Low pH-induced membrane fatty acid alterations in oral bacteria

Abstract

Four oral bacterial strains, of which two are considered aciduric and two are considered acid-sensitive, were grown under glucose-limiting conditions in chemostats to determine whether their membrane fatty acid profiles were altered in response to environmental acidification. Streptococcus gordonii DL1, as well as the aciduric strains S. salivarius 57.I, and Lactobacillus casei 4646 increased the levels of mono-unsaturated membrane fatty acids. The non-aciduric strain S. sanguis 10904 did not alter its membrane composition in response to pH values examined here. Thus, in response to low pH, aciduric oral bacteria alter their membrane composition to contain increased levels of long-chained, mono-unsaturated fatty acids. This suggests that membrane fatty acid adaptation is a common mechanism utilized by bacteria to withstand environmental stress.

Physiological and Transcriptional Response ofLactobacillus caseiATCC 334 to Acid Stress

“…To decrease fluidity, cells may increase the concentration of saturated FAs or cyclopropane FAs (10,15,16), and both events were prominent in the CMFA profiles of acid-adapted versus control cells analyzed in this study ( Table 2). The saturated-to-unsaturated FA ratio increased from 0.4 in nonadapted control cells to 4.2 or 5.3, respectively, after 10 or 20 min of acid adaptation at pH 4.5 because acid-adapted cells had a higher total percentage of saturated FAs and cyclopropane than did control cells (Table 2).…”

“…Fozo et al (15) have previously reported that the CMFA composition of L. casei was altered if cells were incubated at pH 5.0 rather than pH 7.0. Specifically, those authors noted that incubation at the lower pH resulted in increased proportions of C 18:1 and cyclopropane C 19:0 , with concomitant decreases in C 16:0 and cyclopropane C 17:0 (15).…”

“…Although acidurance is considered an innate feature of L. casei, the molecular basis of this capability is only partly defined. L. casei has, for example, been shown to display an ATR, but few reports have addressed its effect on cell physiology (15,21,31,50). Because ATR induction produces physiological changes that enhance acid resistance, more-detailed investigation of this response will reveal the molecular mechanisms used by L. casei to persist in highly acidic environments and may provide new strategies to enhance the industrial utility of this species.…”

“…Work to dissect the L. casei ATR has detected 9 to 11 acid-regulated proteins (21) and shown that cytoplasmic membrane fatty acid (CMFA) content is altered to increase the proportion of C 18:1 and cyclopropane fatty acid (FA) C 19:0 in response to acidification (15). However, information on the mechanisms used by L. casei to modulate ATR and CMFA content, as well as the identities and functions of acid-regulated proteins, is still lacking.…”

Metabolism and physiology of Lactobacilli: a review

“…Lactobacilli present great diversity in the cell surface structure and are known to modify their structural properties in response to changes in the environment (Taranto et al, 2003;Fozo et al, 2004). Different macromolecules constitute the cell wall of these bacteria and contribute to maintaining the integrity of the bacterial cell during environmental stress (Guerzoni et al, 2001).…”