Yuk Hyun-Gyun, Marshall Douglas L
Department of Food Science and Technology, Mississippi Agricultural and Forestry Experiment Station, Mississippi State University, Mississippi State, Mississippi 39762-9805, USA.
Appl Environ Microbiol. 2003 Sep;69(9):5115-9. doi: 10.1128/AEM.69.9.5115-5119.2003.
The influence of heat adaptation (growth at 42 and 45 degrees C) on changes in membrane lipid composition and verotoxin concentration of Escherichia coli O157:H7 (ATCC 43895), an rpoS mutant of ATCC 43895 (FRIK 816-3), a verotoxin mutant E. coli O157:H7 (B6-914), and nonpathogenic E. coli (ATCC 25922) was investigated. D values (57 degrees C) of heat-adapted cells were up to 3.9 min longer than those of control cells for all four strains. Heat adaptation increased the amounts of palmitic acid (16:0) and cis-vaccenic acid (18:1omega7c) in membrane lipids of ATCC 43895 and the rpoS mutant, whereas there was a reduction and no change in the amount of cis-vaccenic acid in nonpathogenic and verotoxin mutant E. coli, respectively. The ratio of palmitic to cis-vaccenic acids decreased in ATCC 43895 and in the rpoS mutant, whereas the ratio increased in nonpathogenic E. coli and was not different in the verotoxin mutant with elevated growth temperature. Total verotoxin concentration decreased due to a reduction in intracellular verotoxin amount in heat-adapted ATCC 43895 and rpoS mutant strains. However, extracellular verotoxin concentration increased in heat-adapted cells. The rpoS gene did not influence membrane lipid composition changes although it did affect heat resistance. Results suggest that increased membrane fluidity may have caused increased verotoxin secretion.
研究了热适应（在42和45摄氏度下生长）对大肠杆菌O157:H7（ATCC 43895）、ATCC 43895的rpoS突变体（FRIK 816-3）、产志贺毒素突变体大肠杆菌O157:H7（B6-914）和非致病性大肠杆菌（ATCC 25922）的膜脂组成变化和志贺毒素浓度的影响。对于所有这四株菌，热适应细胞的D值（57摄氏度）比对照细胞长3.9分钟。热适应增加了ATCC 43895和rpoS突变体膜脂中棕榈酸（16:0）和顺式- vaccenic酸（18:1omega7c）的含量，而非致病性和产志贺毒素突变体大肠杆菌中顺式- vaccenic酸的含量分别减少和没有变化。ATCC 43895和rpoS突变体中棕榈酸与顺式- vaccenic酸的比例降低，而非致病性大肠杆菌中该比例升高，产志贺毒素突变体在生长温度升高时该比例没有差异。热适应的ATCC 43895和rpoS突变体菌株中，总志贺毒素浓度因细胞内志贺毒素量减少而降低。然而，热适应细胞中细胞外志贺毒素浓度增加。rpoS基因虽然影响耐热性，但不影响膜脂组成变化。结果表明，膜流动性增加可能导致志贺毒素分泌增加。
