Responses of bacterial and archaeal communities to nitrate stimulation after oil pollution in mangrove sediment revealed by Illumina sequencing

• Bacterial and archaeal communities respond differently to oil pollution and nitrate addition.
• Nitrate addition enhanced the growth of denitrifying hydrocarbon degraders in oiled mangrove.
• Genera Desulfotignum and Marinobacter can be introduced to oiled mangrove for bioaugmentation.
• In situ bioremediation should pay attention to sediment depth because of microbial variation.

This study aimed to investigate microbial responses to nitrate stimulation in oiled mangrove mesocosm. Both supplementary oil and nitrate changed the water and sediment chemical properties contributing to the shift of microbial communities. Denitrifying genes nirS and nirK were increased several times by the interaction of oil spiking and nitrate addition. Bacterial chao1 was reduced by oil spiking and further by nitrate stimulation, whereas archaeal chao1 was only inhibited by oil pollution on early time. Sampling depth explained most of variation and significantly impacted bacterial and archaeal communities, while oil pollution only significantly impacted bacterial communities (p < 0.05). Despite explaining less variation, nitrate addition coupled with oil spiking enhanced the growth of hydrocarbon degraders in mangrove. The findings demonstrate the impacts of environmental factors and their interactions in shaping microbial communities during nitrate stimulation. Our study suggests introducing genera Desulfotignum and Marinobacter into oiled mangrove for bioaugmentation.