Taxonomic study of a salt tolerant Streptomyces sp. strain C-2012 and the effect of salt and ectoine on lon expression level.

Streptomyces strain C-2012 is a salt tolerant biocontrol PGPR that has been isolated from Iranian soil. The main aim of current study was finding strain C-2012 taxonomic position and to find the genes which are potentially involved in salt tolerance phenotype. Strain C-2012 chemotaxonomic, morphological and molecular characteristics indicate that this strain is a member of the genus Streptomyces. Phylogenetic analyses based on an almost complete 16S rRNA gene sequence revealed that this strain is closely related to Streptomyces rimosus JCM 4667(T). Also, DNA-DNA hybridization test estimated 74% relatedness between two strains and confirmed that C-2012 is a strain of S. rimosus. In order to find novel genes that are differentially expressed in response to the salt treatment, cDNA-AFLP was carried out. One of the selected expressed sequence tags (TDF-1) was found to be homologous to lon gene which produces a bacterial ATP-dependent proteases (proteases LA). Lon gene expression was induced following 450 mM salt (NaCl) treatment and its expression level was further (5.2-fold) increased in response to salt when ectoine was added to the medium. These results suggest that two protein protection systems including ectoine and ATP-dependent proteases synergistically are related. NaCl stress also caused an enhancement in the activity of extracellular protease.