Microbial activity compounds

In situations where conserved internal markers caimot be used, such as in spills of essentially pure compounds, the evidence for enhanced biodegradation may have to be more indirect. Oxygen consumption, increases in microbial activity or population, and carbon dioxide evolution have all been used with success. 

MIcrobiocldes. There are several microbiocides available commercially that can perform an effective function in controlling microbial activity. Some of these chemicals are inorganic, such as chlorine, sodium hypochlorite, calcium hypochlorite, hydrogen peroxide, chromates and compounds of mercury and silver. However, the organic chemicals find the highest use as microbiocides. Some examples of these organic compounds are peracetic acid, paraformaldehyde, polychlorophenols and quaternary ammonium derivatives, to name a few [208]. 

With the extraction procedure we employed (22), ferulic acid was isolated as the most inhibitory component in wheat straw. There could also be other unknown compounds in the straw which would not be evident with this procedure. In addition, we ignored the possible influence of toxin-producing microorganisms. Microorganisms may have influenced the phytotoxicity exhibited by the aqueous wheat extract in Table IX. Although the present study was not concerned with the phytotoxic effects of microbially decomposed wheat straw, an influence of microbial activity on ferulic acid phytotoxicity was observed. From the results shown in Table XI, it appears that the presence of the prickly sida seed carpel enhanced the inhibitory effects of ferulic acid. In addition to ferulic acid in test solutions containing prickly sida seeds with carpels, a second compound, 4-hydroxy-3-methoxy styrene, was also found to be present. This compound is formed by the decarboxylation of ferulic acid and was produced by a bacterium present on the carpel of prickly sida seed. The decarboxylation of ferulic acid was detected in aqueous solutions of ferulic acid inoculated with the bacterium isolated from the carpels of prickly sida seed. No conversion occurred when the bacterium was not present. 

Soil microorganisms produce many compounds that are potentially toxic to higher plants. Examples include members of the following antibiotics (1-6), fatty and phenolic acids (7-12), amino compounds (13-15), and trichothecenes (16, 17). "Soil sickness" and "replant problems" have been reported where certain crops or their residues interfere with establishment of a subsequent crop (18, 19). Toxins resulting from microbial activity sometimes are involved, but it is often unclear whether these are synthesized de novo in microbial metabolism or are breakdown products of the litter itself (20). 

Microbial activity, which is often stimulated during bioremediation projects, can alter the external pH. For instance, the anaerobic degradation of chlorinated compounds produces organic acids and HC1 and the pH may drop to acidic values if the soil has a low buffering capacity. In this case, control of the external pH will be required in order to maintain biodegradation activity at... 

During decomposition of plant remains, many phenolic compounds are released by leaching, microbial degradation or are synthesized by microbial activity. In forestry, problems of natural regeneration and reforestation are connected to the presence of phenolic substances deposited in the soil. Methods for extrachon and identification of toxic substances from different soil types (mineral or organic) are described. The method for extracting of soil phytotoxins is based on the use of ethylacetate and methanol (free phenolics) and alkaline hydrolysis (bound phenolics). 

During the wastewater treatment, an oxidative conversion of the surfactant molecules leads predominantly to the formation of polar compounds. They display a particularly high solubility and mobility in the aqueous medium and, therefore, transportation over relatively long distances can occur if they are not further degraded, resulting in the wide dissemination of these pollutants in riverine systems and thus also to estuaries, coastal regions and ultimately the marine environment (see Chapters 6.2 and 6.3). In the latter, the final levels will mainly be influenced by dilution effects and physical removal by precipitation or adsorption [63] because of relatively low microbial activity in this ecosystem compared with fresh water environments [64]. 

To elucidate the fate of these compounds at sediment-water interfaces, sediment/water mixtures (Lake Macatawa, Holland, MI) were spiked with DCB and incubated at 20 °C for 12 months under anaerobic conditions [72]. Dehalogenation of DCB to benzidine appeared to take place through a transient intermediate, 3-monochlorobenzidine (Fig. 27), which was observed in time-course analyses of the sediment/water mixtures. No metabolites were observed in autoclaved samples, suggesting that dehalogenation of DCB in anaerobic sediment/water systems was mediated by microbial activity. The product of dehalogenation (benzidine, Fig. 27) is more toxic to humans than the parent compound, DCB. From sediment/water distribution experiments, DCB showed greater affinity for the sediment phase than its non-chlorinated derivative,... 

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