The potential of Cycloclasticus and Altererythrobacter strains for use in bioremediation of petroleum-aromatic-contaminated tropical marine environments

Cycloclasticus sp. A5, which has been suggested to be a major degrader of petroleum aromatics spilled in temperate seas, showed higher degrading activities for petroleum aromatics, at both 25 °C and tropical sea temperature 30 °C, than the novel aromatic-degrading isolates, related to Altererythrobacter epoxidivorans (97.5% similarity in the almost full-length 16S rRNA gene sequence) and Rhodovulum iodosum (96.3% similarity), obtained after enrichment on crude oil in a continuous supply of Indonesian seawater. Cycloclasticus A5 degraded petroleum aromatics at a similar rate or faster at 30 °C as compared to 25 °C, but its growth on acetate was severely inhibited at 30 °C. These results suggest that, although their abundance would be low in tropical seas not contaminated with aromatics, the Cycloclasticus strains could be major degraders of petroleum aromatics spilled in tropical seas. The 16S rRNA gene of the Cycloclasticus strains has been identified from Indonesian seawater, and the gene fragments showed 96.7−96.8% similarities to that of Cycloclasticus A5. Introducing Cycloclasticus A5 may be an ecologically advantageous bioremediation strategy for petroleum-aromatic-contaminated tropical seas because strain A5 would disappear at 30 °C after complete consumption of the aromatics. Altererythrobacter and Rhodovulum-related isolates grew well on pyruvate in 10% strength marine broth at 30 °C whereas Cycloclasticus A5 did not grow well on acetate in the broth at 30 °C. These growth results, along with its petroleum-aromatic-degrading activity, suggest that the Altererythrobacter isolate could be an important petroleum-aromatic degrader in and around nutrient-rich tropical marine environments.