Identification and quantitation of species in complex DNA mixtures by real-time polymerase chain reaction

Six TaqMan real-time polymerase chain reaction (PCR) systems using minor groove binding (MGB) probes have been developed for the detection quantitation of bovine, porcine, lamb, chicken, turkey, and ostrich DNA in complex samples. Species-specific amplification was achieved by combining only two fluorogenic probes and 10 oligonucleotide primers targeting mitochondrial sequences, decreasing the cost of the assay significantly. The limits of detection ranged from 0.03 to 0.80 pg of template DNA. Analysis of experimental mixtures containing two to four different species showed the suitability of the assay for detection of more than 1% of pork, chicken, or turkey and of more than 5% of cattle or lamb. The quantitation accuracy in samples containing 10-100% of beef or pork DNA was close to 90%. The system is complemented with one additional TaqMan MGB detector based on consensus sequence segments of the nuclear 18S ribosomal RNA gene. A method to evaluate the presence of unknown eukaryotic DNA in a mixture, where data derived from the species-specific detection are compared with the experimental values obtained from the general 18S detector, is presented. This method allows the validation of the quantitative measurements, providing an internal control of the total content of PCR-amplifiable DNA in the sample. The system was tested on DNA mixtures containing different shares of up to four different species and on DNA extracted from processed commercial food samples.

Interregional foodborne salmonellosis outbreak due to powdered infant formula contaminated with lactose-fermenting Salmonella virchow

Spain's Salmonella surveillance system backed by regionally-based epidemiologists around the country made it possible to detect and halt the spread of a foodborne salmonellosis outbreak due to powdered infant formula contaminated with a lactose-fermenting strain of Salmonella virchow. Forty-eight cases involving children, mostly under 7 months old, were detected in 14 out of Spain's 17 Regions. The outbreak started in January and ended in June 1994. All cases were microbiologically confirmed. The implicated strain had a 3.6 kb plasmid, was susceptible to all antimicrobials tested except nitrofurantoin and was phagetype 4a. Isolates from 8 of 24 Brand "A" milk samples tested had the same characteristics as case isolates. All affected/suspect batches of Brand "A" milk were destroyed and the product withdrawn from sale, which led to the end of the outbreak. This incident underscores the importance of maintaining surveillance systems able to detect and prevent foodborne outbreaks and alert to the possibility of isolating unusual lactose-fermenting Salmonella serotypes in especially sensitive food products.

Improved catalytic performance of a 2-haloacid dehalogenase from Azotobacter sp. by ion-exchange immobilisation

The stability and catalytic efficacy of the L-2-haloacid dehalogenase isolated from Azotobacter sp. RC26 were studied after immobilisation on a DEAE Sephacel solid matrix. While the optimum temperature for the soluble dehalogenase falls in the range of 30-40 degrees C, the activity of the immobilised enzyme shows a four-fold increase at 60 degree C. Immobilisation on a plug-flow bioreactor extends the range of usable substrate concentration. The improved catalytic characteristics after immobilisation of the haloacid dehalogenase may be relevant for its possible utilization in biotechnological applications ranging from waste treatment to synthesis of stereoisomers.

Monochloroacetate dehalogenase activities of bacterial strains isolated from soil

Seven bacterial strains capable of utilizing monochloroacetate (MCA) at a concentration of 50 mM as the sole carbon source were isolated from soil and displayed MCA dehalogenase activity. Three of them were identified as Pseudomonas spp., and the remaining four strains as Alcaligenes sp., Agrobacterium sp., Arthrobacter sp., and Azotobacter sp. This latter is the first reported example of a bacterium fixing atmospheric nitrogen under aerobic conditions that also uses a chloro-organic compound as sole source of carbon and energy. MCA dehalogenase activity in these strains was found to be inducible under different growth conditions. Crude extracts from all seven isolated strains also displayed dehalogenating activity with a relatively wide range of halogenated organic compounds (aliphatic acids, ketones, alcohols, alkanes, and aromatics), which, depending on the strain, were dehalogenated to different extents. The estimated Kmvalues for MCA were used to classify the dehalogenase activities into three groups: high affinity (30–40 μM) in Alcaligenes and Agrobacterium species, medium affinity (100–180 μM) in Pseudomonas and Azotobacter species, and low affinity (100 mM) in Arthrobacter sp. Both the optimal pH range for MCA dehalogenase activity (between pH 8 and 10) and the pH profile of stability (in the neutral–basic range) were found to be similar in all strains, whereas the thermal stability profiles were variable.Key words: dehalogenase, halohydrolase, monochloroacetate, soil.

Properties of gamma-aminobutyraldehyde dehydrogenase from Escherichia coli

gamma-Aminobutyraldehyde dehydrogenase from Escherichia coli K-12 has been purified and characterized from cell mutants able to grow in putrescine as the sole carbon and nitrogen source. The enzyme has an Mr of 195,000 +/- 10,000 in its dimeric form with an Mr of 95,000 +/- 1,000 for each subunit, a pH optimum at 5.4 in sodium citrate buffer, and does not require bivalent cations for its activity. Km values are 31.3 +/- 6.8 microM and 53.8 +/- 7.4 microM for delta-1-pyrroline and NAD+, respectively. An inhibitory capacity for NADH is also shown using the purified enzyme.