Abstract
Accurate identification of cyanobacteria using traditional morphological taxonomy is challenging due to the magnitude of phenotypic plasticity among natural algal assemblages. In this study, molecular approach was utilized to facilitate the accurate identification of cyanobacteria in the Sacramento-San Joaquin Delta and in Clear Lake in Northern California where recurring blooms have been observed over the past decades. Algal samples were collected from both water bodies in 2011 and the samples containing diverse cyanobacteria as identified by morphological taxonomy were chosen for the molecular analysis. The 16S ribosomal RNA genes (16S rDNA) and the adjacent internal transcribed spacer (ITS) regions were amplified by PCR from the mixed algal samples using cyanobacteria generic primers. The obtained sequences were analyzed by similarity search (BLASTN) and phylogenetic analysis (16S rDNA) to differentiate species sharing significantly similar sequences. A total of 185 plasmid clones were obtained of which 77 were successfully identified to the species level: Aphanizomenon flos-aquae, Dolichospermum lemmermannii (taxonomic synonym: Anabaena lemmermannii), Limnoraphis robusta (taxonomic synonym: Lyngbya hieronymusii f. robusta) and Microcystis aeruginosa. To date, Dolichospermum and Limnoraphis found in Clear Lake have only been identified to the genus lavel by microscopy. During the course of this study, morphological identification and DNA barcoding confirmed A. flos-aquae as the predominant cyanobacterium in the Sacramento-San Joaquin Delta indicating a shift from M. aeruginosa that have dominated the blooms in the past decade. Lastly, the species-specific identification of Limnoraphis robusta in Clear Lake is another significant finding as this cyanobacterium has, thus far, only been reported in Lake Atitlan blooms in Guatemala.
Highlights
Harmful cyanobacterial blooms (CyanoHABs) are a serious global concern and are often associated with odorous metabolites in drinking water and toxins in aquaculture facilities and in the environment (Mankiewicz et al 2003; Smith et al 2008)
The samples from the Sacramento-San Joaquin Delta showed that Aphanizomenon spp., Dolichospermum spp., and M. aeruginosa were dominant as observed by microscopy, other cyanobacterial species such as Limnoraphis, Gloeotrichia, and Woronichinia that were found in Clear Lake were not observed in the Delta by traditional microscopy (Table 1)
Microscopic observation coupled with DNA barcoding effectively identified cyanobacterial species in the Sacramento-San Joaquin Delta and in Clear Lake
Summary
Harmful cyanobacterial blooms (CyanoHABs) are a serious global concern and are often associated with odorous metabolites in drinking water and toxins in aquaculture facilities and in the environment (Mankiewicz et al 2003; Smith et al 2008). Different types of toxins are produced from several cyanobacterial species including hepatotoxins (microcystins), cytotoxins (cylindrospermopsin), neurotoxins (anatoxin-a, antillatoxin, saxitoxins), and dermatoxins (lyngbyatoxins). Colonial forms of M. aeruginosa are widely distributed along the 180 km of freshwater and brackish waterways of the delta that may affect indigenous invertebrates and fishes (Lehman et al 2005, 2008, 2010; Ger et al 2010) Other harmful cyanobacteria such as Aphanizomenon, Dolichospermum (formerly recognized as planktic Anabaena) (Wacklin et al 2009), and Oscillatoria have been observed in the Sacramento-San Joaquin Delta, to a lesser extent than Microcystis (Cloern and Dufford 2005; Lehman et al 2010; Spier et al 2010). Because algal bloom studies in the Delta have mainly focused on M. aeruginosa (Lehman et al 2005, 2008, 2010), the occurrence, abundance, and potential role of other toxin-producing cyanobacteria to indigenous fisheries resources are largely unknown
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