Bacillus polymyxa produces (R, R)-2,3-butanediol from a variety of carbohydrates. Other metabolites are also produced including acetoin, acetate, lactate, and ethanol. The excretion of each metabolite was found to depend on the relative availability of oxygen to the culture. When the relative oxygen uptake rate was high, enhanced yields of acetate and acetoin were noted. At an intermediate oxygen availability, the butanediol yield was maximal. When the availability of oxygen was more restricted, higher yields of lactate and ethanol occurred. The cells appeared to regulate themselves such that energy generation is optimal subject to the constraint that the cells do not produce more reducing equivalents than can be oxidized by the electron transport system. The dependence of each product yield on the relative oxygen availability was determined, and this knowledge was used to carry out a fed-batch fermentation that attained a final butanediol concentration of over 40 g/L in 50 h.

Formaldehyde biodegradation by a strain of Pseudomonas putida has been studied. The results indicate that this biodegradation is initiated by a dismutation reaction, yielding as products formic acid and methanol. The degradation of methanol and formic acid begins after exhaustion of formaldehyde in the medium, and presents a diauxic pattern: first formic acid is consumed followed by methanol. Moreover, cell viability, which is affected by the amount of added formaldehyde, has been determined.

Copyright and reuse:The Warwick Research Archive Portal (WRAP) makes this work by researchers of the University of Warwick available open access under the following conditions. Copyright © and all moral rights to the version of the paper presented here belong to the individual author(s) and/or other copyright owners. To the extent reasonable and practicable the material made available in WRAP has been checked for eligibility before being made available.Copies of full items can be used for personal research or study, educational, or not-for-profit purposes without prior permission or charge. Provided that the authors, title and full bibliographic details are credited, a hyperlink and/or URL is given for the original metadata page and the content is not changed in any way. A note on versions:The version presented here may differ from the published version or, version of record, if you wish to cite this item you are advised to consult the publisher's version. Please see the 'permanent WRAP URL' above for details on accessing the published version and note that access may require a subscription. AbstractThe over--expression of proteins in recombinant host cells often requires a significant amount of resources causing an increase in the metabolic load for the host. This results in a variety of physiological responses leading to altered growth parameters, including growth inhibition. Moreover, the expression of other plasmid--encoded genes such as antibiotic resistance genes or repressor proteins may also alter growth.In this work, we have developed a second generation of an Escherichia coli expression system with an antibiotic--free plasmid maintenance mechanism based on an auxotrophic marker (glyA). Metabolic burden related to plasmid maintenance and heterologous protein expression has been minimized by tuning the expression levels of a repressor protein (LacI) and glyA using a selected library of promoters and applying synthetic biology tools that allow the rapid construction of vectors. We apply our engineered antibiotic--free expression 2 system to the FucA over--production, showing increased production levels.Our results showed that the aforementioned approaches are of paramount importance in order to increment the protein production in terms of mass and activity. Acknowledgements:This work was supported by the project "Novel Alternatives for Microbial Production of Enzymes and Multienzymatic stereoselective Synthesis (EnzProSyn)". M. P. acknowledges the Universitat Autònoma de Barcelona for the pre--doctoral grant.

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