Biodegradation of Maya crude oil fractions by bacterial strains and a defined mixed culture isolated from Cyperus laxus rhizosphere soil in a contaminated site

Abstract

Ten bacterial strains were isolated by enrichment culture, using as carbon sources either aliphatics or an aromatic–polar mixture. Oxygen uptake rate was used as a criterion to determine culture transfer timing at each enrichment stage. Biodegradation of aliphatics (10 000 mg L–1) and an aromatic–polar mixture (5000 mg L–1, 2:1) was evaluated for each of the bacterial strains and for a defined culture made up with a standardized mixture of the isolated strains. Degradation of total hydrocarbons (10 000 mg L–1) was also determined for the defined mixed culture. Five bacterial strains were able to degrade more than 50% of the aliphatic fraction. The most extensive biodegradation (74%) was obtained with strain Bs 9A, while strains Ps 2AP and UAM 10AP were able to degrade up to 15% of the aromatic–polar mixture. The defined mixed culture degraded 47% of the aliphatics and 6% of the aromatic–polar mixture. The defined mixed culture was able to degrade about 40% of the aliphatic fraction and 26% of the aromatic fraction when grown in the presence of total hydrocarbons, while these microorganisms did not consume the polar hydrocarbons fraction. The proposed strategy that combines enrichment culture together with oxygen uptake rate allowed the isolation of bacterial strains that are able to degrade specific hydrocarbons fractions at high consumption rates.Key words: biodegradation, defined mixed culture, enrichment culture, hydrocarbon fractions, oxygen uptake.