Abstract
BackgroundType 1 fimbriae are the most commonly found fimbrial appendages on the outer membrane of Salmonella enterica serotype Typhimurium. Previous investigations indicate that static broth culture favours S. Typhimurium to produce type 1 fimbriae, while non-fimbriate bacteria are obtained by growth on solid agar media. The phenotypic expression of type 1 fimbriae in S. Typhimurium is the result of the interaction and cooperation of several genes in the fim gene cluster. Other gene products that may also participate in the regulation of type 1 fimbrial expression remain uncharacterized.ResultsIn the present study, transposon insertion mutagenesis was performed on S. Typhimurium to generate a library to screen for those mutants that would exhibit different type 1 fimbrial phenotypes than the parental strain. Eight-two mutants were obtained from 7,239 clones screened using the yeast agglutination test. Forty-four mutants produced type 1 fimbriae on both solid agar and static broth media, while none of the other 38 mutants formed type 1 fimbriae in either culture condition. The flanking sequences of the transposons from 54 mutants were cloned and sequenced. These mutants can be classified according to the functions or putative functions of the open reading frames disrupted by the transposon. Our current results indicate that the genetic determinants such as those involved in the fimbrial biogenesis and regulation, global regulators, transporter proteins, prophage-derived proteins, and enzymes of different functions, to name a few, may play a role in the regulation of type 1 fimbrial expression in response to solid agar and static broth culture conditions. A complementation test revealed that transforming a recombinant plasmid possessing the coding sequence of a NAD(P)H-flavin reductase gene ubiB restored an ubiB mutant to exhibit the type 1 fimbrial phenotype as its parental strain.ConclusionGenetic determinants other than the fim genes may involve in the regulation of type 1 fimbrial expression in S. Typhimurium. How each gene product may influence type 1 fimbrial expression is an interesting research topic which warrants further investigation.
Highlights
Type 1 fimbriae are the most commonly found fimbrial appendages on the outer membrane of Salmonella enterica serotype Typhimurium
Typhimurium LB5010, when grown in static broth culture for 36–48 h, agglutinated Candida albicans on a glass slide
From the mutants that no longer exhibited the same type 1 fimbrial phenotypes as the parental strain whether grown on solid agar and in static broth cultures, 12 groups were classified according to the putative functions of the genes that were interrupted by the transposons
Summary
Type 1 fimbriae are the most commonly found fimbrial appendages on the outer membrane of Salmonella enterica serotype Typhimurium. Typhimurium to produce type 1 fimbriae, while non-fimbriate bacteria are obtained by growth on solid agar media. Many members of the family Enterobacteriaceae including Salmonella produce type 1 fimbriae, the most commonly found type of fimbrial appendages [4]. Type 1 fimbriae may modulate the bacterial tropism to the gut of the host [8], and type 1-fimbriated Salmonella were more virulent than the fim-minus ones [9]. The fact that more than 80% of Salmonella isolates produce this fimbrial type suggests that type 1 fimbriae play an important role at some stage in the life cycle of bacteria [10]
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