Seasonality and vertical structure of microbial communities in an ocean gyre

Abstract

Vertical, seasonal and geographical patterns in ocean microbial communities have been observed in many studies, but the resolution of community dynamics has been limited by the scope of data sets, which are seldom up to the task of illuminating the highly structured and rhythmic patterns of change found in ocean ecosystems. We studied vertical and temporal patterns in the microbial community composition in a set of 412 samples collected from the upper 300 m of the water column in the northwestern Sargasso Sea, on cruises between 1991 and 2004. The region sampled spans the extent of deep winter mixing and the transition between the euphotic and the upper mesopelagic zones, where most carbon fixation and reoxidation occurs. A bioinformatic pipeline was developed to de-noise, normalize and align terminal restriction fragment length polymorphism (T-RFLP) data from three restriction enzymes and link T-RFLP peaks to microbial clades. Non-metric multidimensional scaling statistics resolved three microbial communities with distinctive composition during seasonal stratification: a surface community in the region of lowest nutrients, a deep chlorophyll maximum community and an upper mesopelagic community. A fourth microbial community was associated with annual spring blooms of eukaryotic phytoplankton that occur in the northwestern Sargasso Sea as a consequence of winter convective mixing that entrains nutrients to the surface. Many bacterial clades bloomed in seasonal patterns that shifted with the progression of stratification. These richly detailed patterns of community change suggest that highly specialized adaptations and interactions govern the success of microbial populations in the oligotrophic ocean.

Spatial variability overwhelms seasonal patterns in bacterioplankton communities across a river to ocean gradient

“…Previous studies of variability and diversity in bacterioplankton communities are restricted to single dimensions, focusing on long-term time series, depth profiles or horizontal surveys across environmental gradients (Morris et al, 2005;Hewson et al, 2006;Lozupone and Knight, 2007;Pommier et al, 2007;Fuhrman et al, 2008;Gilbert et al, 2009;Treusch et al, 2009;Andersson et al, 2010;Nemergut et al, 2011). Here we present a dataset that compares bacterioplankton community composition in all three of these dimensions: spatially from river to surface ocean, by depth from surface to deep ocean, and through time seasonally over an annual cycle.…”

“…Of these factors, salinity, temperature and depth appear to be the most important in distinguishing aquatic communities over large spatial scales, in part because many environmental factors vary with salinity, temperature and depth (for example, light, nutrients, pressure), which results in separation of water masses and thereby communities (Morris et al, 2005;Fuhrman et al, 2008;Carlson et al, 2009;Treusch et al, 2009;Fortunato and Crump, 2011). On a global scale, Lozupone and Knight (2007) showed that the primary determinant of aquatic microbial community composition was salinity, whereas Fuhrman et al (2008) found that changes in diversity of marine bacteria across a latitudinal gradient were highly correlated to temperature.…”

Implications of streamlining theory for microbial ecology

“…Pelagibacterales (SAR11) are the most abundant microbial group in the oceans worldwide, and are also common in freshwater (Giovannoni et al, 1990;Morris et al, 2002;Rusch et al, 2007;Carlson et al, 2009;Eiler et al, 2009;Schattenhofer et al, 2009;Treusch et al, 2009). They are obligate aerobes with full respiratory electron transport systems (Giovannoni et al, 2005;Grote et al, 2012) and the light-dependent proton pump proteorhodopsin, which has been shown to substitute as a power supply when organic carbon nutrients are unavailable from the environment to support respiration .…”

Single-cell enabled comparative genomics of a deep ocean SAR11 bathytype

“…However, many of the most abundant bacterial groups from the deep ocean remain uncultivated, for example, the SAR202, SAR324 and SAR406 clades, which make up significant fractions of microbial communities at depth Gordon and Giovannoni, 1996;Wright et al, 1997;DeLong et al, 2006;Morris et al, 2006;Varela et al, 2008;Schattenhofer et al, 2009;Treusch et al, 2009;Morris et al, 2012). Thus, it remains uncertain how widespread the known adaptations of cultivated isolates are among deep ocean microorganisms.…”