Biovar Research Articles

Regulation of expression of the Lactococcus lactis subsp. lactis biovar diacetylactis citrate transport system

Le metabolisme du citrate chez certaines bacteries lactiques se traduit par la synthese de composes d'arome tels que le diacetyle et l'acetaldehyde. Ces composes contribuent a l'elaboration de la flaveur de certains aliments issus de la fermentation lactique. Le transport du citrate chez Lactococcus lactis subsp. lactis biovar diacetylactis et Leuconostoc mesenteroides subsp mesenteroides est catalyse par un transporteur secondaire, la citrate permease P. Cette permease est essentielle pour l'utilisation du citrate. En son absence le citrate n'est pas metabolise, bien que toutes les enzymes impliquees dans sa conversion soient presentes au niveau de la cellule. Dans cette revue, nous decrivons l'organisation genetique du plasmide codant pour le transport du citrate chez L. diacetylactis, la regulation post-transcriptionnelle de l'operon citQRP et l'influence du pH extracellulaire sur la transcription du gene citP. Par ailleurs, l'etude du transport du citrate et du cometabolisme citrate-glucose a revele un nouveau mecanisme moleculaire permettant une meilleure adaptation de L. diacetylactis a des pH acides.

Determination of DNA Sequences Protected by NodD Proteins

In Rhizobium leguminosarum (R.1.) biovar viciae, the nodulation (nod) gene D encodes a transcriptional activator (NodD). It also represses nodD transcription,and this autoregulation occurs at the divergent and overlapping nodA-nodD promoters.

Isoelectric focusing of beta-lactamases in Mycobacterium fortuitum. Association of a single enzyme pattern with cefoxitin resistance.

The uninduced culture supernatants and cell extracts from 58 strains of the 3 biovariants (biovar) of Mycobacterium fortuitum were all positive for beta-lactamase with the chromogenic cephalosporin substrate. By analytical isoelectric focusing (IEF), 29 of 30 strains of biovar fortuitum exhibited an identical beta-lactamase pattern with 1 major band. In contrast, the beta-lactamases of biovar peregrinum and the unnamed third biovar were heterogeneous, with multiple bands and a variety of patterns. The pH range of isoelectric points for the beta-lactamases was relatively narrow, however, with most bands appearing between pH 4.3 and 5.2. Although additional genetic studies are required, these enzymes appear to be chromosomal, as they are present in all strains including some without detectable plasmids. Repeat isolates from the same patient obtained up to six months apart always had the same beta-lactamase pattern by IEF. Of the third biovar complex, 30% are cefoxitin resistant with minimal inhibitory concentrations greater than 32 micrograms/ml. All 9 cefoxitin-resistant isolates tested had the same unique beta-lactamase pattern by IEF, although this enzyme failed to hydrolyze cefoxitin while hydrolyzing cephalothin and benzylpenicillin. Thus, despite the association of cefoxitin-resistance with a single enzyme pattern, the role of this beta-lactamase in resistance is not known.