Role of Branched-Chain Fatty Acids in pH Stress Tolerance in Listeria monocytogenes

Abstract

In alkaline conditions, Listeria monocytogenes cells develop higher proportions of branched-chain fatty acids (FAs), including more anteiso forms. In acid conditions, the opposite occurs. Reduced growth of pH-sensitive mutants at adverse pH (5.0/9.0) was alleviated by the addition of 2-methylbutyrate (an anteiso-FA precursor), suggesting that anteiso-FAs are important in adaptation to adverse pH. The balance between anteiso-and iso-FAs may be more important than changes in the amounts and/or degrees of saturation of FAs in pH adaptation.Listeria monocytogenes can grow under a wide range of pH stress, i.e., 4.1 to 9.0 (38, 46), increasing its abilities to persist during food processing and attempts to decontaminate food-processing environments (15,(42)(43)(44)(45). It also has particularly impressive capacities to modulate its membrane lipids to maintain membrane fluidity and transport functions (10,40,41) in response to temperature (1), salt (7), and CO 2 /anaerobiotic (21) stress. Such capacities have been suggested to be related to its atypically high iso and anteiso, odd-numbered, branched-chain fatty acid (BCFA) content (1,20) and its ability to modulate the overall content and proportions of BCFAs, straight-chain FAs (SCFAs), and unsaturated FAs (22,23). For example, reductions in environmental temperatures lead to increases in the amount of ai15:0 present in L. monocytogenes cell membranes, while increases in environmental temperatures lead to reductions in the amounts of ai15:0 and other BCFAs present in membranes (1,14,32).Changes in FA profile have been associated with pH adaptation in Streptococcus mutans (16-18), Escherichia coli (5, 48), and Salmonella (24), Pseudomonas (31), and Bacillus species (23). However, little is known about pH stress-associated modulation of FAs in L. monocytogenes (21), the wider role of FA modulation in its responses to nonthermal stresses, or the cross-protection mechanisms which operate in this hardy pathogen (19,27,35,44).The aims of this study were to investigate the modulation of the FA profile of L. monocytogenes membranes in response to changes in environmental pH, investigate the effects of an exogenous BCFA precursor on the pH stress response of BCFA-deficient mutants (1, 49), and examine possible links between the prevalence of anteiso-BCFAs and the adaptation mechanism(s) of L. monocytogenes under adverse pH conditions. Modified brain heart infusion broth (MBHIB; Difco Laboratories, Sparks, MD), suitable for adverse-pH studies, was prepared to pH 5.0, 5.5, and 6.0 in 2 M disodium phosphate Washed cells from mid-exponential-phase cultures of L. monocytogenes 10403S, an isogenic sigB null mutant (3), and isogenic non-BCFA-producing cld-1 and cld-2 mutants (1, 49) were inoculated into preheated (30°C) 100-ml volumes of the buffered MBHIB and grown (30°C/200 rpm) to an optical density at 600 nm of 0.5 to 0.6. Growth rates of cultures (doubling times per hour of cultures in exponential growth) were calculated (2). Mid-exponential-phase cells were recovered by centrif...

Branched-Chain Fatty Acids Promote Listeria monocytogenes Intracellular Infection and Virulence

“…Anteiso-BCFA have been associated with resistance against environmental stresses in L. monocytogenes (1,11,27). Early in RAW 264.7 macrophage infections, we observed that deficiencies in anteiso-BCFA resulted in a marked loss of intracellular CFU ( Fig.…”

“…In this study, we aim to elucidate the contribution of anteiso-BCFA during L. monocytogenes intracellular infection by utilizing the previously characterized cld-2 transposon insertion mutant (1,11,15,26,27) and two independently transduced BKD-deficient mutants in which the cld-2 transposon insertion was transduced into a clean wild-type (WT) background. We show that anteiso-BCFA facilitate intracellular infection of L. monocytogenes by enhancing survival, growth, and phagosomal escape.…”

The Branched-Chain Amino Acid Aminotransferase Encoded by ilvE Is Involved in Acid Tolerance in Streptococcus mutans

“…Previously, we reported that during growth under acidic conditions, S. mutans alters its membrane fatty acid composition by increasing the proportion of unsaturated fatty acids (19,20). Changes in the proportion and type of membrane fatty acid are a common bacterial response to environmental stress (25,27,49). The changes in membrane composition in S. mutans are essential for survival of acid stress, since the inability to incorporate unsaturated fatty acids leads to extreme acid sensitivity and decreased virulence in the rat model of caries (22).…”

Transcriptome Analysis of Alkali Shock and Alkali Adaptation inListeria monocytogenes10403S

“…Also, in alkaline conditions, L. monocytogenes cells develop higher proportions of branched-chain fatty acids, including more anteiso forms that are important in adaptation to adverse pH (Giotis et al, 2007b).…”