Variability in Protist Grazing and Growth on Different Marine Synechococcus Isolates

Abstract

Grazing mortality of the marine phytoplankton Synechococcus is dominated by planktonic protists, yet rates of consumption and factors regulating grazer-Synechococcus interactions are poorly understood. One aspect of predator-prey interactions for which little is known are the mechanisms by which Synechococcus avoids or resists predation and, in turn, how this relates to the ability of Synechococcus to support growth of protist grazer populations. Grazing experiments conducted with the raptorial dinoflagellate Oxyrrhis marina and phylogenetically diverse Synechococcus isolates (strains WH8102, CC9605, CC9311, and CC9902) revealed marked differences in grazing rates-specifically that WH8102 was grazed at significantly lower rates than all other isolates. Additional experiments using the heterotrophic nanoflagellate Goniomonas pacifica and the filter-feeding tintinnid ciliate Eutintinnis sp. revealed that this pattern in grazing susceptibility among the isolates transcended feeding guilds and grazer taxon. Synechococcus cell size, elemental ratios, and motility were not able to explain differences in grazing rates, indicating that other features play a primary role in grazing resistance. Growth of heterotrophic protists was poorly coupled to prey ingestion and was influenced by the strain of Synechococcus being consumed. Although Synechococcus was generally a poor-quality food source, it tended to support higher growth and survival of G. pacifica and O. marina relative to Eutintinnis sp., indicating that suitability of Synechococcus varies among grazer taxa and may be a more suitable food source for the smaller protist grazers. This work has developed tractable model systems for further studies of grazer-Synechococcus interactions in marine microbial food webs.

Co-occurringSynechococcusecotypes occupy four major oceanic regimes defined by temperature, macronutrients and iron

“…Other bottom-up factors likely differentiate the niches of co-occurring clades such as the ability to use organic N and P or differences in the ratio at which multiple nutrients are utilized (Roy and Chattopadhyay, 2007). Topdown pressures such as grazing (Apple et al, 2011) and virus infection (Suttle, 2007) or 'lateral' mechanisms such as commensalism (Morris et al, 2012) and allelopathy (Paz-Yepes et al, 2013) could also contribute to the maintenance of multiple ecotypes. Regardless of the mechanism for co-existence, a potential consequence of the parallel evolution of cooccurring populations is a level of functional redundancy in the community that may influence overall stability (Tilman and Downing, 1994).…”

Toward quantifying the response of the oceans' biological pump to climate change

“…For other components of the pump, where the sign of the change is known, but not the magnitude-such as for the differential sensitivity of grazers vs. phytoplankton to warming, I applied arbitrary changes to the model in an attempt to represent these changes. For example, in the case of reports of the growth rate of microzooplankton responding more to warming than that of their prey (small phytoplankton) (Rose and Caron, 2007), the trophic transfer efficiency has been decreased to mimic a shift in the relationship between increased grazing pressure relative to phytoplankton growth rate (which is a complex coupling, see Apple et al, 2011) in this climate change scenario. In other studies, such as for mesozooplankton under warming scenarios (Isla et al, 2008), a wide range of responses-increased fecal pellet and egg production rates have to be reconciled against elevated mortality rates and reduced net growth efficiency ( Table 3A).…”

Impairment of O-antigen production confers resistance to grazing in a model amoeba–cyanobacterium predator–prey system

“…Bacteria have evolved a variety of mechanisms to evade detection, capture, ingestion, and digestion (13), but very little is known about the molecular mechanisms that govern the interactions between cyanobacteria and their protistan predators (14).…”