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The dehydrogenation of [1-13 C|-and |2-13 C]glucose into gluconate was monitored by NMR spectroscopy in living cell suspensions of two Rhizobium meliloti strains. The synthesis of gluconate was accompanied, in the cellular environment, by the formation of two gluconolactones, a y-lactone being detected in addition to the expected 5-lactone. These lactones -as well as the gluconate -could be further metabolized by the cells. The 5-lactone was utilized faster than the y-lactone. The presence -in significant amounts -and the relative stability of the lactones raise the question of their possible physiological significance.

The bioconversion of octanoic acid into 2-heptanone by spores of Penicillium roquefortii is performed using a fed-batch technique with pH control by addition of the liquid substrate itself. The early stage of this process takes place with a high bioconversion rate and high yield. These values then decrease as a result of germination and growth the biocatalyst. An optimization strategy for the process would thus be to improve the characteristics of this first period, i.e., increase its duration and the reaction rate. An increase in duration is evidenced in two cases: (I) under oxygen limitation: and (ii) when the spore content in the medium is less than 10(7) spores/mL. These conditions give insufficient overall bioconversion rates: better optimization should be achieved without oxygen limitation and with high spore content. Characterization of the first period by material and bioenergetic balances suggests that an increase in the ethanol content of the medium, which acts as an energy source and a permeabilizer, and the use of specific inhibitor of the Krebs cycle, may be a way to further improve the biocatalyst performance and stability.