The human gastric pathogen Helicobacter pylori has a potential acetone carboxylase that enhances its ability to colonize mice.
BACKGROUND
Helicobacter pylori colonizes the human stomach and is the etiological agent of peptic ulcer disease. All three H. pylori strains that have been sequenced to date contain a potential operon whose products share homology with the subunits of acetone carboxylase (encoded by acxABC) from Xanthobacter autotrophicus strain Py2 and Rhodobacter capsulatus strain B10. Acetone carboxylase catalyzes the conversion of acetone to acetoacetate. Genes upstream of the putative acxABC operon encode enzymes that convert acetoacetate to acetoacetyl-CoA, which is metabolized further to generate two molecules of acetyl-CoA.


RESULTS
To determine if the H. pylori acxABC operon has a role in host colonization the acxB homolog in the mouse-adapted H. pylori SS1 strain was inactivated with a chloramphenicol-resistance (cat) cassette. In mouse colonization studies the numbers of H. pylori recovered from mice inoculated with the acxB:cat mutant were generally one to two orders of magnitude lower than those recovered from mice inoculated with the parental strain. A statistical analysis of the data using a Wilcoxin Rank test indicated the differences in the numbers of H. pylori isolated from mice inoculated with the two strains were significant at the 99% confidence level. Levels of acetone associated with gastric tissue removed from uninfected mice were measured and found to range from 10-110 mumols per gram wet weight tissue.


CONCLUSIONS
The colonization defect of the acxB:cat mutant suggests a role for the acxABC operon in survival of the bacterium in the stomach. Products of the H. pylori acxABC operon may function primarily in acetone utilization or may catalyze a related reaction that is important for survival or growth in the host. H. pylori encounters significant levels of acetone in the stomach which it could use as a potential electron donor for microaerobic respiration.
Brahmachary
Priyanka
P
Department of Microbiology, University of Georgia, Athens, Georgia 30602, USA. priyanka.brahmachary@vanderbilt.edu
Wang
Ge
G
Benoit
Stéphane L
SL
Weinberg
Michael V
MV
Maier
Robert J
RJ
Hoover
Timothy R
TR
D000096:Acetone / Q000032:analysis; D000818:Animals; D001426:Bacterial Proteins / Q000502:physiology*; D002262:Carboxy-Lyases / Q000502:physiology*; D005798:Genes, Bacterial / Q000235:genetics; D016481:Helicobacter Infections / Q000382:microbiology*; D016480:Helicobacter pylori / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D009876:Operon; D017354:Point Mutation; D013270:Stomach / Q000737:chemistry / Q000382:microbiology
D001426:Bacterial Proteins; D000096:Acetone; D002262:Carboxy-Lyases; C100963:acetone carboxylase