# Presence of Cyanotoxins in a Mexican Subtropical Monometric Crater Lake
## 1 Introduction  
The increasing global occurrence of toxic algae blooms in both marine and freshwater environments poses a serious threat to public health, animals, and ecosystems [1]. Among many other toxins microcystitis, a group of at least 279 known congeners, many of which are potent hepatotoxins.  
They have a common structure composed of D-aminoacid residues (3), L-aminoacid residues (2), N-methyldehydroalanine, and ADDA (3-amino-9-methoxy-2,6,8-trimethyl-10-phenyldeca-4,6-dienoic acid) residue [2,3]). Several cyanobacteria genera have been identified as microccystin producers [4, 5, 6, 7]. In North America, the most commonly reported genera are _Dolichospermn (Anabaena)_, _Microcystis_, _Plankton trix_ and _Pseudoanabaena_[8,9]. In Mexico, the _Microcystis_ genus seems to be ubiquitous in freshwater bodies and linked to the presence of microccystins [10]. The main mechanism of microccyst toxicity is the inhibition of serine/threonine protein phosphatase 1 and 2A (PP1 and PP2A), leading to the hyperphosphorylation of cytosolic and cytoskeletal proteins [11]. Another important family of toxins is the paralytic shellfish toxins (PSTs), composed of \(\sim\)57 neurotoxic analogs that include saxitoxin and related structural analogs [12,13]. PSTs act by interacting with amino acids of the pore regions SS1 and SS2 in each transmembrane domain of the sodium channels' \(\alpha\)-subunit in nerves and muscle cells, blocking neuronal transmission and leading to muscle paralysis and death by respiratory arrest in mammals [13]. Whilst most commonly associated with certain marine phytoplankton genera, some freshwater cyanobacteria from the order Notsocales (_Dolichospermn (Anabaena)_, _Aphanizomenon_, _Cylindrospermopsis_ and _Lyngbya vollei_) and _Plankton trix_ from the order Oscillatorales have also been reported to produce PSTs [14, 15, 16]. In the marine environment, two dinoflagellate species (_Pyrodinium bahamense_ and _Gymnodinium catenatum_) and several species of the genus _Alexandrium_ spp. produce PSTs [17]. Along Mexican coasts, PSTs have been reported on several occasions [18], whereas there is only one report in a Mexican freshwater system of PSTs, found in the tegogolo snail (_Pomacea patula catenacensis_) from the Lago of Catemaco on the coasts of the Gulf of Mexico [19].  
The Santa Maria del Oro crater lake (SMO), a mesotrophic lake [20], is an important tourist icon in Nayarit, Mexico that attracts thousands of tourists who perform ecotourism and recreational activities, such as the Festival Acuatico Santa Maria del Oro (Figure 1), which has an international reach and contributes to economic benefits for the region. During a water quality monitoring program in the lake, microalgal scums were noted during the first months of the year, with maximal visual biomass between February and March 2015. _Microcystis_ sp. and _Lyngbya_ sp. were preliminarily identified as the main genera in the algal scums [21,22]. Therefore, we assumed the possible presence of cyanobacterial microccystins and PSTs in both the water and the algae biomass. The goal of this work was to identify and quantify, via an HPLC fluorescence detector (HPLC-FLD) and UHPLC-MS/MS, the presence of these toxins in the lake.  
Figure 1: Swimming competition (Festival Acuático Santa Maria del Oro) in Santa Maria del Oro lake, Nayarit, during a cyanobacteria bloom in March 2018. Photo credit: [PERSON].