engleski

Enrichment and isolation of methanotrophic bacteria from different environments

The main objective of this work was the isolation of methanotrophic bacteria from different environments in order to screen potential activity of these ubiquitous bacteria in the transformation of some chlorinated aromatic compounds. The enrichment experiments started by methane injection in the original samples from different habitats (meadow soil, landfill leachate, eutrophic sealake sediment and marine coastal sediments). When subsequent turbidity was observed (optical density determined at 600 nm), the enrichments were subcultured in sealed 120-ml serum bottles containing nitrate mineral salts (NMS) medium or ammonium nitrate mineral salts (ANMS) medium. For marine samples, these media were supplemented with 2.5 per cent of sodium chloride. All enrichments and subcultures were incubated under a methane/air atmosphere either statically or by shaking at 30^oC. The enriched cultures consisted of six to eight different types of heterotrophs and one to two types of methanotrophs. The heterotrophic community members were isolated on Nutrient agar and Marine agar while methanotrophs were grown on ANMS and NMS agarose plates under a methane/air atmosphere. According to their morphological characteristic, the methanotrophic community members from the meadow soil and contaminated marine coastal sediment were identified as type I methanotrophs, and the isolate from eutrophic sealake belonged to type II methanotrophs. The methanotrophic community members from other investigated habitats could not be isolated as a pure culture because most of the heterotrophs grew well on ANMS and NMS agarose plates, forming colonies of tightly bound aggregates with methane utilizing bacteria. The obtained results suggested that methane utilizing bacteria were present in all investigated environments, forming stable associations with heterotrophic bacteria. Methanotrophic-heterotrophic communities are widespread in nature, and mutually dependent relationships that exist between methanotrophic and heterotrophic bacteria make these communities important in the cycling of elements in the biosphere.

methanotrophic bacteria; enrichment; isolation

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