Microbial community analysis along an Atlantic meridional transect (AMT) 22

Marine microorganisms exhibit two key lifestyles; free-living or particle-associated. These lifestyles are distinctly different in their nutrient availability and input. Free-living bacterial are predominantly exposed to an oligotrophic environment with low nutrient availability and experience only sporadic or periodic inputs of high amounts of organic matter and nutrients, such as, during seasonal phytoplankton blooms. Comparatively, particle-associated bacteria live associated or attached to a nutrient-rich but highly environmental variable particle. We analysed both lifestyles over a large transect of the Atlantic ocean to comprehend the spatial variation between and within these two lifestyles. We used 16S rRNA sequencing to analyse the microbial diversity between the lifestyles and identify key organisms associated with each lifestyle. Subsequently, we used FISH and microscopy to enumerate the absolute cellular abundance of these key groups. We visualised the attachment of specific bacterial clades to individual particles using a combination of lectin staining and FISH. This highlighted both the high organic matter content of the particles and visualised the microbial-aggregate interaction.