Biochemical Properties of an Alkaline Xylanase From Bacillus Agaradhaerens C9 and Its Application in Producing Xylo-oligosaccharides With High Degree of Polymerization From Wheat Bran

A xylanase of Bacillus agaradhaerens C9 was heterologously expressed and was then investigated. The recombinant xylanase (rBaxyl11) showed maximal activity at 60°C and pH 8.0-9.0. Under optimal conditions, Kcat of rBaxyl11 for arabinoxylan and glucuronoxylan were 599 s-1 and 330 s-1, respectively. rBaxyl11 showed a good stability at pH ranging from 5.0 to 9.0, and retained 50% of activity after 6-hour incubation at 70°C. However, it was markedly inactivated by transition elements including Fe3+, Ni2+, Mn2+, Co2+, Zn2+, Cu2+ and Fe2+. rBaxyl11 generated xylo-oligosaccharides (XOS) whose degree of polymerization (DP) is greater than 3 when hydrolyzing arabinoxylan, while the DP of XOS ranged from 2 to 6 when acting on glucuronoxylan. Simultaneously producing xylanase and XOS by recombinant E. coli containing rBaxyl11 were then carried out. Results showed that the engineering E. coli generated xylanase and high-DP XOS extracellularly using wheat bran as substrate, and concentration of XOS reached 73 mg/g substrate after 12-hour fermentation. This study indicates the feasibility of producing XOS by a single-step fermentation approach with low cost using rBaxyl11.

Avaliação de bactérias endofíticas para o controle biológico da mancha foliar de Exserohilum turcicum em milho

RESUMO:A eficácia de nove isolados de bactérias endofíticas foi avaliada no biocontrole da mancha foliar de Exserohilum turcicum, pela microbiolização das sementes e da parte aérea do milho híbrido AS-1548 (72 e 24 horas antes e no mesmo dia da inocula ção do patógeno) em condições de casa de vegetação. Verificou-se que Bacillus subtilis 0G, Bacillus lentimorbus, Streptomyces sp. e Bacillus agaradhaerens se destacaram dos demais, quando aplicados na parte aérea, em todos os intervalos testados, com um controle na ordem de 42 a 61%. Quando as bactérias foram aplicadas nas sementes, Bacillus lentimorbus, Streptomyces sp., Ewingella ameri cana e Xanthomonas axonopodis foram os mais eficientes, com um controle entre 37 e 59%.

Texcoconibacillus texcoconensis gen. nov., sp. nov., alkalophilic and halotolerant bacteria isolated from soil of the former lake Texcoco (Mexico)

A novel Gram-positive, rod-shaped, spore-forming bacterium, designated 13CCT was isolated from soil of the former lake Texcoco. The strain was aerobic, catalase-positive and oxidase-negative. It grew at salinities of 0–26 % (w/v) NaCl with an optimum at 9–16 % (w/v) NaCl. The cells contain peptidoglycan type A1γ, A1γ′ with glycine instead of l-alanine and three variations of peptidoglycan type A4γ. The only quinone detected was MK-7. The major fatty acid was anteiso-C15 : 0. The polar lipids fraction consisted of diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine and three different phospholipids. The DNA G+C content was 37.5 mol%. Maximum-likelihood phylogenetic analysis based on 16S rRNA gene sequences revealed that strain 13CCT was closely related to members of the genus Bacillus and shared 92.35 % similarity with Bacillus agaradhaerens , 92.28 % with Bacillus neizhouensis and 92.21 % with Bacillus locisalis . It is proposed based on the phenotypic, genotypic and phylogenetic analyses that the novel isolate should be classified as a representative of a new genus and novel species, for which the name Texcoconibacillus texcoconensis gen. nov., sp. nov. is proposed. The type strain of Texcoconibacillus texcoconensis is 13CCT ( = JCM 17654T = DSM 24696T).