engleski

Growth relationships and interactions within methanotrophic-heterotrophic community

The main objective of this work was to better characterize the methanotrophic-heterotrophic community originating from an aquifer material and characterized to be efficient in cometabolic transformation of trichloroethylene, chlorinated biphenyls and alkylbenzenesulphonates. The specific objective was to study possible relationships and interactions between community populations during growth under the conditions favorable to methanotrophs. When cultured under different methane and oxygen tensions, the community showed to be a "tight" association, consisting of one obligate type II methanotroph (strain Met 1) and four to five heterotrophs of different nutritional and physiological characteristics. Growth stimulation and inhibition effects between community populations were studied by cross-growing the strain Met 1 in the presence of individual heterotrophs and their lysates. All experiments were performed in sealed shake flasks in nitrate mineral salts (NMS) medium with the addition of methane as the only carbon and energy source. Culture growth was monitored by measuring optical density at 600 nm (A_600). When grown under microaerobic conditions and excess methane (O_2, 3-5 percent; CH_4, 10-15 percent), only one heterotroph (unidentified strain Het 4) stimulated the growth of the strain Met 1 while other heterotrophs suppressed its growth. Under aerobic conditions (O_2, 15-18 percent; CH_4, 15-18 percent) all heterotrophs stimulated the growth of the strain Met 1. In contrast, none of the filter-sterilized autolysates of heterotrophic strains showed growth stimulation of the strain Met 1 neither under microaerobic nor aerobic conditions. These results suggested that the growth of the strain Met 1 was not dependent on the specific substances (nutrients, growth factors) excreted by heterotrophs; however, it was affected by their metabolic activity. Significantly stimulated growth of four from the five heterotrophs (except Het 3) both in the presence of the strain Met 1 or its lysate, suggested the most possible role of the strain Met 1 in providing the heterotrophs with carbon source or specific nutrients necessary for their growth in mineral medium with methane as the only carbon source. General conclusion that can be made from the obtained results is that a number of interactions exist within the methanotrophic-heterotrophic community including those based on the provision of specific nutrients, the removal of inhibitory compounds and modifications of the community populations growth parameters. Most of these relationships seem to be reciprocal and beneficial for both the methanotroph and heterotrophs, making the community adaptable to various environmental conditions.

methanotrophic-heterotrophic community; growth interactions

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