Mucus-degrading Bacteroides link carbapenems to aggravated graft-versus-host disease.

The intestinal microbiota is an important modulator of graft-versus-host disease (GVHD), which often complicates allogeneic hematopoietic stem cell transplantation (allo-HSCT). Broad-spectrum antibiotics such as carbapenems increase the risk for intestinal GVHD, but mechanisms are not well understood. In this study, we found that treatment with meropenem, a commonly used carbapenem, aggravates colonic GVHD in mice via the expansion of Bacteroides thetaiotaomicron (BT). BT has a broad ability to degrade dietary polysaccharides and host mucin glycans. BT in meropenem-treated allogeneic mice demonstrated upregulated expression of enzymes involved in the degradation of mucin glycans. These mice also had thinning of the colonic mucus layer and decreased levels of xylose in colonic luminal contents. Interestingly, oral xylose supplementation significantly prevented thinning of the colonic mucus layer in meropenem-treated mice. Specific nutritional supplementation strategies, including xylose supplementation, may combat antibiotic-mediated microbiome injury to reduce the risk for intestinal GVHD in allo-HSCT patients.

A versatile in situ cofactor enhancing system for meeting cellular demands for engineered metabolic pathways.

Cofactor imbalance obstructs the productivities of metabolically engineered cells. Herein, we employed a minimally perturbing system, xylose reductase and lactose (XR/lactose), to increase the levels of a pool of sugar phosphates which are connected to the biosynthesis of NAD(P)H, FAD, FMN, and ATP in Escherichia coli. The XR/lactose system could increase the amounts of the precursors of these cofactors and was tested with three different metabolically engineered cell systems (fatty alcohol biosynthesis, bioluminescence light generation, and alkane biosynthesis) with different cofactor demands. Productivities of these cells were increased 2-4-fold by the XR/lactose system. Untargeted metabolomic analysis revealed different metabolite patterns among these cells, demonstrating that only metabolites involved in relevant cofactor biosynthesis were altered. The results were also confirmed by transcriptomic analysis. Another sugar reducing system (glucose dehydrogenase) could also be used to increase fatty alcohol production but resulted in less yield enhancement than XR. This work demonstrates that the approach of increasing cellular sugar phosphates can be a generic tool to increase in vivo cofactor generation upon cellular demand for synthetic biology.

EvdS6 is a bifunctional decarboxylase from the everninomicin gene cluster.

The everninomicins are bacterially produced antibiotic octasaccharides characterized by the presence of two interglycosidic spirocyclic ortho-δ-lactone (orthoester) moieties. The terminating G- and H-ring sugars, L-lyxose and C-4 branched sugar ß-D-eurekanate, are proposed to be biosynthetically derived from nucleotide diphosphate pentose sugar pyranosides; however, the identity of these precursors and their biosynthetic origin remain to be determined. Herein we identify a new glucuronic acid decarboxylase from Micromonospora belonging to the superfamily of short-chain dehydrogenase/reductase enzymes, EvdS6. Biochemical characterization demonstrated that EvdS6 is an NAD+-dependent bifunctional enzyme that produces a mixture of two products, differing in the sugar C-4 oxidation state. This product distribution is atypical for glucuronic acid decarboxylating enzymes, most of which favor production of the reduced sugar and a minority of which favor release of the oxidized product. Spectroscopic and stereochemical analysis of reaction products revealed that the first product released is the oxidatively produced 4-keto-D-xylose and the second product is the reduced D-xylose. X-ray crystallographic analysis of EvdS6 at 1.51 Å resolution with bound co-factor and TDP demonstrated that the overall geometry of the EvdS6 active site is conserved with other SDR enzymes and enabled studies probing structural determinants for the reductive half of the net neutral catalytic cycle. Critical active site threonine and aspartate residues were unambiguously identified as essential in the reductive step of the reaction and resulted in enzyme variants producing almost exclusively the keto sugar. This work defines potential precursors for the G-ring L-lyxose and resolves likely origins of the H-ring ß-D-eurekanate sugar precursor.

Codon Optimization Improves the Prediction of Xylose Metabolism from Gene Content in Budding Yeasts.

Xylose is the second most abundant monomeric sugar in plant biomass. Consequently, xylose catabolism is an ecologically important trait for saprotrophic organisms, as well as a fundamentally important trait for industries that hope to convert plant mass to renewable fuels and other bioproducts using microbial metabolism. Although common across fungi, xylose catabolism is rare within Saccharomycotina, the subphylum that contains most industrially relevant fermentative yeast species. The genomes of several yeasts unable to consume xylose have been previously reported to contain the full set of genes in the XYL pathway, suggesting the absence of a gene-trait correlation for xylose metabolism. Here, we measured growth on xylose and systematically identified XYL pathway orthologs across the genomes of 332 budding yeast species. Although the XYL pathway coevolved with xylose metabolism, we found that pathway presence only predicted xylose catabolism about half of the time, demonstrating that a complete XYL pathway is necessary, but not sufficient, for xylose catabolism. We also found that XYL1 copy number was positively correlated, after phylogenetic correction, with xylose utilization. We then quantified codon usage bias of XYL genes and found that XYL3 codon optimization was significantly higher, after phylogenetic correction, in species able to consume xylose. Finally, we showed that codon optimization of XYL2 was positively correlated, after phylogenetic correction, with growth rates in xylose medium. We conclude that gene content alone is a weak predictor of xylose metabolism and that using codon optimization enhances the prediction of xylose metabolism from yeast genome sequence data.

Host cell wall composition and localized microenvironment implicated in resistance to basal stem degradation by lettuce drop (Sclerotinia minor).

BACKGROUND: Sclerotinia spp. are generalist fungal pathogens, infecting over 700 plant hosts worldwide, including major crops. While host resistance is the most sustainable and cost-effective method for disease management, complete resistance to Sclerotinia diseases is rare. We recently identified soft basal stem as a potential susceptibility factor to Sclerotinia minor infection in lettuce (Lactuca sativa) under greenhouse conditions. RESULTS: Analysis of stem and root cell wall composition in five L. sativa and one L. serriola accessions with varying growth habits and S. minor resistance levels revealed strong association between hemicellulose constituents, lignin polymers, disease phenotypes, and basal stem mechanical strength. Accessions resistant to basal stem degradation consistently exhibited higher levels of syringyl, guaiacyl, and xylose, but lower levels of fucose in stems. These findings suggest that stem cell wall polymers recalcitrant to breakdown by lignocellulolytic enzymes may contribute to stem strength-mediated resistance against S. minor. CONCLUSIONS: The lignin content, particularly guaiacyl and syringyl, along with xylose could potentially serve as biomarkers for identifying more resistant lettuce accessions and breeding lines. Basal stem degradation by S. minor was influenced by localized microenvironment conditions around the stem base of the plants.

Spathaspora marinasilvae sp. nov., a xylose-fermenting yeast isolated from galleries of passalid beetles and rotting wood in the Amazonian rainforest biome.

Four yeast isolates were obtained from rotting wood and galleries of passalid beetles collected in different sites of the Brazilian Amazonian Rainforest in Brazil. This yeast produces unconjugated allantoid asci each with a single elongated ascospore with curved ends. Sequence analysis of the internal transcribed spacer-5.8 S region and the D1/D2 domains of the large subunit ribosomal RNA (rRNA) gene showed that the isolates represent a novel species of the genus Spathaspora. The novel species is phylogenetically related to a subclade containing Spathaspora arborariae and Spathaspora suhii. Phylogenomic analysis based on 1884 single-copy orthologs for a set of Spathaspora species whose whole genome sequences are available confirmed that the novel species represented by strain UFMG-CM-Y285 is phylogenetically close to Sp. arborariae. The name Spathaspora marinasilvae sp. nov. is proposed to accommodate the novel species. The holotype of Sp. marinasilvae is CBS 13467 T (MycoBank 852799). The novel species was able to accumulate xylitol and produce ethanol from d-xylose, a trait of biotechnological interest common to several species of the genus Spathaspora.

Engineering of Saccharomyces cerevisiae for enhanced metabolic robustness and L-lactic acid production from lignocellulosic biomass.

Metabolic engineering for high productivity and increased robustness is needed to enable sustainable biomanufacturing of lactic acid from lignocellulosic biomass. Lactic acid is an important commodity chemical used for instance as a monomer for production of polylactic acid, a biodegradable polymer. Here, rational and model-based optimization was used to engineer a diploid, xylose fermenting Saccharomyces cerevisiae strain to produce L-lactic acid. The metabolic flux was steered towards lactic acid through the introduction of multiple lactate dehydrogenase encoding genes while deleting ERF2, GPD1, and CYB2. A production of 93 g/L of lactic acid with a yield of 0.84 g/g was achieved using xylose as the carbon source. To increase xylose utilization and reduce acetic acid synthesis, PHO13 and ALD6 were also deleted from the strain. Finally, CDC19 encoding a pyruvate kinase was overexpressed, resulting in a yield of 0.75 g lactic acid/g sugars consumed, when the substrate used was a synthetic lignocellulosic hydrolysate medium, containing hexoses, pentoses and inhibitors such as acetate and furfural. Notably, modeling also provided leads for understanding the influence of oxygen in lactic acid production. High lactic acid production from xylose, at oxygen-limitation could be explained by a reduced flux through the oxidative phosphorylation pathway. On the contrast, higher oxygen levels were beneficial for lactic acid production with the synthetic hydrolysate medium, likely as higher ATP concentrations are needed for tolerating the inhibitors therein. The work highlights the potential of S. cerevisiae for industrial production of lactic acid from lignocellulosic biomass.

Riboflavin overproduction on lignocellulose hydrolysate by the engineered yeast Candida famata.

Lignocellulose (dry plant biomass) is an abundant cheap inedible residue of agriculture and wood industry with great potential as a feedstock for biotechnological processes. Lignocellulosic substrates can serve as valuable resources in fermentation processes, allowing the production of a wide array of chemicals, fuels, and food additives. The main obstacle for cost-effective conversion of lignocellulosic hydrolysates to target products is poor metabolism of the major pentoses, xylose and L-arabinose, which are the second and third most abundant sugars of lignocellulose after glucose. We study the oversynthesis of riboflavin in the flavinogenic yeast Candida famata and found that all major lignocellulosic sugars, including xylose and L-arabinose, support robust growth and riboflavin synthesis in the available strains of C. famata. To further increase riboflavin production from xylose and lignocellulose hydrolysate, genes XYL1 and XYL2 coding for xylose reductase and xylitol dehydrogenase were overexpressed. The resulting strains exhibited increased riboflavin production in both shake flasks and bioreactors using diluted hydrolysate, reaching 1.5 g L-1.

Enhancing xylose-fermentation capacity of engineered Saccharomyces cerevisiae by multistep evolutionary engineering in inhibitor-rich lignocellulose hydrolysate.

Major progress in developing Saccharomyces cerevisiae strains that utilize the pentose sugar xylose has been achieved. However, the high inhibitor content of lignocellulose hydrolysates still hinders efficient xylose fermentation, which remains a major obstacle for commercially viable second-generation bioethanol production. Further improvement of xylose utilization in inhibitor-rich lignocellulose hydrolysates remains highly challenging. In this work, we have developed a robust industrial S. cerevisiae strain able to efficiently ferment xylose in concentrated undetoxified lignocellulose hydrolysates. This was accomplished with novel multistep evolutionary engineering. First, a tetraploid strain was generated and evolved in xylose-enriched pretreated spruce biomass. The best evolved strain was sporulated to obtain a genetically diverse diploid population. The diploid strains were then screened in industrially relevant conditions. The best performing strain, MDS130, showed superior fermentation performance in three different lignocellulose hydrolysates. In concentrated corncob hydrolysate, with initial cell density of 1 g DW/l, at 35°C, MDS130 completely coconsumed glucose and xylose, producing ± 7% v/v ethanol with a yield of 91% of the maximum theoretical value and an overall productivity of 1.22 g/l/h. MDS130 has been developed from previous industrial yeast strains without applying external mutagenesis, minimizing the risk of negative side-effects on other commercially important properties and maximizing its potential for industrial application.

Maltose accumulation-induced cell death in Saccharomyces cerevisiae.

Pretreatment of lignocellulose yields a complex sugar mixture that potentially can be converted into bioethanol and other chemicals by engineered yeast. One approach to overcome competition between sugars for uptake and metabolism is the use of a consortium of specialist strains capable of efficient conversion of single sugars. Here, we show that maltose inhibits cell growth of a xylose-fermenting specialist strain IMX730.1 that is unable to utilize glucose because of the deletion of all hexokinase genes. The growth inhibition cannot be attributed to a competition between maltose and xylose for uptake. The inhibition is enhanced in a strain lacking maltase enzymes (dMalX2) and completely eliminated when all maltose transporters are deleted. High-level accumulation of maltose in the dMalX2 strain is accompanied by a hypotonic-like transcriptional response, while cells are rescued from maltose-induced cell death by the inclusion of an extracellular osmolyte such as sorbitol. These data suggest that maltose-induced cell death is due to high levels of maltose uptake causing hypotonic-like stress conditions and can be prevented through engineering of the maltose transporters. Transporter engineering should be included in the development of stable microbial consortia for the efficient conversion of lignocellulosic feedstocks.

Establishment of low-cost production platforms of polyhydroxyalkanoate bioplastics from Halomonas cupida J9.

Microbial production of polyhydroxyalkanoate (PHA) is greatly restricted by high production cost arising from high-temperature sterilization and expensive carbon sources. In this study, a low-cost PHA production platform was established from Halomonas cupida J9. First, a marker-less genome-editing system was developed in H. cupida J9. Subsequently, H. cupida J9 was engineered to efficiently utilize xylose for PHA biosynthesis by introducing a new xylose metabolism module and blocking xylonate production. The engineered strain J9UΔxylD-P8xylA has the highest PHA yield (2.81 g/L) obtained by Halomonas with xylose as the sole carbon source so far. This is the first report on the production of short- and medium-chain-length (SCL-co-MCL) PHA from xylose by Halomonas. Interestingly, J9UΔxylD-P8xylA was capable of efficiently utilizing glucose and xylose as co-carbon sources for PHA production. Furthermore, fed-batch fermentation of J9UΔxylD-P8xylA coupled to a glucose/xylose co-feeding strategy reached up to 12.57 g/L PHA in a 5-L bioreactor under open and unsterile condition. Utilization of corn straw hydrolysate as the carbon source by J9UΔxylD-P8xylA reached 7.0 g/L cell dry weight (CDW) and 2.45 g/L PHA in an open fermentation. In summary, unsterile production in combination with inexpensive feedstock highlights the potential of the engineered strain for the low-cost production of PHA from lignocellulose-rich agriculture waste.

Experimental evolution reveals an effective avenue for d-lactic acid production from glucose-xylose mixtures via enhanced Glk activity and a cAMP-independent CRP mutation.

d-Lactic acid holds significant industrial importance due to its versatility and serves as a crucial component in the synthesis of environmentally friendly and biodegradable thermal-resistant poly-lactic acid. This polymer exhibits promising potential as a substitute for nonbiodegradable, petroleum-based plastics. The production of d-lactic acid from lignocellulosic biomass, a type of biorenewable and nonfood resources, can lower costs and improve product competitiveness. Glucose and xylose are the most abundant sugar monomers in lignocellulosic biomass materials. Despite Escherichia coli possessing native xylose catabolic pathways and transport, their ability to effectively utilize xylose is often hindered in the presence of glucose. Here, the E. coli strain Rec1.0, previously engineered to overcome carbon catabolite repression, was selected as the initial strain for reengineering to produce d-lactic acid. An adaptive evolution approach was employed to achieve highly efficient fermentation of glucose-xylose mixtures. The resulting strain, QJL010, could produce d-lactic acid of 87.5 g/L with a carbon yield of 0.99 mol/mol. Notably, the consumption rates of glucose and xylose reached 0.75 and 0.82 g/gDCW/h, respectively. Further analysis revealed that increased Glk activity, resulting from glk mutations (A142V and R188H), along with their upregulated expression, contributed to an elevated glucose consumption rate. Additionally, a CRP G141D mutation, cAMP-independent, stimulated the expression of the xylR, xylE, and galABC* genes, resulting in an accelerated xylose consumption rate. These findings provide valuable support for the utilization of E. coli platform strains in the production of value-added chemicals from lignocellulosic biomass.

Spathaspora quercus f.a., sp. nov., a novel yeast isolated from rotting wood and a lichen sample in Kyushu region, Japan.

Four novel d-xylose assimilation yeast strains were isolated from rotting wood and a lichen sample collected in the Kyushu region of Japan. Species identifications were performed by analysing the internal transcribed spacer 5.8S region sequences and the D1/D2 variable domain of the large subunit rRNA gene. Phylogenetic analysis suggested that these isolates are closely related to Spathaspora species isolated in China, such as S. jiuxiensis and S. parajiuxiensis. These isolates also showed sequence similarity to deposited sequences labelled as Schwanniomyces. They did not produce asci and ascospores under any of the test conditions. Based on phylogenetic analysis and phenotypic differences, Spathaspora quercus f.a., sp. nov. is proposed to accommodate these isolates. The holotype of Spathaspora quercus f.a., sp. nov. is NBRC 116146T (CBS18366). This species is able to ferment d-xylose, and a d-xylose fermentation test revealed that this species produces a considerable amount of xylitol.

Efficient production of 1,2,4-butanetriol from corn cob hydrolysate by metabolically engineered Escherichia coli.

Corn cob is a major waste mass-produced in corn agriculture. Corn cob hydrolysate containing xylose, arabinose, and glucose is the hydrolysis product of corn cob. Herein, a recombinant Escherichia coli strain BT-10 was constructed to transform corn cob hydrolysate into 1,2,4-butanetriol, a platform substance with diversified applications. To eliminate catabolite repression and enhance NADPH supply for alcohol dehydrogenase YqhD catalyzed 1,2,4-butanetriol generation, ptsG encoding glucose transporter EIICBGlc and pgi encoding phosphoglucose isomerase were deleted. With four heterologous enzymes including xylose dehydrogenase, xylonolactonase, xylonate dehydratase, α-ketoacid decarboxylase and endogenous YqhD, E. coli BT-10 can produce 36.63 g/L 1,2,4-butanetriol with a productivity of 1.14 g/[L·h] using xylose as substrate. When corn cob hydrolysate was used as the substrate, 43.4 g/L 1,2,4-butanetriol was generated with a productivity of 1.09 g/[L·h] and a yield of 0.9 mol/mol. With its desirable characteristics, E. coli BT-10 is a promising strain for commercial 1,2,4-butanetriol production.

The metal cofactor: stationary or mobile?

Metal cofactors are essential for catalysis and enable countless conversions in nature. Interestingly, the metal cofactor is not always static but mobile with movements of more than 4 Å. These movements of the metal can have different functions. In the case of the xylose isomerase and medium-chain dehydrogenases, it clearly serves a catalytic purpose. The metal cofactor moves during substrate activation and even during the catalytic turnover. On the other hand, in class II aldolases, the enzymes display resting states and active states depending on the movement of the catalytic metal cofactor. This movement is caused by substrate docking, causing the metal cofactor to take the position essential for catalysis. As these metal movements are found in structurally and mechanistically unrelated enzymes, it has to be expected that this metal movement is more common than currently perceived. KEY POINTS: • Metal ions are essential cofactors that can move during catalysis. • In class II aldolases, the metal cofactors can reside in a resting state and an active state. • In MDR, the movement of the metal cofactor is essential for substrate docking.

Construction and characterization of a promoter library with varying strengths to enhance acetoin production from xylose in Serratia marcescens.

Serratia marcescens is utilized as a significant enterobacteria in the production of various high-value secondary metabolites. Acetoin serves as a crucial foundational compound of development and finds application in a broad range of fields. Furthermore, S. marcescens HBQA-7 is capable of utilizing xylose as its exclusive carbon source for acetoin production. The objective of this study was to utilize a constitutive promoter screening strategy to enhance both xylose utilization and acetoin production in S. marcescens HBQA-7. By utilizing RNA-seq, we identified the endogenous constitutive promoter P6 that is the most robust, which facilitated the overexpression of the sugar transporter protein GlfL445I, α-acetyl lactate synthase, and α-acetyl lactate decarboxylase, respectively. The resultant recombinant strains exhibited enhanced xylose utilization rates and acetoin yields. Subsequently, a recombinant plasmid, denoted as pBBR1MCS-P6-glfL445IalsSalsD, was constructed, simultaneously expressing the aforementioned three genes. The resulting recombinant strain, designated as S3, demonstrated a 1.89-fold boost in xylose consumption rate compared with the original strain during shake flask fermentation. resulting in the accumulation of 7.14 g/L acetoin in the final fermentation medium. Subsequently, in a 5 L fermenter setup, the acetoin yield reached 48.75 g/L, corresponding to a xylose-to-acetoin conversion yield of 0.375 g/g.

Deficiency of ß-xylosidase activity in Aspergillus luchuensis mut. kawachii IFO 4308.

In this study, we investigated a deleterious mutation in the ß-xylosidase gene, xylA (AkxylA), in Aspergillus luchuensis mut. kawachii IFO 4308 by constructing an AkxylA disruptant and complementation strains of AkxylA and xylA derived from A. luchuensis RIB2604 (AlxylA), which does not harbor the mutation in xylA. Only the AlxylA complementation strain exhibited significantly higher growth and substantial ß-xylosidase activity in medium containing xylan, accompanied by an increase in XylA expression. This resulted in lower xylobiose and higher xylose concentrations in the mash of barley shochu. These findings suggest that the mutation in xylA affects xylose levels during the fermentation process. Because the mutation in xylA was identified not only in the genome of strain IFO 4308 but also the genomes of other industrial strains of A. luchuensis and A. luchuensis mut. kawachii, these findings enhance our understanding of the genetic factors that affect the fermentation characteristics.

Exploring xylose metabolism in non-conventional yeasts: kinetic characterization and product accumulation under different aeration conditions.

d-Xylose is a metabolizable carbon source for several non-Saccharomyces species, but not for native strains of S. cerevisiae. For the potential application of xylose-assimilating yeasts in biotechnological processes, a deeper understanding of pentose catabolism is needed. This work aimed to investigate the traits behind xylose utilization in diverse yeast species. The performance of 9 selected xylose-metabolizing yeast strains was evaluated and compared across 3 oxygenation conditions. Oxygenation diversely impacted growth, xylose consumption, and product accumulation. Xylose utilization by ethanol-producing species such as Spathaspora passalidarum and Scheffersomyces stipitis was less affected by oxygen restriction compared with other xylitol-accumulating species such as Meyerozyma guilliermondii, Naganishia liquefaciens, and Yamadazyma sp., for which increased aeration stimulated xylose assimilation considerably. Spathaspora passalidarum exhibited superior conversion of xylose to ethanol and showed the fastest growth and xylose consumption in all 3 conditions. By performing assays under identical conditions for all selected yeasts, we minimize bias in comparisons, providing valuable insight into xylose metabolism and facilitating the development of robust bioprocesses. ONE-SENTENCE SUMMARY: This work aims to expand the knowledge of xylose utilization in different yeast species, with a focus on how oxygenation impacts xylose assimilation.

Molecular Modification Enhances Xylose Uptake by the Sugar Transporter KM_SUT5 of Kluyveromyces marxianus.

This research cloned and expressed the sugar transporter gene KM_SUT5 from Kluyveromyces marxianus GX-UN120, which displayed remarkable sugar transportation capabilities, including pentose sugars. To investigate the impact of point mutations on xylose transport capacity, we selected four sites, predicted the suitable amino acid sites by molecular docking, and altered their codons to construct the corresponding mutants, Q74D, Y195K, S460H, and Q464F, respectively. Furthermore, we conducted site-directed truncation on six sites of KM_SUT5p. The molecular modification resulted in significant changes in mutant growth and the D-xylose transport rate. Specifically, the S460H mutant exhibited a higher growth rate and demonstrated excellent performance across 20 g L-1 xylose, achieving the highest xylose accumulation under xylose conditions (49.94 µmol h-1 gDCW-1, DCW mean dry cell weight). Notably, mutant delA554-, in which the transporter protein SUT5 is truncated at position delA554-, significantly increased growth rates in both D-xylose and D-glucose substrates. These findings offer valuable insights into potential modifications of other sugar transporters and contribute to a deeper understanding of the C-terminal function of sugar transporters.

Effect of pH on metabolic pathway shift in fermentation and electro-fermentation of xylose by Clostridium autoethanogenum.

Clostridium autoethanogenum can to convert waste gases (CO2, CO, H2) and xylose from hydrolyzed biomass into acetate, lactate, formate, ethanol and 2,3-butanediol, being a candidate for the transformation of waste streams of lignocellulosic biorefineries. Electro-fermentation (EF) modify the pattern of traditional fermentations resulting in improved product yields as has been shown when using Clostridium strains. The aim of this work was to evaluate the influence of pH on microbial growth and product distribution during fermentation and EF of xylose by C. autoethanogenum DSM10061. Fermentation and EF were carried out in a H-type reactor at three controlled pH: 5.0, 5.5 and 5.8, and at a fixed potential of -600 mV (versus Ag/AgCl) in the EF. The experiments showed that maximum biomass concentration increased as the pH increased in fermentation and EF. In accordance with maximum biomass reached, the highest substrate conversion was observed at pH 5.8 for both systems, with 76.80 % in fermentation and 96.18 % in EF. Moreover, the highest concentrations of acetic acid (1.41 ± 0.07 g L-1) and ethanol (1.45 ± 0.15 g L-1) were obtained at the end of cultures in the EF at pH 5.8. The production of lactic and formic acid decreased by the application of the external potential regardless of the pH value, reaching the lowest productivity at pH 5.8. In contrast, the specific productivity of acetic acid and ethanol was lower in both fermentation and EF at the lowest pH. Furthermore, the presence of 0.06 g L-1 of 2,3-butanediol was only detected in EF at pH 5.8. The results revealed that EF modulated microbial metabolism, which can be explained by a possible increased generation of NADP+/NADPH cofactors, which would redirect the metabolic pathway to more reduced products.