A phylogenetic cluster of marine bacterioplankton has been identified that is numerically abundant in coastal seawater and estuaries of the southeastern U.S. These bacteria, termed the `marine alpha` group, consistently account for up to 30% of the bacterial ribosomal DNA (rDNA) in coastal seawater and in high salinity reaches of major southeastern estuaries, and may constitute the single most dominant bacterial lineage in these systems. Marine alpha bacteria can be readily isolated from seawater samples using low nutrient culturing techniques, and thus some indications of their potential biogeochemical roles have emerged. Many marine alpha isolates are capable of growth on lignin related compounds and humic substances, two types of naturally occurring aromatic compounds found in high concentrations in southeastern U.S. salt marshes and in riverine material exported to the coastal ocean. Other isolates are capable of metabolizing organic sulfur molecules, such as DMSP and methanesulfonic acid, which are important compounds in oceanic sulfur cycling and atmospheric processes. This proposal describes an investigation into the ecology, biogeochemical roles, and physiological capabilities of these numerically dominant coastal marine bacteria. We will determine the distribution and abundance of marine alpha bacterioplankton in southeastern U.S. waters and other selected coastal sites around the U.S., to construct a clone library of marine alpha sequences, to isolate and characterize culturable members of the group, and to use molecular techniques (based on in situ PCR and 16S rDNA approaches) to study the biogeochemical roles of the group in natural seawater.
