Bacterial decay types

Bacteria and soft rot fungi are more tolerant of the low oxygen conditions in saturated wood, and in wood that is buried in sediments bacterial decay tends to predominate. Early reports identified unicellular bacteria in foundation piling and shipwreck timbers, but more recently three bacterial decay types in wood cell walls are now recognised - erosion, tunnelling and cavitation bacterial decay. 

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. 

Attack by wood-degrading bacteria has now been reported from all parts of the world. It is diflScult when reporting on the occurrence to keep the bacterial decay types separate, because it is not always clear if the reported type falls into any of the three categories of attack. Thus, the attack type should only be reported when there is little doubt. 

Anaerobic digestion, like pyrolysis, occurs in the absence of air. But, the decomposition is caused by bacterial action rather than high temperatures. This process takes place in most biological materials, but it is accelerated by warm, wet and airless conditions. It occurs naturally in decaying vegetation in ponds, producing the type of marsh gas that can catch fire. 

The observations have shown that consideration must be given to several different processes of carbonate deposition and/or silica or iron oxide deposition in contact which such bacterial mats. Obviously some important lithification processes take place within the decay zone below the active photosynthetic zone. In most of the cases where lithification was observed there, it was carbonate lithification of a type not related to the photosynthetic depletion of C02. Different filamentous and coccoid cyanobacteria can become more or less lithified depending on slime production, mobilization, outer morphology and microenvironments. 

Fig. 4. Absorbance-change kinetics of photooxidation due to the primary eiectron donor and its decay (re-reduction) [upper paneis] and the oxidation of a c-type cytochrome [iower panels] in C. vinosum (left) and Rp. viridis [right panels]. The C. vinosum sample was poised at a redox potential so that Cyt c555 ("Cyt c422 ) is reduced before flash excitation the ambient redox potential in Rp. viridis was -250 mV, so that only Cyt c5S8 is present in the reduced state before excitation. Figure source left panels (C. vinosum) from Parson (1968) The role of P870 in bacterial photosynthesis. Biochim Biophys Acta 153 254 right panels (Rp. viridis) from Shopes, Levine, Molten and Wraight (1987) Kinetics of oxidation of the bound cytochromes in reaction centers from Rhodopseudomonas viridis. Photosynthesis Res 12 167.

Bacterial Growth. One problem encountered in many Stretford plants treating gas streams other than coke-oven gas is contamination of the system by bacterial growth (Sundstrdm, 1979 Bromel, 1986). The problem can also be present but is quite rare in coke-oven gas or geothermal applications. The absence of bacterial contamination in these two types of Stretford plants is due to the presence of thiocyanate in the former, and boron compounds in the latter (boron in geothermal steam originates from radioactive decay within the earth s mantle). 

A similar type of linkage between coenzyme and protein in which position 8a of the flavin is at the oxidation level of carbonyl was found in thiamine dehydrogenase (from soil bacterial 138) and in P-cyclo-piazonate oxidocyclase from Penicillium cyclopium 88, 155). In these cases, however, it is probable that N(l) of a histidine residue constitutes the bridge to the protein backbone. The oxidation level of position 8a was deduced from decay data similar to those mentioned above for the 8a-thiohemiacetals. Of particular interest is the fluorescence profile of the flavin peptide obtained by trypsin-chymotrypsin hydrolysis of p-cyclopiazonate oxidocyclase. Fluorescence quenching similar to that observed with SD-flavin (9) is observed, but in this case the pK attributed to protonation of the histidine imidazole is shifted from 4.7 to 5.4, and the maximal fluorescence obtained is only 20% of that of FMN 164). Upon performic acid oxidation of the peptide the emission intensity is... 

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