Aluminum-tolerant Pseudomonas fluorescens: ROS toxicity and enhanced NADPH production

Abstract

Aluminum (Al) triggered a marked increase in reactive oxygen species (ROS) such as O(2) (-) and H(2)O(2) in Pseudomonas fluorescens. Although the Al-stressed cells were characterized with higher amounts of oxidized lipids and proteins than controls, NADPH production was markedly increased in these cells. Blue native polyacrylamide gel electrophoresis (BN-PAGE) analyses coupled with activity and Coomassie staining revealed that NADP(+) -dependent isocitrate dehydrogenase (ICDH, E.C. 1.1.1.42) and glucose-6-phosphate dehydrogenase (G6PDH, E.C. 1.1.1.49) played a pivotal role in diminishing the oxidative environment promoted by Al. These enzymes were overexpressed in the Al-tolerant microbes and were modulated by the presence of either Al or hydrogen peroxide (H(2)O(2)) or menadione. The activity of superoxide dismutase (SOD, E.C. 1.15.1.1), an enzyme known to combat ROS stress was also increased in the cells cultured in millimolar amounts of Al. Hence, Al-tolerant P. fluorescens invokes an anti-oxidative defense strategy in order to survive.

Oxidative Stress Evokes a Metabolic Adaptation That Favors Increased NADPH Synthesis and Decreased NADH Production in Pseudomonas fluorescens

“…NADPH is, in fact, the real force that mediates the functioning of these enzymes. Once the ROS have been detoxified, the enzymes have to be recharged directly or indirectly with the help of NADPH (19,22,34). Glutathione, which is required for the activity of glutathione peroxidase, has to be regenerated with the participation of glutathione reductase, an enzyme that utilizes NADPH as the cofactor (11,26).…”

“…Glucose-6-phosphate dehydrogenase (G6PDH), NADP ϩ -isocitrate dehydrogenase (ICDH-NADP ϩ ), malic enzyme (ME), 6-phosphogluconate dehydrogenase (6PGDH), and glutamate dehydrogenase-NADP ϩ (GDH-NADP ϩ ) are some of the important enzymes that enable aerobic cells to fulfill their requirement for NADPH (34). NADH, which is generated essentially during the catabolism of acetyl-coenzyme A via the tricarboxylic acid (TCA) cycle, is a potent prooxidant as its downstream metabolism mediated by complexes I, III, and IV produces the majority of the ROS generated in aerobic organisms (13).…”

Dual regulation of zwf-1 by both 2-keto-3-deoxy-6-phosphogluconate and oxidative stress in Pseudomonas putida

“…NADPH, produced by G6PDH activity, is needed for reductive metabolic pathways and oxidative stress-damage repair reactions (Girò et al, 2006;Lundberg et al, 1999;Singh et al, 2005). Deletion of the zwf gene increases bacterial sensitivity to oxidative stresses (Girò et al, 2006;Lundberg et al, 1999;Ma et al, 1998).…”

Changes in protein expression in Burkholderia vietnamiensis PR1301 at pH 5 and 7 with and without nickel

“…E. coli mutants deficient in SOD were unable to grow with 0.1 mM Ni, while wild-type cells were able to grow at this concentration of Ni (Geslin et al, 2001). Exposure to aluminium citrate resulted in increased SOD activity in Pseudomonas fluorescens (Singh et al, 2005). An increase in SOD also occurred in PR1 in the presence of Ni at pH 5, although this was not significant (Fig.…”