Structure, microbial associations and function of the so-called “mixed segment” of the gut in two soil-feeding termites, Procubitermes aburiensis and Cubitermes severus (Termitidae, Termitinae)

Novel Cesium Resistance Mechanism of Alkaliphilic Bacterium Isolated From Jumping Spider Ground Extract

The radionuclide isotopes (¹³⁴Cs and ¹³⁷Cs) of Cesium (Cs), an alkali metal, are attracting attention as major causes of radioactive contamination. Although Cs⁺ is harmful to the growth of plants and bacteria, alkaliphilic bacterium Microbacterium sp. TS-1, isolated from a jumping spider, showed growth even in the presence of 1.2 M CsCl. The maximum concentration of Cs⁺ that microorganisms can withstand has been reported to be 700 mM till date, suggesting that the strain TS-1 is resistant to a high concentration of Cs ions. Multiple reports of cesium ion-resistant bacteria have been reported, but the detailed mechanism has not yet been elucidated. We obtained Cs ion-sensitive mutants and their revertant mutants from strain TS-1 and identified a Cs ion resistance-related gene, MTS1_00475, by performing SNP analysis of the whole-genome sequence data. When exposed to more than 200 mM Cs⁺ concentration, the intracellular Cs⁺ concentration was constantly lowered by MTS1_00475, which encodes the novel low-affinity Cs⁺/H⁺ antiporter. This study is the first to clarify the mechanism of cesium resistance in unexplained cesium-resistant microorganisms. By clarifying the new cesium resistance mechanism, it can be expected to be used as a bioremediation tool for treating radioactive Cs⁺ contaminated water.

Anatomical specializations of the gizzard in soil-feeding termites (Termitidae, Apicotermitinae): Taxonomical and functional implications

The anatomy of the workers' digestive tube is essential in taxonomical studies of soil-feeding Apicotermitinae termites, especially in soldierless lineages. Two structures, the mesenteric-proctodeal junction and the enteric valve, have long been important to distinguish genera and species. By contrast, the gizzard (proventriculus) has been almost ignored by taxonomists because of its generally regressed state in soil-feeding termites. In this study, we document in detail for the first time the sclerotized structures and ornamentations in the gizzard in the Apicotermitinae subfamily. We identified two main clusters of species: those without ornamentations and those exhibiting a sclerotized pulvillar armature, which may include spicules or spines of diverse sizes, numbers and dispositions. The latter group comprises the majority of African soldierless species, a widely diverse and dominant group in tropical forests and savannas. We outline the potential role of the anatomy of the gizzard in the taxonomy of Apicotermitinae based on the interspecific anatomical variation of the pulvillar armatures. We suggest that sclerotized ornamentations regulate the flow of food particles and break or lacerate aggregates to facilitate the access of enzymes in the midgut.

MotP Subunit is Critical for Ion Selectivity and Evolution of a K+-Coupled Flagellar Motor

The bacterial flagellar motor is a sophisticated nanomachine embedded in the cell envelope. The flagellar motor is driven by an electrochemical gradient of cations such as H⁺, Na⁺, and K⁺ through ion channels in stator complexes embedded in the cell membrane. The flagellum is believed to rotate as a result of electrostatic interaction forces between the stator and the rotor. In bacteria of the genus Bacillus and related species, the single transmembrane segment of MotB-type subunit protein (MotB and MotS) is critical for the selection of the H⁺ and Na⁺ coupling ions. Here, we constructed and characterized several hybrid stators combined with single Na⁺-coupled and dual Na⁺- and K⁺-coupled stator subunits, and we report that the MotP subunit is critical for the selection of K⁺. This result suggested that the K⁺ selectivity of the MotP/MotS complexes evolved from the single Na⁺-coupled stator MotP/MotS complexes. This finding will promote the understanding of the evolution of flagellar motors and the molecular mechanisms of coupling ion selectivity.

Microenvironmental heterogeneity of gut compartments drives bacterial community structure in wood- and humus-feeding higher termites

Symbiotic digestion of lignocellulose in higher termites (family Termitidae) is accomplished by an exclusively prokaryotic gut microbiota. By deep sequencing of amplified 16S rRNA genes, we had identified diet as the primary determinant of bacterial community structure in a broad selection of termites specialized on lignocellulose in different stages of humification. Here, we increased the resolution of our approach to account for the pronounced heterogeneity in microenvironmental conditions and microbial activities in the major hindgut compartments. The community structure of consecutive gut compartments in each species strongly differed, but that of homologous compartments clearly converged, even among unrelated termites. While the alkaline P1 compartments of all termites investigated contained specific lineages of Clostridiales, the posterior hindgut compartments (P3, P4) differed between feeding groups and were predominantly colonized by putatively fiber-associated lineages of Spirochaetes, Fibrobacteres and the TG3 phylum (wood and grass feeders) or diverse assemblages of Clostridiales and Bacteroidetes (humus and soil feeders). The results underscore that bacterial community structure in termite guts is driven by microenvironmental factors, such as pH, available substrates and gradients of O₂ and H₂, and inspire investigations on the functional roles of specific bacterial taxa in lignocellulose and humus digestion.

Predominant expression and activity of vacuolar H(+)-ATPases in the mixed segment of the wood-feeding termite Nasutitermes takasagoensis

The mixed segment is a unique part of the gut present only in the most apical lineage of termites and consists of a complex of overlapping mesenteric and proctodeal epithelia. In spite of its unique structure, the physiological functions of the mixed segment have been poorly studied. We performed transcriptome analysis to identify functional enzymes acting in the mixed segment of the wood-feeding higher termite Nasutitermes takasagoensis. We sequenced the transcripts (4563 isotigs) of the mixed segment and compared them with those of the midgut (4813 isotigs) and the first proctodeal segment (3629 isotigs). We found that vacuolar H(+)-ATPase (V-ATPase) subunits were predominant in the mixed segment, which was confirmed by RT-qPCR analysis. The V-ATPase activity in these three tissues was in a good agreement with the expression patterns, suggesting that V-ATPase is a prevalent enzyme in the mixed segment of the termites. The results confirmed the proposed role of the mixed segment as a transporting epithelium.

Draft Genome Sequence of the Alkaliphilic and Xylanolytic Paenibacillus sp. Strain JCM 10914, Isolated from the Gut of a Soil-Feeding Termite

Panibacillus sp. strain JCM 10914 is a xylanolytic alkaliphile isolated from the gut of a soil-feeding termite. Its draft genome sequence revealed various genes for hydrolytic enzymes and will facilitate studies on adaptation to the highly alkaline gut environment and its role in digesting soil organic matter in the gut.

Cellulolytic environment in the midgut of the wood-feeding higher termite Nasutitermes takasagoensis

Unlike lower termites, xylophagous higher termites thrive on wood without the aid of symbiotic protists. In the higher termite Nasutitermes takasagoensis, both endogenous endo-β-1,4-glucanase and β-glucosidase genes are expressed in the midgut, which is believed to be the main site of cellulose digestion. To further explore the detailed cellulolytic system in the midgut of N. takasagoensis, we performed immunohistochemistry and digital light microscopy to determine distributions of cellulolytic enzymes in the salivary glands and the midgut as well as the total cellulolytic activity in the midgut. Although cellulolytic enzymes were uniformly produced in the midgut epithelium, the concentration of endo-β-1,4-glucanase activity and luminal volume in the midgut were comparable to those of the wood-feeding lower termite Coptotermes formosanus, which digests cellulose with the aid of hindgut protists. However, the size of ingested wood particles was considerably larger in N. takasagoensis than that in C. formosanus. Nevertheless, it is possible that the cellulolytic system in the midgut of N. takasagoensis hydrolyzes highly crystalline cellulose to a certain extent. The glucose produced did not accumulate in the midgut lumen. Therefore, the present study suggests that the midgut of the higher termite provides the necessary conditions for cellulolysis.

Recursos alimentares explorados pelos cupins (Insecta: Isoptera)

Os cupins são insetos sociais pertencentes à ordem Isoptera e constituem um dos grupos de invertebrados dominantes em ambientes terrestres tropicais. Atualmente, existem cerca de 2.900 espécies descritas, que estão distribuídas em sete famílias: Mastotermitidae, Kalotermitidae, Termopsidae, Hodotermitidae, Serritermitidae, Rhinotermitidae e Termitidae. A região neotropical engloba 537 espécies, e dessas, aproximadamente 300 ocorrem no Brasil e pertencem às famílias Kalotermitidae, Rhinotermitidae, Serritermitidae e Termitidae. Apesar dos isópteros serem bastante conhecidos pelo seu potencial como praga, o papel ecológico dos térmitas no ambiente é primordial, visto que desempenham o papel de consumidores primários e/ou decompositores nos ecossistemas naturais. Esses insetos participam ativamente na trituração, decomposição, humificação e mineralização de uma variedade de recursos celulósicos. Uma grande diversidade de material orgânico, em vários estágios de decomposição, pode servir de alimento para os cupins, incluindo madeira (viva ou morta), gramíneas, plantas herbáceas, serapilheira, fungos, ninhos construídos por outras espécies de cupins, excrementos e carcaças de animais, liquens e até mesmo material orgânico presente no solo (húmus). Essa vasta gama de fontes alimentares permitiu aos cupins ocuparem quase todas as regiões quentes e temperadas da Terra, ocorrendo em praticamente todos os ambientes terrestres, naturais ou modificados pela espécie humana. Portanto, os isópteros são encontrados nas matas tropicais e temperadas, cerrados, savanas, caatingas, restingas, mangues, campos, culturas, pastagens e cidades.

Comparison of bacterial communities in the alkaline gut segment among various species of higher termites

The first proctodeal (P1) segment in the hindgut of certain higher termites shows high alkalinity. We examined the bacterial diversity of the alkaline P1 gut segments of four species of higher termites by T-RFLP and phylogenetic analyses based on PCR-amplified 16S rRNA genes. The bacterial community of the P1 segment was apparently different from that of the whole gut in each termite. Sequence analysis revealed that Firmicutes (Clostridia and Bacilli) were dominant in the P1 segments of all four termites; however, the phylogenetic compositions varied among the termites. Although some of the P1 segment-derived sequences were related to the sequences previously reported from the alkaline digestive tracts of other insects, most of them formed phylogenetic clusters unique to termites. Such "termite P1 clusters" were distantly related to known bacterial species as well as to sequences reported from alkaline environments in nature. We successfully obtained enrichment cultures of Clostridia- and Bacilli-related bacteria, including putative novel species under anaerobic alkaline conditions from the termite guts. Our results suggest that the alkaline gut region of termites harbors unique bacterial lineages and are expected to be a rich reservoir of novel alkaliphiles yet to be cultivated.

Localization of symbiotic clostridia in the mixed segment of the termite Nasutitermes takasagoensis (Shiraki)

Phylogeny and the distribution of symbiotic bacteria in the mixed segment of the wood-eating termite Nasutitermes takasagoensis (Shiraki) were studied. Bacterial 16S rRNA genes (rDNA) were amplified from the mixed segment of the gut by PCR, and two kinds of sequences were identified. The phylogenetic tree was constructed by neighbor-joining and maximum parsimony methods to identify symbionts harbored in the mixed segment. They are classified as low-G+C-content gram-positive bacteria and are most closely related to the genus Clostridium. The distribution of these bacteria throughout the whole gut was examined by PCR using specific primers, which suggested that they are confined to the mixed segment despite the presence of bacteria throughout the gut. In situ hybridization indicated that the symbiotic bacteria were localized to the ectoperitrophic space between the midgut wall and the peritrophic membrane in the mixed segment. Electron microscopy revealed the close association between these bacteria and the mesenteric epithelium, suggesting that they have some interactions with the gut tissue of termites.

Cellulose digestion in the wood-eating higher termite, Nasutitermes takasagoensis (Shiraki): distribution of cellulases and properties of endo-beta-1,4-glucanase

beta-Glucosidase [EC 3.2.1.21] and endo-beta-1,4-glucanase [EC 3.2.1.4] activities were measured in the wood-eating higher termite Nasutitermes takasagoensis. beta-Glucosidase activity was present mainly in the salivary glands (66.7%) and midgut (22.2%), whereas endo-beta-1,4-glucanase activity was detected mainly in the midgut (90.1%). Specific activity of endo-beta-1,4-glucanase was also the highest in the midgut, indicating that cellulose is digested in the midgut. The major endo-beta-1,4-glucanase component of N. takasagoensis was purified from whole termites by gel filtration on Sephaoryl S-200 HR, Superdex-75 and hydroxyapatite column chromatography. Subsequently, the endo-beta-1,4-glucanase activity from a crude midgut extract was eluted in an identical volume (Kd = 0.68) to that from whole termites, suggesting the purified endo-beta-1,4-glucanase is identical to that in the midgut. The molecular weight of the purified endo-beta-1,4-glucanase was 47 kDa, and its specific activity was 1,200 units/mg. The optimal pH and temperature were 5.8 and 65 degrees C, respectively. The Km and Vmax values on carboxymethyl cellulose were 8.7 mg/ml and 2,222 units/mg, respectively. The purified endo-beta-1,4-glucanase hydrolyzed cellopentaose to cellotriose and cellobiose, and cellotetraose to cellobiose and a trace of cellotriose and glucose, but cellotriose and cellobiose were not hydrolyzed. The activity and stability on pH and temperature of the purified endo-beta-glucanase are prominent among those from various organisms.

Properties of lactate dehydrogenase in a psychrophilic marine bacterium

Lactate dehydrogenase (EC 1.1.1.27) from Vibrio marinus MP-1 was purified 15-fold and ammonium activated. The optimum pH for pyruvate reduction was 7.4. Maximum lactate dehydrogenase activity occurred at 10 to 15 degrees C, and none occurred at 40 degrees C. The crude-extract enzyme was stable between 15 and 20 degrees C and lost 50% of its activity after 60 min at 45 degrees C. The partially purified enzyme was stable between 8 and 15 degrees C and lost 50% of its activity after 60 min at 30 degrees C. The thermal stability of lactate dehydrogenase was increased by mercaptoethanol, with 50% remaining activity at 42 degrees C.