Response of Shewanella putrefaciens to low temperature regulated by membrane fluidity and fatty acid metabolism

Shewanella putrefaciens is an important spoilage microorganism in chilled Pacific white shrimp. In order to study the cold adaptation behavior of S. putrefaciens, the growth pattern, fatty acid composition, protein content, cell membrane microstructure and membrane fluidity of the isolated strain QY38 cultured at different temperatures (30 degrees C, 10 degrees C, and 4 degrees C) were studied comparatively. The lag phases of S. putrefaciens QY38 cultured at 30 degrees C, 10 degrees C, and 4 degrees C were 2.95 h, 15.42 h and 62.79 h, respectively. The saturated fatty acid content in the bacterial cell decreased with the decrease in incubation temperature, while the content of palmitoleic acid (C16:1), lauric acid (C12:0), and myristic acid (C14:0) increased. Then the cold adaptation process was studied, and membrane fluidity decreased after moving from 30 degrees C to 4 degrees C and increased after a period of adaptation. The differential proteins expressed during cold adaptation process showed that the fatty acid metabolism regulon (FadR) and 3-hydroxyacyl-ACP dehydratases (FabA) were up-regulated during cold acclimation, while 3-oxoacyl-ACP synthase (FabB) and desaturase (Des) were down-regulated. It was hypothesized that in S. putrefaciens QY38, the unsaturated fatty acid was biosynthesized through anaerobic metabolic pathway to recover the membrane fluidity to some extent.