Coastal bacterioplankton community response to diatom‐derived polysaccharide microgels

Abstract

Phytoplankton-derived polysaccharide microgels, including transparent exopolymer particles (TEP), are a major component of the marine organic carbon pool. Previous studies have made correlative links between phytoplankton material and bacterioplankton, and performed experiments that assess general responses to phytoplankton, yet there is a lack of direct empirical evidence of specific bacterioplankton responses to natural phytoplankton polysaccharide microgels. In this study, we used diatom produced TEP in controlled incubation experiments to determine the impact of polysaccharide microgels on a coastal bacterioplankton community. Quantification of bacterial 16S rRNA gene transcripts showed that the addition of TEP caused an increase in bacterioplankton activity. Similarly, high-throughput sequencing of RT-PCR amplified bacterial 16S rRNA gene transcripts showed that active bacterioplankton community structure and diversity also changed in response to microgels. Alteromonadales and Rhodobacterales increased in abundance in response to TEP, suggesting that both bacterioplankton taxa utilize diatom-derived microgels. However, through assessing C-labelled TEP uptake via RNA Stable Isotope Probing, we show that only the Alteromonadales (genus Alteromonas) assimilated the TEP carbon. This study adds utilization of diatom-derived TEP to the metabolic repertoire of the archetypal copiotrophic bacterioplankton Alteromonas, and indicates that the Rhodobacterales may utilize TEP for other purposes (e.g. attachment sites).

Biphasic cellular adaptations and ecological implications of Alteromonas macleodii degrading a mixture of algal polysaccharides

“…suggests different ecological strategies related to polysaccharide utilization. A. macleodii strain 83-1 has been isolated from an alginate-enriched microcosm and represents an ecologically relevant model organism, as A. macleodii degrades the algal polysaccharides laminarin, alginate, pectin, xylan and pullulan [33], dominates polysaccharide degradation in some marine regions [34][35][36] and occurs globally [37]. These traits may also contribute to the close associations and metabolic interactions of A. macleodii with phototrophs, including diatoms [38], prymnesiophyceae [39] and cyanobacteria [40][41][42].…”

“…Due to their gelling capacities, alginate and pectin may also occur in transparent exopolymer particles [50,51]. These particulate forms of polysaccharide mixtures are attractive microhabitats for bacteria, including A. macleodii that colonizes gels derived from macroalgae [34] and diatoms [35].…”

Fungi in aquatic ecosystems

“…It is estimated that fungi can hold the potential to largely affect aquatic foodweb structures, stability and functionality through syntrophic to parasitic interactions with other organisms and organic matter (OM) [21][22][23] . However, for most aquatic ecosystems, little is known about how fungal interactions will affect vital ecosystem functions such as the efficiency of the oceanic carbon pump (carbon pump refers to the mechanism by which atmospheric carbon is sequestered by vertical transfer to deep waters and sediments) and ecosystem health 24 . Consequently, it is urgent to extend our knowledge on diversity and ecology of aquatic fungi, to better understand ecosystem feedback mechanisms to climate and anthropogenic change 10 .…”

Rising bubbles enhance the gelatinous nature of the air–sea interface

“…A recent study suggests that this might have implications for the transport of bacterial communities between different waterbodies (Busch et al 2017). During aggregation, heterotrophic bacteria may change TEP quantity and composition by extracellular enzyme activities (Smith et al 1995) and/or uptake of TEP microgels (Taylor and Cunliffe 2017). Bacteria have also been found to release TEP precursor material and assist in TEP formation from precursor material due to their mobility and sticky coating material on the membrane (Van Loosdrecht et al 1989).…”