Enrichment of anaerobic heterotrophic thermophiles from four Azorean hot springs revealed different community composition and genera abundances using recalcitrant substrates

DGGE analysis combined with a metagenomic approach was used to get insights into heterotrophic anoxic enrichment cultures of four hot springs of Vale das Furnas, Portugal, using the recalcitrant substrate spent coffee ground (SCG). Parallel enrichment cultures were performed using the major components of spent coffee ground, namely arabinogalactan, galactomannan, cellulose, and proteins. DGGE revealed that heterotrophic thermophilic bacteria are highly abundant in the hydrothermal springs and significant differences in community composition depending on the substrate were observed. DNA, isolated from enrichment cultures of different locations that were grown on the same substrate were pooled, and the respective metagenomes were analyzed. Results indicated that cultures grown on recalcitrant substrate SCG consists of a totally different thermophilic community, dominated by Dictyoglomus. Enrichments with galactomannan and arabinogalactan were dominated by Thermodesulfovibrio, while cultures with casein and cellulose were dominated by Thermus. This study indicates the high potential of thermophilic bacteria degrading recalcitrant substrate such as SCG and furthermore how the accessibility to complex polymers shapes the bacterial community.