C1 BACTERIA IN THE WATER COLUMN OF CHESAPEAKE BAY, USA .2. THE DOMINANT O2-TOLERANT AND H2S-TOLERANT METHYLOTROPHIC METHANOGENS, COENRICHEDWITH THEIR OXIDATIVE AND SULFATE-REDUCING BACTERIAL CONSORTS, ARE ALLNEW IMMUNOTYPES AND PROBABLY INCLUDE NEW TAXA

Methylotrophic methanogens were readily enriched with monomethylamine (MMA) in water samples obtained from throughout the stratified but oxy genated water column of Chesapeake Bay, USA. Of the 3 different popula tions of methylotrophic methanogens enriched, O2- and H2S-tolerant met hanogens enriched in bacterially reduced seawater in glass were twice as prevalent as those enrichments either reduced chemically in glass o r reduced bacterially in semipermeable polycarbonate flasks. Thirty-th ree obligately anaerobic, but O2- and H2S-tolerant, methanogenic cultu res from the dominant group were fingerprinted immunologically using a ntibody probes. The antigenic fingerprints divided these cultures into 4 clusters. One cluster was related to Methanosarcina barkeri R1M3, a second was related to M. mazei S6, and a third was related to other s pecies of Methanosarcina. None of these were identical to known specie s and can be considered new immunotypes. These new immunotypes, relate d to described species, were found throughout the water column. A four th cluster was unrelated to any extant genus of methanogens, was absen t from surface waters, and was restricted to the pycnocline and deeper waters. This group of new methanogens constituted 24 % of the pycnocl ine cultures and 39 % of those from bottom waters. Stratification, whi ch is a prerequisite for the development or concentration of methane-c ycle bacteria in the pycnocline, apparently allows unique water-column methanogens to selectively enrich in particulates in the pycnocline t hat can increase in bottom waters before sedimentation. The observed d istribution of known and new taxa of methanogens in the 3 water layers of Chesapeake Bay is illustrated by a model.