Mete Yilmaz

Climatic Influences on Autochthonous and Allochthonous Phytoplankton Blooms in a Subtropical Estuary, St. Lucie Estuary, Florida, USA

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.

IMPROVED METHODS FOR THE ISOLATION OF CYANOBACTERIAL DNA FROM ENVIRONMENTAL SAMPLES

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.

Diversity of and Selection Acting on Cylindrospermopsin cyrB Gene Adenylation Domain Sequences in Florida

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.

Toxicity and genetic diversity of Cylindrospermopsis raciborskii in Florida, USA

Abstract Cylindrospermopsis raciborskii is a potentially toxic cyanobacterium which has become increasingly prominent in algal blooms throughout the USA. Twenty strains of C. raciborskii isolated from Florida, and one strain from Indiana (USA), were tested for the ability to produce three toxins, cylindrospermopsin, microcystin and saxitoxin using newly developed Polymerase Chain Reaction (PCR) primers and Enzyme Linked Immunosorbent Assays (ELISA). None of these strains demonstrated the ability to produce any of the three toxins. Phylogenetic analyses of 16S rRNA gene sequences, a common genetic marker used in taxonomic differentiation, did not delineate these isolates from other C. raciborskii strains. However, Rubisco Large Subunit gene sequences, a less commonly used but useful genetic marker, provided better resolution of differences between Florida strains of C. raciborskii and those from Australia, which are known to be toxic. There may be toxic strains of C. raciborskii in the USA, but none were found among the Florida and Indiana strains examined, suggesting that strains of C. raciborskii in Florida lakes, and perhaps other regions of North America, may not be toxic. The potential management implications of this observation warrant further exploration of the toxicity of this species in the Americas.