MIXOTROPHIC NUTRITION OF PHYTOPLANKTON
Venus Fly Traps of the microbial world
Phytoplankton are protists that
using sunlight and CO2 to obtain energy and produce organic
matter. But there are
that ingest other microorganisms in addition to photosynthesizing.
organisms can capture and digest prey including bacteria, cyanobacteria
and other algae. Because they have the ability to obtain energy and
at two trophic levels (i.e., they "mix" plant and animal nutrition in
same organism), they are often called "mixotrophic" as opposed to
(plant) or heterotrophic (animal). While the existence of mixotrophs
been known for over 100 years, relatively little was understood about
abundance or ecological impact until much more recently. This
lack of information is being
remedied as many scientists throughout the world have begun to
phenomenon during the last 20 years.
NSF funding to myself and co-PI Rebecca Gast, of Woods Hole
Ocenaographic Institution, will allow us to continue to investigate
mixotrophy in the Antarctic environment. Recently we documented
wide-spread occurence of
mixotrophy in the Ross Sea, Antarctica and also in the Arctic (Moorthi,
et al. 2009;
Sanders and Gast, in prep). We will also continue studying an Antarctic dinoflagellate that ingests
phytoplankton and retains functional chloroplasts (kleptoplasty), a somewhat different
alternative nutritional strategy.
In collaboration with co-workers, I
previously explored the distribution,
abundance, and feeding abilities of planktonic mixotrophs in lakes and
the ocean. We also examined physiological attributes of isolated
in laboratory experiments. Mixotrophy may afford algae with some
(relative to purely phototrophic or purely heterotrophic protists of
size) in particular environmental situations. Specifically, mixotrophs'
ability to exploit two different forms of nutrition
and heterotrophy) may allow them to cope with energy or nutrient
in nature. For example, most algae rely on the uptake of dissolved
such as ammonia and phosphate to obtain sufficient nitrogen and
for growth. Mixotrophic algae may be able to obtain these elements by
prey and using the nitrogen and phosphorus from the digested prey (see
selected references below). Other specific nutritional needs (vitamins,
lipids) may also be gained via ingested prey.
As a part of our projects, we surveyed a
number of freshwater and
marine plankton communities to determine the abundances of mixotrophic
algae in nature. We have looked in such disparate environments as
Bank off the New England coast, the Sargasso Sea near Bermuda, the Ross
Sea (Antarctica), the Beaufort Sea (Arctic), and in
lakes in Georgia and in the Pocono mountains of Pennsylvania.
are present in all of these environments, but their abundances vary
over time and distance.
Protists - The term protist is used to group
(mostly) eukaryotes from most of the groups
formerly classified as algae, protozoa, and slime
It is a grouping of convenience since members of the group have
polyphyletic origins. This means that they were
from two or more ancestral groups.
REFERENCES. For more of our
papers on mixotrophy,
including links to abstracts and or PDF files, see "Publications."
RETURN TO SANDERS HOME PAGE
- Moorthi S.D., D.A. Caron, R. Gast, and R.W. Sanders. 2009.
Mixotrophy: a widespread and important ecological strategy for
planktonic and sea-ice nanoflagellates in the Ross Sea, Antarctica.
Aquatic Microbial Ecology 54:269-277.
- Gast, R.J., D.M. Moran, M.R. Dennett, and D.A. Caron. 2007.
Kleptoplasty in an Antarctic dinoflagellate: caught in evolutionary
transition? Environmental Microbiology 9:39-45.
- Sanders, R.W. 1991. Mixotrophic protists in marine and freshwater
Journal of Protozoology 38: 76-81.
- Sanders, R.W. and K.G. Porter. 1988. Phagotrophic
K.C. Marshall, (Ed.) Advances in Microbial Ecology 10: 167-192.
- Caron, D.A., R.W. Sanders, E.L. Lim, C. Marrasé, L.A.
Whitney, R. Aoki, and K.G. Porter. 1993. Light-dependent phagotrophy in
the freshwater mixotrophic chrysophyte Dinobryon cylindricum.
Microbial Ecology 25: 93-111.
- Sanders, R.W., U.G. Berninger, E.L. Lim, P.F. Kemp and D.A.
Heterotrophic and mixotrophic nanoplankton predation on picoplankton in
the Sargasso Sea and on Georges Bank. Marine Ecology Progress Series
- Sanders, R.W., D.A. Caron, J.M. Davidson, M.R. Dennett, and D.
Nutrient acquisition and population growth of a mixotrophic alga in
and bacterized cultures. Microbial Ecology 42:513-523.