Use of 13C-Labeled Substrates to Determine Relative Methane Production Rates in Hypersaline Microbial Communities

Abstract:

Rates and pathways of methane production were determined from photosynthetic soft microbial mats and gypsum-encrusted endoevaporites collected in hypersaline environments from California, Mexico and Chile, as well as an organic-rich mud from a pond in the El Tatio volcanic fields, Chile. Samples (mud, homogenized soft mats and endoevaporites) were incubated anaerobically with deoxygenated site water, and the increase in methane concentration through time in the headspaces of the incubation vials was used to determine methane production rates. To ascertain the substrates used by the methanogens, ¹³C-labeled methylamines, methanol, dimethylsulfide, acetate or bicarbonate were added to the incubations (one substrate per vial) and the stable isotopic composition of the resulting methane was measured. The vials amended with ¹³C-labeled methylamines produced the most ¹³C-enriched methane, generally followed by the ¹³C-labeled methanol-amended vials. The stable isotope data and the methane production rates were used to determine first order rate constants for each of the substrates at each of the sites. Estimates of individual substrate use revealed that the methylamines produced 55 to 92% of the methane generated, while methanol was responsible for another 8 to 40%.