Bacteria transformation

Fig. 7 SEM images of nanopillars of titanium oxide produced by controlled anodic process and model of virus and bacteria transformation by photocatalytic processes using nanopillars of titanium oxide.242...

Once the recombinant vectors have been produced, they are used to transform host cells. In the example of the plasmid pBR322, the host cells are bacteria. Once transformed, the bacteria are plated on selective media so that bacteria transformed with a recombinant plasmid can be easily identified. In the case of plasmid pBR322 shown in Figure 1-6-3, bacteria with recombinant plasmids would be resistant to ampicillin but sensitive to tetracycline. 

The stepwise nature of nitrification during the aerobic decomposition of detrital PON is illustrated in Figure 24.6. Initially, the degradation of PON produces ammonium, which stimulates the growth of the nitrate oxidizers. These bacteria transform the ammonium into nitrite, causing ammonium concentrations to decline and nitrite concentrations to rise. The elevated nitrite levels stimulate the growth of the nitrite oxidizers. These bacteria transform the nitrite into nitrate. Eventually all of the DIN is oxidized to nitrate. The residual pool of PON includes microbial biomass and any PON too inert to be degraded by aerobic marine bacteria. 

Bacteria can grow incredibly fast. Under some conditions, it takes a bacterial cell only 10-20 min to double its size and to divide to form two cells.4 An animal cell may take 24 h for the same process. Equally impressive are the rates at which bacteria transform their foods into other materials. One factor contributing to the high rate of bacterial metabolism may be the large surface to volume ratio. For a small spherical bacterium (coccus) of diameter 0.5 xm, the ratio of the surface area to the volume is 12 x 106 m , while for an ameba of diameter 150 xm the ratio is only 4 x 104 m 1 (the ameba can increase this by sticking out some pseudopods). Thimann33 estimated that for a 90-kg human, the ratio is only 30 m 1. 

Biotransformation mean bacteria transformation rate constant for all three sites of (1.1 0.8) x lO 11 L-organisnrhlr1 (Paris Wolfe 1987 quoted, Steen 1991). 

The bowel, one of the largest and most metabolically active organs, contains bacteria that may change the chemical composition of the human body. In renal failure the altered bacterial flora cause the accumulation of aliphatic amines in the gut (09, S25). Bacteria transform part of the choline in the gut to trimethylamine, which is reabsorbed and then either oxidized or demethylated to dimethylamine in the liver (S24). Dimethylamine enters the circulation and is excreted in the bile and urine. The trimethylamine and dimethylamine in the exhaled air of uremic patients may contribute to the classic fishy breath, which can be improved by hemodialysis or by gut sterilization with nonabsorbable antibiotics (S23, S25). The overall role of these compounds as uremic toxins, however, remains to be defined. 

Traditionally methods of viable counting and microscopy have been used to study phagocytosis of bacteria and subsequent survival or destruction." However, such indirect methods give an underestimate of bacterial survival within cells. It has been shown that bioluminescence acts as a convenient real-time method for monitoring survival of Bordetella bronchiseptica in vitro, whilst a dual gfp-luxABCDE operon has been used to monitor real-time replication of Staphylococcus aureus. The use of clinically important bacteria transformed with the lux cassette overcomes the problems with viable but non-culturable bacteria, as the expression of lux genes depends on the functional biochemistry of the bacteria. ""... 

Methylating bacteria transform a small portion of mercury in alluvium into alkyl mercurials which, because of lipotropy, have a long halftime and increased toxicity in animals. The diverse mercury compounds differ in toxicity according to the species involved and route of entry. Selenium seems to be a biogeochemically important element which counteracts toxicity of naturally occurring mercury. 

Hartmans et al. and Hartmans and de Bont show that vinyl chloride can be used as a primary substrate under aerobic conditions, with vinyl chloride being directly mineralized to carbon dioxide and water. Direct vinyl chloride oxidation has also been reported by Davis and Carpenter, McCarty and Semprini, and Bradley and Chapelle. Aerobic oxidation is rapid relative to reductive dechlorination of dichloroethene and vinyl chloride. Although direct DCE oxidation has not been verified, a recent study has suggested that DCE isomers may be used as primary substrates. Of the chlorinated ethanes, only 1,2-dichloroethane has been shown to be aerobically oxidized. Stucki et al. and Janssen et al. show that 1,2-DCA can be used as a primary substrate under aerobic conditions. In this case, the bacteria transform 1,2-DCA to chloroethanol, which is then mineralized to carbon dioxide. McCarty and Semprini describe investigations in which 1,2-dichloroethane (DCA) was shown to serve as primary substrates under aerobic conditions. 

Plant-derived lignans have no direct estrogen activity, but gut bacteria transform some of them to compounds with hormone-mimicking effects. Flax seeds arrd whole grain cereals contain significant amounts of such lignans. 

Bacteria transform cobalt into cobalamin - the form of cobalt needed by animals and humans, known as vitamin B12. 

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