Hydrocarbon-degrading psychrotrophic bacteria: isolation, characterization and microcosms assay using contaminated Antarctic soil

MAC CORMACK WP, RUBERTO, L.

Hamburgo, Alemania.

Congreso; 3rd International Congress on Extremophiles; 2000

International Society for Extremophiles

Hydrocarbon pollution represents one of the major global environmental problems, which is hampered in low temperature areas due to the low metabolic activity showed by many of the microorganisms able to degrade this compounds. In Antarctica, human activity represent a risk of pollution in a region where temperature and other environmental factors strongly limits bacterial growth rate and psychrotrofic bacteria are essencial to perform a successfull bioremediation process. Quantitative analysis of total bacterial flora (TBF) and hydrocarbon-degrading bacteria (HDB) in chronically polluted sites nearby Jubany Scientific Station (62°14´S, 58°40´W) in king George Island, South Shetland Islands showed significant changes compared with those less affected areas. Increases from 3% to 90-100% in HDB values were observed. From enrichment cultures using crude oil as sole carbon and energy source, two psichrotrophic bacteria capable to grow on hydrocarbons were isolated and characterised. Selected strains obtained from antarctic soil (ADH strain) and highly polluted  urban river (B2-2 strain) showed high 16S ribosomal DNA homology with Rhodococcus and Acinetobacter strains respectively. Both strains were able to grow at 0°C and showed optimun temperature near 25°C and optimum pH near 7.5. Even though both strains produced a significant decrease in surface tension values of the culture medium, whereas B2-2 strain showed homogeneus growth in liquide culture, ADH grew heterogeneously forming macroscopic cellular arrengements in association with hydrocarbons. Bioremediation studies were carried out  with gasoil (1.5%) contaminated antarctic soil (250g) in 1 liter flasks exposed to the extreme climate condition during 51 days. TFB, HDB, pH and total hydrocarbon concentration were evaluated. An important abiotic elimination of contaminants (more than 50%) was observed during the first week. Indigenous microflora showed a significant response to the presence of hydrocarbons, rising the TFB values and leading the HDB fraction near to 100%. The important initial bacterial diversity (determined by morphological and biochemical test) was reduced to only two genera (Pseudomonas and Acinetobacter) when contaminants were present. Addition of N (1.8 g/kg) and P (0.5 g/kg) produced an unexpected loss in the initial bacteria viability whenever these nutrients were added compared with the corresponding non-supplemented condition. When both ADH and B2-2 strains were inoculated to the contaminated soil, HDB counts raised faster and reached a maximum earlier than the indigenous microflora determining the highest hydrocarbon elimination (93%). TBF, HDB and bacterial diversity tended to normalise at the end of the study. Results suggest that although the authoctonous bacterial flora plays an important role in metabolization of hydrocarbons, addition of these psychrotrophic strains to the contaminated soil could be useful to improve bioremediation processes in Antarctica and other hydrocarbon polluted cold areas.