|
|
|
|
|
|
Influence of Growth Temperature on Lipid and Phosphate Contents of Surface Polysaccharides from the Antarctic Bacterium Pseudoalteromonas haloplanktis TAC 125. M. Michela Corsaro, 2004.The chemical structural variations induced by different growth temperatures in the lipooligosaccharide and exopolysaccharide components extracted from the Antarctic bacterium Pseudoalteromonas haloplanktis TAC 125 are described . The increase in phosphorylation with the increase in growth temperature seems to be general, because it happens not only for the lipooligosaccharide but also for the exopolysaccharide . Structural variations in the lipid components of lipid A also occur . In addition, free lipid A is found at both 25 and 4°C but not at 15°C, which is the optimal growth temperature, suggesting a incomplete biosynthesis of the lipooligosaccharide component under the first two temperature conditions . Effects of Physical Properties of Feed on Microbial Ecology and Survival of Salmonella enterica Serovar Typhimurium in the Pig Gastrointestinal Tract. Lene Lind Mikkelsen, 2004.A two-by-two factorial experiment with pigs was conducted to study the effect of feed grinding (fine and coarse) and feed processing (pelleted and nonpelleted) on physicochemical properties, microbial populations, and survival of Salmonella enterica serovar Typhimurium DT12 in the gastrointestinal tracts of pigs . Results demonstrated a strong effect of diet on parameters measured in the stomachs of the pigs, whereas the effect was less in the other parts of the gastrointestinal tract . Pigs fed the coarse nonpelleted (C-NP) diet showed more solid gastric content with higher dry matter content than pigs fed the fine nonpelleted (F-NP), coarse pelleted (C-P), or fine pelleted (F-P) diet . Pigs fed the C-NP diet also showed significantly increased number of anaerobic bacteria (P < 0.05), increased concentrations of organic acids, and reduced pH in the stomach . In addition, pigs fed the C-NP diet showed increased in vitro death rate of S . enterica serovar Typhimurium DT12 in content from the stomach (P < 0.001) . Pigs fed the C-NP diet had a significantly higher concentration of undissociated lactic acid in gastric content than pigs fed the other diets (P < 0.001) . A strong correlation between the concentration of undissociated lactic acid and the death rate of S . enterica serovar Typhimurium DT12 was found . In the distal small intestine, cecum, and midcolon, significantly lower numbers of coliform bacteria were observed in pigs fed the coarse diets than in pigs fed the fine diets (P < 0.01) . Pigs fed the C-NP diet showed the lowest number of coliform bacteria in these segments of the gastrointestinal tract . Pigs fed the coarse diets showed increased concentration of butyric acid in the cecum (P < 0.05) and colon (P < 0.10) compared with pigs fed the fine diets . It was concluded that feeding a coarsely ground meal feed to pigs changes the physicochemical and microbial properties of content in the stomach, which decreases the survival of Salmonella during passage through the stomach . In this way the stomach acts as a barrier preventing harmful bacteria from entering and proliferating in the lower part of the gastrointestinal tract . Differential Expression of Two Catechol 1,2-Dioxygenases in Burkholderia sp . Strain TH2. Katsuhisa Suzuki, 2002.Burkholderia sp . strain TH2, a 2-chlorobenzoate (2CB)-degrading bacterium, metabolizes benzoate (BA) and 2CB via catechol . Two different gene clusters for the catechol ortho-cleavage pathway (cat1 and cat2) were cloned from TH2 and analyzed . Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot analysis showed that while both catechol dioxygenases (CatA1 and CatA2) were produced in BA-grown cells, CatA1 was undetectable when strain TH2 was grown on 2CB or cis,cis-muconate (CCM), an intermediate of catechol degradation . However, production of CatA1 during growth on 2CB or CCM was observed when cat2 genes were disrupted . The difference in the production of CatA1 and CatA2 was apparently due to a difference in inducer recognition by the regulators of the gene clusters . The inducer of CatA1 was found to be BA, not 2CB, by using a 2-halobenzoate dioxygenase gene (cbd) disruptant, which is incapable of transforming (chloro)benzoate . It was also found that CCM or its metabolite acts as an inducer for CatA2 . When cat2 genes were disrupted, the growth rate in 2CB culture was reduced while that in BA culture was not . These results suggest that although cat2 genes are not indispensable for growth of TH2 on 2CB, they are advantageous . Cryo-Transmission Electron Microscopy of Frozen-Hydrated Sections of Escherichia coli and Pseudomonas aeruginosa. Valério R. F. Matias, 2003.High-pressure freezing of Escherichia coli K-12 and Pseudomonas aeruginosa PAO1 in the presence of cryoprotectants provided consistent vitrification of cells so that frozen-hydrated sections could be cut, providing  2-nm resolution of structure . The size and shape of the bacteria, as well as their surface and cytoplasmic constituents, were nicely preserved and compared well with other published high-resolution techniques . Cells possessed a rich cytoplasm containing a diffuse dispersion of ribosomes and genetic material . Close examination of cells revealed that the periplasmic space was compressed during cryosectioning, a finding which provided supporting evidence that this space is filled by a compressible gel . Since the outer membrane and peptidoglycan layer are bonded together via lipoproteins, the space between them (although still part of the periplasmic space) was not as compacted . Even when this cryosectioning compression was taken into account, there was still substantial variability in the width of the periplasmic space . It is possible that the protoplast has some capacity to float freely within the periplasm .
|
© 2005
Transgalactic Ltd (manufacturer of Bioscreen C software) |
Privacy Statement | P.O. Box
1393, 00101 Helsinki, Finland,
Last modified: May 25, 2005
| ||||||
