BACKGROUND: Bio‐hydrogen production from organic residues is an attractive process that combines energy generation with waste treatment. This work describes hydrogen production from molasses and cheese whey by biofilm and suspended‐cells of four hyperthermophilic Thermotoga spp. For the best performing strain, a preliminary process optimization was performed.RESULTS: In experiments with glucose‐fed T. neapolitana, HEPES was the best‐performing buffer, whereas the highest H2 rate was obtained with the biofilm support exposing the highest specific surface. All the Thermotoga strains tested (T. neapolitana, T. maritima, T. naphtophila, T. petrophila) were able to produce H2 from glucose, molasses and cheese whey under both suspended‐ and attached‐cell conditions. T. neapolitana was the best H2 producer with all three substrates. The best H2 production rate was higher on molasses (1.7 mmolH2 L$_{\rm {medium}}^{-1}$ h−1) than on cheese whey (0.94 mmolH2 L$_{\rm {medium}}^{-1}$ h−1), whereas the highest H2/substrate yields were similar for the two substrates (2.95 molH2 mol$_{\rm {monosaccharide consumed}}^{-1}$ on molasses and 2.50 molH2 mol$_{\rm {monosaccharide consumed}}^{-1}$ on cheese whey). With both wastes, the progressive growth medium simplification allowed a drastic reduction of medium cost, without significant losses of process performance.CONCLUSION: Both molasses and cheese whey are suitable substrates for H2 production by suspended‐ and attached‐cells of Thermotoga species. Copyright © 2012 Society of Chemical Industry

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d-Tagatose is a ketohexose, which presents unique properties as a low-calorie functional sweetener possessing a sweet flavor profile similar to d-sucrose and having no aftertaste. Considered a generally recognized as safe (GRAS) substance by FAO/ WHO, d-tagatose can be used as an intermediate for the synthesis of other optically active compounds as well as an additive in detergent, cosmetic, and pharmaceutical formulations. This study reports important features for l-arabinose isomerase (EC 5.3.1.4) (L-AI) use in industry. We describe arabinose (araA) gene virulence analysis, gene isolation, sequencing, cloning, and heterologous overexpression of L-AI from the food-grade GRAS bacterium Enterococcus faecium DBFIQ E36 in Escherichia coli and assess biochemical properties of this recombinant enzyme. Recombinant L-AI (rL-AI) was one-step purified to homogeneity by Ni 2+ -agarose resin affinity chromatography and biochemical characterization revealed low identity with both thermophilic and mesophilic L-AIs but high degree of conservation in residues involved in substrate recognition. Optimal conditions for rL-AI activity were 50 °C, pH 5.5, and 0.3 mM Mn 2+ , exhibiting a low cofactor concentration requirement and an acidic optimum pH. Half-life at 45 °C and 50 °C were 1427 h and 11 h, respectively, and 21.5 h and 39.5 h at pH 4.5 and 5.6, respectively, showing the high stability of the enzyme in the presence of a metallic cofactor. Bioconversion yield for d-tagatose biosynthesis was 45% at 50 °C after 48 h. These properties highlight the technological potential of E. faecium rL-AI as biocatalyst for d-tagatose production. Keywords l-Arabinose isomerase • d-Tagatose • Enterococcus faecium • Virulence gene analysis • d-Galactose

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