Glucose Metabolism in Legionella pneumophila : Dependence on the Entner-Doudoroff Pathway and Connection with Intracellular Bacterial Growth

Abstract

Glucose metabolism in Legionella pneumophila was studied by focusing on the Entner-Doudoroff (ED) pathway with a combined genetic and biochemical approach. The bacterium utilized exogenous glucose for synthesis of acid-insoluble cell components but manifested no discernible increase in the growth rate. Assays with permeabilized cell preparations revealed the activities of three enzymes involved in the pathway, i.e., glucokinase, phosphogluconate dehydratase, and 2-dehydro-3-deoxy-phosphogluconate aldolase, presumed to be encoded by the glk, edd, and eda genes, respectively. Gene-disrupted mutants for the three genes and the ywtG gene encoding a putative sugar transporter were devoid of the ability to metabolize exogenous glucose, indicating that the pathway is almost exclusively responsible for glucose metabolism and that the ywtG gene product is the glucose transporter. It was also established that these four genes formed part of an operon in which the gene order was edd-glk-eda-ywtG, as predicted by genomic information. Intriguingly, while the mutants exhibited no appreciable change in growth characteristics in vitro, they were defective in multiplication within eukaryotic cells, strongly indicating that the ED pathway must be functional for the intracellular growth of the bacterium to occur. Curiously, while the deficient glucose metabolism of the ywtG mutant was successfully complemented by the ywtG(+) gene supplied in trans via plasmid, its defect in intracellular growth was not. However, the latter defect was also manifested in wild-type cells when a plasmid carrying the mutant ywtG gene was introduced. This phenomenon, resembling so-called dominant negativity, awaits further investigation.