Role of large plasmid DNA in salt tolerance of a novel strain <i>gracilibacillus</i> sp. GTY

Abstract

Context: Isolated plasmid DNA from salt tolerant bacteria can play an important role in special environmental conditions.  

Objectives: The main objective of this study was to make a standard protocol for the isolation of large plasmid DNA from a highly salt tolerant bacterial strain, and then the plasmid DNA was eliminated from bacterial genome to know its effect on bacterial adaptation in high saline water.  

Materials and Methods: The strain Gracilibacillus sp. GTY was collected from the coast line of Dalian (North China) and was inoculated in high salt concentrated bacteriological media. Wheatcroft’s modified method was used to isolate plasmid DNA. Then the chemical curing agents such as acridine orange, SDS, sodium benzoate and mitomycin C were applied separately in different concentrations to eliminate plasmid DNA. After the elimination of plasmid DNA, the strain was cultivated in the MS liquid media containing 5%, 15% and 25% (w/v) of NaCl respectively and their growth rates were compared with the non-eliminated culture.  

Results: According to Wheatcroft’s modified method, the plasmid took two more hours to get isolated from the chromosomal DNA and the approximate size of the extracted plasmid DNA was 23.13 kb. Among all of the curing agents, plasmid DNA was eliminated successfully by acridine orange after 24 h of treatment at the concentration of 50 mg/l. Growth rates of plasmid eliminated culture were lower than non-eliminated culture and the growth rates of the plasmid eliminated culture were decreasing significantly with the addition of more NaCl.

Conclusion: The results obtained in this study suggest that the presence of large plasmid DNA in salt tolerant bacteria is related to their survival strategies. The genes located in the large plasmids may encode important traits related to their adaptation to special environmental conditions.  

Keywords: Salt tolerance; halophilic bacteria; curing agent; extrachromosomal DNA; Gracilibacillus sp. GTY.

DOI: http://dx.doi.org/10.3329/jbs.v18i0.8772

JBS 2010; 18(0): 34-39