Bacteria producing poly

Besides heterotrophic bacteria and Archaea, the photo-trophic bacteria, including phototrophic purple bacteria and cyanobacteria, are also PHA producers. A study of 15 strains of nonsulfur purple bacteria and 15 strains of sulfur purple bacteria showed that all of them produced poly(3HB) when the growth medium was supplemented with acetate (Liebergesell et al. 1991). When supplemented with propionate, valerate, heptanoate, or octanoate, most of the strains produced poly (3HB), and the nonsulfur purple bacteria produced poly (3HB-CO-3HV) copolymers even with acetate as the carbon... 

Of the many types of bacteria that produce poly(3HB) [27], R. eutropha is the most intensively investigated. R. eutropha produces poly(3HB) when it is... 

Many bacteria have been screened to produce poly(3HB) or poly(3HB-co-3HV) (a copolymer consisting of 3-hydroxybutyrate and 3-hydroxyvalerate). How-... 

Poly(3HB) is synthesized in bacteria from acetyl-CoA by a three-step reaction (Fig. 1). The first enzyme of the pathway, 3-ketothiolase, catalyzes the condensation of two molecules of acetyl-CoA to form acetoacetyl-CoA. Aceto-acetyl-CoA reductase subsequently reduces acetoacetyl-CoA to R-3-hydroxy-butyryl-CoA, which is then polymerized by the PHA synthase to produce poly(3HB). Since acetyl-CoA is present in plant cells in the cytosol, plastid, mitochondrion, and peroxisome, the synthesis of poly(3HB) in plants could, in... 

Microbially produced poly(3-hydroxyalkanoates) are scientifically fascinating materials and are likely to be of increasing commercial importance. They present many challenges to the scientist, from trying to understand how, and even why, they are produced by bacteria to comprehending the subtleties involved in their melt extrusion, nuclea-tion, crystallization and orientation behaviour. Much more research is required before these biopolymers can become household names like polythene, but it is hoped that this chapter will stimulate further interest in this unique range of environmentally degradable and socially useful thermoplastics. 

The enzyme lysozyme cleaves P-(1 4) glycosidic bonds between N-acetylglucosamine and D-glucosamine. The more chitin is acety-lated, the faster the reaction. The ability to decompose chitin is based on the antimicrobial effects of lysozyme. Some bacteria produce chitinases known as chitodextrinases or poly[p-l,4-(2-acetamido-2-deoxy-D-glucosidases)] and chitosanase (chitosan-N-acetylglucosamine hydrolases), which cleave chitin chains to form N-acetylglucosamine. 

The homopolymer of 3-hydroxybutyric acid or poly(3HB) is the prototype biodegradable PHA that is naturally produced by many bacteria. Because poly(3HB) is a crystalline and relatively brittle substance, it is not a suitable substitute for the commonly used thermoplastics manufactured from petrochemicals. Copolymers of hydroxyalkanoic acids, on the other hand, are less brittle and more elastic. Therefore, a major area of research on PHA is to develop organisms that can produce PHA copolymers with better mechanical properties and biodegradabflity. 

Leaf TA, Peterson MS, Stoup SK, Somers D, Srienc F (1996) Saccharomyces cerevisiae expressing bacterial polyhydroxybutyrate synthase produces poly-3-hydroxybutyrate. Microbiol 142 1169-1180 Lee SY (1996a) Bacterial polyhydroxyalkanoates. Biotechnol Bioeng 49 1-14 Lee SY (1996b) Plastic bacteria Progress and prospects for polyhydroxyalkanoate production in bacteria. Trends Biotechnol 14 431 38 Lee SY (1997) E. coli moves into the plastic age. Nat Biotechnol 15 17-18 Lee SY, Chang HN (1995a) Production of poly(hydroxyalkanoic acid). Adv Biochem Eng Biotechnol 52 27-58... 

All these polyesters are produced by bacteria in some stressed conditions in which they are deprived of some essential component for thek normal metabohc processes. Under normal conditions of balanced growth the bacteria utilizes any substrate for energy and growth, whereas under stressed conditions bacteria utilize any suitable substrate to produce polyesters as reserve material. When the bacteria can no longer subsist on the organic substrate as a result of depletion, they consume the reserve for energy and food for survival or upon removal of the stress, the reserve is consumed and normal activities resumed. This cycle is utilized to produce the polymers which are harvested at maximum cell yield. This process has been treated in more detail in a paper (71) on the mechanism of biosynthesis of poly(hydroxyaIkanoate)s. 

P. putida and some microorganisms [42-44] are capable of synthesizing poly(nHAMCL)s from non-alkyl based organic substrates, especially from glucose. P. putida grown with glucose produced PHAs containing both saturated and unsaturated 3HA units, and the seven types of 3HA units found in the PHA are sequential intermediates in the fatty acid synthetic pathway of bacteria. Therefore, the 3HA units in these PHAs are most likely produced by de novo... 

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