Diversity and Bioprospecting of Culturable Plant-Associated Bacteria from Saline Soils in the Aydarkul Lake Region, Uzbekistan

Abstract: Plants are largely considered as meta-organisms due to their dependence on the communities of plant growth promoting soil bacteria (PGPB). These beneficial PGPBs are known to enhance plant tolerance to several abiotic stresses, especially drought and salt stresses. In this work, we investigated plant-associated soil microbial communities collected from different coastal sites of the East Aydarkul Lake region to establish a microbial bioinoculant with abilities to improve and restore the currently lost or being lost agricultural lands. By using specifically aimed enrichment strategy and based on PGP activity screening, 66 bacterial strains were selected and identified among 118 pure cultures obtained. Of these, 4 individual strains belonging to Stutzerimonas stutzeri were characterized for their salt and heat stress tolerance and possession of multiparametric PGP activities. One strain, S. stutzeri M205-2, significantly enhanced its exopolysaccharide (EPS) biosynthesis under salt stress conditions. This alginate-like EPS was isolated and its efficient water-retaining capacities in saline soil were determined. Genome sequencing of M205-2 revealed a very broad spectrum of its additional PGP activities such as fixation of atmospheric nitrogen, production of desferrioxamine E siderophore, heavy metals detoxification, organic pollutants degradation and the ability to produce the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase. Overall, our data indicate that S. stutzeri M205-2 exhibits versatile metabolic and degradation potential, which has a variety of biotechnological implications and also represents an important genomic source for the deciphering and redesigning novel plant growth promotion strategies at the molecular level.