Effect of drought on the growth and survival of the stress-tolerant bacterium Rhizobium sp. NBRI2505 sesbania and its drought-sensitive transposon Tn 5 mutant.
Studies were conducted to elucidate the nature of drought tolerance in the bacterium Rhizobium sp. NBRI2505 sesbania and its transposon Tn 5 induced mutant to assess the role of salt, pH, and temperature stresses in contributing to drought tolerance, and to correlate drought tolerance and symbiotic effectiveness. Rhizobium sp. NBRI2505 sesbania tolerated yeast extract mannitol broth (YEB) containing 28% salt (NaCl; wt/vol) for up to 18 h of incubation at 30 degrees C, survived a 2-h incubation in YEB at 65 degrees C, and when subjected to drought stress, tolerated YEB containing 45% polyethylene glycol 6000 (PEG; wt/vol) for up to 5 days of incubation at 30 degrees C. One drought-sensitive mutant Rhizobium sp. NBRI2505 sesbania T112 (T112) containing a single Tn 5 insertion was selected after screening about 10,000 clones. T112 was specifically defective in its tolerance for drought: when subjected to drought stress, it tolerated YEB containing 45% PEG for up to 2 days of incubation at 30 degrees C. T122 mutant was also more sensitive to the heat and desiccation stresses, compared with Rhizobium sp. NBRI2505 sesbania in the presence of 45% PEG. Our results demonstrated a positive effect of calcium on the survival of Rhizobium sp. sesbania under acidic stress conditions. The observed enhanced survival at pH 3 of Rhizobium sp. NBRI2505 sesbania and T112 in the presence of 5% CaCO(3) suggests the requirement of calcium for growth and survival, which may have an ecological significance in acidic soils. Mutant strain T112 produced ineffective symbiosis with the plant host in the presence of 2.5 and 5% PEG, indicating that drought tolerance is required for effective symbiosis.
Rehman
Ateequr
A
Microbiology Group, National Botanical Research Institute, P.B. No. 436, Rana Pratap Marg, Lucknow 226 001, India.
Nautiyal
Chandra Shekhar
CS
D004251:DNA Transposable Elements / Q000235:genetics; D004190:Disasters; D007887:Fabaceae / Q000254:growth & development; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D007194:India; D016296:Mutagenesis; D009586:Nitrogen Fixation; D011092:Polyethylene Glycols / Q000378:metabolism*; D012231:Rhizobium / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D012965:Sodium Chloride / Q000378:metabolism*; D012988:Soil Microbiology
D004251:DNA Transposable Elements; D011092:Polyethylene Glycols; D012965:Sodium Chloride