Open AccessSilent genes in bacteria: the previously designated ‘cryptic’ ilvHI locus of ‘ Salmonella typhimurium LT2′ is active in natural isolates
Author(s) -
Burns Dennis M.,
Burger Michelle J.,
Beacham Ifor R.
Publication year - 1995
Publication title -
fems microbiology letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.899
H-Index - 151
eISSN - 1574-6968
pISSN - 0378-1097
DOI - 10.1111/j.1574-6968.1995.tb07772.x
Subject(s) - biology , salmonella , salmonella enterica , locus (genetics) , genetics , escherichia coli , gene , nonsense mutation , microbiology and biotechnology , serotype , enterobacteriaceae , frameshift mutation , bacteria , mutation , missense mutation
Gene ilvG in Escherichia coli K‐12 and ilvl in ‘ Salmonella typhimurium LT2′ ( S. enterica serotype Typhimurium, strain LT2) are inactive due to frameshift or nonsense mutations, respectively. These inactive genes have been suggested to be part of ‘cryptic’ genetic systems which are defined as being of long‐term regulatory and evolutionary significance. We have shown that the nonsense mutation in ilvI is present only in derivatives of the laboratory strain ‘ S. typhimurium LT2′. All natural isolates of Salmonella examined have an arginine codon at the corresponding location of their ilvl sequences. Further, two randomly selected natural isolates of serotype Typhimurium are shown to each have an active ALS III isozyme. Our findings strongly suggest that the only Salmonella strains which lack a functional ilvHI locus are LT2 isolates. We suggest that the mutations leading to inactivation of both ilvI in ‘ S. typhimurium LT2′ and ilvG in E. coli K‐12 are more likely to have been acquired during laboratory storage and/or cultivation, rather than representing cryptic systems of gene regulation.