Acid and Base Stress and Transcriptomic Responses in Bacillus subtilis

Abstract

Acid and base environmental stress responses were investigated in Bacillus subtilis. B. subtilis AG174 cultures in buffered potassium-modified Luria broth were switched from pH 8.5 to pH 6.0 and recovered growth rapidly, whereas cultures switched from pH 6.0 to pH 8.5 showed a long lag time. Log-phase cultures at pH 6.0 survived 60 to 100% at pH 4.5, whereas cells grown at pH 7.0 survived <15%. Cells grown at pH 9.0 survived 40 to 100% at pH 10, whereas cells grown at pH 7.0 survived <5%. Thus, growth in a moderate acid or base induced adaptation to a more extreme acid or base, respectively. Expression indices from Affymetrix chip hybridization were obtained for 4,095 protein-encoding open reading frames of B. subtilis grown at external pH 6, pH 7, and pH 9. Growth at pH 6 upregulated acetoin production (alsDS), dehydrogenases (adhA, ald, fdhD, and gabD), and decarboxylases (psd and speA). Acid upregulated malate metabolism (maeN), metal export (czcDO and cadA), oxidative stress (catalase katA; OYE family namA), and the SigX extracytoplasmic stress regulon. Growth at pH 9 upregulated arginine catabolism (roc), which generates organic acids, glutamate synthase (gltAB), polyamine acetylation and transport (blt), the K ؉ /H ؉ antiporter (yhaTU), and cytochrome oxidoreductases (cyd, ctaACE, and qcrC). The SigH, SigL, and SigW regulons were upregulated at high pH. Overall, greater genetic adaptation was seen at pH 9 than at pH 6, which may explain the lag time required for growth shift to high pH. Low external pH favored dehydrogenases and decarboxylases that may consume acids and generate basic amines, whereas high external pH favored catabolism-generating acids.Bacillus subtilis can grow over several log units of environmental pH while maintaining cytoplasmic pH within a relatively narrow range that preserves protein and nucleic acid stability (19, 50, 55a). Environmental pH is important for the pathogenesis of related Bacillus species, such as the food-borne pathogen Bacillus cereus, which encounters acidic environments in the gastrointestinal tract and in food products where organic acids are used as preservatives (9, 64). B. cereus shows an acid tolerance response in which vegetative growth in a moderate acid induces proteins that enable survival under extreme acid conditions (64). In Bacillus anthracis, the lethal factor toxin undergoes a low-pH-driven structural change as it passes through acidic vesicles, which allows it to translocate into the cytosol (45). The Bacillus thuringiensis toxin is activated by alkaline pH upon entering the midgut of insect larvae (13), and bacterial growth is inhibited by acids (46).Cytoplasmic pH homeostasis has been studied extensively in B. subtilis, which maintains cytoplasmic pH within approximately pH 7.3 to pH 7.6 during vegetative growth over a range of environmental pH, from pH 6.0 to pH 9.0 (14, 50, 55a). At high external pH, cytoplasmic pH homeostasis involves Na ϩ /H ϩ antiporters as well as other Na ϩ transport components (14,26,50,67,68). Low pH triggers spore germi...

Batch Submerged Fermentation in Shake Flask Culture and Bioreactor: Influence of Different Agricultural Residuals as the Substrate on the Optimization of Xylanase Production by Bacillus subtilis and Aspergillus brasiliensis

“…Similar trend was also observed in the study of Kapoor M, et al [39]. Consequently, pH became more alkaline over fermentation time due to the generation of basic amides [40]. Notable, the study by Ouoba LI, et al [41] also corresponded to the issue of the increase of medium pH during fermentation process.…”

“…When the pH of the medium changes, it changes the condition of the medium that may not favor the growth of cells and production of xylanase. When it becomes more alkaline, it causes base stress to the cells and thus, terminates the growth of the cells and eventually forms the endo-spores [40]. As a result, it affects the xylanase production.…”

“…Medium pH decreased over time due to the production of acid such as citric acid by the fungi during batch fermentation process [53]. Although A. brasiliensis favors the condition of slight acidic, as fermentation prolonged, the pH reached beyond the tolerated pH and thus, causing acid stress to the growth and reduced the biomass production and hence the xylanase activity [40]. As for bioreactor, the medium pH was maintained and thus, the production of xylanase by A. brasiliensis was anticipated to be higher compared to shake flask culture.…”

Glutamate Dehydrogenase Affects Resistance to Cell Wall Antibiotics in Bacillus subtilis

“…Next, we examined the effect of alkaline growth pH (conditions known to induce rocG expression and the W regulon [42,44]) on the susceptibility of B. subtilis to CEF. The wild-type strain showed a remarkable reduction in susceptibility to CEF under alkaline growth conditions (Fig.…”

Disruption of the alsSD operon of Enterococcus faecalis impairs growth on pyruvate at low pH

“…An acidic induction of C4 genes has also been described for Klebsiella terrigena (Mayer et al, 1995), Staphylococcus aureus (Weinrick et al, 2004) and B. subtilis (Wilks et al, 2009). These data prompted us to analyse whether the Pals promoter of Ent.…”