Title: "Microbial population responses to environmental change in the Delaware Bay"

Speaker: Dr. Barbara Campbell, Clemson University

Abstract: Bacteria dominate in abundance, diversity and potentially metabolic activity in most environments. Our current knowledge on the influence of specific individual taxa on these processes is largely lacking. We chose to examine a variety of microbial populations in estuaries, because they are a natural habitat of continuous spatial as well as seasonal environmental change. Size fractionated samples were collected along the salinity gradient of the Delaware Bay during three months in 2014: March, August and November. Both DNA and cDNA were sequenced by JGI from 24 selected samples from low, mid and high salinity sites within the bay. We characterized the abundance, distribution, replication rates and differential gene expression of several metagenome assembled genomes (MAGs), phylogenetically associated with the SAR11 clade, Rhodobacterales order and Bacteroidetes phylum. Overall, the most change in abundance and gene expression of individual populations occurred between sampling times and salinities, with lesser amounts of differential replication and gene expression between size fractions. Time of day had variable numbers of genes differentially expressed, depending on the taxon. Many genes were differentially expressed in taxa associated with the Rhodobacteriales compared to either the SAR11 or Bacteroidetes groups. Additionally, we observed niche specificity in gene content and expression, especially in the SAR11 clade. Our results demonstrate the breadth of both functional potential and functions of individual populations of bacteria in estuarine environments.