Diversity of and Selection Acting on CylindrospermopsincyrBGene Adenylation Domain Sequences in Florida

Abstract

Aphanizomenon ovalisporumis the only confirmed cylindrospermopsin producer identified in the United States to date. On the other hand,Cylindrospermopsis raciborskiiis a prominent feature of many lakes in Florida and other regions of the United States. To see the variation in cylindrospermopsincyrBgene 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 wereA. ovalisporum-like (>99% identity). Interestingly, 6% of sequences were very similar (>99% identity) tocyrBsequences ofC. raciborskiifrom Australia and ofAphanizomenonsp. from Germany. Neutrality tests suggest thatA. ovalisporum-likecyrBadenylation 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.