Karenia brevis

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A Microbial Biorealm page on the genus Karenia brevis

Classification

Higher order taxa

Eukaryota; Alveolata; Dinophyceae; Gymnodiniales; Gymnodiniaceae; Karenia

Species

NCBI: Taxonomy

Karenia brevis

Description and Significance

Karenia brevis is an aquatic marine organism in the phylum Dinoflagellate and super group Alveolates. These flagellated Protists also referred to as algae, are of microscopic proportion usually between 20 and 40 mm in size. They are unicellular, flagellated, photosynthetic organisms with cellulose plates (theca) that surround the cell as the outer surface. The plates are secreted by Alveoli (membrane bound vesicles just below the cell membrane) hence their super group name and create the outer boundary for the cell. Located on the cellulose plates are two grooves called the transverse and longitudinal groove where K. brevis’s two flagellum are located and attached. One flagellum wraps around the body of the cell in the transverse groove, while the other extends from the body of the cell on the longitudinal groove. Using their flagella for locomotion they are able to have some source of propelling movement in the water column. These dinoflagellates are usually found in abundant masses near coastal waters in warmer conditions. Though they are found in several other places in the vast ocean water, this area is of particular concern. K. brevis has an active involvement in harmful algal blooms or “red tides” off the coasts of many places around the world. This is a problem due to the potent neurotoxins called brevetoxin’s that these cells create. When there is an abundance or bloom of these organisms’ resources become limited. There is more competition for space and sunlight, as these organisms die from lack of resources they release their neurotoxins. The neutoxin’s cause all sorts of environmental and economic problems such as massive fish kills, fisheries crashing, paralytic shellfish poisoning, etc. This is a dangerous time for humans to eat seafood and can cause some major health problems.

Genome structure

K. brevis has a large haploid genore consisting of about 1 x 10¹¹ bp. It consists of permanently condensed chromatin which lacks nucleosomes. The condensed chromosomes have a characteristic banding pattern with stacked disks that form a continuous left-handed twist along the longitudinal axis. The disks end in less tightly packed loops of DNA that contain actively transcribed DNA. The K. brevis genome has not yet been sequenced due to its large size.

Cell structure and metabolism

Karenia brevis is an unarmored dinoflagellate. It uses its two flagellas to move more easly through the water. K. brevis is about 18-45 μm in size. The nucleus is round and commonly found in the lower left quadrant of the cell. Cholorplasts are present within the cell which makes the cell a yellow-green color.

Ecology

Karenia brevis is a dinoflagellate which is found in the Gulf of Mexico, along the coasts of Texas, Louisiana, Florida, and North Carolina. They are photosynthetic and perform much of the area's primary production. Because they require light, they cannot live at depths below 200 feet. Karenia brevis has a temperature range between 4 and 33 degrees Celsius. However, their optimal range is 22-28 degrees Celsius. In addition, this organism can live in a salinity of between 25-45 ppt. While they are not symbiotic organisms, they do provide a great deal of oxygen to the environment with one estimate stating they perform around 20% of the primary production in the West Florida Shelf during blooms or red tides. While researchers are unsure of the conditions necessary for these red tides, several hypotheses revolve around the species' requirements for metals.

Pathology

Algal blooms can occur when there is a change in chemical levels in the water. A chemical change in the water can take place for multiple reasons. The most common is when chemicals are dumped in the water from local run off zones. These chemicals can come from certain fertilizers used for agricultural growth near a coastal run off zone. If chemical levels such as nitrogen increases passed normal levels, the algae will use this for nitrogen fixation and reproduce rapidly.  This is what we call the “algal bloom”, and these blooms can deplete the oxygen in the water and create a shade from the sun, preventing organisms that need sunlight from obtaining it.  K. Brevis produces harmful algal blooms that cause red tides. When red tides occur toxins are let out in the oceans and may kill or harm marine animals. Not to mention several human illnesses that can arise from eating seafood that have retained levels of these toxins.

            K. brevis produce neurotoxins when there is a bloom. The toxins are called brevetoxins and the brevetoxins specific to K. brevis is labeled PbTx-2. These lipid soluble brevetoxins adversely affect human health as well at ecological ecosytems. These toxins will activate voltage-gated sodium channels in the body directly harming the nervous system of an organism even at small concentrations. This can result in neurological symptoms in the affected organisms. The most common way for humans to be exposed to these toxins is by the consumption of contaminated shellfish.  Though these toxins do not affect the shellfish, the brevetoxins will subside in the tissues of the shellfish. A human eating shellfish to close to a red tide can get an illness called Neurotoxic Shellfish Poisoning. Ecological health effects include massive mortality rates for invertebrates, fish, birds and even some marine mammals.  This could be do either by direct exposure to the toxins themselves, or from the brevetoxins in the food web.

            For marine organisms these toxins can cause disorientation, lacking their ability to hunt or navigate the oceans, and can also cause them to not be able to swim properly. Putting them in a paralyzed position causing death. For humans the effects of ingesting these toxins are severe.

Current Research

Food-web disruption during Karenia brevis red tides. Zooplankton feed on phytoplankton and thus control their growth. Some phytoplankton, however, can create harmful algal blooms (HABs) that make them less edible to zooplankton and alter the balance of the ecosystem. The release of these HAB species can lead to a positive feedback interaction that supports the blood formation and proliferating while simultaneously starving the grazing species of the ecosystem. The red tides produced by the dinoflagellate Karenia brevis are routinely present along the western coast of Florida. The blooms are usually monospecific and becomes highly toxic due to the release of brevetoxins. While there are multiple brevetoxins, the most potent varieties, PbTx-1, PbTx-2, and PbTx-3, are all produced by K. brevis. It has been noted that during the K. brevis blooms, many grazing species select against consuming K. brevis and will even live on lower ingestion and reproductive rates. Researchers contribute this change in diet to the brevetoxin levels within the blooms. In order to test what effect the brevetoxins were having on the ecosystem Waggett et al. tested the consumption and reproduction rates of grazers with diets consisting of either highly toxic, mildly toxic, and non-toxic brevetoxins. Results showed that the grazing population with exposure to the highly toxic K. brevis brevetoxins had lower consumption rates, reduced egg production, and individuals that consumed the toxins showed lower survival rates than the individuals that chose to starve instead of consume the K. brevis. It was concluded from these results that the alteration in the grazer dies is specifically due to the brevetoxins in the bloom that were not only nutritionally insufficient but also increased consumer mortality rates. The results from the experiments with the mildly toxic and non-toxic brevetoxin diets also showed reduced consumption and insufficient nutritional value which decreased egg production. This was attributed to the fact that K. brevis lacks the ability to produce cholesterol which many grazing population require from their food source. This result shows that it is not only the toxicity of the bloom that alters the balance of the ecosystem, but the proliferation of the K. brevis species with little outside competition from other phytoplankton species that causes grazer mortality rates to increase. This study provides evidence that Karenia brevis has evolved mechanisms to reduce grazing pressure and promote their own survival during blooms, which alters food web dynamics in the immediate ecosystem and leads to further wide-spread effects.

Utilizing competing phytoplankton to decrease Karenia brevis bloom toxicity. Red ties in the Gulf of Mexico occur during blooms of Karenia brevis which produce brevetoxins. The production of the brevetoxins has a wide-spread effect ecologically, and is known to be harmful to organisms ranging from marine inverterates, fish, and seabirds, to manatees and dolphins. A current study by Redshaw et al. proposed that by lowering brevetoxins through the presence of competitive phytoplankton, the harmful effects of the toxins on marine invertebrates was reduced. It was found that a range of competitor phytoplankton species were able to reduce the concentrations of PbTx-1 and PbTx-2, the most toxic and abundant varieties of brevetoxins. While it is hard to currently predict the level of toxicity a bloom will create, it may be possible to use competative phytoplankton as a biocontrol agent to reduce the toxic effects of the brevetoxins. Redshaw et al. suggest that populations of competing phytoplankton or proteins derived from them should be utilized as a method to control bloom toxicity and reduce ecosystem-wide deleterious impacts.

Cool Factor

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References

http://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi

http://www.cdc.gov/nceh/hsb/hab/default.htm

Van Dolah, F.M., et al., The Florida red tide dinoflagellate Karenia brevis: New insights into cellular and molecular processes underlying bloom dynamics. Harmful Algae (2009), doi:10.1016/j.hal.2008.11.004      http://m.plankt.oxfordjournals.org/content/29/3/301.full

Edited by student of Iris Keren