Improved enrichment culture technique for methane-oxidizing bacteria from marine ecosystems: the effect of adhesion...

Cultivation of microbial representatives of specific functional guilds from environmental samples depends largely on the suitability of the applied growth conditions. Especially the cultivation of marine methanotrophs has received little attention, resulting in only a limited number of ex situ cultures available. In this study we investigated the effect of adhesion material and headspace composition on the methane oxidation activity in methanotrophic enrichments obtained from marine sediment. Addition of sterilized natural sediment or alternatively the addition of acid-washed silicon dioxide significantly increased methane oxidation. This positive effect was attributed to bacterial adhesion on the particles via extracellular compounds, with a minimum amount of particles required for effect. As a result, the particles were immobilized, thus creating a stratified environment in which a limited diffusive gas gradients could build up and various microniches were formed. Such diffusive gas gradient might necessitate high headspace concentrations of CH₄ and CO₂ for sufficient concentrations to reach the methane-oxidizing bacteria in the enrichment culture technique. Therefore, high concentrations of methane and carbon dioxide, in addition to the addition of adhesion material, were tested and indeed further stimulated methane oxidation. Use of adhesion material in combination with high concentrations of methane and carbon dioxide might thus facilitate the cultivation and subsequent enrichment of environmentally important members of this functional guild. The exact mechanism of the observed positive effects on methane oxidation and the differential effect on methanotrophic diversity still needs to be explored.