Characterization of a halotolerant acetoclastic methanogen highly enriched from marine sediment and its application in removal of acetate

Abstract

A marine sediment collected from Hiroshima Bay was cultured in artificial seawater, containing 0.51M NaCl and 60mM acetate and was found to exhibit active methane production at 37°C. Following four successive serial dilutions of cultures in medium containing 0.51M NaCl, 60mM acetate, and antibiotics, the well-acclimated methanogen was found to exhibit growth over a range of NaCl concentration (between 0M and 2.06M). The specific growth rates of the highly enriched methanogen, termed strain HA, in the absence of NaCl and in the presence of 1.54M NaCl were estimated to be 0.037h(-1) and 0.027h(-1), respectively. The pH and temperature for optimum growth were determined to be 7.0-8.8 and 37°C, respectively. Although cells that had morphology similar to Methanosaeta sp. became dominant in the culture, methane production was still detected in the medium containing 0.51M NaCl and other substrates such as methanol, formate, and methylamine, indicating contamination with other methanogens. The phylogenetic tree based on 16S rRNA gene sequences revealed that the strain HA was closely related to Methanosaeta harundinacea 6Ac and 8Ac(T), with sequence similarity of 98% and 97%, respectively. The continuous removal of acetate with upflow anaerobic filter reactor for industrial use of strain HA determined a methane production rate of 70mM/d under condition of 0.51M NaCl and successful methane production even under 1.54M NaCl.