coli was due to the absence of essential genes
that are not linked to the cloned pqq operon, but are present in the P. ananatis chromosome, and whose products are responsible for enhancement of the PQQ pool in the latter microorganism. To distinguish between these possibilities, additional investigations are necessary. It should especially be mentioned, as well, that the homologous pqq operon from K. pneumoniae earlier cloned into the E. coli could lead to the production of visible amounts of PQQ only being amplified in multicopy-number recombinant plasmids (Meulenberg et al., 1990; Sode et al., 1996). It is possible that new E. coli strains that grow efficiently on glucose using the PQQ-mGDH-mediated pathway could be constructed in further studies. At minimum, these strains have to grow on glucose no worse than in the presence of PQQ added to the minimal cultivation medium. These Bafilomycin A1 concentration strains could have some CYC202 chemical structure advantages for applied biotechnology. It has been shown that strains with a PTS−/glucose+ phenotype could be useful for biotechnological applications in which large quantities of phosphoenolpyruvate have to be consumed for biosynthesis of the target product (Flores et al., 1996; Hernández-Montalvo et al., 2003). By decoupling glucose transport from phosphoenolpyruvate consumption,
the metabolic availability of this intermediate molecule is significantly increased when compared with a PTS+ strain. The production of other metabolites with phosphoenolpyruvate as a precursor should therefore be enhanced in a PTS−/glucose+ strain. This expectation has been confirmed using strains designed to direct carbon flow to the common aromatic pathway (Báez-Viveros et al., 2004). It goes without saying that the construction of such glucose-oxidizing strains for biotechnology is a complex task. At minimum, in addition to the optimization of P. ananatis pqq operon Sinomenine expression
in E. coli, it seems necessary to make the expression of some genes CRP-independent (gcd, gntKU, for example), to perhaps increase the expression level of the E. coli pgl gene (Thomason et al., 2004; Zimenkov et al., 2005) for the efficient conversion of glucono-1,5-lactone into gluconate. At the final stage, it seems necessary to balance the rate of gluconic acid production and its further utilization preventing the acidification of a growth media. We wish to thank Irina L. Tokmakova and Natalia V. Gorshkova for helpful discussion and participation in determining GDH activity and the accumulated extracellular PQQ level. Participation of a postgraduate student (I.G. Andreeva) in this work was supported in part by grant NK127P-4 from the Russian Federation Education Agency. Table S1. Primers used for PCR in this study. Fig. S1. Scheme for in vivo cloning of the Pantoea ananatis pqq operon. Please note: Wiley-Blackwell is not responsible for the content or functionality of any supporting materials supplied by the authors.