When riverine dissolved organic matter (DOM) meets labile DOM in coastal waters: changes in bacterial community activity and composition

Abstract

Heterotrophic bacterial communities in marine environments are exposed to a heterogeneous mixture of dissolved organic compounds with different bioreactivity that may control both their activity and composition. The coastal environment is an example of a mixing area where recalcitrant allochthonous organic matter from rivers can encounter labile organic matter from marine phytoplanktonic blooms. The objective of this study was to explore the effects of mixed qualities of dissolved organic matter (DOM) on bacterial community activity (BCA) and bacterial community composition (BCC) and to test for a priming effect when DOM sources are added in combination. Coastal marine bacterial communities were incubated separately with a mixture of amino acids and with natural riverine DOM or with both sources together for 42 days. Addition of amino acids alone or in combination with riverine DOM led to a similar stimulation of BCA compared to control condition, whereas addition of riverine DOM alone did not modify BCA compared to the control. On the contrary, BCC analyzed by 16S rRNA gene pyrosequencing was not affected by the addition of amino acids alone, but changed dramatically with riverine DOM alone or in combination with amino acids. Our 2 results show that changes in BCA and BCC can be driven by different types of DOM, but that these changes are not necessarily coupled. Moreover, the addition of labile DOM did not modify the microbial decomposition of riverine DOM, nor the BCC, suggesting that a priming effect did not occur under these experimental conditions.

Heterotrophic nanoflagellate grazing facilitates subarctic Atlantic spring bloom development

“…Consumption of riverine DOC in the fjord is supported by the high BP in the river and river plume water (Table 3) and the negative correlation of BP to salinity. The differences in DOM concentration and composition has been suggested as a driver for diversification of bacterial communities (Crump and Hobbie, 2005;Blanchet et al, 2016;Roiha et al, 2016). Our study suggests that the labile character of the river-DOM may have a role stimulating and shaping the activity and structure of bacterial communities in the fjord, by favoring fast growing bacteria.…”

Effects of zooplankton carcasses degradation on freshwater bacterial community composition and implications for carbon cycling

“…Therefore it appears that the availability of a high quality and abundant LOM source can reduce the biodiversity by favouring a small number of copiotrophs dominating the community: in the present study about half of all sequences in the HD and D microcosms belonged to a single OTU (OTU 1, Pseudomonas sp .). In a similar study of Blanchet and colleagues (), the bacterial diversity was not affected by amino acid additions, possibly because free amino acids are simple compounds which can be consumed simultaneously by many members of the community (Trusova et al ., ). Thus, this pattern can be best explained by the fact that zooplankton carcasses provide microbial habitats and complex, yet labile carbon sources shifting the overall bacterial community toward a less diverse, more uneven, and more copiotrophic community.…”

“…have been used. Although some authors have found support for ROM priming by more labile organic matter, mainly of algal origin (van Nugteren et al ., ; Guenet et al ., ; Hotchkiss et al ., ; Bianchi et al ., ; Gontikaki et al ., ), others did not reveal any evidence for a positive priming effect (Bengtsson et al ., ; Catalán et al ., ; Dorado‐García et al ., ; Blanchet et al ., ), or even found a negative priming effect (Gontikaki et al ., ) with ROM being decomposed slower in the presence of a labile carbon source. Thus, it appears that the absence or presence of the priming effect may strongly depend on specific environmental or experimental conditions, which may also explain the absence of humic matter degradation in our HD treatments using Daphnia carcasses LOM as the primer.…”

Nutrient dynamics and stream order influence microbial community patterns along a 2914 kilometer transect of the Mississippi River

“…Far from a homogenous jumble of organisms ferried downriver, microbial community composition changes with distance from the river mouth and/or from the influence of tributaries (Kolmakova et al ; Read et al ; Savio et al ), resulting from altered nutrient concentrations (Staley et al a ; Van Rossum et al ; Meziti et al ), differing dissolved organic matter sources (Ruiz‐González et al ; Zeglin ; Blanchet et al ), and land use changes (Staley et al b ; Van Rossum et al ; Zeglin ). Past studies of the Thames, Danube, Yenisei, and Columbia Rivers have found that planktonic river microbial assemblages were dominated by the phyla Actinobacteria, Proteobacteria, and Bacteriodetes; and taxa such as acI Actinobacteria, Polynucleobacter spp., GKS9 and LD28 Betaproteobacteria , CL500‐29 Actinobacteria, LD12 SAR11 Alphaproteobacteria , and Novosphingobium spp.…”

“…When considering total nitrogen, up to 62% can occur as nitrate (NO 2 3 ) (Goolsby and Battaglin 2001). This massive discharge of excess eutrophic nutrients, primarily from corn and soybean (nitrogen) and animal manure (phosphorus) runoff (McIsaac et al 2001;Turner and Rabalais 2004;Alexander et al 2008;Schilling et al 2010;Duan et al 2014;Staley et al 2014a), fuels one of the largest marine zones of seasonal coastal hypoxia in the world (Rabalais et al 2002(Rabalais et al , 2007Bianchi et al 2010;Bristow et al 2015). Studying microbial relationships to river eutrophication will improve our understanding of their contributions to either mitigating or exacerbating nutrient input.…”