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The soil microbial biomass is studied as the agent of transformation of both fresh organic inputs to soil and of native soil organic matter itself.

Microbial biomass C and organic C were measured in 5 soils selected from 5 long term field cultivation at Bastam area of Shahrood region in Iran. Nitrogen, Glucose and plant residues were used as treatments in a factorial randomized block design with four replications The results were used to discuss the effects of Nitrogen, Glucose and organic C in these soils and the relationships between biomass C and total organic C. This suggests that changes in soil biomass C provide an early indication of changes in total soil organic C following changes in soil management.

The dynamics of decomposition and transformation of different substrates (nitrogen, glucose and straw) and the effects of substrate incorporation on the turnover of soil biomass C and the decomposition of soil organic C was studied in 5 soils with different characteristics (e.g. clay content, biomass and organic C contents). From this the mechanisms of priming effects (i.e. accelerated decomposition of soil organic matter following incorporation of substrates) were established. It was also concluded that the measurement of biomass C by fumigation–incubation requires the use of a "control" (unfumigated soil) to estimate the basal respiration (the mineralization of non-biomass organic C) of the fumigated soil during 20, 40 and 60 days of incubations. Soil containing more organic C and receiving larger fresh organic C inputs also have faster rates of soil organic C mineralization, suggesting that the turnover of organic C in such soils is probably faster than in soils containing less organic C and receiving less fresh organic inputs.

The aromatic compounds metabolism in particular phenol and its derivates is a subject of intensive studies in prokaryotes. Nowadays the investigations of different yeast species that metabolize aromatic compounds are of significant scientific interest. Trichosporon yeast strains, isolated from various sources, polluted with toxic compounds are among the most studied yeast with respect to aromatic compound biodegradation in eukaryotes. Usually the environmental pollution is a result of different compounds simultaneously.

The object of present study is a strain Trichosporon cutaneum R 57 able to grow and degrades phenol as a sole carbon and energy source up to 1 g/l in a short period of time (16-18h). The strain is also able to degrade phenol in a very short period of time in rich medium despite the presence of additional carbon source (such as peptone or amino acid).

The aim of the present investigation is to carry out the influence of additional carbon sources such as glucose and acetate on the phenol degradation in Trichosporon cutaneum R57 strain. The activity of two key enzymes for catabolism of phenol as phenol hydroxylase [EC 1.14.13.7] and catechol -1,2- dioxygenase [EC 1.13.11.1] were determined in cells grown in a medium Yeast Nitrogen Base without Amino Acids used for analyses of carbon assimilation in yeast strains comprising different mixtures of the mentioned above carbon sources.

The effect of glucose and acetate on the phenol degradation ability of Trichosporon cutaneum R57 strain was examined in the condition of batch cultivation. It was established that in YNB w/o AA medium the glucose and phenol assimilation flowed simultaneously so that the assimilation rate of glucose was much higher than that of phenol. Some delay in phenol degradation was observed in the experiments for studying the acetate influence in the medium. In these experiments however the phenol was completely degraded by the time of acetate assimilation.

The results obtained after enzymes analyses in the cells cultivated in the medium with two carbon sources such as phenol and acetate that are known to be utilized by Trichosporon cutaneum R57 are of special interests. In our experiments in a culture medium with 0,5 g/l phenol included the presence of acetate (1.8 g/l) did not influence negatively the phenol hydroxylase activity (0,833 U/mg protein), compared to the activity in the same medium without other than phenol carbon source (1,14 U/mg protein), but obviously lowered twice the activity of catechol-1,2-dioxygenase (0,108 U/mg protein and 0,206 U/mg protein respectively).

On the contrary, the influence of glucose presence in the media had much stronger influence on the activity of both investigated enzymes. In a culture medium containing 0.5 g/l phenol and 1.5 g/l glucose the activity of the phenol hydroxylase dropped to 0.225 U/mg protein and catechol-1,2-dioxygenase activity was 0.65 U/mg protein. It should be pointed that some basal activity of both enzymes (3-5 mU/mg protein) was established even in cells cultivated in a medium with glucose as a sole carbon source.

Our results showed that in these experiments the presence of acetate, respectively glucose do not repress and /or inactivate phenol degradation enzymes such as phenol hydroxylase and catechol 1,2 dioxygenase in the investigated Trichosporon cutaneum R 57 strain.

On the basis of our previous and recent analyses, the investigated strain could be considered to have a good potential for application in remediation of phenol contaminated environment and improvement of phenol removing treatment of industrial wastewaters.