Identification of the genetic determinants of Salmonella enterica serotype Typhimurium that may regulate the expression of the type 1 fimbriae in response to solid agar and static broth culture conditions.
BACKGROUND
Type 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.


RESULTS
In 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.


CONCLUSIONS
Genetic 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.
Chuang
Yin-Ching
YC
Department of Medical Research, Chi Mei Medical Center, 901 Chung Hwa Road, Yong Kang City, Tainan 710, Taiwan. chuangkenneth@hotmail.com
Wang
Ke-Chuan
KC
Chen
Yi-Tseng
YT
Yang
Chia-Huei
CH
Men
Shang-Chin
SC
Fan
Chia-Chun
CC
Chang
Li-Huan
LH
Yeh
Kuang-Sheng
KS
D000942:Antigens, Bacterial / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D003470:Culture Media / Q000737:chemistry*; D004251:DNA Transposable Elements; D038181:FMN Reductase / Q000235:genetics / Q000378:metabolism; D036781:Fimbriae Proteins / Q000235:genetics; D010861:Fimbriae, Bacterial / Q000235:genetics* / Q000378:metabolism / Q000648:ultrastructure; D015870:Gene Expression; D015723:Gene Library; D005816:Genetic Complementation Test; D016254:Mutagenesis, Insertional; D010641:Phenotype; D012486:Salmonella typhimurium / Q000235:genetics* / Q000378:metabolism / Q000648:ultrastructure; D014158:Transcription, Genetic
D000942:Antigens, Bacterial; D001426:Bacterial Proteins; D003470:Culture Media; D004251:DNA Transposable Elements; C110675:SEF21 protein, Salmonella enteritidis; D036781:Fimbriae Proteins; D038181:FMN Reductase