Multiple cyanotoxin congeners produced by sub-dominant cyanobacterial taxa in riverine cyanobacterial and algal mats

Abstract

35 Benthic cyanobacterial proliferations in rivers are have been reported with increasing 36 frequency worldwide. In the Eel and Russian rivers of California, more than a dozen dog deaths 37 have been attributed to cyanotoxin toxicosis since 2000. Periphyton proliferations in these 38 rivers comprise multiple cyanobacterial taxa capable of cyanotoxin production, hence there is 39 uncertainty regarding which taxa are producing toxins. In this study, periphyton samples 40 dominated by the cyanobacterial genera Anabaena spp. and Microcoleus spp. and the green 41 alga Cladophora glomerata were collected from four sites in the Eel River catchment and one 42 site in the Russian River. Samples were analysed for potential cyanotoxin producers using 43 polymerase chain reaction (PCR) in concert with Sanger sequencing. Cyanotoxin 44 concentrations were measured using liquid chromatography tandem-mass spectrometry, and 45 anatoxin quota determined using droplet digital PCR. Sequencing indicated Microcoleus sp. 46 and Nodularia sp. were the putative producers of anatoxins and nodularins, respectively, 47 regardless of the dominant taxa in the mat. Anatoxin concentrations in the mat samples varied 48 from 0.1 to 18.6 μg g -1 and were significantly different among sites (p < 0.01, Wilcoxon test); 49 however, anatoxin quotas were less variable (< 5-fold). Dihydroanatoxin-a was generally the 50 most abundant variant in samples comprising 38% to 71% of the total anatoxins measured. 51 Mats dominated by the green alga C. glomerata contained both anatoxins and nodularin-R at 52 concentrations similar to those of cyanobacteria-dominated mats. This highlights that even 53 when cyanobacteria are not the dominant taxa in periphyton, these mats may still pose a serious 54 health risk and indicates that more widespread monitoring of all mats in a river are necessary. 55 56 57 58 59 60 61 62 63 64 65 66 67 68 1. Introduction 69 70 Reports of toxic benthic cyanobacterial proliferations have been described over the past 30 71 years [e.g. 1, 2, 3] and are now increasing in frequency globally [4-9]. Despite these reports, 72 investigations into benthic cyanotoxin producers, and variability in toxin production are limited 73 [7]. Many benthic cyanobacteria are now known to produce cyanotoxins, for example, 74 Anabaena, Phormidium, Lyngbya, Oscillatoria, Nostoc, Nodularia and Microcoleus. While 75 these taxa are often dominant in proliferations [7], they are also common components of 76 periphyton mats where other algae are more abundant [e.g. Cladophora glomerata; 10, 11], 77 and the risks these mats pose is relatively unknown. 78 79 Cyanotoxins are typically classified by their different toxicological properties into neurotoxins 80 (e.g., anatoxins and saxitoxins [STXs; 12], hepatotoxins (e.g., microcystins [MCYs], 81 nodularins [NODs] and cylindrospermopsins [CYNs]), cytotoxins and dermatotoxins [13, 14]. 82 Among benthic cyanobacteria, anatoxins are the most commonly reported cyanotoxin. 83 Anatoxins comprise four main structural congeners;...

Microcoleus (Cyanobacteria) form watershed‐wide populations without strong gradients in population structure

“…The region has a Mediterranean climate with seasonal summer droughts, and each summer benthic mats of attached algae proliferate (Power et al, 2008). Microcoleus (Oscillatoriales, Cyanobacteria) are common throughout the watershed in summer (Bouma‐Gregson et al, 2018; Kelly et al, 2019).…”

Toxic benthic freshwater cyanobacterial proliferations: Challenges and solutions for enhancing knowledge and improving monitoring and mitigation

“…In these instances, the use of less‐specific detection techniques such as a MS/MS precursor ion screen, with detects ions with characteristics of MCs (Kleinteich et al., 2018) or ELISAs, may be useful for a preliminary screen although false positives will need to be checked. Geographic differences in the congener profiles of anatoxins produced by Microcoleus or Phormidium have also been observed between New Zealand, France, and U.S.A. (Echenique‐Subiabre, Tenon, et al, 2018; Kelly, Bouma‐Gregson, et al, 2019; McAllister et al., 2016); highlighting the continued need for exploratory work on toxins from benthic cyanobacteria.…”

“…Molecular tools are now routinely used to screen benthic cyanobacteria mat samples for genes involved in toxin production for both research and routine monitoring (e.g. Kelly, Bouma‐Gregson, et al, 2019). Commercially available quantitative PCR kits are available and have been applied for this purpose in a number of countries (personal communication, Wood and Davis).…”

Cyanotoxins Associated with Macrophytes in Berlin (Germany) Water Bodies – Occurrence and Risk Assessment

“…on Cladophora sp. in Californian rivers (Kelly et al, 2019;Power et al, 2015). In Tegeler See, the cyanobacteria appeared rather as single filaments on Fontinalis tufts and were tentatively identified as tychoplanktonic Tychonema sp.…”