The fate of recombinant DNA in thermally treated fermented sausages

Abstract

The fate of recombinant DNA (rDNA) from genetically modified starter organisms in thermally treated fermented sausages (Kochsalami) was monitored by a polymerase chain reaction (PCR)-based estimation of the concentration of the rDNA. We defined an rDNA titre as the smallest volume of the DNA solution which still results in a detectable amplicon on PCR. In sausages a degradation of the rDNA was observed during storage. However, this did not proceed so far that rDNA was no longer detectable after 9 weeks of incubation. It was observed that the rDNA is strongly protected against the activity of DNase I in the meat matrix. To include the aspect of release of rDNA from genetically modified starter organisms into the meat matrix, Kochsalami-type sausage was produced with the aid of recombinant strains of Lactobacillus curvatus as starter organisms. It was shown that only a minute part of the rDNA contained in the starter organisms can be recovered from the meat matrix by extraction as "free" DNA. To recover the total rDNA, cell wall lytic enzymes were necessary. No significant effect on the detectability of the rDNA was observed on variation of the ecological factors prevailing during the production and storage of the sausages, such as the temperature of thermal treatment, pH and fat content. The concomitant presence of Staphylococcus aureus (>106 cfu/g) producing heat-stable nuclease did not affect the detection of the rDNA.