Abstract
The trophic interactions between bacteria and their main predators, the heterotrophic nanoflagellates (HNFs), play a key role in the structuring and functioning of aquatic microbial food webs. Grazing regulation of bacterial communities, both of biomass and community structure, have been frequently reported. Additionally, bottom-up responses of the HNF at the population level (numerical responses) have also been extensively described. However, the functional response of HNF at the single-cell level has not been well explored. In this study, we concurrently measured the physiological structure of bacterial communities and HNF single-cell activities during re-growth cultures of natural aquatic communities. We found that changes in the abundance and proportion of the preferred, highly active bacterial prey, caused by the feeding activity of their predators (HNF), induced a negative feedback effect on the single-cell activity of these HNF. These shifts in the specific cellular activity of HNF occur at a much shorter time scale than population level shifts in flagellate abundance, and offer a complementary mechanism to explain not only the tight coupling between bacteria and HNF, but also the relative constancy of bacterial abundance in aquatic ecosystems.
Highlights
Bacteria play a key role in aquatic biogeochemical cycles (Cho and Azam, 1988)
The physiological structure of these complex bacterial communities can be described using flow cytometry and fluorescent markers that target different aspects of bacterial singlecell activity and composition (Gasol and del Giorgio, 2000). We combine these approaches to explore the potential interactions between single-cell digestive activity of mixed estuarine heterotrophic nanoflagellates (HNFs) communities, and the physiological structure of their bacterial prey community. We explored this question in re-growth cultures using natural estuarine bacterial and HNF communities, where we followed both HNF activity and bacterial abundance and physiologic structure through the different phases of the predator/prey dynamics that develop in these cultures through time
DYNAMICS OF THE HETEROTROPHIC BACTERIAL AND NANOFLAGELLATE ABUNDANCE The dynamics of the bacterial and HNF abundance in these re-growth cultures has been previously described in Sintes and del Giorgio (2010)
Summary
Bacteria play a key role in aquatic biogeochemical cycles (Cho and Azam, 1988). It is clear that trophic interactions, including viral infection and grazing by unicellular protists, play a major role in regulating the overall bacterial biomass and activity in both the water column and sediments of oceans and lakes. Environmental conditions, including temperature (Choi et al, 1999), starvation (Lopez-Amoros et al, 1995; Reis et al, 2005), and nutrient availability (Gasol et al, 1999), influence the physiological structure of bacterioplankton assemblages Another key determinant of the composition and physiologic structure of bacterial communities are trophic interactions. HNF have been shown to be highly selective (Montagnes et al, 2008), with feeding preferences based on taxonomic composition (Christoffersen et al, 1997; Jezbera et al, 2005; Gerea et al, 2013), prey morphology (Jürgens and Matz, 2002), and prey activity (Gasol et al, 1999; Gasol and del Giorgio, 2000). This selectivity may result in profound shifts in both the composition www.frontiersin.org
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
