Impact of exogenous nitrogen on cyanobacterial abundance and community in oil-contaminated sediment mesocosms

High concentrations of crude oil are toxic to cyanobacteria but can facilitate the emergence of cyanobacterial aggregation at an appropriate concentration range; however, the exact inducing factor has never been clearly elucidated. We hypothesized that increasing exposure to elevated concentrations of nitrogen would inhibit the accumulation of cyanobacteria in oil-contaminated sediments. To test this hypothesis, we simulated an oil spill in estuarine sediment microcosms with and without the removal of nitrogen limitation by supplementation of exogenous nitrogen. An integrated MiSeq sequencing of 16S rRNA gene analysis along with metatranscriptome sequence was performed to achieve a comprehensive study of cyanobacterial blooms. The number of cyanobacterial sequences increased over time in both oil-contaminated and non-oil-contaminated sediments at different time points after 42 days of incubation. And, supplementation with a nitrogen resource could accelerate cyanobacterial blooms under uncontaminated microcosms but delay the bloom phenomenon and reduce the cyanobacterial abundance to a great degree when exposed to oil. Our results clearly illustrated that nitrogen limitation was a vital driver of the increased abundance of cyanobacteria in oil-contaminated mesocosms. In addition, the abundance and compositions of blooming cyanobacteria varied significantly among the different treatment groups, and Oscillatoria may play a potential and non-negligible role in oil-contaminated mesocosms.