Growth of Photorhabdus luminescens in batch and glucose fed-batch culture

Photorhabdus luminescens, a bacterial symbiont of entomopathogenic biocontrol nematodes, was grown in batch and glucose fed-batch culture. The cell density, bioluminescence, production of antibiotic substances, number of cells with inclusion bodies, glucose concentration and oxygen uptake rate were recorded. The addition of 12.4 g 1(-1) glucose prolonged the growth, and the yield almost doubled, from 6.85 g 1(-1) to 12.45 g 1(-1) dry mass. The production of antibiotic substances increased by 140%. Bioluminescence was higher in the batch culture. A shift of P. luminescens to phase II variants was not detected.

Phosphoenolpyruvate is a signal metabolite in transcriptional control of the cbb CO2 fixation operons in Ralstonia eutropha

The two highly homologous cbb operons of the facultative chemoautotroph Ralstonia eutropha H16 encode most enzymes of the Calvin-Benson-Bassham carbon reduction cycle. Their transcriptional regulation was investigated both in vitro and in vivo to identify a metabolic signal involved in this process. For this purpose an in vitro transcription system employing the DNA-dependent RNA polymerase purified from R. eutropha was established. The enzyme from Escherichia coli was also used in verifying comparative studies. Plasmid DNA carrying the control region of the chromosomal cbb operon served as template. In the homologous as well as the heterologous system specific transcripts synthesized under the control of the operon promoter PcbbL were observed, depending on the structure of the tested promoter variant as well as the presence or absence of the activator protein CbbR. Unlike mutationally improved PcbbL variants, the wild-type promoter remained inactive, even in the presence of CbbR together with various potential signal metabolites. CbbR stimulated PcbbL mutants with intermediate basal activity. Phosphoenolpyruvate (PEP) was identified as a negative effector of CbbR that inhibited PcbbL-directed transcription and increased the operator-binding affinity of the protein. This CbbR-mediated inhibition was confirmed by assaying wild-type PcbbL operon fusions in glucose- or succinate-grown cells of E. coli, which contain greatly different concentrations of PEP. It is concluded that at least one additional protein must participate in the overall control of the cbb operons in R. eutropha.

Mutational analysis of the cbb operon (CO2 assimilation) promoter of Ralstonia eutropha

PL promoters direct the transcription of the duplicated cbb operons from the facultative chemoautotroph Ralstonia eutropha H16. The operons encode most enzymes of the Calvin-Benson-Bassham carbon reduction cycle required for CO2 assimilation. Their transcription depends on the activator protein CbbR. Structure-function relationships in the cloned chromosomal promoter region were analyzed by site-directed mutagenesis. PL was altered in its presumed hexameric -35 and/or -10 box or in the spacer region between the boxes to achieve a greater or lesser resemblance to the structure of the sigma70 consensus promoter of Escherichia coli. PL::lacZ transcriptional fusions of various promoter variants were assayed in transconjugant strains of R. eutropha as well as in corresponding cbbR deletion mutants. Mutations increasing the similarity of the -35 and/or -10 box to the consensus sequence stimulated PL activity to various extents, whereas mutations deviating from the consensus decreased the activity. The length of the spacer region also proved to be critical. The conversion of the boxes, either individually or simultaneously, into the consensus sequences resulted in a highly active PL. All improved PL mutants, however, retained the activation under inducing or derepressing growth conditions, although the full-consensus promoter was nearly constitutive. They were also activated in the cbbR mutants. The activity of the overlapping, divergently oriented cbbR promoter was less affected by the mutations. The half- and full-consensus PL mutants were comparably active in E. coli. Two major conclusions were drawn from the results: (i) the location and function of PL were verified, and (ii) indirect evidence was obtained for the involvement of another regulator(s), besides CbbR, in the transcriptional control of the R. eutropha cbb operons.