The rfaH gene, which affects lipopolysaccharide synthesis in Salmonella enterica serovar Typhi, is differentially expressed during the bacterial growth phase

Abstract

We have cloned and sequenced the rfaH gene from Salmonella enterica serovar Typhi Strain Ty2. The gene shoed a high degree of similirity to the rfaH genes from Escherichia coli K-12 and S. enterica serovar Typhimurium. A rafH mutant was constructed by site-directed mutagenegis. This mutant produced a rough lipopolysaccharide (LPS), with an incomplete core region. The defect in LPS expression that rsults from the rafH mutation was corrected by a plasmid carrying the intact gene. The plasmid-borne rafH gene also restored normal LPS synthesis in a rafH mutant of E. coli. Reverse transcription-polymerase chain reaction analyses were performed to determine the effects of various environmental conditions on the expression of rafH. The transcription of rafH showed a growth-phase-dependent regulation, with maximal expression at the late exponential phase. Other environmental conditions, such as temperature or medium osmolarity, did not affect transcription of rafH.