Cellulolytic flagellated protists inhabit the hindgut of termites. They are unique and essential to termites and related wood-feeding cockroaches, enabling host feeding on cellulosic matter. Protists of two genera in the family Teranymphidae (phylum Parabasalia), Eucomonympha and Teranympha, are phylogenetically closely related and harbor intracellular endosymbiotic bacteria from the genus Treponema. In order to obtain a clearer understanding of the evolutionary history of this triplex symbiotic relationship, the molecular phylogenies of the three symbiotic partners, the Teranymphidae protists, their Treponema endosymbionts, and their host termites, were inferred and compared. Strong congruence was observed in the tree topologies of all interacting partners, implying their cospeciating relationships. In contrast, the coevolutionary relationship between the Eucomonympha protists and their endosymbionts was more complex, and evidence of incongruence against cospeciating relationships suggested frequent host switches of the endosymbionts, possibly because multiple Eucomonympha species are present in the same gut community. Similarities in the 16S rRNA and gyrB gene sequences of the endosymbionts were higher among Teranympha spp. (>99.25% and >97.2%, respectively), whereas those between Teranympha and Eucomonympha were lower (<97.1% and <91.9%, respectively). In addition, the endosymbionts of Teranympha spp. formed a phylogenetic clade distinct from those of Eucomonympha spp. Therefore, the endosymbiont species of Teranympha spp., designated here as “Candidatus Treponema teratonymphae”, needs to be classified as a species distinct from the endosymbiont species of Eucomonympha spp.
The activity of nitrogen fixation measured by acetylene reduction was examined in chemosynthetic microbial mats at 72–75°C in slightly-alkaline sulfidic hot springs in Nakabusa, Japan. Nitrogenase activity markedly varied from sampling to sampling. Nitrogenase activity did not correlate with methane production, but was detected in samples showing methane production levels less than the maximum amount, indicating a possible redox dependency of nitrogenase activity. Nitrogenase activity was not affected by 2-bromo-ethane sulfonate, an inhibitor of methanogenesis. However, it was inhibited by the addition of molybdate, an inhibitor of sulfate reduction and sulfur disproportionation, suggesting the involvement of sulfate-reducing or sulfur-disproportionating organisms. Nitrogenase activity was affected by different O2 concentrations in the gas phase, again supporting the hypothesis of a redox potential dependency, and was decreased by the dispersion of mats with a homogenizer. The loss of activity that occurred from dispersion was partially recovered by the addition of H2, sulfate, and carbon dioxide. These results suggested that the observed activity of nitrogen fixation was related to chemoautotrophic sulfate reducers, and fixation may be active in a limited range of ambient redox potential. Since thermophilic chemosynthetic communities may resemble ancient microbial communities before the appearance of photosynthesis, the present results may be useful when considering the ancient nitrogen cycle on earth.
We tested a formulation composed of a mixture of Bidens pilosa var. radiata extract (BPE) and nematode-trapping fungi for its effects on Meloidogyne incognita. In earlier evaluations of the effects of plant extracts on the hyphal growth of 5 species of nematode-trapping fungi with different capture organs (traps), the growth of all species was slightly inhibited. However, an investigation on the number of capture organs and nematode-trapping rates revealed that Arthrobotrys dactyloides formed significantly more rings and nematode traps than those of the control. An evaluation of simple mixed formulations prepared using sodium alginate showed that nematodes were captured with all formulations tested. The simple mixed formulation showed a particularly high capture rate. Furthermore, in a pot test, although the effects of a single formulation made from the fungus or plant extract were acceptable, the efficacy of the simple mixed formulation against M. incognita root-knot formation was particularly high.
Limited information is currently available on the contribution of eukaryotes to the reactor performance of membrane bioreactors (MBRs). Using high-throughput Illumina sequencing of 18S rRNA genes and microscopic observations, we investigated eukaryotic microbiomes in membrane-attached biofilms in MBRs treating piggery wastewater. Protozoa preying on bacteria were frequently detected under stable conditions when membrane clogging was suppressed. However, the eukaryotes preying upon protozoa became predominant in biofilms when membrane fouling rapidly progressed. We herein demonstrated that a comprehensive investigation of eukaryotic microbiomes using high-throughput sequencing contributes to a better understanding of the microbial ecology involved in wastewater treatment.