Strains of Bacillus cereus vary in the phenotypic adaptation of their membrane lipid composition in response to low water activity, reduced temperature and growth in rice starch

Abstract

The phenotypic adaptation of membrane lipids in seven strains of the food-poisoning bacterium Bacillus cereus, isolated from Bangladeshi rice, is reported in relation to their ability to grow under conditions of low water activity (a w ), reduced temperature and the presence of soluble rice starch. The strains have different membrane phospholipid head-group and fatty acyl compositions, and they display individual differences in their responses to both low a w and reduced temperature. The extent of the increase in anionic membrane lipids in response to low a w varies from strain to strain, is solute specific and in one strain does not occur. Growth is stimulated by the presence of soluble rice starch and results in a large rise in the proportion of diphosphatidylglycerol (DPG) at the expense of phosphatidylglycerol (PG), without any change in the proportion of total anionic phospholipids. Growth at 15 6C compared with 37 6C increases the proportions of DPG and phosphatidylethanolamine at the expense of PG. At the lower temperature there are changes in phospholipid fatty acyl composition characteristic of those expected to maintain membrane fluidity, including increases in the amount of total branched fatty acids and the anteiso-/iso-branched ratio, and a decrease in the equivalent chain-length, but there are strain differences in how those changes were achieved. In contrast to some other bacilli, there are persistent large increases in the proportions of unsaturated fatty acyl chains in phospholipids during growth at 15 6C.

Osmolality, Temperature, and Membrane Lipid Composition Modulate the Activity of Betaine Transporter BetP in Corynebacterium glutamicum

“…Yersinia pseudotuberculosis was found to respond to decreasing growth temperatures by an increase in phosphatidyletha- nolamine and a decrease in CL (4). In contrast, in membranes of B. cereus, which predominantly consist of CL, the content of PG and phosphatidylethanolamine was further decreased when a culture was shifted to low temperature (24). It is therefore conceivable that chill activation of BetP is influenced by the membrane lipid composition.…”

“…Several types of stress response have been described; these include synthesis of cold shock proteins (18), synthesis of branched-chain and unsaturated fatty acids (24), and uptake and synthesis of compatible solutes (3,21,22,55). Detailed data are available at the biochemical level for L. monocytogenes, where the primary betaine transporter, Gbu, was found to be directly activated by exposure to low temperatures (22,49).…”

“…Besides alteration of the fatty acid composition, adaptation to temperature also results in changes in saturation and branching (4,37,54). Bacillus cereus strains respond to a decrease in growth temperature from 37 to 15°C with an increase in the ratio of anteiso-branched fatty acids to iso-branched fatty acids, as well as in the ratio of unsaturated fatty acids to saturated fatty acids (24). E. coli cells respond to chill stress by increasing the fraction of unsaturated fatty acids (15), whereas in L. monocytogenes the content of anteiso-C15:0 fatty acids is increased (37,60).…”

Identification of Bacillus cereus Genes Specifically Expressed during Growth at Low Temperatures

“…Modifications in the cell wall and/or membrane composition (e.g., changes in the ratio of saturated to unsaturated FAs) are also important for bacteria to adapt to the cold (29). Induced expression of the products of some of the identified genes (BC1235, BC2489, and BC4851) presumably targets precursors for FA metabolism.…”

“…Because of the psychrotrophy of many strains, B. cereus sensu lato is a good model for research on the molecular mechanisms of low-temperature adaptation in Bacillus species and still offers wide scope for investigation. Previous work is scant and piecemeal, dealing for instance with the analysis of cold shock proteins (23) or changes in membrane FA profiles at a suboptimal temperature (21 or 15°C) (29,33). In fact, the establishment of B. cereus in the food environment under refrigeration probably requires the coordinated activity of many genes whose identities and modes of action are still largely unknown.…”