Analysis of Cultured Methanogenic Archaea from the Tarkhankut Peninsula Coastal Methane Seeps

Abstract

The major substrates for methanogenesis were used for investigation of cultured methanogenic archaea from coastal methane seeps near the Tarkhankut Peninsula, Black Sea. Analysis of the 16S rRNA gene sequences revealed that growth of the classical methanogenic Euryarchaeota occurred in all enrichments but was absent in the controls without the substrates. Enrichments from the seep differed in microbial composition from those from the background point. The most numerous archaea belonged to the genera Methanolobus (medium with methanol and hydrogen), Methanosarcina (trimethylamine and hydrogen), Methanococcoides (trimethylamine), and Methanococcus (hydrogen and CO₂). Syntrophic growth of hydrogenotrophic archaea of the genus Methanogenium with clostridia and members of the family Thermotogaceae probably occurred in enrichments with acetate. Relatively low similarity of the recovered 16S rRNA gene sequences with the closest cultured relatives (94% and lower) indicated that the Methanogenium phylotype belonged to a new species. The same was true for the Methanosarcina phylotype revealed in the culture with trimethylamine and hydrogen (97% and less similarity of the 16S rRNA gene sequences to those of the closest cultured relatives).