Exploring the variation of bacterial community and nitrogen transformation functional genes under the pressure of heavy metals in different coastal mariculture patterns

Equilibrium in microbial dynamics and nitrogen transformation in the sediment is critical for maintaining healthy mariculture environment. However, our understanding about the impact of heavy metals on the bacterial community and nitrogen transformation functional genes in different mariculture patterns is still limited. Here, we analyzed 30 sediment samples in the vertical distribution from three different mariculture patterns mainly include open mariculture zone (K), closed mariculture pond (F) and pristine marine area (Q). Illumina MiSeq Sequencing was applied to investigate the bacterial community and structure in the sediment. Quantitative polymerase chain reaction (qPCR) was used to determine the effect of heavy metals on nitrogen transformation functional genes. Results showed that bacterial community and structure varied greatly in different mariculture patterns. Chloroflexi, Proteobacteria and Desulfobacterota were predominant phyla in the coastal mariculture area. High concentrations of heavy metals mainly enriched in the up layer (5-40 cm) of the sediment in the mariculture zone. The abundance of functional genes in the closed mariculture pond was much higher than the open mariculture zone and pristine marine area. And the high abundance of nitrification and denitrification functional genes mainly accumulated at the depth from 5 cm to 40 cm. Heavy metals content such as Fe, Cr, Mn, Ni, As, Cd, Pb and nutrient content NH4+-N, NO3--N and NO2--N were highly associated with bacterial community and nitrogen transformation functional genes. This study comprehensively elaborated the effect of heavy metals on the bacterial community and nitrogen transformation functional genes in different coastal mariculture patterns, indicating the possible role of closed mariculture pond in reducing nitrogen transformation efficiency, which will provide useful information for preventing pollution risk in the mariculture area.