EFFECT OF INSERTION SITE AND METABOLIC LOAD ON THE ENVIRONMENTAL FITNESS OF A GENETICALLY-MODIFIED PSEUDOMONAS-FLUORESCENS ISOLATE

An isolate of Pseudomonas fluorescens (SBW25) was modified with differ ent marker genes (lacZY, aph-1, and xylE). These marker genes were ins erted singly or id combination into two separate (1 Mbp apart) and pre sumably nonessential sites (-6- and Eel on the chromosome of SBW25, Th is allowed the production of a range of genetically modified SBW25 var iants that differed with respect to insertion site of the marker genes and metabolic burden. The environmental fitness of the different SBW2 5 variants was tested in soil, in the rhizosphere of wheat and pea, an d on the phylloplane of wheat. Reduced environmental fitness of the di fferent variants was mainly attributed to the extra metabolic burden o f novel gene expression, whereas choice of insertion site was of littl e significance. Changes in environmental fitness were dependent on the environmental conditions; an environment, such as soil, with a low mi crobial carrying capacity had a negative effect on the environmental f itness of variants with a large metabolic load. In environments with a larger carrying capacity, such as the rhizosphere of pea, environment al fitness of variants with a large metabolic load was not significant ly different from that of variants with a smaller metabolic burden.