Effects of biostimulation on growth of indigenous bacteria in sub-Antarctic soil contaminated with oil hydrocarbons

In order to evaluate the efficiency of biostimulation of soil contaminated with oil hydrocarbons under sub-Antarctic conditions, a mesocosm study was initiated in May 2001 in the Kerguelen Archipelago (49degrees21'S, 70degrees13'E). The effects of temperature and fertilizer addition (Inipol EAP-22, Elf Atochem) on soil bacterial assemblages contaminated with hydrocarbons were studied in 6-1 batches of subantarctic soil incubated in the dark. Six different conditions were used at three temperatures (4,10 and 20degreesC): control, fertilizer (50 ml), diesel oil (100 ml), diesel oil (100 ml) + fertilizer (50 ml), "Arabian light" crude oil (100 ml) and crude oil (100 ml) + fertilizer (50 ml). Mesocosms were sampled on a regular basis over a seven-month period. All samples were analyzed for total bacteria, viable heterotrophic assemblages and hydrocarbon-utilising microflora. The results clearly showed a significant response of sub-Antarctic microbial soil communities to hydrocarbon contamination. Large increases in total, heterotrophic and hydrocarbon-utilising bacteria were observed (from less than 5 x 10(5) MPN g-1 to more than 10(8) MPN g(-1) for hydrocarbon degrading bacteria). Temperature elevation had no significant impact on the total or heterotrophic assemblages but induced a one order of magnitude increase in hydrocarbon-utilising bacteria in contaminated mesocosms. In contrast, fertilizer addition had no clear effect on hydrocarbon-degrading specific bacteria but stimulated heterotrophic growth in diesel oil-contaminated soils.