Conversion to the mucoid phenotype, which results from the production of the exopolysaccharide alginate, is a feature typical of Pseudomonas aeruginosa strains causing chronic pulmonary infections in patients with cystic fibrosis. In this study, we further characterized a recombinant plasmid, called pJF15, that contains DNA from the 65-to 70-min region of the chromosome of mucoid P. aeruginosa FRD1 and has loci involved in alginate conversion. Plasmid pJF15 complements algT mutations in trans and confers the mucoid phenotype in cis following gene replacement. However, the phenotype of nonmucoid P. aeruginosa carrying pJF15 is unchanged. Here we report the identification of a locus immediately downstream ofalgT, called algN, that may be a negative regulator that blocks algT from activating alginate production. Inactivation ofalgN by transposon TnSOl insertion allowed algT to stimulate alginate production in trans. The DNA sequence of this region identified an open reading frame that predicts an algN gene product of 33 kDa, but no homology was found to other proteins in a sequence data base. Clones of algT in which algN was deleted caused the activation of alginate biosynthesis in transconijugants of several P. aeruginosa strains. DNA containing a~gT was shown to hybridize to the genomes of several Pseudomonas species, including P. putida, P. stutzeri, and P. fluorescens. Transconjugants of these species carrying algT DNA (with a deletion of algN) from pJF15 showed a mucoid phenotype and increased production of uronic acid-containing polymers that resembled alginate.Pseudomonas aeruginosa often causes chronic pulmonary infections in cystic fibrosis (CF) patients. The strains isolated from these patients usually have a mucoid colony morphology because of the production of the exopolysaccharide alginate (6). Alginate is a high-molecular-weight, unbranched polymer composed of two uronic acids, D-mannuronate and L-guluronate. P. aeruginosa strains from environmental and other clinical sources rarely have a mucoid colony morphology. The association between mucoid P. aeruginosa and pulmonary infections in CF patients suggests that this phenotype is important for the pathogenesis of this bacterium in these patients. The proposed roles of alginate in pathogenesis include resistance to phagocytosis and adherence (1,26,27).Nonmucoid strains of P. aeruginosa from environmental and non-CF clinical sources may have the potential for alginate production, although their genes for alginate biosynthesis are silent (15). Genetic studies by Fyfe and Govan (12) showed that muc mutations in the late region of the chromosome give strain PA01 a mucoid, alginate-producing (Alg') phenotype. Ohman and Chakrabarty (22) examined the spontaneous conversion of mucoid, Alg' CF strain FRD1 to the nonmucoid, non-alginate-producing (Alg-) form and mapped responsible loci to the late region of the chromosome by demonstrating linkage to hisL. A 7.6-kb EcoRI fragment from FRD1 cloned into the broad-host-range plas-* Corresponding author. mid pLAFR1...

The sensitivity of genotypic expression to the environment can be depicted as the reaction norm, which is defined as the array of phenotypes produced by a single genotype over a range of environments. We studied selection on reaction norms of the gall-inducing insect Eurosta solidaginis (Diptera; Tephritidae), which attacks tall goldenrod Solidago altissima (Compositae). Gall size was treated as a component of insect phenotype and attributes of the host plant as environmental influences on gall development. Genetic differences in the response of gall size to plant lag time (the number of days before a plant responds to the gall maker) were examined. Reaction norms for full-sib families of flies were quantified as linear functions; the elevation of the function denoted gall size produced by the family averaged across all plants, and the function's slope denoted family sensitivity to lag time. Expected fitness of each family was regressed over reaction norm elevation and slope to yield selection gradients on these reaction norm parameters.Directional selection on gall size averaged across environments is four times stronger than selection on sensitivity. Yet, genetic variation for sensitivity contributes more than twice as much to gall phenotypic variance as family mean gall size. Our results suggest that selection on environmental sensitivity will be weak for populations restricted to a narrow segment of an environmental gradient, but strong for broadly distributed species.

No abstract

No abstract