タンザニア ホクトウブ サン Rice yellow mottle virus ノ カイセキ

アフリカにおいて重要な穀物のひとつであるイネ(Oryza sativa L.)は,Rice yellow mottle virusによる重大な被害を受けており,タンザニアにも広がっている。水稲栽培の最も進んだ地域の一つであるローワーモシ灌漑地区を含む北東部で,ウイルス病様病徴の認められる灌漑水田において検体の採集を行った。採集した試料は,電子顕微鏡を用いたウイルス粒子の観察,DAS-ELISA法,PCR法による検出を行ったところ,RYMVの感染が確認された。3つの分離株Tz-12-20,Tz12-22,Tz10-36の PCR産物については,遺伝子解析を行い系統と血清型の判別を行った。その結果,S4型(Pinel et al., 2009)分離株であることが示され,また,系統解析から,ビクトリア湖周辺分離株であるS4-lvやS4-lm,S4-mgとは異なる単一のクラスターを形成し,新しいグループ(S4-mk)であると考えられた。さらに系統樹から,S4-mk分離株はケニアの西南地域からタンザニアの北東部において広がっている分離株であることを示した。系統樹において単一のクラスターを形成した一方,S4-mk分離株と他のS4型分離株(S4-lv,S4-lm,S4-mg)間のアミノ酸配列で,96%以上の高い相同性を示した。また,アミノ酸配列から血清型の判別が可能(Fargette et al., 2002)であることから,タンザニア産RYMVでこの手法を用いて血清型を検討したところ,類別可能な5種類の血清型のうち,Ser4に分類された。Rice (Oryza sativa L.) is an important cereal-grain in some African countries and known to be attacked by Rice yellow mottle virus (RYMV). Rice plants with virus like symptoms were collected from lower Moshi and other areas in the north-eastern region of Tanzania. RYMV was detected by DAS-ELISA, RT-PCR and/or electron microscopy from almost all collected samples. Some RYMV isolates were sequenced and identified as strain S4. Also, three of them, Tz-12-20, Tz-12-22 and Tz-10-36, were clustered as a new group named S4-mk (Mt. Kilimanjaro). Cluster of S4-mk formed a monophyletic group of isolates in strain S4-lv reported from the Tanzanian side of the Lake Victoria. However, S4-mk and S4-lv lineages are separated from each other and S4-mk has the characteristic three amino acid substitutions. The isolates of S4-mk were also closely related to that of strain S4-mg. Amino acid sequences of the coat protein of the isolates in group S4-mk showed over 96% identity with those in other strain S4 varieties, S4-lv, S4-mg and S4-lm. The phylogenetic tree also indicated the possibility of strain S4-mk to have dispersed from south-western Kenya to north eastern Tanzania. As for the serotyping, followed by Fargette et al. (2002), these three isolates in S4-mk were classified into serotype 4

Modes of transmission and stability of Rice yellow mottle virus

Rice yellow mottle virus (RYMV) is the most important rice virus in Africa. We examined RYMV transmission via soil and water contaminated with RYMV-infected rice plants and by serial cutting with RYMV-contaminated scissors. Transmission of RYMV via dried rice straw kept at 27°C was also examined. The results showed the virus could be transmitted via soil and water, and by scissors. Rice straw that was RYMV-infected was not infective if it was dried and was kept longer than 42 days. By insect transmission experiments and ELISA, long-horned grasshoppers (Conocephalus spp.) were found to be a possible vector of RYMV in Uganda

Modes of transmission and stability of Rice yellow mottle virus

Rice yellow mottle virus (RYMV) is the most important rice virus in Africa. We examined RYMV transmission via soil and water contaminated with RYMV-infected rice plants and by serial cutting with RYMV-contaminated scissors. Transmission of RYMV via dried rice straw kept at 27°C was also examined. The results showed the virus could be transmitted via soil and water, and by scissors. Rice straw that was RYMV-infected was not infective if it was dried and was kept longer than 42 days. By insect transmission experiments and ELISA, long-horned grasshoppers (Conocephalus spp.) were found to be a possible vector of RYMV in Uganda

A Novel D-Psicose 3-Epimerase from Halophilic, Anaerobic <i>Iocasia fonsfrigidae</i> and Its Application in Coconut Water

D-Psicose is a rare, low-calorie sugar that is found in limited quantities in national products. Recently, D-psicose has gained considerable attention due to its potential applications in the food, nutraceutical, and pharmaceutical industries. In this study, a novel D-psicose 3-epimerase (a group of ketose 3-epimerase) from an extremely halophilic, anaerobic bacterium, Iocasia fonsfrigidae strain SP3-1 (IfDPEase), was cloned, expressed in Escherichia coli, and characterized. Unlike other ketose 3-epimerase members, IfDPEase shows reversible epimerization only for D-fructose and D-psicose at the C-3 position but not for D-tagatose, most likely because the Gly218 and Cys6 at the substrate-binding subsites of IfDPEase, which are involved in interactions at the O-1 and O-6 positions of D-fructose, respectively, differ from those of other 3-epimerases. Under optimum conditions (5 µM IfDPEase, 1 mM Mn2+, 50 °C, and pH 7.5), 36.1% of D-psicose was obtained from 10 mg/mL D-fructose. The IfDPEase is highly active against D-fructose under NaCl concentrations of up to 500 mM, possibly due to the excessive negative charges of acidic amino acid residues (aspartic and glutamic acids), which are localized on the surface of the halophilic enzyme. These negative charges may protect the enzyme from Na+ ions from the environment and result in the lowest pI value compared to those of other 3-epimerase members. Moreover, without adjusting any ingredients, IfDPEase could improve coconut water quality by converting D-fructose into D-psicose with a yield of 26.8%. Therefore, IfDPEase is an attractive alternative to enhancing the quality of fructose-containing foods