Exopolysaccharide Yield and Environmental Adaptation of Rhizobia Regulated by Gene envZ,iscS and asnC
[Objective]Rhizobium yanglingense CCBAU 01603 form efficient nitrogen-fixing nodules with Caragana legumes.Alk_40,one of the offspring of CCBAU 01603,was obtained through experimental evolution in alkaline medium for 500 generations.It was discovered that a significant decrease in exopolysaccharide(EPS)yields of Alk_40 with specific SNPs changes in the gene envZ,iscS,and asnC.EPS yields and environmental adaptability of rhizobia regulated by these key genes were investigated.[Method]Three mutants of rhizobia were created by deleting gene envZ,iscS,and asnC,respectively.EPS yields and growth under different environmental conditions of mutants were assessed.[Result]In comparison to CCBAU 01603,the envZ,iscS,and asnC mutants presented significantly lower EPS yields in YMA medium,demonstrated diminished fitness in acidic environments,and had a weakened tolerance to high temperatures of 65℃.This observation suggests a correlation between the EPS yield of rhizobia and their resistances to acidic or heat stress.In addition,the mutants lacking the envZ and asnC genes showed the sensitivity to NaCl,resulting in severely limited growth and reproduction in NaCl-containing media.Furthermore,their adaption in alkalescent environments significantly reduced as well.[Conclusion]It is discovered that EPS yields of rhizobia can be regulated by gene envZ,iscS,and asnC.
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