Bacterioplankton niche partitioning in the use of phytoplankton-derived dissolved organic carbon: quantity is more important than quality

Abstract

Some prokaryotes are known to be specialized in the use of phytoplankton-derived dissolved organic carbon (DOCp) originated by exudation or cell lysis; however, direct quantification measurements are extremely rare. Several studies have described bacterial selectivity based on DOCp quality, but very few have focused on the quantity of DOCp, and the relative importance of each of these variables (for example, quantity versus quality) on prokaryote responses. We applied an adapted version of the MAR-FISH (microautoradiography coupled with catalyzed reporter deposition fluorescence in situ hybridization) protocol using radiolabelled exudates from axenic algal cultures to calculate a specialization index (d') for large bacterioplankton phylogenetic groups using DOCp from different phytoplankton species and at different concentrations to elucidate to what extent the bacterial response to DOCp is driven by resource quantity (different DOCp concentrations) or by quality (DOCp from different phytoplankton species). All bacterial phylogenetic groups studied had lower d' at higher DOCp concentration, indicating more generalist behavior at higher resource availabilities. Indeed, at increasing resource concentrations, most bacterial groups incorporated DOCp indiscriminately, regardless of its origin (or quality). At low resource concentrations, only some specialists were able to actively incorporate the various types of organic matter effectively. The variability of bacterial responses to different treatments was systematically higher at varying concentrations than at varying DOCp types, suggesting that, at least for this range of concentrations (10-100 μM), DOCp quantity affects bacterial responses more than quality does. Therefore, resource quantity may be more relevant than resource quality in the bacterial responses to DOCp and affect how bacterioplankton use phytoplankton-derived carbon.

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.…”

“…The bacterial community patterns observed in Flavobacteriia and Gammaproteobacteria indicate resource partitioning consistent with previous studies (Teeling et al 2012). However, Gammaproteobacteria, as is typical for copiotrophs, may behave as generalists, due to their capability for using various algal-derived DOC sources (Sarmento et al 2016) and enrichment treatments (Teira et al 2010). Betaproteobacteria are similar to Gammaproteobacteria in their DOM consumption Kirchman 2000, Hoikkala 2012 andreferences therein) and are positively associated with increased DOC concentrations in estuarine environments (Bouvier & del Giorgio 2002).…”

Strain‐specific consumption and transformation of alga‐derived dissolved organic matter by members of the Limnohabitans‐C and Polynucleobacter‐B clusters of Betaproteobacteria

“…() reporting that alga‐derived, carbohydrate‐rich C was preferentially allocated for respiration by lake bacteria. Overall, bacterial OM consumption was directly proportional to the standing stock (i.e., quantity) of different OM compounds released by each alga suggesting non‐selective substrate consumption, as reported for marine bacterioplankton assimilating algal exudates (Sarmento et al ., ). Correspondingly, it becomes obvious that other unidentified alga‐derived OM compounds (e.g., organic acids, fatty acids and polymers) must have significantly contributed to meet the overall bacterial carbon demand.…”

Diatoms shape the biogeography of heterotrophic prokaryotes in early spring in the Southern Ocean

“…Considering each site independently, the varying contributions of the most abundant diatom species could represent different stages of the spring phytoplankton development at a given location with potential consequences on the prokaryotic community composition. The qualitative and quantitative differences in the DOM produced by the various diatoms are likely to present an important selection process (Landa et al, 2016;Sarmento et al, 2016).…”