The Pseudomonas aeruginosa rhlAB operon encodes the enzyme rhamnosyltransferase 1, which produces the biosurfactant mono-rhamnolipid; rhlAB induction is dependent on the quorum-sensing transcription ...activator RhlR complexed with the autoinducer N-butyryl-homoserine lactone (C4-HSL). In this work we studied rhlAB induction in a P. aeruginosa and Escherichia coli background. We found that, in both bacteria, its expression is not induced during the logarithmic phase of growth even in the presence of RhlR and C4-HSL. Additionally, we found that rhlAB expression is partially sigmas dependent.
A transposon (Tn5-SC) was constructed that can be used to quantify genetic deletions or amplifications. This transposon was used to evaluate the genomic stability of Xanthomonas campestris pv. ...campestris NRRL B1459 and we found that the genome of this bacterium is as stable as other Gram-negative bacteria or even more stable. Homologous recombination between plasmid sequences was determined in strain NRRL B1459 and was found to occur at a similar level to that reported for other Gram-negative bacteria. We report here that in X.c.c. NRRL B1459 there is no straightforward correlation between the occurrence of genetic rearrangements and frequency of homologous recombination. These data are discussed with respect to the reported instability of strain NRRL B1459 for xanthan gum production.
The regulatory systems controlling expression of the ctxAB genes encoding cholera toxin (CT) in the classical and El Tor biotypes of pathogenic Vibrio cholerae have been characterized and found to be ...almost identical. Notwithstanding this, special in vitro conditions, called AKI conditions, are required for El Tor bacteria to produce CT. The AKI conditions involve biphasic cultures. In phase 1 the organism is grown in a still tube for 4 h. In phase 2 the medium is poured into a flask to continue growth with shaking. Virtually no expression of CT occurs if this protocol is not followed. Here we demonstrated that CT expression takes place in single-phase still cultures if the volume-to-surface-area ratio is decreased, both under air and under an inert atmosphere. The expression of key genes involved in the regulation of CT production was analyzed, and we found that the expression pattern closely resembles the in vivo expression pattern. PUBLICATION ABSTRACT
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