Comparative genomics of plant growth promoting phosphobacteria isolated from acidic soils.

Despite being one of the most abundant elements in soil, phosphorus (P) often becomes a limiting macronutrient for plants due to its low bioavailability, primarily locked away in insoluble organic and inorganic forms. Phosphate solubilizing and mineralizing bacteria, also called phosphobacteria, isolated from P-deficient soils have emerged as a promising biofertilizer alternative, capable of converting these recalcitrant P forms into plant-available phosphates. Three such phosphobacteria strains-Serratia sp. RJAL6, Klebsiella sp. RCJ4, and Enterobacter sp. 198-previously demonstrated their particular strength as plant growth promoters for wheat, ryegrass, or avocado under abiotic stresses and P deficiency. Comparative genomic analysis of their draft genomes revealed several genes encoding key functionalities, including alkaline phosphatases, isonitrile secondary metabolites, enterobactin biosynthesis and genes associated to the production of indole-3-acetic acid (IAA) and gluconic acid. Moreover, overall genome relatedness indexes (OGRIs) revealed substantial divergence between Serratia sp. RJAL6 and its closest phylogenetic neighbours, Serratia nematodiphila and Serratia bockelmanii. This compelling evidence suggests that RJAL6 merits classification as a novel species. This in silico genomic analysis provides vital insights into the plant growth-promoting capabilities and provenance of these promising PSRB strains. Notably, it paves the way for further characterization and potential application of the newly identified Serratia species as a powerful bioinoculant in future agricultural settings.

Downsizing Class II Lasso Peptides: Genome Mining-Guided Isolation of Huascopeptin Containing the First Gly1-Asp7 Macrocycle.

A new lasso peptide, huascopeptin, was isolated following genome-mined discovery of a new biosynthetic gene cluster in extremotolerant Streptomyces huasconensis HST28T from Salar de Huasco, Atacama Desert, Chile. Compound 1 is a 13-residue class II lasso peptide containing a novel Gly1-Asp7 macrolactam ring, a three-residue loop, and a three-residue tail, making it the smallest lasso peptide isolated to date. The lasso structure was confirmed using NOE restraint-based molecular dynamics simulations.

Streptomyces altiplanensis sp. nov., an alkalitolerant species isolated from Chilean Altiplano soil, and emended description of Streptomyces chryseus (Krasil'nikov et al. 1965) Pridham 1970.

A polyphasic approach was used for evaluating the taxonomic status of strain HST21T isolated from Salar de Huasco in the Atacama Desert. The results of 16S rRNA gene and multilocus sequence phylogenetic analyses assigned strain HST21T to the genus Streptomyceswith Streptomyces albidochromogenes DSM 41800Tand Streptomyces flavidovirens DSM 40150T as its nearest neighbours. Digital DNA-DNA hydridization (dDDH) and average nucleotide identity (ANI) values between the genome sequences of strain HST21T and S. albidochromogenes DSM 41800T (35.6 and 88.2 %) and S. flavidovirens DSM 40105T (47.2 and 88.8 %) were below the thresholds of 70  and 95-96 % for prokaryotic conspecific assignation. Phenotypic, chemotaxonomic and genetic results distinguished strain HST21T from its closest neighbours. Strain HST21T is characterized by the presence of ll-diaminopimelic acid in its peptidoglycan layer; glucose and ribose as whole cell sugars; diphosphatidylglycerol, phosphatidylmethylethanolamine, phosphatidylethanolamine, phosphatidylinositol, glycophospholipids, unknown lipids and phospholipids as polar lipids; and anteiso-C15 : 0 (21.6 %) and anteiso-C17 : 0 (20.5 %) as major fatty acids (>15 %). Based on these results, strain HST21T merits recognition as a novel species, for which the name Streptomyces altiplanensis sp. nov. is proposed. The type strain is HST21T=DSM 107267T=CECT 9647T. While analysing the phylogenies of strain HST21T, Streptomyces chryseus DSM 40420T and Streptomyces helvaticus DSM 40431T were found to have 100 % 16S rRNA gene sequence similarity with digital DNA-DNA hydridization (dDDH) and average nucleotide identity (ANI) values of 95.3 and 99.4 %, respectively. Therefore, S. helvaticus is considered as a later heterotypic synonym of S. chryseus and, consequently, we emend the description of S. chryseus.

Streptomyces huasconensis sp. nov., an haloalkalitolerant actinobacterium isolated from a high altitude saline wetland at the Chilean Altiplano.

Streptomyces strain HST28T isolated from the Salar de Huasco, an athalassohaline and poly-extreme high altitude saline wetland located in northern Chile, was the subject of a polyphasic taxonomic study. Strain HST28T showed morphological and chemotaxonomic features in line with its classification in the genus Streptomyces. Optimal growth of strain HST28T was obtained at 28 °C, pH 8-9 and up to 10 % (w/v) NaCl. Single (16S rRNA) and multi-locus gene sequence analyses showed that strain HST28T had a distinct phylogenetic position from its closest relatives, the type strains of Steptomyces aureus and Streptomyces kanamyceticus. Digital DNA-DNA hybridization (23.3 and 31.0 %) and average nucleotide identity (79.3 and 85.6 %) values between strain HST28T and its corresponding relatives mentioned above were below the threshold of 70 and 96 %, respectively, defined for assigning a prokaryotic strains to the same species. Strain HST28T was characterised by the presence of ll-diaminopimelic acid in its peptidoglycan layer; galactose, glucose, ribose and traces of arabinose and mannose as whole-cell sugars; phosphatidylmethylethanolamine, phosphatidylinositol, aminolipid, glycophospholipid and an unidentified lipid as polar lipids; and the predominating menaquinones MK-9(H6), MK-9(H8) and MK-9(H4) (>20 %) as well as anteiso-C15 : 0 and anteiso-C17 : 0 as major fatty acids (>15 %). Based on the phenotypic and genetic results, strain HST28T (DSM 107268T=CECT 9648T) merits recognition as a new species named Streptomyces huasconensis sp. nov.