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ABSTRACT: The St. Lucie Estuary, located on the southeast coast of Florida, provides an example of a subtropical ecosystem where seasonal
changes in temperature are modest, but summer storms alter rainfall regimes and external inputs to the estuary from the watershed
and Atlantic Ocean. The focus of this study was the response of the phytoplankton community to spatial and temporal shifts
in salinity, nutrient concentration, watershed discharges, and water residence times, within the context of temporal patterns
in rainfall. From a temporal perspective, both drought and flood conditions negatively impacted phytoplankton biomass potential.
Prolonged drought periods were associated with reduced nutrient loads and phytoplankton inputs from the watershed and increased
influence of water exchange with the Atlantic Ocean, all of which restrict biomass potential. Conversely, under flood conditions,
nutrient loads were elevated, but high freshwater flushing rates in the estuary diminished water residence times and increase
salinity variation, thereby restricting the buildup of phytoplankton biomass. An exception to the latter pattern was a large
incursion of a cyanobacteria bloom from Lake Okeechobee via the St. Lucie Canal observed in the summer of 2005. From a spatial
perspective, regional differences in water residence times, sources of watershed inputs, and the proximity to the Atlantic
Ocean influenced the composition and biomass of the phytoplankton community. Long water residence times in the North Fork
region of the St. Lucie Estuary provided an environment conducive to the development of blooms of autochthonous origin. Conversely,
shorter residence times in the mid-estuary limit autochthonous increases in biomass, but allochthonous sources of biomass
can result in bloom concentrations of phytoplankton.
KeywordsRainfall–Waster residence time–Harmful algal blooms–
Microcystis aeruginosa
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Akashiwo sanguinea
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Skeletonema costatum
Estuaries and Coasts 04/2012; 35(1):335-352. · 2.11 Impact Factor
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Lake and Reservoir Management. 09/2011; 27(3):235-244.
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ABSTRACT: Aphanizomenon ovalisporum is the only confirmed cylindrospermopsin producer identified in the United States to date. On the other hand, Cylindrospermopsis raciborskii is a prominent feature of many lakes in Florida and other regions of the United States. To see the variation in cylindrospermopsin cyrB gene adenylation domain sequences and possibly discover new cylindrospermopsin producers, we collected water samples for a 3-year period from 17 different systems in Florida. Positive amplicons were cloned and sequenced, revealing that approximately 92% of sequences were A. ovalisporum-like (>99% identity). Interestingly, 6% of sequences were very similar (>99% identity) to cyrB sequences of C. raciborskii from Australia and of Aphanizomenon sp. from Germany. Neutrality tests suggest that A. ovalisporum-like cyrB adenylation domain sequences are under purifying selection, with abundant low-frequency polymorphisms within the population. On the other hand, when compared between species by codon-based methods, amino acids of CyrB also seem to be under purifying selection, in accordance with the one proposed amino acid thought to be activated by the CyrB adenylation domain.
Applied and environmental microbiology 02/2011; 77(7):2502-7. · 3.69 Impact Factor
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ABSTRACT: One of the most common and widespread bloom-forming cyanobacteria associated with toxin production is Microcystis aeruginosa (Kutzing) Lemmerman. While normally associated with fresh water environments, this toxigenic species has been observed at bloom concentrations in a number of major estuaries worldwide. This study examined the effect of salinity on growth and toxin production by M. aeruginosa strain PCC 7806 under controlled laboratory conditions. Salt concentrations above 12.6 ppt resulted in total cessation of growth. Toxin production was similarly affected, with cul-tures grown in salt concentrations of 4.6 ppt and above yielding less toxin than the control after 20 days of culture. Toxin concentrations after 20 days of culture were 40% of the control at 4.6 ppt. The relative proportion of extracellu-lar to intracellular toxin increased over time in cultures with salt concentrations greater than 4.6 ppt. Extracellular toxins persisted in the media long after the cessation of growth. The results suggest that the influence of M. aeruginosa and/or its toxins can extend well out into estuarine environments under the influence of significant freshwater inputs.
Journal of Environmental Protection. 01/2011; 2:669-674.
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ABSTRACT: Cyanobacteria, red algae, and cryptomonad algae utilize phycobilin chromophores that are attached to phycobiliproteins to harvest solar energy. Heme oxygenase (HO) in these organisms catalyzes the first step in phycobilin formation through the conversion of heme to biliverdin IXalpha, CO, and iron. The Synechocystis sp. PCC 6803 genome contains two open reading frames, ho1 (sll1184) and ho2 (sll1875), whose products have in vitro HO activity. We report that HO2, the protein encoded by ho2, was induced in the cells growing under a microaerobic atmosphere [0.2% (v/v) O(2)], whereas HO1 was constitutively expressed under both aerobic and microaerobic atmospheres. Light intensity did not have an effect on the expression of both the HOs. Cells, in which ho2 was disrupted, were unable to grow microaerobically at a light intensity of 40 micromol m(-2) s(-1), but did grow microaerobically at 10 micromol m(-2) s(-1) light intensity. These cells grew normally aerobically at both light intensities. Comparative analysis of complete cyanobacterial genomes revealed that possession of two HOs is common in cyanobacteria. In phylogenetic analysis of their amino acid sequences, cyanobacterial HO1 and HO2 homologs formed distinct clades. HO sequences of cyanobacteria that have only one isoform were most similar to HO1 sequences. We propose that HO2 might be the more ancient HO homolog that functioned under low O(2) tension, whereas the derived HO1 can better accommodate increased O(2) tension in the environment.
Photosynthesis Research 11/2009; 103(1):47-59. · 3.24 Impact Factor
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ABSTRACT: DNA isolated from environmental samples often contains enzyme inhibitors disruptive to downstream molecular applications. Most of the existing methods of cyanobacterial DNA isolation do not effectively eliminate these inhibitors from sediment samples or cells collected from freshwater ecosystems. We describe improved methods based on the xanthogenate-SDS nucleic acid isolation (XS) method of Tillett and Neilan (2000). Our improved methods provided high-quality cyanobacterial DNA that could be amplified in PCR and digested with a restriction enzyme. Results were superior to several commercial kits. The DNA yield was also similar to that obtained via the standard XS method. These methods should provide valuable new tools for the expanded application of molecular genetics to limnological and oceanographic research.
Journal of Phycology 03/2009; 45(2):517 - 521. · 2.07 Impact Factor
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ABSTRACT: The toxin cylindrospermopsin (CYN) is produced by a variety of cyanobacterial genera. One of these, Cylindrospermopsis raciborskii, is generally assumed to be the source of CYN in lakes and rivers in Florida, USA. However, in this study, none of the eight Florida isolates of this species tested contained the genetic determinants involved in toxin production nor did they produce CYN. We show for the first time that Aphanizomenon ovalisporum isolated from a pond in this state has the genes putatively associated with CYN production. Analysis by liquid chromatography with mass spectrometric detection (LC/MS) revealed that it produced CYN in the range of 7.39-9.33 microg mg(-1) freeze-dried cells. 16S rDNA sequences of this strain showed 99.6% and 99.9% identity to published A. ovalisporum and Anabaena bergii 16S sequences, respectively. These results help to explain the general lack of a defined relationship between the abundance of C. raciborskii in freshwater ecosystems of Florida and observed concentrations of CYN. The latter observation raises the potential that previous reports of CYN may be coincidental with unrecorded presence of another CYN-producing species.
Toxicon 02/2008; 51(1):130-9. · 2.51 Impact Factor
