‘CandidatusAncillula trichonymphae’, a novel lineage of endosymbiotic Actinobacteria in termite gut flagellates of the genus Trichonympha

Abstract

Termite gut flagellates are colonized by host-specific lineages of ectosymbiotic and endosymbiotic bacteria. Previous studies have shown that flagellates of the genus Trichonympha may harbour more than one type of symbiont. Using a comprehensive approach that combined cloning of SSU rRNA genes with fluorescence in situ hybridization and electron microscopy, we investigated the phylogeny and subcellular locations of the symbionts in a variety of Trichonympha species from different termites. The flagellates in Trichonympha Cluster I were the only species associated with 'Endomicrobia', which were located in the posterior part of the cell, confirming previous results. Trichonympha species of Cluster II from the termite genus Incisitermes (family Kalotermitidae) lacked 'Endomicrobia' and were associated with endosymbiotic Actinobacteria, which is highly unusual. The endosymbionts, for which we suggest the name 'Candidatus Ancillula trichonymphae', represent a novel, deep-branching lineage in the Micrococcineae that consists exclusively of clones from termite guts. They preferentially colonized the anterior part of the flagellate host and were highly abundant in all species of Trichonympha Cluster II except Trichonympha globulosa. Here, they were outnumbered by a Desulfovibrio species associated with the cytoplasmic lamellae at the anterior cell pole. Such symbionts are present in both Trichonympha clusters, but not in all species. Unlike the intracellular location reported for the Desulfovibrio symbionts of Trichonympha agilis (Cluster I), the Desulfovibrio symbionts of T. globulosa (Cluster II) were situated in deep invaginations of the plasma membrane that were clearly connected to the exterior of the host cell.

Acetogenesis from H2plus CO2and nitrogen fixation by an endosymbiotic spirochete of a termite-gut cellulolytic protist

“…In the case of the endosymbiont of Trichonympha, the sequenced genome carries neither acetyl-CoA pathway genes nor nitrogen fixation genes. However, associations of the second bacterial symbionts, which are different species depending on the Trichonympha lineages, have been reported, and they likely involve H 2 metabolism (19,41,42). One of them belongs to the genus Desulfovibrio, and genes for sulfate reduction and hydrogenase are identified (41).…”

Intranuclear verrucomicrobial symbionts and evidence of lateral gene transfer to the host protist in the termite gut

“…The closest phylotypes to the two Nucleococcus species are those obtained from Trichonympha cells in the gut of Incisitermes termites (Strassert et al, 2012) (Figure 2). The sequence similarity is as high as 96-97%; these are possibly also intranuclear symbionts of the Trichonympha species.…”

“…Several phylotypes have been found in subdivision 6 and in the orders Opitutales and Puniceicoccales in subdivision 4 (Hongoh et al, 2003Nakajima et al, 2005;Yang et al, 2005;Hongoh et al, 2007a;IkedaOhtsubo et al, 2010;Strassert et al, 2012). These phylotypes comprise one or more termite-specific clusters in each clade, and most members are as yet unculturable.…”

“…These were recovered from Trichonympha cells in the gut of the kalotermitid termites Incisitermes schwarzi and I. tabogae, respectively (Strassert et al, 2012). Phylotype RsTaN-K2 shared 96% sequence identity with another uncultured clone, ItbTcA-142, from a Trichonympha cell in the gut of I. tabogae (Strassert et al, 2012) and formed a monophyletic cluster together with the other three clones from termite guts (Figure 2). These two clusters further formed a monophyletic cluster that exclusively consisted of uncultured clones from lower termites in the genera Cryptotermes and Reticulitermes and one clone from a wood-feeding higher termite, Microcerotermes sp.…”

“…The complete genome sequence analysis of phylotype Rs-D17 suggested that the endosymbionts contribute to the host protists and termites by the synthesis of amino acids and cofactors, which are deficient in the ingested wood materials (Hongoh et al, 2008a). Likewise, termite gut protists generally harbor diverse intracellular and/or extracellular symbiotic prokaryotes comprising members of the orders Spirochaetales, Bacteroidales, 'Endomicrobiales', Desulfovibrionales, Actinomycetales and Methanobacteriales (Hongoh and Ohkuma, 2011;Desai and Brune, 2012;Strassert et al, 2012).…”