Sequence Polymorphism of GroEL Gene in Natural Population of Bacillus and Brevibacillus spp. that Showed Variation in Thermal Tolerance Capacity and mRNA Expression

Abstract

GroEL, a class I chaperonin, plays an important role in the thermal adaptation of the cell and helps to maintain the viability of the cell under heat shock condition. Function of groEL in vivo depends on the maintenance of proper structure of the protein which in turn depends on the nucleotide and amino acid sequence of the gene. In this study, we investigated the changes in nucleotide and amino acid sequences of the partial groEL gene that may affect the thermotolerance capacity as well as mRNA expression of bacterial isolates. Sequences among the same species having differences in the amino acid level were identified as different alleles. The effect of allelic variation on the groEL gene expression was analyzed by comparison and relative quantification in each allele under thermal shock condition by RT-PCR. Evaluation of K a/K s ratio among the strains of same species showed that the groEL gene of all the species had undergone similar functional constrain during evolution. The strains showing similar thermotolerance capacity was found to carry same allele of groEL gene. The isolates carrying allele having amino acid substitution inside the highly ATP/ADP or Mg(2+)-binding region could not tolerate thermal stress and showed lower expression of the groEL gene. Our results indicate that during evolution of these bacterial species the groEL gene has undergone the process of natural selection, and the isolates have evolved with the groEL allelic sequences that help them to withstand the thermal stress during their interaction with the environment.

Differential Response of Bacterial Microdiversity to Simulated Global Change

“…The high number of synonymous mutations thus allows protein-coding regions such as groEL to resolve finer-scale differences in diversity than even variable regions of the 16S region can. Of course, selection for particular groEL genes in our treatments is possible; the groEL gene codes for a stress response chaperonin, and mutations therein may confer tolerance to different stress conditions ( 39 , 40 ). However, the vast majority of genetic variability observed in groEL diversity is likely neutral with respect to our treatments and, because HGT of the gene is rare, linked to other regions in the genome that are under selection.…”