Because of the lack of reports, the base levels of microbial contamination on stored fuels are unknown in tropical regions and it is
unclear whether these levels have some influence on fuel quality parameters. Therefore, fungal quality in automobile fuels stored across
Costa Rican territory was evaluated during two years according to the standard ASTM D6974-04. For a total of 96 samples, counts and
identification of molds and yeasts were performed on regular gas, premium gas and diesel taken from the bottom and superior part of
the container tanks. The highest contamination was found on the bottom of the tanks, where an aqueous phase was usually identified,
showing populations over the ones present in the hydrocarbon itself (up to 108 CFU/L). Diesel was the most contaminated fuel (up to
107 CFU/L); however, an alteration on the physicochemical parameters was not observed in any kind of fuel. Seventy-five mold strains
were isolated, Penicillium sp. being the most common genus (45.8% of the samples), and ten yeast strains, from the genera Candida sp.
and Rhodotorula sp. Four of the yeasts were able to grow on diesel as the sole carbon source, at concentrations ranging from 0.5% to
25%. Increasing the frequency of tank cleaning, adding antimicrobial agents and monitoring microbial populations are recommended
strategies to improve microbial quality of stored fuels. 相似文献
Petroleum hydrocarbons, mainly consisting of n-alkanes and polycyclic aromatic hydrocarbons (PAHs), are considered as priority pollutants and biohazards in the environment, eventually affecting the ecosystem and human health. Though many previous studies have investigated the change of bacterial community and alkane degraders during the degradation of petroleum hydrocarbons, there is still lack of understanding on the impacts of soil alkane contamination level. In the present study, microcosms with different n-alkane contamination (1%, 3% and 5%) were set up and our results indicated a complete alkane degradation after 30 and 50 days in 1%- and 3%-alkane treatments, respectively. In all the treatments, alkanes with medium-chain length (C11-C14) were preferentially degraded by soil microbes, followed by C27-alkane in 3% and 5% treatments. Alkane contamination level slightly altered soil bacterial community, and the main change was the presence and abundance of dominant alkane degraders. Thermogemmatisporaceae, Gemmataceae and Thermodesulfovibrionaceae were highly related to the degradation of C14- and C27-alkanes in 5% treatment, but linked to alkanes with medium-chain (C11-C18) in 1% treatment and C21-alkane in 3% treatment, respectively. Additionally, we compared the abundance of three alkane-monooxygenase genes, e.g., alk_A, alk_P and alk_R. The abundance of alk_R gene was highest in soils, and alk_P gene was more correlated with alkane degradation efficiency, especially in 5% treatment. Our results suggested that alkane contamination level showed non-negligible effects on soil bacterial communities to some extents, and particularly shaped alkane degraders and degrading genes significantly. This study provides a better understanding on the response of alkane degraders and bacterial communities to soil alkane concentrations, which affects their biodegradation process.