Introduction
    The largest estuary in the United States, the Chesapeake once teemed with oysters. In fact, its name comes from the Algonquin word Chesepioooc, which translates to the Great Shellfish Bay (3). The National Oceanic and Atmospheric Administration (NOAA) now reports that the native oyster population of the Chesapeake Bay has diminished to 1% the original value (6). The microbiotas of marine mollusks are vitally important for their survival, homeostasis, and development (McFall-Ngai et al., 2013). Widespread use of the herbicide atrazine has generated much research into its toxicity in aquatic systems. 
    Atrazine, which has been banned from use by the European Union is nevertheless the second most widely used herbicide in the United States, with an estimated annual production of 76 million pounds. When applied, atrazine acts as a chemical contaminant of both surface and ground waters.  Atrazine (6-Chloro-n-ethyl-n’-(1-methylethyl)-triazine-2,4-diamine) is a synthetic herbicide commonly used on crops like corn, sugar cane, and evergreens, especially during spring and summer months (Agency for Toxic Substances and Disease Registry, 2003) and paired with significant rainfall events, washes into the tributaries which carry it over oyster reefs and eventually into the estuaries such as the Chesapeake Bay. One of the beneficial roles of microbiota in oysters is to protect against pathogens and environmental stressors, evidence has recently been investigated (S Ossai et., al 2017; Lockmore and Wegner 2015). However, the response of resident bacteria in the host to chemical contamination remains largely unexplored.
    The Eastern oyster, Crassostrea virginica, is one of the most frequently cultivated bivalve species in the world and is typically reared in estuarine environments that have become increasingly threatened by exposure to pollutants. Among pollutants, herbicide/pesticide contamination of shellfish has become more common in estuarine areas over the past several decades due, in part, to chemical run-off from terrestrial agriculture (Banerjee et al. 1996, khan et al. 2017). The microbial communities of suspension-feeding bivalves include both resident and transient microbiota. Bivalves have the ability to filter large quantities of water (e.g., 3–9 L/h/g dry mass for oysters; Newell et al. 2005, Cranford et al. 2011), and so come into contact with, and pass through their bodies, both free-living and particle-associated microbes. The bacteria with which they interact and harbor have the potential to be particularly important to physiological and biochemical enantiostasis.
    Research using culture-dependent methods demonstrated that Achromobacter, Aeromonas, Altermonas, Pseudomonas, Flavobacterium/Cytophaga, Micrococcus, and Vibrio were bacterial genera commonly isolated from bivalves (Colwell & Liston 1960, Vasconcelos & Lee 1972, Pillai 1980, Kueh & Chan 1985, Olafsen et al. 1993, Pujalte et al. 1999). Findings also indicated that bac- terial concentrations in bivalves are higher by an order of magnitude than those in seawater, and dominance of culturable bacteria is classically linked to sea- sonality and water temperature (Motes et al. 1998, Cavallo et al. 2009, Zurel et al. 2011). More recent culture-independent work has shown that although these genera are commonly present, they do not necessarily represent most of the com- munity (Romero et al. 2002, Winters et al. 2010, Wegner et al. 2013, Trabal et al. 2014, Li & Wang 2017).