Isolation a new strain of Kocuria rosea capable of tolerating extreme conditions

A new actinobacterial strain was isolated from Ab-e-Siah spring (dark water) taken from the Ramsar city in Iran, and subjected to several stress conditions investigation. The isolate, named MG2 strain, was Gram-positive, aerobic, diplococci or tetrad shaped, non-spore forming and non-motile. Phylogenetic analysis of the isolate using 16S rDNA sequence indicated that the organism matched best with the genus Kocuria and the highest sequence similarities (98.55%) being found with Kocuria rosea. The 16S rDNA sequence determined in this study has been deposited in the NCBI database with the accession no. (JX534199), K. rosea strain MG2. The isolated strain was an alkaliphilic-mesophilic bacterium because the optimal growth was observed at pH 9.2 and temperature of 28 °C under aerobic condition. MG2 was a halotolerant strain and tolerated maximally to 15% NaCl concentraion. Viability analysis by flow cytometry indicated that this strain had highly resistance to UV-C radiation and moderately resistance to desiccation after 28 days. The viability of K. rosea strains MG2 and Deinococcus radiodurans R1 were determined D₈₇ and D₉₈ according to D index, respectively, by a dose radiation 25 J/cm (Appukuttan et al., 2006). Thus the UV resistance of strain MG2 was comparable with representative radiation resistant Deinococcus. Also MG2 was grown at 1–4% of H₂O₂ as an oxidant agent. This research is the first study on multiple extreme resistance of Kocuria rosea new strain (MG2) isolated in Iran. - Highlights: • We have reported a new mesophilic–alkaliphilic radioresistant bacterial strain from radioactive spring Abe-Siah in Ramsar, Iran. • The isolate was identified as Kocuria rosea strain MG2 by molecular and phylogenetical analysis. • This strain showed high resistance to UV-C radiation and desiccation that analyzed by flow cytometry for cell viability. • Also the strain MG2 was resisted to other extreme conditions including: salinity, alkaline pH and hydrogen peroxide