First isolation of a type II methanotroph from a soda lake

摘要

Soda lakes are alkaline environments, often with high mineralization. In microbial communities of alkaline and saline reservoirs, members of the genera Methylomicrobium and Methylobacter, type I methanotrophs using the most efficient ribulose monophosphate (RMF) pathway for assimilation of e 1 compounds, are the major aerobic methanotrophs [1]. This is probably the result of selective pressure of high alkalinity and salinity, which require additional expenditure of energy to maintain ionic homeostasis. Moreover, in the course of enrichment and isolation of pure cultures, enhanced content of mineral salts favored the most adapted forms. Since no type II methanotrophs have been isolated by approaches that considered in situ conditions and the physiological differences between two main methanotrophic groups, their existence in soda lakes seemed doubtful. However, recent molecular biological studies of soda lakes of Mongolia, Southeastern Transbaikalia, and the United States suggested the presence of type II methanotrophs (with the serine pathway of carbon assimilation) [2–4]. The goal of the present work was therefore isolation and primary characterization of a morphotype II methanotroph from a Southeastern Transbaikalia soda lake.