Formate dehydrogenese gene phylogeny in higher termites suggests gut microbial communities have undergone an evolutionary bottleneck, convergent evolution, and invasion

The majority of termites and termite species on the planet belong to the phylogenetically ‘higher’ termite family Termitidae. Higher termites thrive on diverse lignocellulosic substrates with the aid of symbiotic gut microbiota. H2 consuming CO2 reductive acetogenic bacteria are an important group of symbionts that produce a significant fraction of the acetate used by their insect host as its primary carbon and energy source. A recent metagenomic analysis of the hindgut paunch bacterial community of a woodfeeding higher termite suggested spirochetes are the dominant acetogens in higher termites, as they appear to be in phylogenetically lower termites. However, a certain genetic feature of actogenesis in higher termites was not resolved. Genes for hydrogenase-linked formate dehydrogenase (FDHH), an enzyme implicated in H2 turnover and CO2 fixing capacities of a termite gut acetogenic spirochete isolate and many uncultured lower termite gut acetogens, were notably depleted with respect to abundance and diversity relative to other acetogenesis genes in the metagenome and the gut communities of lower termites. Here, we use FDHH primers to determine whether higher termite gut communities are as poor in FDHH genes as previous data suggest. We