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* see Materials and Methods

* see Materials and Methods

3.2. Screening for ASS biodegraders from nature

The enrichment culture technique was applied for the selection of ASS degrading organisms from diverse natural sources. Enrichment media used for cultivation of microbial cultures were designed to contain a limited number of specific substrates that preferentially promoted the growth of ASS degraders. Repeated inoculations of microbial populations into ASS containing enrichment media permitted exponential growth of the organisms with the ability to adapt to the surfactants and to use them as a carbon and an energy source. Adaptation of microorganisms was facilitated by gradual increase of surfactant concentration in enrichment media from 0.1 to 1 g/1. Morphologically, obtained mixed cultures contained nearly entirely Gram-negative bacterial populations. ASS degradation activity of mixed cultures sustained over prolonged period of storage in spent cultivation media at 4°C. From enriched mixed cultures, only a few bacterial strains with stable capabilities of ASS degradation and assimilation were isolated (Table 3).

Table 3

Isolation of ASS degraders by enrichment of natural microorganisms.

Source of microorganisms

Specific substrate of enrichment

Mixed culture

Isolate

Identification of isolate

soil polluted by detergent and mineral oil

di-n-hexyl

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