Novel Biomarker Degradation Pattern by Microbial Enrichments Initiated from Two Microhabitats of the USS Arizona

Carol A. Savoie¹, Amanda M. Graham¹, Thomas. J. McDonald³, Matthew Russell⁴, Larry Murphy⁴, and Pamela J. Morris^1,2

¹ Marine Biomedicine and Environmental Sciences Center, Medical University of South Carolina, Charleston, SC

and Hollings Marine Laboratory, Charleston, SC

² NOAA/National Ocean Service CCEHBR and Hollings Marine Laboratory, Charleston, SC

³ School of Rural Public Health, Texas A&M University System Health Science Center, College. Station, TX

⁴ Submerged Resources Center., National Park Service, Santa Fe, NM

Before the USS Arizona sank in 1941, the oil bunkers were filled with 4,630 tons of Bunker C fuel.  Today, it is estimated that 2,300 tons still remains aboard, with 2 liters of oil leaking from the ship daily.  However, little is known about the composition of the leaking oil and the impact of in situ microbial communities on oil composition.  Aerobic enrichment cultures were initiated from sediments adjacent to the USS Arizona and from a microbial biofilm associated with a coating of oil along the ceiling in one of the ship’s compartments.  Cultures were grown with GP2 artificial seawater medium amended with nitrate and 2 mg/ml USS Arizona (USAR) oil (30°C, 200 rpm).  After three monthly transfers (4% inoculum) the oil was extracted for chemical analysis and compared with sterile controls.  Gas-chromatographic traces indicated that the n-alkanes and the branched alkanes (pristane and phytane) were completely degraded within 30 days.  Gas chromatography coupled with mass spectrometry (GC-MS) demonstrated extensive loss of polyaromatic hydrocarbons (PAHs).  Ratios of total PAHs to the conserved biomarker 18α oleanane in enrichments were 15.49±0.74 versus 465.02±58.15 for sterile controls.  A novel pattern of biomarker degradation was observed, characterized by conservation of C₃₀ hopane and depletion of the C₂₈ and C₂₉ tricyclic terpanes and C₂₇ steranes.  To examine whether this pattern was microbial community-specific, we provided the USAR enrichments with Bonny Light crude (BLC) oil.  In parallel, two cultures known to degrade C₃₀ hopane in BLC oil (DLC enrichments) were provided USAR oil.  After 60 days incubation, GC-MS analysis showed that the DLC enrichments degraded C₃₀ hopane in the USAR oil, while the USAR enrichments exhibited the same C₃₀ hopane conservation and degradation of the C₂₈ and C₂₉ tricyclic terpane and C₂₇ sterane previously observed with USAR oil.  Denaturing gradient gel electrophoresis showed that the microbial community profiles of the USAR and DLC enrichments were initially different, and that the dominant members persisted after exposure to the alternate oil.  Therefore, the novel oil biomarker pattern observed appears to be specific to the microbial communities residing in sediments adjacent to the USS Arizona and independent of oil type.