In Vivo Gene Expression: The IVET System

Abstract

Bacteria of the genus Pseudomonas have been found in quite diverse aerobic environments, their metabolic versatility and capacity to adapt to changing conditions being a major reason for their ubiquity. A classical approach in studies carried out with pseudomonads and other bacteria, has been the analysis of a specific phenotype of interest and the subsequent identification of the gene/s responsible for such character, either by inactivation of a suspect gene or by random mutagenesis. Expression patterns of many genes have been investigated under laboratory conditions, and in vivo gene activity has in some cases been documented. However, as more complex inquiries about the biology of Pseudomonas in specific environments have been undertaken, the limitations of this genetic approach have become apparent. The interactions of bacteria with their environment, or with other organisms, are determined by a number of different factors—not only the bacterium’s particular genetic stock, but also those ofsurrounding bacteria, or ofthe organisms they interact with, as well as physicochemical conditions. Thus, the ecological performance of a bacterium is the result of a combination of intrinsic and external elements, and it is often difficult to assess the role of one particular gene product simply by its inactivation. This is the case in human pathogenesis, plant virulence, and plant protection against infection by pathogens—all conditions involving Pseudomonas sp. In such situations, confirmation of the role of a certain gene in bacterial fitness has quite often required competition studies between wild-type and mutant strains, indicating the existence of genes whose contribution to the adaptation of some bacteria to their natural habitats depends upon their bio-environment. Often these genes have been found to be unimportant for growth in the laboratory.