Overexpressing antioxidant enzymes enhances naphthalene biodegradation in Pseudomonas sp. strain As1

Abstract

We tested the hypothesis that during metabolism of naphthalene and other substrates by Pseudomonas sp. strain As1 oxidative stress arises and can be reduced by antioxidant enzymes. Our approach was to prepare plasmid constructs that conferred expression of two single antioxidant enzymes [Fpr (ferredoxin-NADP + reductase) and SOD (superoxide dismutase)] and the pair of enzymes SOD plus AhpC (alkyl hydroperoxide reductase). The fpr, sodA and ahpC genes were placed under the transcriptional control of both the constitutive lac promoter and their respective native promoters. Both HPLC and growth-rate analyses showed that naphthalene metabolism was enhanced in the recombinant strains. All antioxidant-overexpressing recombinant strains, with the exception of one with an upregulated sodA gene due to the lac promoter [strain As1(sodA)], exhibited resistance to the superoxide generating agent paraquat (PQ). The growth of strain As1(sodA) was inhibited by PQ, but this growth defect was rapidly overcome by the simultaneous overproduction of AhpC, which is a known hydrogen peroxide scavenger. After PQinduced oxidative damage of the [Fe-S] enzyme aconitase, recovery of enzyme activity was enhanced in the recombinant strains. Reporter strains to monitor oxidative stress in strain As1 were prepared by fusing gfp (encoding green fluorescent protein, GFP) to the fpr promoter. Growth on salicylate and naphthalene boosted the GFP fluorescent signal 21-and 14-fold, respectively. Using these same oxidative stress reporters, overexpression of fpr and sodA was found to considerably reduce PQ-induced stress. Taken together, these data demonstrate that the overproduction of Fpr or SodA contributes to oxidative tolerance during naphthalene degradation; however, elevated SOD activity may trigger the generation of excess hydrogen peroxide, resulting in cell death.

Functional Genomic Study of Exogenous n -Butanol Stress in Escherichia coli

“…Specific genes, such as those encoding chaperones, have been reported to relieve up to 85% of the growth decrease caused by the addition of n-butanol in Clostridium (46) and based on our results may prove to be a valuable approach in E. coli as well. Similar relief may be provided via expression of redox stress response enzymes such as SodA and YqhD, both of which have also been reported for use in relieving growth defects due to oxidative stresses (23,35).…”

Effects of di-n-butyl phthalate on the physiology and ultrastructure of cucumber seedling roots

“…As a result, the decrease in the quality of vegetables caused by DBP pollution has posed a potential risk for human health through the food chain. Previous studies have shown that many pollutants are redox-active (Kang et al 2007; Kreiner et al 2002). The redox products could attack the cell membrane bringing about oxidative stress to the body and even causing cell death or canceration (Zhang et al 2003).…”

Plasmid-Encoded Tetracycline Efflux Pump Protein Alters Bacterial Stress Responses and Ecological Fitness of Acinetobacter oleivorans

“…It has been shown that the hexadecane degradation pathway is present in the A. oleivorans DR1 genome [38]–[41]. Many genes involved in hexadecane utilization, including alkane 1-monooxygenase encoded by alkB (AOLE_10550) and aldehyde dehydrogenase encoded by putA (AOLE_06655) were downregulated in the presence of the plasmid (Table 3).…”