Tertiary endosymbiosis driven genome evolution in dinoflagellate algae

Dinoflagellates are important aquatic primary producers and cause "red tides." The most widespread plastid (photosynthetic organelle) in these algae contains the unique accessory pigment peridinin. This plastid putatively originated via a red algal secondary endosymbiosis and has some remarkable features, the most notable being a genome that is reduced to 1-3 gene minicircles with about 14 genes (out of an original 130-200) remaining in the organelle and a nuclear-encoded proteobacterial Form II Rubisco. The "missing" plastid genes are relocated to the nucleus via a massive transfer unequaled in other photosynthetic eukaryotes. The fate of these characters is unknown in a number of dinoflagellates that have replaced the peridinin plastid through tertiary endosymbiosis. We addressed this issue in the fucoxanthin dinoflagellates (e.g., Karenia brevis) that contain a captured haptophyte plastid. Our multiprotein phylogenetic analyses provide robust support for the haptophyte plastid replacement and are consistent with a red algal origin of the chromalveolate plastid. We then generated an expressed sequence tag (EST) database of 5,138 unique genes from K. brevis and searched for nuclear genes of plastid function. The EST data indicate the loss of the ancestral peridinin plastid characters in K. brevis including the transferred plastid genes and Form II Rubisco. These results underline the remarkable ability of dinoflagellates to remodel their genomes through endosymbiosis and the considerable impact of this process on cell evolution.     

Polymerase Chain Reaction in Detection of Gymnodinium mikimotoi and Alexandrium minutum in Field Samples from Southwest India

Polymerase chain reaction (PCR) primers were constructed for the detection of two toxic dinoflagellate species, Gymnodinium mikimotoi and Alexandrium minutum. The primers amplified a product of expected size from cultured cells of G. mikimotoi and A. minutum. The species-specific primers targeting G. mikimotoi did not yield any product with a wide range of other cultured algae used as negative controls. Primers designed for A. minutum were species-group-specific since it PCR yielded a product from the closely related species A. ostenfeldii and A. andersonii, but not from other species of this genus tested. The confirmation of PCR products was performed by digestion of the products with restriction enzymes. Sensitivity analyses of the primers on DNA template from cultured cells was positive by PCR at a DNA template concentration of 1.5 × 10⁻⁴ ng/μl (0.3 cells/L) for A. minutum, and at a DNA concentration of 2.5 × 10⁻² ng/μl (697 cells/L) for G. mikimotoi. The PCR method for detection of G. mikimotoi and A. minutum was applied on field samples collected with a plankton net. Gymnodinium mikimotoi could be detected in 11 field samples by microscopy, and all these field samples were positive by PCR. The cell counts of G. mikimotoi in simultaneously collected water samples ranged from 306 to 2077/L. Alexandrium minutum could be detected by microscopy in 3 different field samples. The cell counts in water samples collected at the same time as the net samples ranged from 115 to 1115 cells/L. Alexandrium minutum was detected by PCR in these field samples, with the exception of the sample displaying the lowest cell count (115 cells/L). Plankton samples that were negative by microscopy for any of the two target species were also negative by PCR. All the PCR products from field samples were confirmed by restriction enzyme digestion. The application of PCR-based detection of harmful algal bloom species for aquaculture and monitoring purposes in natural field samples is discussed. Received April 4, 2000; accepted September 25, 2000.     

温度对旋链角毛藻(Chaetoceros curvisetus)和米氏凯伦藻(Karenia mikimotoi)生长及硝酸还原酶活力的影响

选用东海常见的两种赤潮肇事藻种:旋链角毛藻和米氏凯伦藻,采用一次性培养实验,研究了不同温度对两种赤潮藻生长及硝酸还原酶活力(NRA)的影响.研究结果表明,在10℃~30℃条件下旋链角毛藻均能正常生长,且生长曲线均符合S-logistic2种群增长模型;而米氏凯伦藻在10℃和30℃条件下不能正常生长,在其他温度条件下生长情况与旋链角毛藻相似.温度适宜时,两种藻的硝酸还原酶活力最大值(NRAmax)、最大生长速率(μmax)和终止生物量(Bf)随温度的变化趋势基本一致,说明温度的高低可通过影响细胞硝酸还原酶活力大小间接影响藻类的生长.旋链角毛藻单位体积的NRAmax和最大生长速率均大于米氏凯伦藻,说明旋链角毛藻能够更好地吸收利用硝酸盐.     

Environmental exposures to Florida red tides: Effects on emergency room respiratory diagnoses admissions

Human exposure to Florida red tides formed by Karenia brevis, occurs from eating contaminated shellfish and inhaling aerosolized brevetoxins. Recent studies have documented acute symptom changes and pulmonary function responses after inhalation of the toxic aerosols, particularly among asthmatics. These findings suggest that there are increases in medical care facility visits for respiratory complaints and for exacerbations of underlying respiratory diseases associated with the occurrence of Florida red tides.This study examined whether the presence of a Florida red tide affected the rates of admission with a respiratory diagnosis to a hospital emergency room in Sarasota, FL. The rate of respiratory diagnoses admissions were compared for a 3-month time period when there was an onshore red tide in 2001 (red tide period) and during the same 3-month period in 2002 when no red tide bloom occurred (non-red tide period). There was no significant increase in the total number of respiratory admissions between the two time periods. However, there was a 19% increase in the rate of pneumonia cases diagnosed during the red tide period compared with the non-red tide period. We categorized home residence zip codes as coastal (within 1.6 km from the shore) or inland (>1.6 km from shore). Compared with the non-red tide period, the coastal residents had a significantly higher (54%) rate of respiratory diagnoses admissions than during the red tide period. We then divided the diagnoses into subcategories (i.e. pneumonia, bronchitis, asthma, and upper airway disease). When compared with the non-red tide period, the coastal zip codes had increases in the rates of admission of each of the subcategories during the red tide period (i.e. 31, 56, 44, and 64%, respectively). This increase was not observed seen in the inland zip codes.These results suggest that the healthcare community has a significant burden from patients, particularly those who live along the coast, needing emergency medical care for both acute and potentially chronic respiratory illnesses during red tide blooms.     

Improved monitoring of HABs using autonomous underwater vehicles (AUV)

Blooms of toxic algae are increasing in magnitude and frequency around the globe, causing extensive economic and environmental impacts. On the west coast of Florida, blooms of the toxic dinoflagellate Karenia brevis (Davis) have been documented annually for the last 30 years causing respiratory irritation in humans, fish kills, and toxin bioaccumulation in shellfish beds. As a result, methods need to be established to monitor and predict bloom formation and transport to mitigate their harmful effects on the surrounding ecosystems and local communities. In the past, monitoring and mitigation efforts have relied on visual confirmation of water discoloration, fish kills, and laborious cell counts, but recently satellite remote sensing has been used to track harmful algal blooms (HABs) along the Florida coast. Unfortunately satellite ocean color is limited by cloud cover, lack of detection below one optical depth, and revisit frequency, all of which can lead to extended periods without data. To address these shortcomings, an optical phytoplankton discriminator (OPD) was developed to detect K. brevis cells in mixed phytoplankton assemblages. The OPD was integrated into autonomous underwater vehicle (AUV) platforms to gather spatially and temporally relevant data that can be used in collaboration with satellite imagery to provide a 3D picture of bloom dynamics over time. In January 2005, a Remote Environmental Monitoring UnitS (REMUS) AUV with an OPD payload was deployed on the west coast of Florida to retrieve a similarity index (SI), which indicates when K. brevis dominates the phytoplankton community. SI was used to monitor a K. brevis bloom in relation to temperature, salinity, chlorophyll, and ocean currents. Current speed, SI, temperature, salinity, and chlorophyll a from the AUV were used to quantify a 1 km displacement of the K. brevis bloom front that was observed over the deployment period. The ability to monitor short term bloom movement will improve monitoring and predictive efforts that are used to provide warnings for local tourism and fishing industries. In addition, understanding the fine scale environmental conditions associated with bloom formation will increase our ability to predict the location and timing of K. brevis bloom formation. This study demonstrates the use of one autonomous platform and provides evidence that a nested array of AUVs and moorings equipped with new sensors, combined with remote sensing, can provide an early warning and monitoring system to reduce the impact of HABs.     

The degradation of Karenia brevis toxins utilizing ozonated seawater

Florida red tides impose both an economic and health impact on the state. The purpose of this research was to examine the effectiveness of ozone to reduce the numbers of Florida red tide organism (Karenia brevis Davis) and its associated toxins in an artificial seawater environment. The results obtained in this experiment showed an approximate 1.25 log₁₀ unit reduction in the major toxin groups recovered after 10 min of ozone exposure (approximately 135 mg). In initial trials, K. brevis toxins were extracted and reintroduced into an artificial seawater (ASW) media. Subsequent experiments exposed whole cell K. brevis culture to ozone treatment. Samples from both experiments displayed approximately 1.10 log₁₀ unit reduction in total toxin and an approximate 1.25 log₁₀ unit reduction in three of the six major toxins associated with K. brevis (PxTx-1, -2, -9). The reduction in toxin concentration, as measured by high performance liquid chromatography (HPLC) analysis, displayed a positive correlation with the reduction of toxicity as determined by a fish (Cyprinodon variegatus) bioassay. Despite large total doses of ozone applied, as compared to levels that might be found at a commercial ozonation facility, some toxins were still recoverable by HPLC after ozone treatment.     

Recreational exposure to aerosolized brevetoxins during Florida red tide events

During two separate Karenia brevis red tide events, we measured the levels of brevetoxins in air and water samples, conducted personal interviews, and performed pulmonary function tests on people before and after they visited one of two Florida beaches. One hundred and twenty-nine people participated in the study, which we conducted during red tide events in Sarasota and Jacksonville, FL, USA. Exposure was categorized into three levels: low/no exposure, moderate exposure, and high exposure. Lower respiratory symptoms (e.g. wheezing) were reported by 8% of unexposed people, 11% of the moderately exposed people, and 28% of the highly exposed people. We performed nasal–pharyngeal swabs on people who experienced moderate or high exposure, and we found an inflammatory response in over 33% of these participants. We did not find any clinically significant changes in pulmonary function test results; however, the study population was small. In future epidemiologic studies, we plan to further investigate the human health impact of inhaled brevetoxins.