|
|
|
|
|
|
Heterologous Expression of Lactose- and Galactose-Utilizing Pathways from Lactic Acid Bacteria in Corynebacterium glutamicum for Production of Lysine in Whey. Eoin Barrett, 2004.The genetic determinants for lactose utilization from Lactobacillus delbrueckii subsp . bulgaricus ATCC 11842 and galactose utilization from Lactococcus lactis subsp . cremoris MG 1363 were heterologously expressed in the lysine-overproducing strain Corynebacterium glutamicum ATCC 21253 . The C . glutamicum strains expressing the lactose permease and ß-galactosidase genes of L . delbrueckii subsp . bulgaricus exhibited ß-galactosidase activity in excess of 1,000 Miller units/ml of cells and were able to grow in medium in which lactose was the sole carbon source . Similarly, C . glutamicum strains containing the lactococcal aldose-1-epimerase, galactokinase, UDP-glucose-1-P-uridylyltransferase, and UDP-galactose-4-epimerase genes in association with the lactose permease and ß-galactosidase genes exhibited ß-galactosidase levels in excess of 730 Miller units/ml of cells and were able to grow in medium in which galactose was the sole carbon source . When grown in whey-based medium, the engineered C . glutamicum strain produced lysine at concentrations of up to 2 mg/ml, which represented a 10-fold increase over the results obtained with the lactose- and galactose-negative control, C . glutamicum 21253 . Despite their increased catabolic flexibility, however, the modified corynebacteria exhibited slower growth rates and plasmid instability . Elucidation of the Transmission Patterns of an Insect-Borne Bacterium. A. C. Darby, 2003.Quantitative data on modes of transmission are a crucial element in understanding the ecology of microorganisms associated with animals . We investigated the transmission patterns of a  -proteobacterium informally known as pea aphid Bemisia-like symbiont (PABS), also known as T-type, which is widely but not universally distributed in natural populations of the pea aphid, Acyrthosiphon pisum . The vertical transmission of PABS to asexual and sexual morphs and sexually produced eggs was demonstrated by a diagnostic PCR-based assay, and the maximum estimated failure rate was 2% . Aphids naturally lacking PABS acquired PABS bacteria administered via the diet, and the infection persisted by vertical transmission for at least three aphid generations . PABS was also detected in two of five aphid honeydew samples tested and in all five siphuncular fluid samples tested but in none of 15 samples of salivary secretions from PABS-positive aphids . However, PABS-negative aphids did not acquire PABS when they were cocultured with PABS-positive aphids; the maximal estimated level of horizontal transmission was 18% . A deterministic model indicated that the force of infection by a horizontal transmission rate of 3% is sufficient to maintain a previously described estimate of the prevalence of PABS-positive aphids (37%), if the vertical transmission rate is 98% . We concluded that PABS infections in A . pisum can be maintained by high vertical transmission rates and occasional horizontal transmission, possibly via the oral route, in the absence of selection either for or against aphids bearing this bacterium .
|
© 2005
Transgalactic Ltd (manufacturer of Bioscreen C software) |
Privacy Statement | P.O. Box
1393, 00101 Helsinki, Finland,
Last modified: May 25, 2005
| ||||||
