Shifts in bacterial community composition associated with increased carbon cycling in a mosaic of phytoplankton blooms

Abstract

Marine microbes have a pivotal role in the marine biogeochemical cycle of carbon, because they regulate the turnover of dissolved organic matter (DOM), one of the largest carbon reservoirs on Earth. Microbial communities and DOM are both highly diverse components of the ocean system, yet the role of microbial diversity for carbon processing remains thus far poorly understood. We report here results from an exploration of a mosaic of phytoplankton blooms induced by large-scale natural iron fertilization in the Southern Ocean. We show that in this unique ecosystem where concentrations of DOM are lowest in the global ocean, a patchwork of blooms is associated with diverse and distinct bacterial communities. By using on-board continuous cultures, we identify preferences in the degradation of DOM of different reactivity for taxa associated with contrasting blooms. We used the spatial and temporal variability provided by this natural laboratory to demonstrate that the magnitude of bacterial production is linked to the extent of compositional changes. Our results suggest that partitioning of the DOM resource could be a mechanism that structures bacterial communities with a positive feedback on carbon cycling. Our study, focused on bacterial carbon processing, highlights the potential role of diversity as a driving force for the cycling of biogeochemical elements.

Ecological Genomics of the Uncultivated Marine Roseobacter Lineage CHAB-I-5

“…S3 in the supplemental material). In contrast, in all sampled stations from tropical/subtropical oceans, the Roseobacter communities are overrepresented by the SAG-O19 lineage (each 40 to 60% of all roseobacters) (see Table S3 in the supplemental material), and in samples from the Southern Ocean the lineage DC5-80-3 dominates (ϳ40%) (see Table S3 in the supplemental material), the latter consistent with previous studies based on the analysis of the 16S rRNA gene sequences (49)(50)(51). In several other oceans, the Roseobacter communities appear to be dominated by multiple uncultivated lineages.…”

Shifts in phytoplankton community structure modify bacterial production, abundance and community composition

“…However, we found no significant differences in the BCC between the CONTR2 and BB treatment. Shifts in the bacterioplankton composition may be caused by changes in the quality of the DOM (Pinhassi et al 2004, Landa et al 2016, but the quantity of the released DOM may also be important (Sarmento et al 2016). We can make no further conclusions about this topic, based on our data, because we did not characterize the DOM pool in detail.…”

“…Among them, temperature and light are important environmental factors during the development of the spring bloom ) that can also affect bacterial activity and, thus, the bacteria−phytoplankton coupling (Lindh et al 2013, von Scheibner et al 2014, Landa et al 2016. For example, an increase in temperature from the in situ temperature (2.5°C) to 6−8°C boosted bacterial production (BP) and decreased the time lag between PP and secondary production peaks in several experiments (Hoppe et al 2008, von Scheibner et al 2014.…”

Linking Seasonal Reduction of Microbial Diversity to Increase in Winter Temperature of Waters of a Chilean Patagonia Fjord

“…In aquatic environments, microbial activity and diversity are considered to be closely linked to overall ecosystem function (Finlay et al, 1997), and changes in diversity have been positively associated with organic matter availability and heterotrophic activity (Landa et al, 2016). Our data indicate a minor proportion of OTUs might be replaced during warm periods, and so we need to look into potential loss of functions in surface water microbial communities with temperature increase.…”