Abstract
Toxic cyanobacterial blooms are a growing threat to freshwater bodies worldwide. In order for a toxic bloom to occur, a population of cells with the genetic capacity to produce toxins must be present together with the appropriate environmental conditions. In this study, we investigated the distribution patterns and phylogeny of potentially-toxic Microcystis (indicated by the presence and/or phylogeny of the mcyD and mcyA genes). Samples were collected from the water column of almost 60 water bodies across widely differing gradients of environmental conditions and land use in Israel. Potentially, toxic populations were common but not ubiquitous, detected in ~65% of the studied sites. Local environmental factors, including phosphorus and ammonia concentrations and pH, as well as regional conditions such as the distance from built areas and nature reserves, were correlated with the distribution of the mcyD gene. A specific phylogenetic clade of Microcystis, defined using the sequence of the mcyA gene, was preferentially associated with aquaculture facilities but not irrigation reservoirs. Our results reveal important environmental, geospatial, and land use parameters affecting the geographic distribution of toxinogenic Microcystis, suggesting non-random dispersal of these globally abundant toxic cyanobacteria.
Highlights
Cyanobacteria, as part of a larger algal community, form the base of the food web in many aquatic environments
The goals of the study were: (1) to map the distribution of potentially-toxic Microcystis strains during the period of the year when blooms are most common, using a highly conserved fragment of the mcyD gene; (2) to characterize the environmental factors associated with the presence of toxin-producing strains in the water column, and, (3) to determine, using the phylogenetically-informative mcyA gene, whether toxinogenic strains in Israel belong to a single or multiple populations, each potentially associated with a specific aquatic niche
To map the distribution of potentially toxic Microcystis across different environmental conditions in Israel, we sampled 58 different water bodies belonging to seven functional categories: fish ponds, irrigation reservoirs, lakes, natural springs, spring systems, rivers and salterns
Summary
Cyanobacteria, as part of a larger algal community, form the base of the food web in many aquatic environments (both marine and freshwater; Paerl and Paul, 2012). Under appropriate conditions, many cyanobacterial species can grow at a rapid rate and form massive “blooms” which negatively impact water quality, especially when the blooming species produces toxins (Schinder and Valentyne, 2008; Paerl and Otten, 2013). Over the last several decades the frequency and severity of reported cyanoHABs has increased significantly, and toxic blooms have been observed in water bodies where they have not previously been recorded (Sukenik et al, 2012) To date, it is unknown whether these newly-observed blooms occur due to cyanobacteria that were always part of the microbial population (and potentially had bloomed but this was not reported) or whether these organisms have recently colonized the water body in question. If the latter is true, it is unclear whether the newlyintroduced cyanobacteria migrated naturally (e.g., carried by the wind, animals or birds, Sukenik et al, 2012; van Leeuwen et al, 2012), or were introduced by man, for example through fish stocking or ballast water (Padilla and Williams, 2004)
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