|
|
|
|
|
|
Identification and Inactivation of Genetic Loci Involved with Lactobacillus acidophilus Acid Tolerance. M. Andrea Azcarate-Peril, 2004.Amino acid decarboxylation-antiporter reactions are one of the most important systems for maintaining intracellular pH between physiological limits under acid stress . We analyzed the Lactobacillus acidophilus NCFM complete genome sequence and selected four open reading frames with similarities to genes involved with decarboxylation reactions involved in acid tolerance in several microorganisms . Putative genes encoding an ornithine decarboxylase, an amino acid permease, a glutamate  -aminobutyrate antiporter, and a transcriptional regulator were disrupted by insertional inactivation . The ability of L . acidophilus to survive low-pH conditions, such as those encountered in the stomach or fermented dairy foods, was investigated and compared to the abilities of early- and late-stationary-phase cells of the mutants by challenging them with a variety of acidic conditions . All of the integrants were more sensitive to low pH than the parental strain . Interestingly, each integrant also exhibited an adaptive acid response during logarithmic growth, indicating that multiple mechanisms are present and orchestrated in L . acidophilus in response to acid challenge .
Glyceraldehyde-3-Phosphate Dehydrogenase Has No Control over Glycolytic Flux in Lactococcus lactis MG1363. Christian Solem, 2003.Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) has previously been suggested to have almost absolute control over the glycolytic flux in Lactococcus lactis (B . Poolman, B . Bosman, J . Kiers, and W . N . Konings, J . Bacteriol . 169:5887-5890, 1987) . Those studies were based on inhibitor titrations with iodoacetate, which specifically inhibits GAPDH, and the data suggested that it should be possible to increase the glycolytic flux by overproducing GAPDH activity . To test this hypothesis, we constructed a series of mutants with GAPDH activities from 14 to 210% of that of the reference strain MG1363 . We found that the glycolytic flux was unchanged in the mutants overproducing GAPDH . Also, a decrease in the GAPDH activity had very little effect on the growth rate and the glycolytic flux until 25% activity was reached . Below this activity level, the glycolytic flux decreased proportionally with decreasing GAPDH activity . These data show that GAPDH activity has no control over the glycolytic flux (flux control coefficient = 0.0) at the wild-type enzyme level and that the enzyme is present in excess capacity by a factor of 3 to 4 . The early experiments by Poolman and coworkers were performed with cells resuspended in buffer, i.e., nongrowing cells, and we therefore analyzed the control by GAPDH under similar conditions . We found that the glycolytic flux in resting cells was even more insensitive to changes in the GAPDH activity; in this case GAPDH was also present in a large excess and had no control over the glycolytic flux .
|
© 2005
Transgalactic Ltd (manufacturer of Bioscreen C software) |
Privacy Statement | P.O. Box
1393, 00101 Helsinki, Finland,
Last modified: May 25, 2005
| ||||||
