MICROORGANISMS DELIBERATELY RELEASED INTO THE ENVIRONMENT AFTER RIGOROUS TESTING ARE UNLIKELY TO PROVE A DIRECT THREAT (I.E. AS PATHOGENS), AND PREDICTION OF SUCH RISKS IS ALMOST IMPOSSIBLE. HOWEVER, THE MAIN RISK IS THE PROSPECT OF CREATING POTENTIALLY HAZARDOUS NEW ORGANISMS FOLLOWING THE TRANSFER OF MOBILE GENES TO NATIVE BACTERIA. MANY BACTERIA CAN EXCHANGE GENETIC MATERIAL, INCLUDING PLASMIDS AND TRANSPOSONS; THEREFORE THE PERSISTENCE AND SPREAD OF BOTH THE ORGANISMS AND GENES ARE BOTH IMPORTANT AND WOULD BE AFFECTED BY A VARIETY OF SELECTIVE PRESSURES.
THE RESULTS TO BE EXPECTED BY THIS STUDY ARE RELEVANT AT THE METHODOLOGICAL LEVEL AS WELL AS FOR ITS LONG TERM OBJECTIVES.
TECHNIQUES FOR SAMPLING BACTERIA IN THE SOIL AND FOR SCREENING FOR THE SPREADING OF THE MANIPULATED MICROORGANISMS IN THE FIELD, SHOULD BE STANDARDIZED. A PRECISE EVALUATION OF THE EFFECT OF THE SELECTION PRESSURE EFFECT IN THE FIELD OF DIFFERENT SYSTEMS SHOULD BE OBTAINED.
AN OVERALL ASSESSMENT OF POTENTIAL RISKS INVOLVED IN THE RELEASE OF THE RESPECTIVE BACTERIA INTO THE ENVIRONMENT WOULD COME FROM THE ANALYSIS OF THE PERSISTENCE OF THE INOCULANT STRAINS IN THE FIELD AND FROM THE EVALUATION OF THE TRANSFER OF THE INTRODUCED GENES TO OTHER BACTERIA IN THE SOIL.
To investigate survival of introduced strains and their genes and to develop and assess monitoring methods, genetically marked derivatives of 2 common soil bacteria were used: Rhizobium which fixes atmospheric nitrogen in the root nodules of legumes (and has a long history) of safe and effective use as an agricultural inoculant) was used in both field and laboratory experiments; Enterobacter agglomerans which fixes nitrogen in association with cereal roots was studied in the laboratory. Strains were marked with genes conferring antibiotic resistance, either by selecting naturally occurring chromosomal mutations, or by insertion of transposon Tn5 to conjugative plasmids. In addition, native Rhizobium populations were screened for circumstantial evidence that genetic exchange occurs (over a long period) in the environment.
The Tn5 marker enabled extensive monitoring of the Rhizobium inoculant, which showed significant variation in survival in field soils of the collaborating countries. The host plant was not required for its establishment. Spread from the site of application over short distances indicated migration along extending roots; over moderate distances it was associated with standing surface water; and over greater areas by bulk soil movement. In the field, no Tn5 transfer to other Rhizobium (isolated from nodules) was found, although populations were below the level at which transfer could be detected in the laboratory. In culture, the inoculant could transfer Tn5 to Escherichia coli and E agglomerans, in addition to a range of Rhizobium species (in contrast to E agglomerans which transferred its plasmid only to closely related strains). Field populations of Rhizobium showed considerable evidence that genetic exchange between soil bacteria must occur in the long term.
AIM OF THE RESEARCH TO BE CONDUCTED IN THIS RESEARCH PROJECT IS, - IN COOPERATION WITH TWO OTHER EUROPEAN LABORATORIES - TO MONITOR THE PERSISTENCE OF GENETICALLY MANIPULATED BACTERIA INTRODUCED INTO AGRICULTURAL SOILS AND TO SCREEN FOR THE SPREAD OF GENES CARRIED BY THESE MICRO-ORGANISMS TO OTHER MEMBERS OF THE SOIL FLORA.
SCREENING FOR THE SPREADING OF THE GENES WILL BE PERFORMED BY SELECTION FOR THE ANTIBIOTIC RESISTANCE MARKERS AND BY SPECIFIC HYBRIDIZATION OF DNA FROM THE FIELD STRAINS WITH LABELLED PROBES FOR THE INTRODUCED GENES.
Funding SchemeCSC - Cost-sharing contracts
AL5 2JQ Harpenden, Herts