Bacterial community composition and diversity in the ballast water of container ships arriving at Yangshan Port, Shanghai, China

Ballast water is a major vector of invasion by protozoans and metazoans. Bacterial invasion is less-well understood. We surveyed the bacterial diversity of ballast water from 26 container ships arriving at the Yangshan Deepwater Port, Shanghai, China during 2015-2016. We characterized the ballast microbiome using high-throughput sequencing (HTS) based on V4-V5 region of 16S rRNA genes. We simultaneously monitored physicochemical parameters of the ballast water, including temperature, pH, dissolved oxygen (DO), salinity, turbidity, total suspended solid (TSS), particulate organic carbon (POC), NO2, NH4, PO4. Proteobacteria was the dominant phylum, comprising more than 50% of the OTUs of almost all vessels, followed by Bacteroidetes (12.08%), Actinobacteria (4.86%) Planctomycetes (3.24%) and Cyanobacteria (1.95%). The relative abundance of Cyanobacteria differed among vessels. It was negatively correlated with temperature, NO3, pH, TSS, PO4, and turbidity and positively correlated with NH4, POC. The genus Synechococcus was the most common Cyanobacteria in our results. Escherichia coli were relatively rare; they are indicator-species of D-2 standards published by the IMO. The relative abundance of the genus Vibrio ranged from 0.003% to 24.88% among different vessels. Our results showed that HTS was able to profile the bacterial communities in ballast-waters, even when the approach was restricted by technical and other obstacles.