Preliminary Study towards Enhanced Crude Oil Biodegradation Reveals Congeneric Total Peroxidases with Striking Distinctions

Abstract

Peroxidases (POXs) are the key extracellular enzymes produced by crude oil degrading microbes. Knowledge of optimum conditions for POXs activity is crucial for providing effective environment for bioremediation. In this study, physicochemical properties of POXs produced by Actinomyces israelii and Actinomyces viscosus during growth on crude oil were studied. The POXs exhibited similarities in activity and stability with striking differences in response to two divalent metal ions. The POXs from both species had optimum pH of 7.0 and were very stable over a narrow pH range (6.0 -8.0). The POXs demonstrated similar thermostability exhibiting relative residual activity of 62% at 50˚C after 30 min incubation and 45% residual activity at the same temperature after 60 min despite the fact that POXs from A. viscosus and A. israelii had optimum temperatures of 50˚C and 40˚C, respectively. The POXs from A. viscosus and A. israelii were greatly activated by Fe 2+ at 5.0 and 10.0 mM. The enzymes were both strongly inhibited by Cu 2+ , Mg 2+ and Hg 2+ . Surprisingly, these congeneric POXs demonstrated striking differences in their response to Ca 2+ and Mn 2+ . POX from A. viscosus was activated by Ca 2+ and Mn 2+ exhibiting relative activity of 136% and 106% at 5 mM, respectively. In contrast, POX from A. israelii was strongly inhibited by Ca 2+ and Mn 2+ exhibiting 62.5% relative activity in the presence of 5 mM of each metal ion. Increasing the concentration of Ca 2+ and Mn 2+ led to further activation of POX from A. viscosus and inhibition of POX from A. israelii. Results provide deeper insights into functional properties of studied POXs from closely related microbes. The physicochemical properties are very similar; however, notable differences provide a strong basis for structural characterization of these congeneric enzymes.

Isolation and Screening of Biosurfactant-Producing Bacteria from Hydrocarbon-Contaminated Soils in Awka, Southeast, Nigeria

“…All the isolates recovered except Actinomyces AS1 have been reported as biosurfactant-producing bacteria [3,17,36,45,46]. However, Actinomyces israelii and Actinomyces viscosus have been reported to produce peroxidases, extracellular enzymes used by crude oil degrading microbes [47]. Since Actinomyces AS1 produces biosurfactant, it is likely to be a strain representing a new class of biosurfactant producers.…”