Organics-dependent Microbial Growths

Actinomycetes are filamentous bacteria that are often observed on stone surfaces and a large range of types has been isolated from stone. Like fungi, the filaments cause mechanical damage to stone by penetration and development of an extended web of hyphae in the stone (mycelium). These bacteria can produce patches of growth on stone particles and around stone pores, often interacting with salt crystals, which can further enhance the deteriogenic effects of salts. 

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Vitamins and Minerals. Milk is a rich source of vitamins and other organic substances that stimulate microbial growth. Niacin, biotin, and pantothenic acid are required for growth by lactic streptococci (Reiter and Oram 1962). Thus the presence of an ample quantity of B-complex vitamins makes milk an excellent growth medium for these and other lactic acid bacteria. Milk is also a good source of orotic acid, a metabolic precursor of the pyrimidines required for nucleic acid synthesis. Fermentation can either increase or decrease the vitamin content of milk products (Deeth and Tamime 1981 Reddy et al. 1976). The folic acid and vitamin Bi2 content of cultured milk depends on the species and strain of culture used and the incubation conditions (Rao et al. 1984). When mixed cultures are used, excretion of B-complex vita-... 

Two possible explanations can be readily put forward as to why this form of equation should be suitable for describing the dependence of microbial growth rate on feed concentration. The first of these is that the equation has the same form as the theoretically based Michaelis-Menten equation used to describe enzyme kinetics. The chemical reactions occurring inside a microbial cell are generally mediated by enzymes, and it would be reasonable to suppose that one of these reactions is for some reason slower than the others. As a result the growth kinetics of the micro-organism would be expected to reflect the kinetics of this enzyme reaction, probably modified in some way, but in essence having the form of the Michaelis-Menten equation. 

To inhibit microbial growth in blood samples taken for the determination of ethanol, sodium fluoride is added. As a volatile organic analyte is measured, the sample containers should prevent evaporation. Clinical chemistry samples have a variety of preservatives depending on the specific analysis, e.g., heparin or citrate to prevent clotting of a whole blood sample. In this instance the tube already has the preservative in place before the sample is added all that is required is that the container is gently mixed to disperse the preservative throughout the sample. 

Organic solvents such as chloroform and toluene have been used for many years to prevent microbial growth in aqueous solutions. Many solvents, e.g. toluene [73], phenethyl alcohol [28], ethanol [74], and butanol [75] elicit a rapid release of cytoplasmic constituents from microbial cells. Disorganization of the membrane is probably due to penetration of the solvents into the hydrocarbon interior of the membrane. The amount of damage caused to the membrane seems to depend upon the concentrations of solvent in the lipid phase equal degrees of lysis of protoplasts of M. lysodeikticus are produced by equal thermodynamic activities of aliphatic alcohols [76]. 

The intensity of microbial growth on plastic material depends on the type of synthetic polymer, but also on the type of additives, especially plasticizers used to improve the processing characteristics of the polymer. There are plasticizers such as fatty acid esters and long-chain dicarboxylic acid esters which are most susceptible to fungal growth while phthalate and phosphate esters with alkylol substituents are generally resistant. However, as plastic materials in operation are always subject to contamination with traces of nutrients for micro-organisms. 

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