Bacteria: acid tolerant

Several experiments have shown the bactericidal effect of fluoride ions at high concentrations [180,181]. This effect generally occurs at concentrations well above those generally observed in saliva however, the use of fluoridated toothpaste or dental topical applications of fluoride may temporarily elevate the fluoride concentration in the oral cavity to bactericidal levels. It has been demonstrated that fluoride affects the metabolism of oral bacteria and reduces its acid tolerance. It is most effective at acidic pH values and, for example, fluoride levels as low as 0.1 mM can cause the complete arrest of glycolysis by Steptococcus mutans. It has been suggested that modifying the biological fluids related to the presence... 

Patel, M. A., Ou, M., Harbrucker, R., Aldrich, H., Buszko, M., Ingram, L., and Shanmugam, K. 2006. Isolation and characterixation of acid-tolerant, thermophilic bacteria for effective fermentation of biomass-derived sugars to lactic acid. Appl. Environ. Microbiol., 72, 3228-3235. 

Acid-tolerant lactic acid bacteria would solve this latter problem and have indeed been obtained from screening [44] and via whole genome shuffling [45]. Alternatively, a lactate dehydrogenase gene could be inserted in a yeast, such as S. cerevisiae. These grow well at low pH and efficiently channel carbon into the glycolysis pathway under anaerobic conditions [46, 47]. Such constructs were indeed found to produce up to 55 g L-1 of lactic acid at pH 3.6 [46]. 

Gluconobacter these are also rod bacteria. They exhibit high acid tolerance and are almost identical in size to bacteria of the Acetobacter group. 

MLF most commonly occurs after alcoholic fermentation but may occur simultaneously with the primary fermentation. Because relying on natural microflora can be unpredictable and difficult to control, starter cultures of pure strains of bacteria have been developed (Henick-Kling, 1993 Krieger et al., 1993 Kunkee et al., 1964 Nielsen et al., 1996 Pilone, 1995). Although selected strains of Lactobacillus can be inoculated, O. oeni is the primary species to conduct MLF because of acid tolerance and the flavor profile produced (Guzzo et al., 1994 Krieger et al., 1993 Kunkee et al., 1964 Liu, 2002 Nielsen et al., 1996 Wibowo et al., 1985). 

Type of bacteria Sensitive to organic acid activity Resistant to organic acids Acid tolerance... 

Saccharomyces cerevisiae Lactic acid production A muscle bovine lactate dehydrogenase gene (LDH-A) was expressed in S. cerevisiae, a nd lactic acid was produced in titers of 20 g/liter with productivities of 11 g/liter/h due to the acid tolerance of S. cerevisiae this organism may serve as an alternative for substitution of bacteria for lactic acid prxrduction 108... 

T. ferrooxidans is another acid-tolerant bacteria that is capable of oxidizing both thiosulfate and ferrous iron ... 

---