Impact of thermal variations on biochemical and physiological traits in Pectinatus sp

The influence of temperature on cellular fatty acid composition and on heat stress tolerance was studied in the two species of Pectinatus, an anaerobic gram-negative bacterium. Cellular fatty acid (FA) patterns were determined for Pectinatus species cultivated in MRS medium at various defined conditions of temperature and pH. Our study shows that fluctuations of growth temperature and pH induced important changes in the ratio of unsaturated FAs (UFAs) to saturated FAs (SFAs). The major differences in the FA composition as a function of growth temperature concerned C 15:0 and C 17:0 for the SFAs and C 15:1 and C 17:1 for the UFAs. The most significant adaptation of lipid composition to lower growth temperatures was the strong increase of UFAs, particularly for C 15:1 and C 17:1 concomitantly with a decrease of SFAs (C 15:0 and C 17:0). When the pH of the culture medium was lowered from 6.2 to 4.0, a notable drop in the synthesis of the UFAs C 15:1 and C 17:1 was observed together with an important increase of C 18-cyclopropane (C 18-cyc) and high carbon number SFAs. Thermal modifications also provoked changes in Pectinatus behaviour. We observed that P. cerevisiiphilus was more heat sensitive than P. frisingensis. Mild exponential phase cells were treated for 1 h, at 40°C for P. cerevisiiphilus or at 41°C for P. frisingensis. This thermal adaptation induced tolerance against heat challenge (49 and 50°C for P. cerevisiiphilus and P. frisingensis, respectively). Survival of P. cerevisiiphilus and P. frisingensis adapted cells was, respectively, 3400- and 790-fold higher than control. Interestingly, adapted cells of P. cerevisiiphilus were more thermotolerant than P. frisingensis pretreated cells.