Extraction of microbial DNA from sewage and manure slurries

Abstract

Sewage and manure slurries are environments where rather high numbers of micro-organisms are found. The microbial composition and metabolic activity is strongly dependent on several biotic and abiotic factors (e.g., nutrient availability, duration of storage, pretreatment). Sewage and manure slurries are supposed to play a central role in the natural circulation of pathogens, plasmid-encoded antibiotic or heavy metal resistance genes. Therefore, these habitats are of great interest in view of microbial ecology and hygiene. However, different bacteria of hygienic importance like Shigella dysenteria [7], Salmonella typhimurium [24], Salmonella enteritidis [16], Campylobacter jejuni [8,13,14], Escherichia coli [2,3], Vibrio cholera [5] or Vibrio vulnificus [26] were described to enter the viable but nonculturable state. The potential health hazard presented by pathogens existing in the nonculturable state may be significant because it has been shown that nonculturable bacteria can be resuscitated [11] and remain potentially pathogenic [4]. Furthermore, genetically modified micro-organisms used in industrial settings might be undeliberately released via sewage into the environment. In view of the fact that genetically modified strains like E. coli K12 producing biologically active substances might enter the viable but nonculturable state under environmental stress one should not rely on cultivation methods only when tracking the fate of recombinant micro-organisms in the environment. Therefore, microbial ecologists have recently developed methods obviating the need for cultivation by applying molecular techniques to directly extracted nucleic acids from different environmental habitats [6,12,21].