscopy, TEM, and zeta potential analysis. The AgNPs were polydispersed, stable, spherical, and small, with an average size of 23 nm. The FTIR study revealed the presence of bonds characteristic of proteins that cover nanoparticles. These proteins were then studied by using liquid chromatography with tandem mass spectrometry (LC-MS/ MS) and identified with the highest similarity to hypothetical protein and porin with molecular masses equal to 41 and 38 kDa, respectively. Our AgNPs exhibited remarkable antibacterial activity against Escherichia coli and Pseudomonas aeruginosa. The combined, synergistic action of these synthesized AgNPs with commercial antibiotics (ampicillin, kanamycin, streptomycin, and tetracycline) enabled dose reductions in both components and increased their antimicrobial efficacy, especially in the case of streptomycin and tetracycline. Furthermore, the in vitro activity of the AgNPs on human cancer cell lines (MCF-7, A375, A549, and HepG2) showed cancer-specific sensitivity, while the genotoxic activity was evaluated by Ames assay, which revealed a lack of mutagenicity on the part of nanoparticles in Salmonella Typhimurium TA98 strain. We also studied the impact of the AgNPs on the catalytic and photocatalytic degradation of methyl orange (MO). The decomposition of MO was observed by a decrease in intensity of absorbance within time. The results of our study proved the easy, fast, and efficient synthesis of AgNPs using acidophilic actinomycete SL19 strain and demonstrated the remarkable potential of these AgNPs as anticancer and antibacterial agents. However, the properties and activity of such particles can vary by biosynthesized batch.

Actinospica acidithermotolerans sp. nov., a novel actinomycete isolated from sediment from an Indonesian hot spring

A polyphasic study was designed to resolve the taxonomic position of isolate MGRD01-02^T which was recovered from an acidic hot spring in Indonesia and assigned to the genus Actinospica. Phylogenetic analyses based on 16S rRNA gene sequences show that the isolate is most closely related to the type strains of Actinospica acidiphila (98.5%), Actinospica robiniae (97.8%) and Actinospica durhamensis (96.8%). Morphological and chemotaxonomic data underpin the assignment of the isolate to the genus Actinospica as it forms an extensively branched substrate mycelium which carries tufts of white aerial hyphae that differentiate into straight to flexuous chains of cylindrical spores with faint rugose surfaces, contains 2,6-diamino-3-hydroxydiaminopimelic acid in the peptidoglycan, mixtures of hydrogenated menaquinones with nine isoprene units, iso-C _15:O and iso-C _16:O as major fatty acids and phosphatidylethanolamine as the diagnostic phospholipid. Whole-genome sequence analyses show that the isolate, A. durhamensis CSCA 57^T and Actinocrinis puniceicyclus DSM 45168^T have genome sizes of 7.9, 9.6 and 6.7 Mbp, respectively. A phylogenomic tree shows that they form distinct branches in a well-supported clade, a result supported by associated phenotypic data. Average nucleotide identity and digital DNA:DNA hybridization similarities are below the recommended thresholds for assigning strains to the same species; they also indicate that isolate MGRD01-02^T is most closely related to the A. durhamensis and A. robiniae strains. Corresponding amino acid identity and conserved protein data not only support these relationships but also confirm the taxonomic integrity of the genus Actinocrinis. Based on these results, it is proposed that isolate MGRD01-02^T (= CCMM B1308^T = ICEBB-09^T = NCIMB 15218^T) be classified in the genus Actinospica as Actinospica acidithermotolerans sp. nov. The draft genome of the isolate and its closest phylogenomic neighbours contain biosynthetic gene clusters with the potential to produce new natural products, notably antibiotics.

Catenulispora pinistramenti sp. nov., novel actinobacteria isolated from pine forest soil in Poland

The taxonomic status of two filamentous actinobacteria, isolates NF23 and NL8^T, recovered from the litter layer of a pine forest soil in Poland was established in a genome-based polyphasic study. The isolates showed a combination of chemotaxonomic, morphological and physiological properties associated with their classification in the genus Catenulispora. They formed a well supported lineage within the Catenulispora 16S rRNA gene tree and were most closely related to the type strains of Catenulispora acidiphila (99.1%), Catenulispora pinisilvae (99.9 %) and Catenulispora rubra (99.1 %), and like them, were found to have large genomes (10.8 and 11.5 Mbp, respectively). A phylogenomic tree based on the draft genomes of isolates NF23 and NL8^T and their phylogenetic neighbours showed that they formed a distinct branch in the Catenulispora clade that was most closely related to C. pinisilvae DSM 111109^T. The isolates shared a combination of genomic, genotypic and phenotypic features, and had high average nucleotide index (ANI) and digital DNA:DNA hybridization (dDDH) similarities consistent with their assignment to the same species. The isolates were distinguished from the C. acidiphila, C. pinisilvae and C. rubra strains by a wealth of taxonomic data and by low ANI (84.9-93.9 %) and dDDH (29.6-54.7 %) values. It is proposed that the isolates be classified in the genus Catenulispora as C. pinistramenti sp. nov. with isolate NL8^T (=DSM 111110^T=PCM 3045^T) as the type strain. The genomes of strains NF23 and NL8^T are rich in natural product-biosynthetic gene clusters hence these strains have the potential to synthesize new specialised metabolites.