Metabolic deprivation: a lead to containment in bacterial releases

Experiments were carried out in non-sterile soil, with or without several substrates (sucrose, citrate, lactose) as energy source, and with or without bacterial inoculates able or unable to utilize these substrates. The bacteria were Enterobacter agglomerans, Escherichia coli, Pseudomonas aeruginosa or Pseudomonas aureofaciens; they either did or did not contain plasmid RP4. It was found that sucrose is degraded by the indigenous microflora and/or free soil enzymes to give extracellular glucose and fructose, to support growth and plasmid transfer of all inoculated bacteria, e.g. sucrose-positive and sucrose-negative bacteria. In contrast, the growth and plasmid transfer of inoculates which do not degrade citrate is reduced in soil containing that substrate when compared to such inoculates which do degrade citrate. The growth and plasmid transfer of inoculates which do not degrade lactose is reduced strongly in soil containing that substrate, when compared to such inoculates which do degrade lactose. Lactose is degraded slowly in soil by the indigenous microflora, without giving rise to extracellular glucose. These findings indicate a possible way to achieve biological containment, via genetic defects in metabolic pathways.