Interactions between marine snow and heterotrophic bacteria: aggregate formation and microbial dynamics

Abstract

Macroscopic aggregates (marine snow) contribute to new production and nutrient dynamics in the upper ocean and vertical fluxes of organic matter to the deep ocean. To test whether microorganisms play a significant role in phytoplankton aggregate formation we studied particle abundance and size as well as abundance, colonization behaviour, and community composition of bacteria during the growth of 2 marine diatoms (Thalassiosira weissflogii and Navicula sp.) under axenic and non-axenic conditions. Community composition of free-living and attached bacteria during phytoplankton growth and aggregation was studied by amplification of 16S rRNA gene fragments and denaturing gradient gel electrophoresis (DGGE). Our results show that the presence of bacteria was a prerequisite for aggregation of T. weissflogii but not of Navicula sp. Occurrences of distinct populations of free-living and attached bacteria depended on phytoplankton growth and aggregation dynamics. The community composition of especially attached bacteria significantly differed between the 2 algal cultures. Our study suggests that phytoplankton aggregation and vertical fluxes are closely linked to interactions between the marine phytoplankton and the ambient microbial community. KEY WORDS: Heterotrophic bacteria · Marine diatoms · Aggregates · DGGE · Image analysis · Bacterial behaviour Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 42: [19][20][21][22][23][24][25][26] 2006 ria that can grow in suspension as well as on particles ('generalists'). The predominance of one functional type of bacteria may be indicative of specific interactions between bacterial and algal communities in the course of phytoplankton blooms.The production of source particles and their subsequent aggregation is under continuous influence of the aforementioned microbial processes in the ocean. In previous studies we have developed an encounter model to predict the rate at which bacteria colonize marine snow particles (Kiørboe et al. 2002). Using agar spheres as model aggregates, we studied bacterial attachment, detachment, growth, cell-cell interactions, and predation in detail (Kiørboe et al. 2001, 2002, Grossart et al. 2003b. In the present study we examined how the microbial community affect marine snow formation, and in turn how marine snow affects microbial community composition and activities. We tested the following specific hypotheses: (1) aggregate formation is enhanced by the presence of attached bacteria; (2) the ambient bacterial community will shift from one dominated by 'generalists' to 2 distinct populations, one of 'particle specialists' and one of freeliving bacteria, as aggregate abundance increases; (3) the attached bacterial community is specific to the nature of POM (e.g. algal species). Our results show that the presence of bacteria significantly changes phytoplankton aggregation, suggesting that the fate of algal aggregates may hinge on complex mutual effects between the marine phytoplankton and the ...

Effect of bacteria on growth and biochemical composition of two benthic diatoms Halamphora coffeaeformis and Entomoneis paludosa

“…and Methylophaga sp., as these bacteria are known to rely on phytoplankton for carbon and energy sources (Bertrand et al, 2015). It is however difficult to evaluate the bacterial part in this carbon balance, as bacteria also excrete and/or transform exopolysaccharides of the biofilm (Grossart et al, 2006a(Grossart et al, , 2006bAmin et al, 2012). Nevertheless, results of this study confirmed the close interactions between diatoms physiology and bacteria that are known to characterize biota in benthic environment.…”

Interspecific interactions drive chitin and cellulose degradation by aquatic microorganisms

“…First, the Csources in our experiments (chitin and cellulose) both constitute a large fraction of available C in natural aquatic environments (Gooday 1990, Hopkinson & Vallino 2005. Second, aggregation of bacterial species in response to protist grazing has been observed in several other bacteria−protist combinations and experimental conditions (Grossart et al 2006): anti-predation strategies such as formation of biofilms or microcolonies minimize the impact of flagellate predation (Matz & Kjelleberg 2005), although they can incur energetic costs ('defence cost' paradigm; Coustau et al 2000), limiting the ecological success of grazingresistant strains, and can be complicated by interactions with other organisms and viruses (Våge et al 2014).…”

Mesocosm study of particle dynamics and control of particle-associated bacteria by flagellate grazing

“…Several studies have shown the presence of at least 3 functional groups of bacteria with respect to marine snow dynamics: free-living bacteria, particle-specialists, and generalists (Riemann et al 2000, Kirchman 2002, Grossart et al 2005. These functional groups differ not only in their particle-colonizing behavior, but also in their genetic composition (Grossart et al 2006). Our present study showed that particle-associating bacteria were distinctly different from free bacteria genetically even in the absence of a sustained phytoplankton bloom or increased concentrations of organic aggregates.…”