Spatial and temporal variations of bacterioplankton in the Chesapeake Bay: A re-examination with high-throughput sequencing analysis

Chesapeake Bay is a large, dynamic, and productive temperate estuary, which plays an important role in transporting terrestrial materials into the Atlantic Ocean. The bacterioplankton communities experience strong environmental changes both seasonally and along the central axis of the Bay. The goal of this study was to explore the spatiotemporal and interannual patterns of the bacterioplankton communities in the estuary using high-throughput sequencing of 16S rRNA genes. Deep sequencing uncovered many new bacterial groups not found in earlier studies, and showed that Chesapeake Bay contained highly diverse and dynamic bacterial communities. Bacterioplankton in the Bay in summer and autumn were more diverse and stable than those in winter and spring. The spatial pattern was overruled by strong temporal variations when the samples from all seasons were analyzed together. But, the spatial trend became more visible when samples were analyzed separately in individual seasons. Bacterial diversity indices decreased from the upper Bay to lower Bay. The spatial and temporal distributions of bacterioplankton were best explained by variations of salinity and temperature. In addition, nutrient availability (nitrogen and phosphorus), chlorophyll a, and light availability also contributed significantly to the spatiotemporal variation. Despite the interannual variation of the bacterioplankton communities, a stable and reoccurring spatiotemporal pattern was observed in the Chesapeake Bay, suggesting limited functional redundancy for planktonic estuarine microbiomes. Our results highlight the resilience of the planktonic bacterial communities in estuaries with long residence time, and different bacterial groups have unique responses/adaptation to dynamic environmental gradients.