Diversity of Formyltetrahydrofolate Synthetases in the Guts of the Wood-Feeding Cockroach Cryptocercus punctulatus and the Omnivorous Cockroach Periplaneta americana

Abstract

We examined the diversity of a marker gene for homoacetogens in two cockroach gut microbial communities. Formyltetrahydrofolate synthetase (FTHFS or fhs) libraries prepared from a wood-feeding cockroach, Cryptocercus punctulatus, were dominated by sequences that affiliated with termite gut treponemes. No spirochetelike sequences were recovered from the omnivorous roach Periplaneta americana, which was dominated by Firmicutes-like sequences.The guts of wood-feeding termites and Cryptocercus punctulatus cockroaches share an unusual pattern of electron flow, as high rates of CO 2 -reductive acetogenesis typically supplant methanogenesis as the terminal electron sink (2, 3). Past studies have shown that from 10 to 30% of gut acetate produced in environments of termites and wood-feeding cockroaches is microbially generated from CO 2 (3, 28), ultimately powering 18 to 26% of the host insect's own respiratory energy metabolism (25). Nevertheless, most termites emit methane (2), and termite emissions constitute approximately 4% of the global methane budget (27). Cockroaches have been proposed to represent an additional source of note (9). Interestingly, methanogenic termites and cockroaches exhibit increased acetogenesis following addition of exogenous H 2 (3,29). This suggests that these insects are host to a robust population of bacteria that are capable of homoacetogenesis but may be primarily using alternative electron donors (and other substrates and pathways) in vivo.Acetogenic bacteria belonging to two bacterial phyla, Firmicutes and Spirochaetes, have been isolated from the guts of termites (1,4,11,12,14). Several surveys have targeted and used the gene for formyltetrahydrofolate synthetase (FTHFS), a key gene in the Wood-Ljungdahl pathway of acetogenesis (16), as a potential marker for the pathway (15, 18). For the wood-feeding termites that have been examined, the studies have revealed an abundance of FTHFS sequences that form a coherent phylogenetic cluster, together with genes from homoacetogenic termite gut spirochetes belonging to the genus Treponema (24,26,30). This suggests that treponemes may be among the more abundant of the homoacetogens active in these environments.Little is known about the population structure and biology of CO 2 -reducing, acetogenic bacteria in the guts of either omnivorous or wood-feeding cockroaches. The wood-feeding cockroach Cryptocercus hosts an abundance of flagellate protozoa closely related to those believed to dominate polysaccharide fermentation in the guts of termites (5,6,22), suggesting that at least one key environmental niche is filled by similar microbes in both termites and Cryptocercidae. Additionally, Cryptocercidae cockroaches, like termites, house diverse spirochetes and are the site of intense CO 2 reduction into acetate (3, 7). Possibly, spirochetes capable of CO 2 reduction into acetate are present in the hindguts of cockroaches. However, no evidence has yet been presented for the existence of homoacetogenic treponemes in environments other than the guts of...

Formyltetrahydrofolate Synthetase Gene Diversity in the Guts of Higher Termites with Different Diets and Lifestyles

“…1; phylogenetic detail is in Fig. 3), as do a large fraction of FTHFS sequences recovered in a similar study of the gut microbiota of the omnivorous cockroach Periplaneta americana (24). Clostridium sp.…”

“…However, this does not preclude homoacetogenic capacity for other members of the M62/1 clade; many members have intermediate (Ͼ90) to high (Ͼ95) HS scores. P. americana is known to exhibit low but detectable rates of acetate synthesis from CO 2 (4,11), and organisms belonging to this clade remain the best candidates for potential acetogens of the FTHFS sequences recovered in libraries of P. americana (24). Observations of soil-feeding Cubitermes termites, which also have low measured rates of in situ CO 2 fixation to acetate (3,34), also show a robust population of CO 2 -reductive acetogens, detectable when gut homogenates are incubated with inhibitors of methanogenesis (34).…”

‘Candidatus Adiutrix intracellularis’, an endosymbiont of termite gut flagellates, is the first representative of a deep‐branching clade of Deltaproteobacteria and a putative homoacetogen

“…After the isolation of T. primitia, the first representative of the phylum Spirochaetes that was capable of reductive acetogenesis (Leadbetter et al, 1999;Graber and Breznak, 2004), numerous studies using functional marker genes and metagenomic approaches have documented the importance of homoacetogenic spirochetes in this process (e.g. Ottesen et al, 2006;Pester and Brune, 2006;Warnecke et al, 2007;Ottesen et al, 2010;Matson et al, 2011;Zhang et al, 2011).…”

Localizing transcripts to single cells suggests an important role of uncultured deltaproteobacteria in the termite gut hydrogen economy

“…Leveraging the predictive power of existing hydrogenase-linked FDH (fdhF) and FTHFS gene inventories (9,11,19), gut environmental metatranscriptomic data were used to identify highly expressed alleles for each of these functional gene types. High-throughput cDNA sequencing (RNASeq) is increasingly used to quantify transcriptional intensity.…”

“…Gene-based community analyses have led to a guiding hypothesis that some, most, or all of the contributors to gut acetogenesis may be spirochetes, many of which have not yet been cultivated. In contrast, there has been no support for an important homoacetogenic role of endospore-forming Firmicutes species isolated at low abundances from termites or their close relatives (6,(8)(9)(10)(11)(12). The hypothesis that spirochetes may account for most or all of termite gut acetogenesis remains largely Significance Most environments host a poorly understood microbial diversity.…”