The metabolic cost of flagellar motion in Pseudomonas putida KT2440

Abstract

Although the flagellar machinery of environmental bacteria endows cells with a phenomenal survival device, it also consumes much of the metabolic currency necessary for fuelling such a vigorous nanomotor. The physiological cost of flagella-related functions of the soil bacterium Pseudomonas putida KT2440 was examined and quantified through the deletion of a ∼ 70 kb DNA segment of the genome (∼ 1.1%), which includes relevant structural and regulatory genes in this micro-organism. The resulting strain lacked the protruding polar cords that define flagella in the wild-type P. putida strain and was unable of any swimming motility while showing a significant change in surface hydrophobicity. However, these deficiencies were otherwise concomitant with clear physiological advantages: rapid adaptation of the deleted strain to both glycolytic and gluconeogenic carbon sources, increased energy charge and, most remarkably, improved tolerance to oxidative stress, reflecting an increased NADPH/NADP+ ratio. These qualities improve the endurance of nonflagellated cells to the metabolic fatigue associated with rapid growth in rich medium. Thus, flagellar motility represents the archetypal tradeoff involved in acquiring environmental advantages at the cost of a considerable metabolic burden.