Natronosporangium hydrolyticum gen. nov., sp. nov., a haloalkaliphilic polyhydrolytic actinobacterium from a soda solonchak soil in Central Asia

Abstract

During a cultural diversity survey on hydrolytic bacteria in saline alkaline soils, a hydrolytic actinobacterium strain ACPA39^T was enriched and isolated in pure culture from a soda solonchak soil in southwestern Siberia. It forms a substrate mycelium with rod-shaped sporangia containing 1–3 exospores. The isolate is obligately alkaliphilic, growing at pH 7.5–10.3 (optimum at 8.5–9.0) and moderately halophilic, tolerating up to 3 M total Na⁺ in the form of sodium carbonates. It is an obligately aerobic, organoheteroterophic, saccharolytic bacterium, utilizing various sugars and alpha/beta-glucans as growth substrates. According to the 16S rRNA gene-based phylogenetic analysis, strain ACPA39^T forms a distinct branch within the family Micromonosporaceae, with the sequence identities below 94.5% with type strains of other genera. This is confirmed by phylogenomic analysis based on the 120 conserved single copy protein-based markers and genomic indexes (ANI, AAI). The cell-wall of ACPA39^T contained meso-DAP, glycine, glutamic acid and alanine in a equimolar ratio, characteristic of the peptidoglycan type A1γ'. The whole-cell sugars include galactose and xylose. The major menaquinone is MK-10(H₄). The identified polar lipids consist of phosphatidylglycerol, diphosphatidylglycerol, phosphatidylethanolamine and phosphatidylinositol. The polar lipid fatty acids were dominated by anteiso-C_17:0, iso-C_16:0, iso-C_17:0, 10 Me-C_18:0 and C_18:1ω9. Based on the distinct phylogeny, the chemotaxonomy features and unique phenotypic properties, strain ACPA39^T (DSM 106523^T = VKM 2772^T) is classified into a new genus and species in the family Micromonosporaceae for which the name Natronosporangium hydrolitycum gen. nov., sp. nov. is proposed.