Arsenate microbial

Product specifications for microbial food enzymes have been estabUshed by JECEA and ECC. They limit or prescribe the absence of certain ubiquitous contaminants such as arsenic, heavy metals, lead, coliforms, E. coli and Salmonella. Furthermore, they prescribe the absence of antibacterial activity and, for fungal enzymes only, mycotoxins. 

Bentley R, TG Chasteen (2002) Microbial methylation of metalloids arsenic, antimony and bismuth. Microbiol Mol Biol Rev 66 250-271. 

Microbial virulence is often the outcome of the complex interactions that take place as the pathogen establishes itself in the human host. The molecular determinants of pathogenicity include factors that cause damage to the host cell and those that help the microbe establish productive infection for survival [35]. The human host immune response counters the presence of these microbes with its acquired or innate immune response arsenal with outcomes that range from acute to chronic or latent infections. A clear definition of the host and microbial... 

Fig. 33.1. Results of a batch experiment (symbols) by Blum et al. (1998) in which Bacillus arsenicoselenatis grows on lactate, using arsenate [As(V)] as an electron acceptor. Solid lines show results of integrating a kinetic rate model describing microbial respiration and growth.

Capturing energy liberated by the reaction, the microbial population grew almost 40-fold over the course of the experiment, which lasted about 3 days. Reaction proceeded increasingly rapidly as the microbial population, and hence the system s catalytic ability increased. After about a day, however, the reaction started to slow, and then it stopped altogether, even though all the lactate and arsenate had not been consumed. 

The principal controls on the microbial reaction rate in our example, then, are biomass and thermodynamic drive (Fig. 33.2). Initially, in the presence of abundant lactate and arsenate, the rate is controlled by the size of the microbial population available to catalyze lactate oxidation. As the population increases, so does reaction rate. Later, as reactants are consumed and products accumulate, the reaction approaches the point at which the energy liberated by its progress is balanced by that needed in the cell to synthesize ATR Reaction rate is governed now by the energy available to drive forward the cellular metabolism, this energy represented by the thermodynamic potential factor Ft over the course of the experiment, the kinetic factors Fd and Fa play minor roles. 

Bardgett, R.D., T.W. Speir, DJ. Ross, G.W. Yeates, and H.A. Kettles. 1994. Impact of pasture contamination by copper, chromium, and arsenic timber preservative on soil microbial properties and nematodes. Biol. Fertil. Soils 18 71-79. 

Freeman, M.C., J. Aggett, and G. O Brien. 1986. Microbial transformations of arsenic in Lake Ohakuri, New Zealand. Water Res. 20 283-294. 

Wang, D.S., R.W. Weaver, and J.R. Melton. 1984. Microbial decomposition of plant tissue contaminated with arsenic and mercury. Environ. Pollut. 34A 275-282. 

Arsenic in upper finer sediment has been releasing due to the microbial degradation driven by the dissolution of the Fe-AI minerals ... 

On the other hand, there are a number of human diseases associated with an overactivity of neutrophil function. Many facets of the neutrophil antimicrobial arsenal, such as reactive oxygen metabolites and proteases, can attack host tissues as effectively as they can attack microbial targets. For this reason, activation of neutrophils under physiological conditions is carefully regulated and damage restricted for the following reasons ... 

Newman DK, Ahmann D, Morel EMM. 1998. A brief review of microbial arsenate reduction. Geomicrobiology 15 255-68. 

Anaerobic metabolism occnrs nnder conditions in which the diffusion rate is insufficient to meet the microbial demand, and alternative electron acceptors are needed. The type of anaerobic microbial reaction controls the redox potential (Eh), the denitrification process, reduction of Mu and SO , and the transformation of selenium and arsenate. Keeney (1983) emphasized that denitrification is the most significant anaerobic reaction occurring in the subsurface. Denitrification may be defined as the process in which N-oxides serve as terminal electron acceptors for respiratory electron transport (Firestone 1982), because nitrification and NOj" reduction to produce gaseous N-oxides. hi this case, a reduced electron-donating substrate enhances the formation of more N-oxides through numerous elechocarriers. Anaerobic conditions also lead to the transformation of organic toxic compounds (e.g., DDT) in many cases, these transformations are more rapid than under aerobic conditions. 

Langner, H.W Inskeep,W.P. (2000) Microbial reduction of arsenate in the presence of ferri-hydrite. Environ. Sci. Techn. 34 3131-3136... 

The classic studies by Challenger (127-129) on microbial methyla-tion of arsenic still provide the basis of our understanding of these processes. Although Challenger s work focused on mycological methyla-tions (he mistakenly believed that bacteria did not methylate arsenic), the scheme he proposed is applicable to other biological systems as well. It is briefly discussed here, together with the confirmatory studies of Cullen and co-workers. 

In metabolic studies with animals it is often difficult to distinguish between processes carried out by the animal and those performed by resident microorganisms, such as the gut microflora. In the following, the transformations refer to those taking place within the marine animal, whether microbially mediated or otherwise. Metabolic studies with marine animals are faced with further complications because water can be an important uptake route. A chemical, in this instance arsenic in its various forms, may undergo microbial conversions in the water, and the resultant metabolites may be accumulated by the marine animal. Thus, careful experimentation may be required to determine what is occurring inside rather than outside the animal. 

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