Hydration reaction, microbial

We found a new microbial enzyme named "nitrile hydratase" which catalyzes the hydration reaction of nitrile to amides. it has been proven that acrylonitrile and methacrylonitrile are easily converted to the corresponding amides. When Rhodococcus rhodochrous J1 resting cells were used as the catalyst, more than 600 g of acrylamide was produced in 1 liter of reaction mixture with a yield of nearly 100 % for acrylonitrile. Since 1991, immobilized R. rhodochrous cells have been used for the industrial production of acrylamide (Fig. 1). At present, more than 10,000 tonnes of acrylamide is produced per year by Nitto Chemical Industries Ltd. 

The process of deterioration happens over a period of time rather than being the result of a single event. Seasonal and diurnal cycles have been reported to be involved (Arnold and Zehnder, 1991). Initiation of hydration may take only minutes rather than hours or days, depending on the specific environmental conditions and material components at site. There are different approaches to prevent these deterioration processes (i) stabilisation by climate control, (ii) stabilisation by chemical reactions, (iii) extraction of ions and (iv) microbial activity. 

This chapter focuses on the catalytic transformations that result in the cyclic biosynthesis and breakdown of fatty acids. These metabolic pathways will serve as a paradigm for three classes of chemical reactions carbon-carbon bond formation and cleavage, oxidation and reduction, and hydration—dehydration. The most extensively studied reactions are those involved in microbial fatty acid biosynthesis (Type II fatty acid synthase (FAS-II)) and mammalian fatty acid /3-oxidation. In both pathways, the reactions are catalyzed by separate enzymes that have been cloned and overexpressed, thus providing a ready source of material for structural and mechanistic studies. In contrast, mammalian fatty acid biosynthesis and microbial fatty acid breakdown are catalyzed by multifunctional enzymes (MFEs) that have historically been less amenable to analysis. 

Fig. 14.22 Schematic illustration of gas hydrate deposits and biogeochemical reactions in near-surface sediments on southern Hydrate Ridge. High gradients in pore water sulfate and methane are typical of methane hydrate-rich environment close to sulfate-rich seawater. At the sulfate-methane interface (also named sulphate-methane transition in earlier chapters of the book) a microbial consortium of methanothrophic archaea and sulfate-reducing bacteria (Boetius et al. 2000) perform anaerobic oxidation of methane (AOM) leading to carbonate precipitation. AOM rates influence hydrogen sulfide fluxes and gradients, which are reflected on the seafloor by the distribution of vent communities around active gas seeps and gas hydrate exposures (Sahling et al. 2002).

Salt Stress. The previously described microbial reactions result in the production and accumulation of salts (except in aquatic environments). Due to their hydrophilic nature, salts are usually hydrated, increasing the water content of porous materials (comparable to biofilms, as described before). This may increase the susceptibility to a physical attack by freezing/ thawing, because of the volume change in water/ ice crystals. 

Attack caused by the salt which itself may have been produced as the result of reactions between anions (which are final products of microbial metabohsm) and cationic components of ceramic materials. The results of these reactions could range ftom swelling of the porous material (due to the hydration of these... 

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