Bacteria cell-wall-degrading

Among the family of Enterobacteriaceae, two species of the genus Erwinia define the soft rot group E. chrysanthemi and E. carotovora. The main characteristic of the soft rot bacteria is their ability to produce large quantities of plant cell wall degrading enzymes. The maceration of plant tissue resulting from... 

The approach of Casiot et al. [21] was soon accepted and followed in the held of Se speciation. Wrobel et al. [91] applied a bacterium (Arthrobacter luteus) derived lysing enzyme mixture added with PMSF to study the intermediary molecules of Se metabolism of Se-enriched yeast without proteolysis. In order to tailor the cell wall degrading mechanism to the samples under test, Michalke et al. [77] used bacterial lisozyme and pronase E, either alone or in combination, for the Se speciation of Se-enriched lactic acid bacteria. Independent and simultaneous experiments were carried out with the two enzymes, thus achieving outstanding total Se-extraction efficiency (85-105 percent) with the sole application of pronase E and relatively low chromatographic recovery (8-12 percent) (still... 

Cell-Wall-Degrading Bacteria. The classification of bacterial decay types is based on the micromorphology of attack. Three main types of bacterial attack have been described so far through microscopy erosion, tunneling, and cavitation. They have been named after specific characteristics of the attack. Observations suggest that further forms of attack await description. Several other decay patterns of wood cells are suspected of being caused by bacteria, but no definite evidence is available. 

In nature, there are several sources of enzymes that are capable of catalysing the hydrolysis of PHB. The polymer itself is produced by bacteria and occurs in cells as discrete inclusion bodies. These bodies contain the necessary enzymes for degrading the polymer, preventing its build-up in the cell. As well as this, there are numerous bacteria and fungi, many of which are found in the soil, that are capable of secreting the necessary enzymes outside their cell walls, and thus of iiufiating degradation of PHB. 

The plant cell wall is a polymeric mesh consisting of cellulose, hemicellulose, pectin and protein. Cellulose and hemicellulose are integral components of the cell wall, but pectic substances are located mainly in the outer wall regions within the middle lamella (McNeil et ai, 1984). Pectic substances are more susceptible to enzymatic degradation, because they are more exposed than other cell wall components. Therefore, pectin-degrading enzymes may play a central role in the penetration of plant tissue by bacteria. 

Erwinia spp. are commonly present on vegetables at harvest. This bacterium has the characteristic of producing extracellular enzymes that degrade plant cell walls. Moreover, many Erwinia spp. such as E. carotovora are capable of using compounds as energy that are normally not utilized by most common bacteria (Jay 1992). Moreover, these species produce many enzymes (such as pectate lyase, polygacturonase,... 

Bacterial attack is an early stage in the degradation of wood exposed in wet or moist conditions. Bacteria can be the dominant form of attack when fungal decay is suppressed by a wood-preserving treatment. Bacteria can attack the cell wall of wood by tunnelling, cavitation or erosion mechanisms (Eaton and Hale, 1993). 

Another major component of the cell membranes are the lipopolysaccharides, which are present as phospholipid bilayers. Following the death of bacteria, the biopolymers that constitute their cell walls and membranes become part of the detrital organic carbon pool. The great abundance of these biopolymers in seawater and the sediments is a reflection of their resistance to chemical degradation and the important role that bacterioplankton play in marine biomass production. 

The toxicity of monomeric phenolic acids and aldehydes of graminaceous cell walls to microflora in the rumen has been examined by several workers (3,27-32). In general, frans-p-coumaric acid was found to be the most toxic of the phenolic acids and decreased the rate of digestion of the cell walls. An important effect of the acid is that it limits the attachment of wall-degrading bacteria (32). The toxicity of p-hydroxybenzaldehyde was similar to p-coumaric acid but only very small amounts of the aldehyde... 

Preservation of cell structure, food taste, and avoidance of thermal degradation are reasons for the removal of moisture from such materials by sublimation. The process is preceded by quick freezing which forms small crystals and thus minimum damage to cell walls, and is likely to destroy bacteria. Some of the materials that are being freeze dried commercially are listed in Table 19.9(b). 

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