GENETIC-ENGINEERING OF SERRATIA-MARCESCENS WITH BACTERIAL HEMOGLOBIN GENE - EFFECTS ON GROWTH, OXYGEN UTILIZATION, AND CELL-SIZE

The bacterial hemoglobin from Vitreoscilla has been shown to increase growth yield and yield of genetically engineered product in Escherichi a coli. To test the generality of this phenomenon, the approximately 5 60-bp bacterial (Vitreoscilla) hemoglobin gene (vgb) (including the na tive promoter), cloned into the vector pUC8 in two constructs containi ng about 1650 and 850 bp, respectively, of Vitreoscilla DNA downstream of vgb, was transformed into Serratia marcescens. After several trans fers of the transformants on selective media, both plasmids became sta ble in this host and the resulting strains produced hemoglobin. Both t ransformants were compared, regarding growth in liquid Luria-Bertani ( LB) medium, with untransformed S. marcescens and S. marcescens transfo rmed with pUC8. The vgb-bearing strains had about 5 times lower maximu m viable cell numbers than the strains without hemoglobin, but the for mer also had late log or early stationary phase cells that were 5-10 t imes larger than those of the latter. Further, on a dry cell mass basi s the presence of vgb inhibited cell growth in liquid media. In contra st, growth of the vgb-bearing strains on LB plates based on cell mass (determined from colony size) was markedly enhanced compared with that of the pUC8 transformant. Respiration of the vgb-bearing strains was lower than that of the strains without vgb on a cell mass basis. These results show that the presence of vgb can have idiosyncratic effects and is not always an aid to cell growth so that its use for genetic en gineering must be tested on a case by case basis. (C) 1998 John Wiley & Sons, Inc.