Stimulation of Bathyarchaeota in enrichment cultures by syringaldehyde, 4-hydroxybenzaldehyde and vanillin under anaerobic conditions

Bathyarchaeota covering about 25 subgroups are a newly discovered archaeal phylum with widespread in anaerobic environments including marine sediments, soils and subsurface petroleum reservoirs. Although recent studies showed that Bathyarchaeota can use lignin as an energy source to get enrichment, there is a lack of the pure culture and thus the understanding about Bathyarchaeota is still based on genomic information. In this study, lignin and three aldehyde compounds, namely syringaldehyde, 4-hydroxybenzaldehyde, and vanillin, which were recognized as the metabolic intermediates of lignin biodegradation, were used as substrates to enrich Bathyarchaeota from mangrove sediments, and enrichment cultures of Bathyarchaeota was successfully established in the laboratory. The changes in gene-copy numbers, microbial composition and consumption of the substrates indicated that the syringaldehyde significantly stimulated the growth of Bathyarchaeota in the enrichment culture. Meanwhile, the relative abundance of Bathyarchaeota was as high as 97.13% in term of the archaeal composition, especially bathyarchaeotal genome subgroup-6 accounted for more than 99.9% in Bathyarchaeota, and 4.74 mmol L−1 methane were also detected in the enrichment culture amended with syringaldehyde as a substrate after about 117 days of incubation, compared to 4-HBA (3.75 mmol L−1) and VA (3.75 mmol L−1). This work will facilitate the design of high-efficiency enrichment cultures and understanding about the metabolic and ecological functions of Bathyarchaeota in nature.