A Functional Approach To Uncover the Low-Temperature Adaptation Strategies of the Archaeon Methanosarcina barkeri

Low-temperature anaerobic digestion (LTAD) technology is underpinned by a diverse microbial community. The methanogenic archaea represent a key functional group in these consortia, undertaking CO2 reduction as well as acetate and methylated C1 metabolism with subsequent biogas (40 to 60% CH4 and 30 to 50% CO2 ) formation. However, the cold adaptation strategies, which allow methanogens to function efficiently in LTAD, remain unclear. Here, a pure-culture proteomic approach was employed to study the functional characteristics ofMethanosarcina barkeri (optimum growth temperature, 37�C), which has been detected in LTAD bioreactors. Two experimental approaches were undertaken. The first approach aimed to characterize a low-temperature shock response (LTSR) ofM. barkeri DSMZ 800T grown at 37�C with a temperature drop to 15�C, while the second experimental approach aimed to examine the low-temperature adaptation strategies (LTAS) of the same strain when it was grown at 15�C. The latter experiment employed cell viability and growth measurements (optical density at 600 nm [OD600 ]), which directly comparedM. barkeri cells grown at 15�C with those grown at 37�C. During the LTSR experiment, a total of 127 proteins were detected in 37�C and 15�C samples, with 20 proteins differentially expressed with respect to temperature, while in the LTAS experiment 39% of proteins identified were differentially expressed between phases of growth. Functional categories included methanogenesis, cellular information processing, and chaperones. By applying a polyphasic approach (proteomics and growth studies), insights into the low-temperature adaptation capacity of this mesophilically characterized methanogen were obtained which suggest that the metabolically diverseMethanosarcinaceae could be functionally relevant for LTAD systems.