Microbial enzymes capable

Microbial cells are very attractive as a source of catalysts for the production of organic chemicals because of their broad range of enzymes capable of a wide variety of chemical reactions, some of which are illustrated in Table 2.1. 

Desulfurization using purified enzymes Investigations into enzymatic desulfurization as an alternative to microbial desulfurization has revealed several enzymes capable of the initial oxidation of sulfur. A study reported use of laccase with azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) as a mediator for oxidation of DBT [181]. The rate of this reaction was compared to hydrogen peroxide-based phosphotungstic acid-catalyzed oxidation and the latter was found to be about two orders of magnitude higher. The authors also oxidized diesel oil sulfur to no detectable levels via extraction of the oxidized sulfur compounds from diesel. In Table 9, the enzymes used in oxidation of DBT to DBTO are reported. 

A class of enzymes capable of removing sulfur from alkane sulfonates exists, which may have relevance in microbial desulfurization of alkyl sulfides. A gene cluster ssuEADCB was identified in E. coli. The enzyme SsuD was capable of conversion of pentane sulfonic acid to pentaldehyde and sulfite. It was reported to be capable of conversion of alkyl sulfonates from C2 to CIO, as well as substituted ethanesulfonates and sulfonated buffers. The SsuE was a flavin-reducing enzyme that provided FMNH2 to the SsuD. 

A microbial biocatalyst in context of BDS is defined as a microorganism expressing enzymes capable of removing sulfur selectively from organosulfur compounds. The definition of a biocatalyst, in general, also includes use of one or more enzymes, by themselves or in a cellular extract (used either in suspended form or carrier-supported form) for removal of sulfur. Additionally, biocatalyst can be a microbial consortium as well. Aerobic as well as anaerobic pathways for sulfur removal have been reported. The anaerobic routes, however, have been plagued with lack of reproducibility preventing further development. 

Carboxylesterases and amidases catalyze hydrolysis of carboxy esters and carboxy amides to the corresponding carboxylic acids and alcohols or amines. In general those enzymes capable of catalyzing hydrolysis of carboxy esters are also amidases, and vice versa (110). The role of these enzymes in metabolsim of drugs and insecticides has been reviewed (111, 112). In addition to the interest in mammalian metabolism of drugs and environmental chemicals, microbial esterases have been used for enantioselective hydrolyses (113, 114). 

Biodegradation depends on the microbial production of enzymes capable of catalyzing chemical reactions that will transform (or, ideally, mineralize) pollutants. Bioremediation technologies can be enhanced in several ways, but the existing biochemical capabilities of the organisms should be reviewed before any anticipated genetic alterations are considered. 

In designing a microbial conversion process many important aspects require careful consideration, for example, the selection of a compound to be synthesized, a survey of available substrates, and the routes or reactions needed. Another point (the most important one) is to find microbial enzymes which are suitable for the processes designed, and to subsequently evaluate the enzyme s potential. Moreover, the discovery of a new enzyme or a new reaction provides a clue for designing a new microbial transformation process. To find microbial enzymes that are suitable as potent catalysts, the capabilities of well-known enzymes or reactions need to be reassessed, and novel microbial strains or enzymes need to be discovered. Screening may be one of the most efficient and successful ways of searching for new or suitable microbial enzymes. 

The soil is a complex structure with close interrelationship among factors that influence biodegradation of pesticides, such as the structure of the pesticide, presence of an effective, active microbial community capable of degradation, and bioavailability of the compound in space and time (sorption, moisture content, temperature, nutrients, and soil pH) to enzymes or to whole cells (Aislabie and Lloydjones, 1995). 

Other microbial strains capable of carrying out Baeyer-Villiger oxidations on steroids are Fusarium lint IFO 7156443, Fusarium solani413, Hwnicola sp.447, Paecilomyces sp.44S and Peni-cillium lilacinum NRRL 895416. The substrate specificity can be broadened by the use of a purified enzyme from Cylindrocarpon radicicola in this case several other steroids are oxidized422 423. 

Skopintsev (1982) has pointed out the enormous potential of marine humic substances as an organic nutrient resource (15 x 10 kcal). We are unaware of any published work demonstrating that dissolved humic substances can serve as a heterotrophic food source. Microbial enzymes should be capable of using the free carboxyl end of the marine humic substances as a simple fatty acid. However, this is conjecture and should be investigated by microbiologists and planktologists. 

Although some microbial enzymes can degrade lactic acid-based polymers and stereocopolymers in vitro [18], biodegradation in vivo was soon excluded because humans do not possess enzymes capable of degrading high molar mass lactic acid polymers [19]. 

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