Efficacy of molecular DNA methods for confirming species identifications on morphologically variable populations of toxin-producing Anabaena (Nostocales)

Abstract

Algal samples were analyzed from 3 lakes, Crane Prairie Reservoir and Odell Lake in Oregon and an Anonymous North East System, using both standard taxonomic criteria for identification and DNA sequencing techniques. Two toxin-producing Anabaena populations, one with consistent akinete structure and another with variable akinete structure, were investigated. Samples were characterized based on several genetic markers (nifH, cpcBA-IGS, ITS1), toxins (anatoxin-a, saxitoxin, and microcystin) and morphological variation. Taxonomy within the Nostacales is based on vegetative and terminal cell structure, filament type and aggregation, and position and structure of heterocysts and akinetes. Many taxonomists rely heavily on akinete structure for microscopic identification. Identification from material preserved with Lugol's solution is challenging due to the breakup of colonies, cell distortion, and masking of pigment color. Based on morphological variation, the Crane Prairie and Odell populations were identified as A. flos-aquae, A. circinalis, or A. lemmermannii, and toxin analysis detected the presence of microcystin. These populations were most similar to A. lemmermannii (cpcBA-IGS) or Anabaena sp. (ITS1) by DNA sequence analysis. The Anonymous North East System population was identified as A. flos-aquae, A. circinalis or A. spiroides based on morphological variation, and both microcystin and anatoxin-a were detected in these samples. Sequences most similar to A. cylindrica (nifH), A. planktonica (cpcBA-IGS), A. spiroides or Aphanizomenon flos-aquae (ITS1) were identified in the Anonymous North East System samples, but there were no definitive matches. Although molecular methods can be useful tools for confirming identification based on field material, their ability to resolve issues of taxonomic identification are dependent on the comprehensiveness of the sequence database. Taxonomic keys based on cell morphology and identification based on current DNA sequence databases are subject to similar levels of variation and uncertainty.

Key words:

• akinete
• Anabaena
• anatoxin-a
• Aphanizomenon
• cpcBA-IGS
• DNA
• ITS1
• microcystin
• nifH