A metaproteomic approach for identifying proteins in anaerobic bioreactors converting coal to methane

Abstract To understand the processes involved in bioconversion of coal to methane, a metaproteomic approach was taken to identify proteins in microcosms containing coal, standard medium and an adapted microbial community. Concentrated and dialyzed protein samples were subjected to further cleanup and trypsin digestion followed by mass spectrometric analysis. Searching the generated peaklists against domains of bacteria, archaea and fungi revealed 152 ± 1.4, 96.5 ± 2.1 and 38 ± 1.4 protein families, respectively. Proteins associated with bacteria were distributed among transporter and membrane proteins (33.1%), cellular metabolism (28.5%), substrate utilization/conversion (7.3%), oxidative stress (5.3%), cell movement (3.3%) and hypothetical proteins (22.5%). Among the total archaea proteins, 37.8% were for substrate utilization related to methane production, 27.6% were for cellular metabolism, 6.1% responded to stress, 5.1% were transporter and membrane proteins and 23.5% were those with unknown functions. Proteins produced by fungi fell in two groups: cell metabolisms (45.7%) and hypothetical proteins (54.3%). Based on key enzymes identified, a pathway for methanogenesis in the tested samples was proposed. This pathway illustrated methane production from four starting compounds, acetate, formate, methanol and CO 2 . The proposed pathway will serve as a solid foundation for future effort aiming to increase methane yield from coal.