Hirofumi Watanabe - Academia.edu (original) (raw)

Papers by Hirofumi Watanabe

Proceedings of the National Academy of Sciences, 2018

Symbiotic digestion of lignocellulose in wood-feeding higher termites (family Termitidae) is a tw... more Symbiotic digestion of lignocellulose in wood-feeding higher termites (family Termitidae) is a two-step process that involves endogenous host cellulases secreted in the midgut and a dense bacterial community in the hindgut compartment. The genomes of the bacterial gut microbiota encode diverse cellulolytic and hemicellulolytic enzymes, but the contributions of host and bacterial symbionts to lignocellulose degradation remain ambiguous. Our previous studies of Nasutitermes spp. documented that the wood fibers in the hindgut paunch are consistently colonized not only by uncultured members of Fibrobacteres, which have been implicated in cellulose degradation, but also by unique lineages of Spirochaetes. Here, we demonstrate that the degradation of xylan, the major component of hemicellulose, is restricted to the hindgut compartment, where it is preferentially hydrolyzed over cellulose. Metatranscriptomic analysis documented that the majority of glycoside hydrolase (GH) transcripts expr...

Molecular Ecology, 2004

Termites are among the most important cellulose-digesting animals on earth, and are wellknown for... more Termites are among the most important cellulose-digesting animals on earth, and are wellknown for the symbiotic relationship they have with cellulolytic trichomonad and oxymonad flagellates (unicellular eukaryotes). Perhaps less well-known is the fact that ∼ ∼ ∼ ∼ 75% of the ∼ ∼ ∼ ∼ 2600 described termite species-those belonging to the family Termitidae-do not harbour such flagellates. Unlike most termites from other families, the majority of termitids do not consume wood, feeding instead on soil, leaf litter, fungi, grass, or lichen. Recent years have seen the characterization of the endogenous cellulase enzymes that help termites digest cellulose, from one flagellate-harbouring species (Reticulitermes speratus), as well as one termitid (Nasutitermes takasagoensis). The genes encoding the enzymes in these two termites are similar. However, their site of expression differs markedly-the salivary glands in R. speratus and the midgut in N. takasagoensis. To investigate this difference further, we performed a comparative study of cellulase expression in various termitid and flagellateharbouring species, using enzyme assays and reverse transcription polymerase chain reactions. Taxa from phylogenetically basal lineages were consistently found to express endogenous genes specifically in the salivary glands, whilst those from a relatively apical lineage containing termitids expressed cellulases solely in the midgut. Relatively low levels of cellulase activity were found in nonwood-feeding species, while the wood-feeding Coptotermes formosanus-arguably the most destructive pest species worldwide was found to have high levels of activity in all parts of the gut when compared to all other termites. In the light of these results, as well as recently accumulated phylogenetic data, we discuss scenarios for the evolution of cellulose digestion in termites.

Molecular Biology and Evolution, 2003

Bacteria of the genus Blattabacterium are intracellular symbionts that reside in specialized cell... more Bacteria of the genus Blattabacterium are intracellular symbionts that reside in specialized cells of cockroaches and the termite Mastotermes darwiniensis. They appear to be obligate mutualists, and are transmitted vertically in the eggs. Such characteristics are expected to lead to equivalent phylogenies for host and symbiont, and we tested this hypothesis using recently accumulated data on relationships among termites and cockroaches and their Blattabacterium spp. Host and symbiont topologies were found to be highly similar, and various tests indicated that they were not statistically different. A close relationship between endosymbionts from termites and members of the wood-feeding cockroach genus Cryptocercus was found, supporting the hypothesis that the former evolved from subsocial, wood-dwelling cockroaches. The majority of the Blattabacterium spp. sequences appear to have undergone similar rates of evolution since their divergence from a common ancestor, and an estimate of this rate was determined based on early Cretaceous host fossils. The results support the idea that the stem group of modern cockroaches radiated sometime between the late Jurassic and early Cretaceous-not the Carboniferous, as has been suggested on the basis of roach-like fossils from this epoch.

Biology Letters, 2013

In addition to harbouring intestinal symbionts, some animal species also possess intracellular sy... more In addition to harbouring intestinal symbionts, some animal species also possess intracellular symbiotic microbes. The relative contributions of gut-resident and intracellular symbionts to host metabolism, and how they coevolve are not well understood. Cockroaches and the termite Mastotermes darwiniensis present a unique opportunity to examine the evolution of spatially separated symbionts, as they harbour gut symbionts and the intracellular symbiont Blattabacterium cuenoti . The genomes of B. cuenoti from M. darwiniensis and the social wood-feeding cockroach Cryptocercus punctulatus are each missing most of the pathways for the synthesis of essential amino acids found in the genomes of relatives from non-wood-feeding hosts. Hypotheses to explain this pathway degradation include: (i) feeding on microbes present in rotting wood by ancestral hosts; (ii) the evolution of high-fidelity transfer of gut microbes via social behaviour. To test these hypotheses, we sequenced the B. cuenoti g...

Journal of Wood Science, 2010

Wood-feeding termites have evolved an effi cient cellulose-decomposing system. The termite has tw... more Wood-feeding termites have evolved an effi cient cellulose-decomposing system. The termite has two independent cellulose-digesting systems: one in the midgut and the other in the hindgut. Because the digestion system in the midgut should be the sole source of soluble sugars for the host termite, the details of the decomposition of wood particles in the midgut were clarifi ed in one of the most common pest species, Coptotermes formosanus. The spatial distribution of cellulase in the midgut was found by immunohistochemistry, and the amount of endogenous cellulases and the volume of the endoperitrophic space were determined. The size of wood particles in the foregut and the midgut were compared. The results showed that one of the characteristics of wood degradation by termites is the mechanical grinding of food by the mandibles and the cuticular apparatus of the foregut. This process greatly increases the surface area of the substrates. Extremely high concentrations of cellulase attack the ground-up wood in the midgut, and the glucose produced is removed quickly through the peritrophic membrane.

Applied Microbiology and Biotechnology, 2011

Annual Review of Entomology, 2010

Journal of Applied Glycoscience, 2001

Nature, 1998

The traditional view of cellulose digestion in animals is that they cannot produce their own cell... more The traditional view of cellulose digestion in animals is that they cannot produce their own cellulase, and so rely on gut microorganisms to hydrolyse cellulose. A classic example of this symbiosis is that between phylogenetically lower termites and the unicellular organisms ( ...

Annual Review of Ecology, Evolution, and Systematics, 2012

The prevailing view that insects lack endogenous enzymes for plant cell wall (PCW) digestion had ... more The prevailing view that insects lack endogenous enzymes for plant cell wall (PCW) digestion had led to the hypothesis that PCW digestion evolved independently in different insect taxa through the establishment of symbiotic relationships with microorganisms. However, recent studies reporting endogenous PCW-degrading genes and enzymes for several insects, including phylogenetically basal insects and closely related arthropod groups, challenge this hypothesis. Here, we summarize the molecular and biochemical evidence on the mechanisms of PCW digestion in insects to analyze its evolutionary pathways. The evidence reveals that the symbiotic-independent mechanism may be the ancestral mechanism for PCW digestion. We discuss the implications of this alternative hypothesis in the evolution of plant-insect interactions and suggest that changes in the composition of lignocellulolytic complexes were involved in the evolution of feeding habits and diet specializations in insects, playing import...

The Journal of General and Applied Microbiology, 2013

Protein Engineering Design and Selection, 2007

Proceedings of the Royal Society B: Biological Sciences, 2003

Physiological Entomology, 2005

Abstract. Throughout the history of studies on cellulose digestion in termites, carboxymethyl-cel... more Abstract. Throughout the history of studies on cellulose digestion in termites, carboxymethyl-cellulose has been preferably used as a substrate for measuring cellulase activity in termites due to its high solubility. However, carboxymethyl-cellulose degradation is not directly related to ...

Journal of Insect Physiology, 1997

Larval and adult Psacothea hilaris feed on mulberry wood and leaves, respectively. High levels of... more Larval and adult Psacothea hilaris feed on mulberry wood and leaves, respectively. High levels of endogenous activity against the major dietary carbohydrates, cellulose, hemicellulose, starch and soluble sugars were secreted in the gut of larvae and adults. Activity against pectin was also high and multiple polygalacturonase (EC 3.2.1.15) components were secreted in the gut of larvae. One glycanase component, ␤-EG1, which was primarily an endo-␤-1,4-glucanase (EC 3.2.1.4) and another, ␤-EG2, which was mostly an endo-␤-1,4-xylanase (EC 3.2.1.8), were also secreted, while at least four additional components hydrolysed laminarin, lichenin and crystalline cellulose. The ␤-glycosidase component ␤-GD1 was associated with most of the ␤mannosidase (EC 3.2.1.25) and ␤-xylosidase (EC 3.2.1.37) activity secreted in the gut of larvae, while another, ␤-GD2, was a ␤-glucosidase (EC 3.2.1.21), the activity of which was directed against cellobiose and other ␤-linked disaccharides, and a ␤-fucosidase (EC 3.2.1.38). A ␤galactosidase (EC 3.2.1.23), which did not hydrolyse lactose, was also secreted, as were distinct ␤-N-acetylhexosaminidase (EC 3.2.1.52), trehalase (EC 3.2.1.28), ␣-l-arabinosidase (EC 3.2.1.55), ␣-galactosidase (EC 3.2.1.22) and a minimum of four ␣-glucosidase (EC 3.2.1.20) components, one of which was also likely to be associated with a peak of ␣-mannosidase (EC 3.2.1.24) activity. The ␣-glucosidase components varied in their specificity for ␣-linked disaccharides, but none was active against sucrose, which was hydrolysed by a ␤-fructofuranosidase (EC 3.2.1.26) component. Overall average levels of activity in larvae were twice those of adults, but the secretion of individual carbohydrases in both was not regulated in response to the relative abundance of particular carbohydrate components in their respective diets.