New multi-author paper on biogeography of oceanic constitutive mixotrophs


Bob Sanders participated in writing a paper on the biogeography of protists that have an innate ability to photosynthesize, but also are phagotrophic.

Leles, S.G., A. Mitra, K.J. Flynn, U. Tillmann, D. Stoecker, H.J. Jeong, J. Burkholder, P.J. Hansen, D.A. Caron, P.M. Glibert, G. Hallegraeff, J. Raven, R.W. Sanders, M. Zubkov. 2019. Sampling bias misrepresents the biogeographic significance of constitutive mixotrophs across global oceans. Global Ecology and Biogeography 28:418-428. [doi: 10.1111/geb.12853]

Multi-author paper on acquired mixotrophy online August 2017


Bob Sanders participated in writing a paper on the biogeography of protists that acquire the ability to photosynthesize via symbiosis or kleptoplasty.

Leles, S.G., A. Mitra, K.J. Flynn, D.K. Stoecker, P.J. Hansen, A. Calbet, G B. McManus, R.W. Sanders, D.A. Caron,  F. Not, G. M. Hallegraeff, P. Pitta, J.A. Raven, M.D. Johnson, P.M. Glibert, S. Våge. 2017. Oceanic protists with different forms of acquired phototrophy display diverse biogeographies and abundance. 2017. Proceedings of the Royal Society B 284: 20170664. [doi: 10.1098/rspb.2017.0664]

New pubs: DeVaul et al. in J. Phycol.; Mitra et al. in Protist


Temperature-dependent phagotrophy and phototrophy in a mixotrophic chrysophyte by Sarah DeVaul Princiotta, Brian T. Smith and Robert W. Sanders has been published in the Journal of Phycology (52:432-440) and can be found here.

Defining planktonic protist functional groups on mechanisms for energy and nutrient acquisition: incorporation of diverse mixotrophic strategies by Aditee Mitra and 22 co-authors (including R.W. Sanders) was published in Protist (167:106-120) and is available online at

Papers published in ‘Limnology & Oceanography’ and ‘Freshwater Biology’


Sanders, R.W., S.L. Cooke, J.M. Fischer, S.B. Fey, A.W. Heinze*, W.H. Jeffrey, A.L. Macaluso*, R.E. Moeller, D.P. Morris, P.J. Neale, M. Olson, J.D. Pakulski, J.A. Porter, D.M. Schoener*, C.E. Williamson. 2015. Shifts in microbial food web structure and productivity after additions of naturally occurring dissolved organic matter: results from large-scale lacustrine mesocosms. Limnology & Oceanography. 60: 2130-2144. DOI: 10.1002/lno.10159

Cooke, S.L., J.M. Fischer, K. Kessler, Craig E. Williamson, R.W. Sanders, D.P. Morris, J.A. Porter, W.H. Jeffrey, S.B. DeVaul*, J.D. Pakulski. 2015. Direct and indirect effects of additions of chromophoric dissolved organic matter on zooplankton during large-scale mesocosm experiments in an oligotrophic lake. Freshwater Biology. 60:2362-2378.  DOI:10.1111/fwb.12663

*Current or former graduate students in the lab.

Graham paper published in JEMBE


Erin’s final paper from her Ph.D. work was published: Graham, E.R., A. Parekh, R.K. Devassy and R.W. Sanders. 2015. Carbonic anhydrase activity changes in response to increased temperature and pCO2 in Symbiodinium-zoanthid associations.Journal of Experimental Marine Biology and Ecology 473:218-226.  Here’s a link.

Amy Parekh and Roni Devassy were undergraduate researchers in the lab.

Congrats to them all!


McKie-Krisberg paper published in Microbial Ecology


McKie-Krisberg, Z.M., R.J. Gast and R.W. Sanders. 2015. Physiological responses of three species of Antarctic mixotrophic phytoflagellates to changes in light and dissolved nutrients. Microbial Ecology 70:21-29.

Abstract: Antarctic phototrophs are challenged by extreme temperatures, ice cover, nutrient limitation and prolonged periods of darkness. Yet this environment may also provide niche opportunities for phytoplankton utilizing alternative nutritional modes. Mixotrophy, the combination of photosynthesis and particle ingestion, has been proposed as a mechanism for some phytoplankton to contend with the adverse conditions of the Antarctic. We conducted feeding experiments using fluorescent bacteria-sized tracers to compare the effects of light and nutrients on bacterivory rates in three Antarctic marine photosynthetic nanoflagellates representing two evolutionary lineages: Cryptophyceae (Geminigera cryophila), and Prasinophyceae (Pyramimonas tychotreta and Mantoniella antarctica). Only G. cryophila had previously been identified as mixotrophic. We also measured photoautotrophic abilities over a range of light intensities (P vs. I) and used dark survival experiments to assess cell population dynamics in the absence of light. Feeding behavior in these three nanoflagellates was affected by either light, nutrient levels, or a combination of both factors in a species-specific manner that was not conserved by evolutionary lineage. The different responses to environmental factors by these mixotrophs supported the idea of tradeoffs in the use of phagotrophy and phototrophy for growth.

Ocean Acidification pub by Erin Graham accepted


“Species-specific photosynthetic responses of symbiotic zoanthids to thermal stress and ocean acidification” by Erin R. Graham and Robert W. Sanders is accepted for publication in Marine Ecology.

ABSTRACT: Increasing sea surface temperatures and ocean acidification (OA) are impacting physiological processes in a variety of marine organisms. Many sea anemones, corals, and jellies in the phylum Cnidaria, form endosymbiotic relationships with the dinoflagellate Symbiodinium spp., which supplies the hosts with fixed carbon from photosynthesis. Much work has focused on the generally negative effects of rising temperature and OA on calcification in Symbiodinium-coral symbioses, but has not directly measured symbiont photosynthesis in hospite or fixed carbon translocation from symbiont to host. Symbiodinium species or types vary in their environmental tolerance and photosynthetic capacity, therefore, primary production in symbiotic associations is directly related to symbiont type. However, symbiont type has not been identified in a large portion of Symbiodinium-cnidarian studies. Future climate conditions and OA may favor non-calcifying, soft-bodied cnidarians, including zoanthids, over coral species. Here we show that two zoanthid species, Palythoa sp. and Zoanthus sp., harboring different symbiont types (C1 and A4), had very different responses to increased temperature and increased pCO2/low pH. Thermal stress did not affect carbon fixation or fixed carbon translocation in the Zoanthus sp./A4 association, and high pCO2/low pH increased carbon fixation. In contrast, both thermal stress and high pCO2/low pH greatly inhibited carbon fixation in the Palythoa sp./C1 association. However, the combined treatment of high temperature and high pCO2 increased carbon fixation relative to the treatment of high temperature alone. Our observations support the growing body of evidence that demonstrates that the response of symbiotic cnidarians to thermal stress and OA must be considered on a host-specific and symbiont-specific basis. In addition, we show that the effects of increased temperature and pCO2 on photosynthesis may change when these two stressors are combined. Understanding how carbon fixation and translocation varies among different host-symbiont combinations is critical to predicting which Symbiodinium associations may persist in warm, acidified oceans.

Graham et al. published in BMC Research Notes


Erin Graham (Ph.D. 2014) had another paper published.

Graham, E.R., Z.M. McKie-Krisberg and R.W. Sanders. 2014. Photosynthetic carbon from algal symbionts supplements Ambystoma maculatum embryos during the later stages of embryonic development. BMC Research Notes 7:764 [link]


Background: It was recently discovered that symbiotic algae in the eggs of the salamander Ambystoma maculatum translocate fixed carbon from photosynthesis to developing embryos. Fixed carbon translocation was shown in embryos at one time point during development however, it was unknown if fixed carbon translocation occurs throughout all developmental stages.  Findings: In this study, fixed carbon translocation was measured in salamander eggs at six time points over the latter half of development. Fixed carbon translocation did not occur until the middle tailbud portion of development (stages 26-30), and translocation was measured in 20% or less of eggs sampled. Peak carbon translocation occurred during the late tailbud phase of development (stages 31-35), where as much as 87% of eggs sampled showed translocation, and average percent translocation was 6.5%. During the final stages of development, fixed carbon translocation declined, and translocation was not detected in embryos five days prior to hatching.  Conclusions: The onset of fixed carbon translocation from Oophila to A. maculatum embryos during the second half of embryonic development is likely due to the corresponding settlement and concentration of Oophila in the inner egg envelope. In addition, carbon translocation ceases in late stage embryos as the inner egg envelope thins and ruptures in preparation for hatching.

Grier Sellers publishes paper and completes his Ph.D.


Grier graduated in August and had one of the chapters of his dissertation accepted for publication in Journal of Phycology. Here’s the link.


The peridinin-containing plastid found in most photosynthetic dinoflagellates is thought to have been replaced in a few lineages by plastids of chlorophyte, diatom, or haptophyte origin. Other distinct lineages of phagotrophic dinoflagellates retain functional plastids obtained from algal prey for different durations and with varying source species specificity. 18S rRNA gene sequence analyses have placed a novel gymnodinoid dinoflagellate isolated from the Ross Sea (RSD) in the Kareniaceae, a family of dinoflagellates with permanent plastids of haptophyte origin. In contrast to other species in this family, the RSD contains kleptoplastids sequestered from its prey, Phaeocystis antarctica. Culture experiments were employed to determine whether the RSD fed selectively on P. antarctica when offered in combination with another polar haptophyte or cryptophyte species, and whether the RSD, isolated from its prey and starved, would take up plastids from P. antarctica or from other polar haptophyte or cryptophyte species. Evidence was obtained for selective feeding on P. antarctica, plastid uptake from P. antarctica, and increased RSD growth in the presence of P. antarctica. The presence of a peduncle-like structure in the RSD suggests that kleptoplasts are obtained by myzocytosis. RSD cells incubated without P. antarctica were capable of survival for at least 29.5 months. This remarkable longevity of the RSD’s kleptoplasts and its species specificity for prey and plastid source is consistent with its prolonged co-evolution with P. antarctica. It may also reflect the presence of a plastid protein import mechanism and genes transferred to the dinokaryon from a lost permanent haptophyte plastid.

Kyle Gilroy has paper published


Kyle, a graduate student in Engineering, designed a project in Biology 5436 (Freshwater Ecology) that was expanded to result in a recently published paper:  Gilroy, K.D., S. Neretina and R.W. Sanders. 2014. Behavior of gold nanoparticles in an experimental algal-zooplankton food chain. Journal of Nanoparticle Research 16:2414. Link


The release of engineered nanomaterials offers a significant concern due to their unexpected behavior in biological systems. In order to establish the level of threat from releasing nanomaterials into ecosystems, simplified food webs are an effective method to determine toxicity and bioassessment. A study is presented examining the behavior of citrate-capped gold nanoparticles (AuNPs) introduced into a model food chain consisting of a phytoplankton food (Ankistrodesmus falcatus) and a zooplankton grazer (Daphnia magna). UV–Vis spectroscopy is used to monitor the behavior of AuNPs in the presence of algae (Ankistrodesmus) and Daphnia over the span of 5 days. Transmission electron microscopy shows the attachment of gold aggregates to the surface of the Ankistrodesmus. Bright field microscopy shows significant accumulation of AuNPs in the gut of Daphnia via uptake of contaminated Ankistrodesmus and directly from water. No toxicity was evident for Daphnia exposed to AuNPs at the concentration used (880 µg L−1).

Zaid McKie-Krisberg published in ISME Journal


Zaid’s paper “Phagotrophy by the picoeukaryotic green alga Micromonas: implications for Arctic Oceans” (McKie-Krisberg, Z.M. and R.W. Sanders) is now on line at ISME Journal (Nature Publishing Group). Here’s the link

Abstract: Photosynthetic picoeukaryotes (PPE) are recognized as major primary producers and contributors to phytoplankton biomass in oceanic and coastal environments. Molecular surveys indicate a large phylogenetic diversity in the picoeukaryotes, with members of the Prymnesiophyceae and Chrysophyseae tending to be more common in open ocean waters and Prasinophyceae dominating coastal and Arctic waters. In addition to their role as primary producers, PPE have been identified in several studies as mixotrophic and major predators of prokaryotes. Mixotrophy, the combination of photosynthesis and phagotrophy in a single organism, is well established for most photosynthetic lineages. However, green algae, including prasinophytes, were widely considered as a purely photosynthetic group. The prasinophyte Micromonas is perhaps the most common picoeukaryote in coastal and Arctic waters and is one of the relatively few cultured representatives of the picoeukaryotes available for physiological investigations. In this study, we demonstrate phagotrophy by a strain of Micromonas (CCMP2099) isolated from Arctic waters and show that environmental factors (light and nutrient concentration) affect ingestion rates in this mixotroph. In addition, we show size-selective feeding with a preference for smaller particles, and determine P vs. I (photosynthesis vs. irradiance) responses in different nutrient conditions. The widespread distribution and frequently high abundances of Micromonas suggest that these green algae may have significant impact on prokaryote populations in several oceanic regimes.

Scott Fay paper in Aquatic Microbial Ecology


Scott Fay, a former post-doc in the lab has had some of the work he did at Temple University published in Aquatic Microbial Ecology:  Fay, S.A., R.J. Gast, and R.W. Sanders. accepted. Linking bacterivory and phyletic diversity of protists with a marker gene survey and experimental feeding with BrdU-labeled bacteria. Here’s a link to the open access paper: Fay, Gast, Sanders AME