C1 bacteria in the water column of Chesapeake Bay USA. II. The dominant O2- and H2S-tolerant methylotrophic methanogens, coenriched with their oxidative and sulphate reducing bacterial consorts, are all new immunotypes and probably include new taxa

Abstract

Methylotrophic methanogens were readily enriched with monomethylamine (MMA) in water samples obtained from throughout the stratified but oxygenated water column of Chesapeake Bay, USA. Of the 3 different populations of methylotrophic methanogens enriched, 02-and H2S-tolerant methanogens enriched in bacterially reduced seawater in glass were twice as prevalent as those enrichments either reduced chemically in glass or reduced bacterially in semipermeable polycarbonate flasks. Thirty-three obligately anaerobic, but 02and H2S-tolerant, methanogenic cultures from the dominant group were fingerprinted immunologically using antibody probes. The antigenic fingerprints divided these cultures into 4 clusters. One cluster was related to Methanosarcina barkeri RlM3, a second was related to M. mazei S6, and a third was related to other species of Methanosarcina. None of these were identical to known species and can be considered new immunotypes. These new immunotypes, related to described species, were found throughout the water column. A fourth cluster was unrelated to any extant genus of methanogens, was absent from surface waters, and was restricted to the pycnocline and deeper waters. This group of new methanogens constituted 24 % of the pycnocline cultures and 39 % of those from bottom waters. Stratification, which is a prerequisite for the development or concentration of methane-cycle bacteria in the pycnocline. apparently allows unique water-column methanogens to selectively enrich in particulates in the pycnocline that can increase in bottom waters before sedimentation. The observed distribution of known and new taxa of methanogens in the 3 water layers of Chesapeake Bay is illustrated by a model.