Souichiro Kato

In anaerobic biota, reducing equivalents (electrons) are transferred between different species of microbes [interspecies electron transfer (IET)], establishing the basis of cooperative behaviors and community functions. IET mechanisms described so far are based on diffusion of redox chemical species and/or direct contact in cell aggregates. Here, we show another possibility that IET also occurs via electric currents through natural conductive minerals. Our investigation revealed that electricall

Methanogenesis is an essential part of the global carbon cycle and a key bioprocess for sustainable energy. Methanogenesis from organic matter is accomplished by syntrophic interactions among different species of microbes, in which interspecies electron transfer (IET) via diffusive carriers (e.g. hydrogen and formate) is known to be the bottleneck step. We report herein that the supplementation of soil microbes with (semi)conductive iron-oxide minerals creates unique interspecies interactions an

A cellulose-degrading defined mixed culture (designated SF356) consisting of five bacterial strains (Clostridium straminisolvens CSK1, Clostridium sp. strain FG4, Pseudoxanthomonas sp. strain M1-3, Brevibacillus sp. strain M1-5, and Bordetella sp. strain M1-6) exhibited both functional and structural stability; namely, no change in cellulose-degrading efficiency was observed, and all members stably coexisted through 20 subcultures. In order to investigate the mechanisms responsible for the obser

A stable cellulose-degrading microflora enriched from composting materials has been analyzed in our laboratory. Cellulose-degrading efficiency of an anaerobic cellulolytic isolate, Clostridium straminisolvens CSK1, was remarkably lower than that of the original microflora. We successfully constructed bacterial communities with effective cellulose degradation by mixing C. straminisolvens CSK1 with aerobic non-cellulolytic bacteria isolated from the original microflora. Comparison of the cellulose

Pure-culture studies have shown that dissimilatory metal-reducing bacteria are able to utilize iron-oxide nanoparticles as electron conduits for reducing distant terminal acceptors; however, the ecological relevance of such energy metabolism is poorly understood. Here, soil microbial communities were grown in electrochemical cells with acetate as the electron donor and electrodes (poised at 0.2 V versus Ag/AgCl) as the electron acceptors in the presence and absence of iron-oxide nanoparticles, a

Extracellular electron transfer (EET) is a microbial metabolism that enables efficient electron transfer between microbial cells and extracellular solid materials. Microorganisms harbouring EET abilities have received considerable attention for their various biotechnological applications, including bioleaching and bioelectrochemical systems. On the other hand, recent research revealed that microbial EET potentially induces corrosion of iron structures. It has been well known that corrosion of ir

Corrosion of iron occurring under anoxic conditions, which is termed microbiologically influenced corrosion (MIC) or biocorrosion, is mostly caused by microbial activities. Microbial activity that enhances corrosion via uptake of electrons from metallic iron [Fe(0)] has been regarded as one of the major causative factors. In addition to sulfate-reducing bacteria and methanogenic archaea in marine environments, acetogenic bacteria in freshwater environments have recently been suggested to cause M

Extracellular electron transfer (EET) is a type of microbial respiration that enables electron transfer between microbial cells and extracellular solid materials, including naturally-occurring metal compounds and artificial electrodes. Microorganisms harboring EET abilities have received considerable attention for their various biotechnological applications, in addition to their contribution to global energy and material cycles. In this review, current knowledge on microbial EET and its applicat

A novel anaerobic, thermophilic and cellulolytic bacterium (strain CSK1(T)) was isolated from a cellulose-degrading bacterial community. On the basis of 16S rRNA gene sequence similarity, strain CSK1(T) was mapped to cluster III of the genus Clostridium. Strain CSK1(T) is closely related to Clostridium thermocellum (96.2 %) and Clostridium aldrichii (95.1 %). Strain CSK1(T) is a non-motile, spore-forming, straight or slightly curved rod. The optimum temperature and initial pH for its growth and

Recently, we developed a simple method for detecting a secretory signal sequence encoded by a cDNA fragment. In this study, we used this method to select cDNA clones encoding secretory proteins from a human full-length cDNA library. Full-sequencing analysis of the candidate clones revealed that one clone encoded a novel TGF-beta superfamily protein. The clone encodes a protein of 308 amino acids of which the C-terminal region shows a characteristic feature of TGF-beta superfamily proteins: seven

Some bacteria utilize (semi)conductive iron-oxide minerals as conduits for extracellular electron transfer (EET) to distant, insoluble electron acceptors. A previous study demonstrated that microbe/mineral conductive networks are constructed in soil ecosystems, in which Geobacter spp. share dominant populations. In order to examine how (semi)conductive iron-oxide minerals affect EET paths of Geobacter spp., the present study grew five representative Geobacter strains on electrodes as the sole el

In natural and engineered ecosystems, diverse species of microbes coexist and interact, resulting in the emergence of community functions. Since microbes have evolved under such circumstances, it is reasonable to deduce that they have acquired strategies for specific interspecies interactions in complex microbial communities. In this review, we discuss the ecological and evolutionary interactions in syntrophic methanogenic consortia comprised of organic acid-oxidizing bacteria and methanogenic a

Most microorganisms living in the environment have yet to be cultured, owing at least in part to their slow and poor propagation properties and susceptibility to oxidative stress. Our previous studies demonstrated that a simple modification in the preparation of agar media, i.e., autoclaving the phosphate and agar separately (termed "PS" medium), can greatly improve the culturability of microorganisms by mitigating oxidative stress compared with the use of "PT" medium (autoclaving the phosphate

Anaerobic degradation of lignin-derived aromatics is an important metabolism for carbon and nutrient cycles in soil environments. Although there are some studies on degradation of lignin-derived aromatics by nitrate- and sulfate-reducing bacteria, knowledge on their degradation under methanogenic conditions are quite limited. In this study, methanogenic microbial communities were enriched from rice paddy field soil with lignin-derived methoxylated monoaromatics (vanillate and syringate) and thei