Transduction of Escherichia coli W3110(R702) and J53(RP4) (104 to 105 CFU/g of soil) by lysates of temperature-sensitive specialized transducing derivatives of bacteriophage P1 (104 to 105 PFU/g of soil) (P1 Cm cts, containing the resistance gene for chloramphenicol, or P1 Cm cts::TnSOI, containing the resistance genes for chloramphenicol and mercury [Hg]) occurred in soil amended with montmorillonite or kaolinite and adjusted to a-33-kPa water tension. In nonsterile soil, survival of introduced E. coli and the numbers of E. coli transductants resistant to chloramphenicol or Hg were independent of the clay amendment. The numbers of added E. coli increased more when bacteria were added in Luria broth amended with Ca and Mg (LCB) than when they were added in saline, and E. coli transductants were approximately 1 order of magnitude higher in LCB; however, the same proportion of E. coli was transduced with both types of inoculum. In sterile soil, total and transduced E. coli and P1 increased by 3 to 4 logs, which was followed by a plateau when they were inoculated in LCB and a gradual decrease when they were inoculated in saline. Transduction appeared to occur primarily in the first few days after addition of P1 to soil. The transfer of Hg or chloramphenicol resistance from lysogenic to nonlysogenic E. coli by phage P1 occurred in both sterile and nonsterile soils. On the basis of heat-induced lysis and phenotype, as well as hybridization with a DNA probe in some studies, the transductants appeared to be the E. coli that was added. Transduction of indigenous soil bacteria was not unequivocally demonstrated. The survival of P1, E. coli hosts, and transductants for at least 28 days in nonsterile soil indicated the potential for genetic transfer via transduction in soil.

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Agromyces ramosus occurs in high numbers in many soils. It also is a known predator of various gram-positive and gram-negative soil bacteria, including Azotobacter vinelandii. Based on this, it would seem that, in natural soil, A. ramosus should control the population sizes of these soil bacteria. As a partial test of this assumption, we examined the possibility that soil might contain other bacterial predators that could hold A. ramosus in check. Three gram-negative bacterial predators of A. ramosus were isolated from soil. When one of these predators, strain N-1, was added to natural soil, it exhibited an attack – counter attack phenomenon in its interactions with A. ramosus. The indigenous A. ramosus cells in soil, or added A. ramosus cells, produced mycelium that approached, then lysed, approximately one-third of the N-1 cells. The surviving N-1 cells, however, then proceeded to lyse the A. ramosus mycelium, but not the rod-form cells that had fragmented from the mycelium. Strain N-1 then multiplied. This sequence also occurred if Azotobacter vinelandii was added with A. ramosus to soil, either with or without addition of N-1 cells. N-1 attacked the A. ramosus mycelium that was attacking Azotobacter vinelandii. In soil and with pure cultures in the laboratory, the dormant rod-form cells of A. ramosus that fragmented from the mycelium were not attacked. A growth initiation factor seemed to be involved in the attack – counter attack relationship of N-1 and A. ramosus. Strain N-1 and the other two gram-negative predators mentioned above could attack a variety of bacterial species in soil, in addition to A. ramosus which in itself is a predator. Thus, some sort of hierarchy of bacterial predation seems to exist in soil.

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Since the commercial introduction of genetically modified (GM) plants in agriculture over two decades ago, technology developers and regulatory authorities have gained significant experience in assessing their safety based on assessing potential impact to humans, animals and the environment.  Over 3500 independent regulatory agency reviews have positively concluded on the safety of GM plants for food and feed. Yet, divergent and increased regulatory requirements have led to delayed and asynchronous approvals, and have restricted access to innovative products for farmers and consumers. With accumulated knowledge from safety assessments conducted so far, an enhanced understanding of plant genomes, and a history of safe use, it is time to re-evaluate the current approaches to the regulation of GM plants used for food and feed.  A stepwise approach using weight-of-evidence should be sufficient for the safety assessment of newly expressed proteins in GM plants.  A set of core studies including molecular characterization, expression and characterization of the newly expressed proteins (or other expression product), and safety assessment of the introduced protein are appropriate to characterize the product and assess safety.  Using data from core studies, and employing a “problem formulation” approach, the need for supplementary hypothesis-driven or case-by-case studies can be determined.  Employing this approach for the evaluation of GM plants will remove regulatory data requirements that do not provide value to the safety assessment and provide a consistent framework for global regulation. doi: 10.21423/jrs-v09i1waters