The impact of oil on the diversity of cyanobacteria in the sediments of a laboratory microcosm

Abstract:

[Objective] We studied the oil degradation pattern and the responses of cyanobacteria to crude oil at a series of concentrations, analyzed the resistance of cyanobacteria when treated with oil, explored the succession of cyanobacterial phylotypes under oil stress, and to provide scientific basis to judge if secondary environmental problems such as eutrophication would be caused by oil. [Methods] Microcosm experiments including untreated control (CK) and those treated with crude oil at a series of concentrations (25, 125 and 250 g/kg dry weight (wt), designated as, Light oil (LO), Medium oil (MO) and Heavy oil (HO), respectively) were set up in the laboratory. Gas chromatography-flame ionization detector (GC-FID) was adopted to analyze the degradation of crude oil. Cyanobacterial 16S rRNA genes were used to illustrate the diversity and richness of cyanobacteria and the alteration of genus during incubation period. [Results] A green mat appeared on the surfaces of sediments in the LO group on day 31 and didn’t occur in other groups. Clone libraries of cyanobacterial 16S rRNA genes revealed that the diversity of cyanobacteria reduced in the oiled sediments, while few genus such as Oscillatoria and Prochlorococcus increased at later stage. In addition, large proportion of sequences affiliated to uncultured genus might imply novel species. [Conclusion] This study indicated that cyanobacteria exhibited high resistance to crude oil. Oil could stimulate the cyanobacteria growth and might lead to cyanobacteria bloom in some situations. This study circumvents traditional cumbersome technologies, such as isolation and culture-based methods for cyanobacteria investigation, which is significant to molecular ecology analysis on cyanobacteria.