Streptacidiphilus toruniensis sp. nov., isolated from a pine forest soil

Streptacidiphilus alkalitolerans sp. nov., Streptacidiphilus cavernicola sp. nov. and Streptacidiphilus jeojiensis sp. nov. isolated from a cave, and an emended description of the genus Streptacidiphilus

Six Gram-reaction-positive, strictly aerobic, mycelium-forming actinobacteria were isolated from soils collected from a natural cave in Jeju, Republic of Korea. The isolates produced well-developed, branched, substrate mycelia and white aerial mycelia that differentiated into straight or flexuous chains of smooth-surfaced spores. Cells showed growth at 15-30 °C, pH 3.5-8.0 and 0-1% (w/v) NaCl. Most of the isolates also grew at pH 10.0. The cell-wall peptidoglycan in common contained ll-diaminopimelic acid, galactose, glucose, mannose and rhamnose. The major menaquinone was MK-9(H6) and MK-9(H8). The polar lipids in common contained phosphatidylglycerol, phosphatidylinositol and an unidentified phospholipid, with the presence of diphosphatidylglycerol and phosphatidylethanolamine in some strains. The predominant fatty acids in common were anteiso-C15 : 0, iso-C16 : 0 and C16 : 0. Strains N1-1T, N1-3 and N1-12 contained genomes of 8.44-8.77 Mbp, and strains N1-5 and N1-10T consisted of genomes of 9.00-9.17 Mbp, while strain N8-3T contained the smallest genome (7.33 Mbp) among the isolates. The genomic DNA G+C contents of the isolates were 71.5-72.2%. Three representatives of the isolates encompassed 16-29 biosynthetic gene clusters predicted to encode for secondary metabolites. The core genome-based phylogenomic tree showed that they formed three distinct clusters within the genus Streptacidiphilus, with the closest relative, the type strain of Streptacidiphilus carbonis, which was also supported by 16S rRNA gene phylogeny. The orthologous average nucleotide identity (≤88.2%) and digital DNA-DNA hybridization (≤30.3%) between three representatives of the isolates and members of the genus Streptacidiphilus and among them supported that the isolates represent three new species of the genus Streptacidiphilus, for which the names Streptacidiphilus alkalitolerans [type strain, N1-1T (=KCTC 19224T=DSM 45080T)], Streptacidiphilus cavernicola [type strain, N8-3T (=KCTC 29470T=DSM 117389T)] and Streptacidiphilus jeojiensis sp. nov. [type strain, N1-10T (=KCTC 19257T=DSM 117391T=NRRL B-24556T)] are proposed.

Streptantibioticus silvisoli sp. nov., acidotolerant actinomycetes from pine litter, reclassification of Streptomyces cocklensis, Streptomyces ferralitis, Streptomyces parmotrematis and Streptomyces rubrisoli as Actinacidiphila cocklensis comb. nov., Streptantibioticus ferralitis comb. nov., Streptantibioticus parmotrematis comb. nov. and Streptantibioticus rubrisoli comb. nov., and emended descriptions of the genus Streptantibioticus, the family Streptomycetaceae and Streptomyces iconiensis

Filamentous actinomycetes, designated SL13 and SL54T, were isolated from pine litter and their taxonomic status resolved using a polyphasic approach. The isolates exhibit chemotaxonomic and morphological properties consistent with their classification in the family Streptomycetaceae. They form extensively branched substrate mycelia bearing aerial hyphae that differentiate into straight chains of cylindrical spores. The whole-organism hydrolysates contain ll-diaminopimelic acid, glucose, mannose and ribose, the predominant isoprenologue is MK-9(H8), the polar lipids are diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol, phosphatidylglycerol and glycophospholipids, and the major fatty acids are anteiso-C15 : 0, iso-C15 : 0, iso-C16 : 0 and anteiso-C17 : 0. Phylogenetic trees based on 16S rRNA gene sequences and multilocus gene sequences of conserved housekeeping genes show that the isolates form a well-supported lineage that is most closely related to Streptomyces parmotrematis NBRC 115203T. All of these strains form a well-defined clade in the multilocus sequence analysis tree together with Streptantibioticus cattleyicolor DSM 46488T, Streptomyces ferralitis DSM 41836T and Streptomyces rubrisoli DSM 42083T. Draft genomes assemblies of the isolates are rich in biosynthetic gene clusters predicted to produce novel specialized metabolites and stress-related genes which provide an insight into how they have adapted to the harsh conditions that prevail in pine litter. Phylogenomically, both isolates belong to the same lineage as the type strains of S. cattleyicolor, S. ferralitis, S. parmotrematis and S. rubrisoli; these relationships are underpinned by high average amino acid identity, average nucleotide identity and genomic DNA-DNA hybridization values. These metrics confirm that isolates SL13 and SL54T belong to a novel species that is most closely related to S. parmotrematis NBRC 115203T and that these strains together with S. ferralitis DSM 41836T, S. rubrisoli DSM 42083T belong to the genus Streptantibioticus. Consequently, it is proposed that the isolates be recognized as a new Streptantibioticus species, Streptantibioticus silvisoli comb. nov., with isolate SL54T (=DSM 111111T=PCM3044T) as the type strain, and that S. ferralitis, S. parmotrematis and S. rubrisoli be transferred to the genus Streptantibioticus as Streptantibioticus ferralitis comb. nov., Streptantibioticus parmotrematis comb. nov. and Streptantibioticus rubrisoli comb. nov. Emended descriptions are given for the genus Streptantibioticus, the family Streptomycetaceae and for Streptomyces iconiensis which was found to be a close relative of the isolates in the 16S rRNA gene sequence analyses. It is also proposed that Streptomyces cocklensis be transferred to the genus Actinacidiphila as Actinacidiphila cocklensis comb. nov based on its position in the MLSA and phylogenomic trees and associated genomic data.

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.

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.

Streptacidiphilus fuscans sp. nov., a novel actinobacterium isolated from the root of pumpkin (Cucurbita moschata)

A novel acidophilic actinobacterium, designated strain NEAU-YB345^T, was isolated from a pumpkin root collected from Mudanjiang, Heilongjiang Province, northeast PR China. Based on 16S rRNA gene sequence similarity and chemotaxonomic and morphological properties, the isolate was assigned to the genus Streptacidiphilus, with the high 16S rRNA gene sequence similarities to Streptacidiphilus melanogenes JCM 16224^T (99.2 %), Streptacidiphilus anmyonensis JCM 16223^T (99.1 %) and Streptacidiphilus jiangxiensis JCM 12277^T (98.7 %). Its cell wall contained ll-diaminopimelic acid as the major diamino acid. Rhamnose, ribose, glucose and galactose were the detected sugars from the whole-cell hydrolysates. The phospholipid profile consisted of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol, phosphatidylinositol mannoside and an unidentified phospholipid. The menaquinones were MK-9(H₈) and MK-9(H₆). Major fatty acids were C_16 : 0, iso-C_16 : 0, iso-C_15 : 0 and anteiso-C_15 : 0. Phylogenetic analysis using 16S rRNA gene and whole-genome sequences placed the strain in distinct clades but within the genus Streptacidiphilus. The DNA G+C content was 71.2 mol%. Based on DNA-DNA relatedness and physiological and biochemical data, the isolate could be distinguished from its closest relatives. Therefore, strain NEAU-YB345^T represents a novel species of the genus Streptacidiphilus, for which the name Streptacidiphilus fuscans sp. nov. is proposed. The type strain is NEAU-YB345^T (=CCTCC AA 2020030^T=JCM 33976^T).

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

Two actinobacteria, strains NF3 and NH11^T, isolated from a pine forest soil, near Torun, Poland were examined for diverse chemotaxonomic and morphological properties that placed them in the genus Catenulispora. They produced an extensively branched stable mycelium, contained LL-diaminopimelic acid as the diamino acid of the peptidoglycan, arabinose as the diagnostic whole-organism sugar, tetra-, hexa- and octa-hydrogenated menaquinones with nine isoprenoid units as the predominant isoprenologues, iso-C_16:0 and anteiso-C_17:0 as major fatty acids, and formed a well supported clade within the Catenulispora 16S rRNA gene tree together with Catenulispora acidiphila DSM 44928^T and Catenulispora rubra DSM 44948^T sharing sequence similarities with the latter of 98.8 and 99.0%, respectively. The sizes of whole genome sequences generated for the isolates and the C. rubra strain ranged from 11.20 to 12.80 Mbp with corresponding in silico DNA G+C values of 69.9-70.0%. The isolates and the C. acidiphila and C. rubra strains formed a well supported branch in the actinobacterial phylogenomic tree. Isolates NF3 and NH11^T belong to the same species as they have identical 16S rRNA gene sequences, share many chemotaxonomic, cultural and phenotypic features and show very high average nucleotide identity (ANI) and digital DNA:DNA relatedness (dDDH) similarities. They can be distinguished from their closest phylogenomic neighbours by using a combination of chemotaxonomic and phenotypic properties and by ANI and dDDH values well below the thresholds of these metrics used to assign closely related strains to different species. Consequently, we propose that the isolates be classified as a new Catenulispora species, Catenulispora pinisilvae sp. nov., the type strain is NH11^T (=DSM 111109^T =PCM 3046^T). An emended description is given for C. rubra based on data acquired in the present study. Analyses of the draft genomes of the isolates and the C. acidiphila and C. rubra strains revealed the presence of many biosynthetic gene clusters with the potential to synthesize novel drug-like metabolites. In vitro screens showed that the isolates inhibited the growth of Gram-positive bacteria and wheat pathogens belonging to the genus Fusarium.

Streptacidiphilus bronchialis sp. nov., a ciprofloxacin-resistant bacterium from a human clinical specimen; reclassification of Streptomyces griseoplanus as Streptacidiphilus griseoplanus comb. nov. and emended description of the genus Streptacidiphilus

The taxonomic position of strain 15-057A^T, an acidophilic actinobacterium isolated from the bronchial lavage of an 80-year-old male, was determined using a polyphasic approach incorporating morphological, phenotypic, chemotaxonomic and genomic analyses. Pairwise 16S rRNA gene sequence similarities calculated using the GGDC web server between strain 15-057A^T and its closest phylogenetic neighbours, Streptomyces griseoplanus NBRC 12779^T and Streptacidiphilus oryzae TH49^T, were 99.7 and 97.6 %, respectively. The G+C content of isolate 15-057A^T was determined to be 72.6 mol%. DNA-DNA relatedness and average nucleotide identity between isolate 15-057A^T and Streptomyces griseoplanus DSM 40009^T were 29.2±2.5 % and 85.97 %, respectively. Chemotaxonomic features of isolate 15-057A^T were consistent with its assignment within the genus Streptacidiphilus: the whole-cell hydrolysate contained ll-diaminopimelic acid as the diagnostic diamino acid and glucose, mannose and ribose as cell-wall sugars; the major menaquinone was MK9(H8); the polar lipid profile consisted of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol, glycophospholipid, aminoglycophospholipid and an unknown lipid; the major fatty acids were anteiso-C15 : 0 and iso-C16 : 0. Phenotypic and morphological traits distinguished isolate 15-057A^T from its closest phylogenetic neighbours. The results of our taxonomic analyses showed that strain 15-057A^T represents a novel species within the evolutionary radiation of the genus Streptacidiphilus, for which the name Streptacidiphilus bronchialis sp. nov. is proposed. The type strain is 15-057A^T (=DSM 106435^T=ATCC BAA-2934^T).

Insights on the Effects of Heat Pretreatment, pH, and Calcium Salts on Isolation of Rare Actinobacteria from Karstic Caves

The phylum Actinobacteria is one of the most ubiquitously present bacterial lineages on Earth. In the present study, we try to explore the diversity of cultivable rare Actinobacteria in Sigangli Cave, Yunnan, China by utilizing a combination of different sample pretreatments and under different culture conditions. Pretreating the samples under different conditions of heat, setting the isolation condition at different pHs, and supplementation of media with different calcium salts were found to be effective for isolation of diverse rare Actinobacteria. During our study, a total of 204 isolates affiliated to 30 genera of phylum Actinobacteria were cultured. Besides the dominant Streptomyces, rare Actinobacteria of the genera Actinocorallia, Actinomadura, Agromyces, Alloactinosynnema, Amycolatopsis, Beutenbergia, Cellulosimicrobium, Gordonia, Isoptericola, Jiangella, Knoellia, Kocuria, Krasilnikoviella, Kribbella, Microbacterium, Micromonospora, Mumia, Mycobacterium, Nocardia, Nocardioides, Nocardiopsis, Nonomuraea, Oerskovia, Pseudokineococcus, Pseudonocardia, Rhodococcus, Saccharothrix, Streptosporangium, and Tsukamurella were isolated from these cave samples.

Silver nanoparticles from Pilimelia columellifera subsp. pallida SL19 strain demonstrated antifungal activity against fungi causing superficial mycoses

In this study, we present the in vitro antifungal activity of silver nanoparticles (AgNPs) synthesized from acidophilic actinobacterium Pilimelia columellifera subsp. pallida SL19 strain, alone and in combination with antibiotics viz., amphotericin B, fluconazole, and ketoconazole against pathogenic fungi, namely Candida albicans, Malassezia furfur, and Trichophyton erinacei. The minimum inhibitory concentration (MIC) and minimum biocidal concentration (MBC) of AgNPs against test fungi were evaluated. The fractional inhibitory concentration (FIC) index was determined to estimate antifungal activity of AgNPs combined with antibiotics. Antifungal activity of AgNPs varied among the tested fungal strains. M. furfur was found to be most sensitive to biogenic silver nanoparticles, followed by C. albicans and T. erinacei. The lowest MIC of AgNPs was noticed against M. furfur (16 μg ml^-1 ). Synergistic effect was observed on C. albicans when AgNP were combined with amphotericin B and ketoconazole and on M. furfur with fluconazole and ketoconazole (FIC index of 0.5). Cytotoxic effect of AgNPs on HeLa and 3T3 cell lines was evaluated. The IC₅₀ values were found to be 55 and 25 μg ml^-1 , respectively. The present study indicates that silver nanoparticles from P. columellifera subsp. pallida SL19 strain have antifungal activity, both alone and in combination with antibiotics, and offer a valuable contribution to nanomedicine.