Acid tolerance

Smittle RB and Flowers RS. 1982. Acid tolerant microorganisms involved in the spoilage of salad dressings. J Food Prot 45 977-983. 

The rate of acid-induced demetalation depends only slightly on the nature of the head substituents X (Table I). In contrast, the tail-R groups dramatically affect k and, for the most part, k3, suggesting that tail amide O-atoms are sites of peripheral protonation. Thus, the acid tolerant Fem-TAML catalysts with tail electron-withdrawing groups should be more acid resistant and replacement of R = Me with R = F results in a remarkable stabilization. The rate constants (Table I) show that under weakly acidic conditions (pH 2-3), when the k pathway dominates over k3, fluorinated lk is 105-fold more H +-tolerant than la. 

Fur is itself part of the family of gene regulatory proteins throughout many bacterial species. The major subclass is mainly involved, like Fur in E. coli, in the control of iron homeostasis, but it can also function in acid tolerance and protection against oxidative stress. Fur also controls the iron-regulated expression of bacterial virulence determinants. One class of the Fur family, Zur, is involved in the regulation of zinc uptake (see below). 

Decomposition rates of some organic substrates are reduced. Substantial changes in the species composition of primary producers occur. The richness of phytoplankton species is reduced, while biomass and productivity of phytoplankton are not reduced by acidification. The biomass of herbivorous and predaceous zooplankton is probably reduced because of reductions in numbers of organisms and/or reduction in their average size. Many benthic invertebrates such as species of snails, clams, crayfish, amphipods, and various aquatic insects are intolerant of low pH and are seldom found in acidic lakes. However, certain large aquatic insects such as water boatmen and gyrinids are very acid tolerant and may become the top predators in some acidified lakes. Acidification of aquatic systems has major effects on fish population. 

The solubilized aluminium is the main toxic agent to plants in acidic soils, and acid tolerant (calcifuge) plants are usually also aluminium tolerant. The ECEC method determines the levels of AP+, H+, Ca + and Mg + extracted by 1 M potassium chloride and is described in Method 5.2. 

Slattery, J. F. and Coventry, D. R. 1995. Acid-tolerance and symbiotic effectiveness of Rhizobium leguminosarum bv. trifolii isolated from subterranean clover growing in permanent pastures. Soil Biology and Biocheistry, 27 111-115. 

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... 

Possible explanations for the increase in silica in LRL at pH 4.7 include hydrologic differences, presence of a somewhat acid-tolerant diatom community, and the influence of another silica-utilizing community. Overall,... 

Miller, L.G. and Kasper, C.W. (1994) Escherichia coli 0157 H7 acid tolerance and survival in apple cider. Journal of Food Protection 57(7), 645. 

The catalytic synthesis of dienyl esters by dimerization of alkynes and addition of carboxylic acids tolerates a large variety of functional groups and carboxylic... 

Bearson, B., Wilson, L., Foster, J. A low pH-inducible, PhoPQ-dependent acid tolerance response protects Salmonella typhimurium against inorganic acid stress. J Bacteriol 180 (1998) 2409-2417. 

Perhaps the acid-tolerant, thermophilic Bacillus coagulans is the only known biocatalyst that naturally produces lactic acid from xylose via the pentose phosphate pathway, not the phosphoketolase pathway (Patel et al., 2006). Three strains, 17C5, P4-102B, and 36D1, can ferment both hexoses and pentoses to pure L(+)-lactic acid at 50 °C and pFI 5.0, an optimal environment... 

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. 

The natural penicillins, primarily G and V, have a relatively narrow spectrum. They act mostly on gram-positive organisms. The fact that proper selection of precursors could lead to new variations in the penicillin side chain offered the first source of synthetic penicillins. Penicillin V, derived from a phenoxy-acetic acid precursor, attracted clinical use because of its greater acid tolerance, which made it more useful in oral administration. Also, the widespread use of penicillin eventually led to a clinical problem of penicillin-resistant staphylococci and streptococci. Resistance for the most part involved the penicillin-destroying enzyme, penicillinase, which attacked the beta-lactam structure of the 6-aminopenicillanic acid nucleus (6-APA). Semisynthetic penicillins such as ampicillin and carbenicillin have a broader spectrum. Some, such as methicillin, orafi-cillin, and oxacillin, are resistant to penicillinase. In 1984, Beecham introduced Augmentin, which was the first combination formulation of a penicillin (amoxicillin) and a penicillinase inhibitor (clavulanic acid). Worldwide production of semisynthetic penicillins is currently around 10,000 tons/year, the major producers are Smith Kline Beecham, DSM, Pfizer, and Toyo Jozo. 

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]. 

De-novo fermentation of ASA in an acid-tolerant yeast, combined with in-pro-cess product removal, has the potential of eliminating salt production altogether. Unfortunately, there is no microbe that naturally produces ASA and the reported yields are minute until now [176]. 

Rnstler, S. and Stolz, A. 2007. Isolation and characterization of a nitrile hydrolysing acid tolerant black yeast—Exophiala oligosperma R1. Applied Microbiology and Biotechnology, 75 899-908. 

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

Historically, hydrogen derived from dissociation of hydrogen iodide has been utilized widely for reduction. Acceleration of the hydrogenolysis rate is achieved by addition of phosphorus to remove the iodine formed.In general reduction with HI is efficient for acid-tolerant substrates and is a useful alternative to catalytic methods, especially to achieve chemoselectivity (equations 95 and 96).Application of HI to cleavage of allylic centers has not been useful as allylic and other unsaturated centers are more susceptible to HI addition and elimination effects. 

Cyclopropanes are less reactive than alkenes retroaddition also occurs less readily, and cyclopropane adducts have a high acid tolerance. The nucleophiles that react include OH, OR, OCOR, O H, O R and RCN. 

Modified phosphorus halides, which allow more controlled reaction conditions, have been developed more recently. Thus 2,2,2-tribromo- and 2,2,2-trichloro-1,3,2-benzodioxaphospholes (la) and (lb), "" as well as dichloro- and dibromo-phosphoranes (2a) and (2b)" have been used successfully in the preparation of a number of aromatic and aliphatic acid halides. These reactions can be carried out at room temperature or slightly above and convert carboxylic acids or anhydrides in good yield to the acid halides. Also, unsaturated acids tolerate these reaction conditions. In many cases products can be isolated by distilling the acid halide directly from the reaction mixture. An advantage of these reagents is their... 

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