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    Effect of Vitreoscilla hemoglobin on production of a chemotherapeutic enzyme, L-asparaginase, by Pseudomonas aeruginosa
    (2006) Geckil H.; Gencer S.; Ates B.; Ozer U.; Uckun M.; Yilmaz I.
    The production of L-asparaginase, an enzyme widely used in cancer chemotherapy, is mainly regulated by carbon catabolite repression and oxygen. This study was carried out to understand how different carbon sources and Vitreoscilla hemoglobin (VHb) affect the production of this enzyme in Pseudomonas aeruginosa and its VHb-expressing recombinant strain (PaJC). Both strains grown with various carbon sources showed a distinct profile of the enzyme activity. Compared to no carbohydrate supplemented medium, glucose caused a slight repression of L-asparaginase in P. aeruginosa, while it stimulated it in the PaJC strain. Glucose, regarded as one of the inhibitory sugars for the production L-asparaginase by other bacteria, was determined to be the favorite carbon source compared to lactose, glycerol and mannitol. Furthermore, contrary to common knowledge of oxygen repression of L-asparaginase in other bacteria, oxygen uptake provided by VHb was determined to even stimulate the L-asparaginase synthesis by P. aeruginosa. This study, for the first time, shows that in P. aeruginosa utilizing a recombinant oxygen uptake system, VHb, L-asparaginase synthesis is stimulated by glucose and other carbohydrate sources compared to the host strain. It is concluded that carbon catabolite and oxygen repression of L-asparaginase in fermentative bacteria is not the case for a respiratory non-fermentative bacterium like P. aeruginosa. © 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
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    Production of L-DOPA and dopamine in recombinant bacteria bearing the Vitreoscilla hemoglobin gene
    (2009) Kurt A.G.; Aytan E.; Ozer U.; Ates B.; Geckil H.
    Given the well-established beneficial effects of Vitreoscilla hemoglobin (VHb) on heterologous organisms, the potential of this protein for the production of L-DOPA and dopamine in two bacteria, Citrobacter freundii and Erwinia herbicola, was investigated. The constructed recombinants bearing the VHb gene (vgb+) had substantially higher levels of cytoplasmic L-DOPA (112 mg/L for C. freundii and 97 mg/L for E. herbicola) than their respective hosts (30.4 and 33.8 mg/L) and the vgb- control strains (35.6 and 35.8 mg/L). Further, the vgb+ recombinants of C. freundii and E. herbicola had 20-fold and about two orders of magnitude higher dopamine levels than their hosts, repectively. The activity of tyrosine phenol-lyase, the enzyme converting L-tyrosine to L-DOPA, was well-correlated to cytoplasmic L-DOPA levels. As cultures aged, higher tyrosine phenol-lyase activity of the vgb+ strains was more apparent. © 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.