Aquatic microenvironments in bacterial ecology and diversity

Abstract

Molecular surveys have revealed tremendous bacterial diversity in the world's oceans; yet how do these diverse bacteria with the same essential nutrient requirements co-exist in the same environment? This study examines the role of aquatic microenvironments in generating bacterial diversity: closely related organisms may co-exist in the same environment without competing for resources by a combination of habitat, metabolic, and behavioral differentiation. This hypothesis has been approached from several angles: (i) Within the bacterial family Vibrionaceae is there evidence for microenvironmental specialization or functional differentiation? (ii) Is there small scale clustering of bacteria around phytoplankton in the coastal ocean? Microdiverse clusters (< 1% 16S rRNA gene divergence) of Vibrionaceae were found to be differentially distributed between zooplankton-enriched, particulate, and planktonic water column microenvironments. However microhabitat preferences may not correspond to metabolic capabilities; chitin metabolism was observed to be a near ubiquitous metabolic characteristic of the Vibrionaceae, yet does not appear to be linked to colonization of chitinous zooplankton or particles. Finally, the microscale patchiness of bacterial cells was examined over an annual cycle, revealing seasonal variation and a positive correlation with eukaryotic cell number, suggesting that bacteria may cluster in the nutrient-rich microzones around algae in the environment. This study seeks to answer several fundamental questions about marine bacterial populations: how do closely related species co-exist in the same environment, do bacteria adapt to distinct microscale environments and how important are these microenvironments to bacterial productivity.