Received: January 14, 2020; Published: January 21, 2020
Corresponding author: Jian Yuan, Department of Veterinary Diagnostic and Production Animal Medicine, Iowa State University, USA
Freshwater toxic cyanobacteria can produce potent cyanotoxins which are detrimental and lethal to animals. Water from farm ponds contaminated by cyanotoxins can carry the toxins to nearby livestock facilities, posing a threat of animal poisoning when toxins reach a dangerous level. Therefore, fast and precise means should be conducted to reveal the existence and levels of cyanotoxins and toxic cyanobacteria to find out such threats in a timely fashion.
Keywords: Toxic cyanobacteria; cyanotoxins; farm ponds; livestock; facilities
Abbreviations: HAB: Harmful Algal Bloom; ELISA: Enzyme Linked Immunosorbent Assay; HPLC: High Performance Liquid Chromatography; MS: Mass Spectrometry; PCR: Polymerase Chain Reaction
Cyanobacteria, colloquially called blue-green algae, are a group
of photoautotrophic prokaryotic microalgae which inhabit a variety
of environments on earth. Their ubiquity in global freshwater
bodies has made them important cosmopolitan organisms in
freshwater habitats. Being able to proliferate explosively under
appropriate ambient conditions, for example sufficient nitrogen
and/or phosphorus nutrients, cyanobacteria can easily become
dominant in inhabited ecosystems and form an ecological
phenomenon/disaster named HAB. An HAB can bring about many
deleterious impacts on local ecosystems such as hypoxia caused
by over consumption of oxygen by bacteria for degrading dead
cyanobacterial cells. What is even worse, some cyanobacteria can
produce potent cyanotoxins toxic to animals and humans, and the
toxins can be enriched to a dangerous level in an HAB, causing health
and sanitation problems [1,2]. Cyanotoxins contain a tremendous
number of species and are categorized by their toxicological
effects into hepatotoxin, neurotoxins, cytotoxin, etc. Microcystin,
anatoxin-a, and cylindrospermopsin are the most prevalent
representative toxins that fall into the three categories, respectively.
They can kill a poisoned animal in a very low dose (e.g, 3 ppb for a
nursery pig) . As a secondary metabolite, these toxins are mostly
produced by cyanobacterial species in Microcystis, Anabaena, and
Cylindrospermopsis, respectively, although their production is also
found in other genera. The process of toxin production is well
profiled and regulated under a synthetic mechanism by a group
of enzymes that are translated from clustered toxin synthetase
genes [3-5]. Direct detection of cyanotoxins can be conducted using
ELISA, HPLC, and MS. These techniques are already characterized
with satisfactory specificities and sensitivities. Moreover, detection
of toxic cyanobacteria can be done as an alternative approach for
identifying toxicity. Because a toxic species actually has toxic strains
as well as non-toxic strains that share identical morphologies but
lack the toxin synthetase genes, traditional microscopic examination
cannot fulfill the purpose of accurate recognition of toxicity. As a
result, molecular methods targeting the existence of toxin genes is
an effective approach to find out the toxic cyanobacteria, of which
PCR is the most popular. While, intuitively, existence of genes doesn’t
equate to production of toxins as there is likely a “switching on/off”
mechanism of the genes (frankly, “toxigenic” is more accurate than
“toxic” per se), findings of good correlations for their existence as well as quantities suggest revelation of toxic cyanobacteria is an
excellent indicator of toxicity .
Microcystis and Anabaena exist across extensive latitudes, and Cylindrospermopsis can be discovered in temperate zones despite it was found in tropical zones. They grow in some waterbodies which are also water sources for livestock. Although the water is sometimes treated to remove possible contaminants, it is directly transported to facilities for animals’ consumption, increasing the likelihood of cyanotoxin poisoning. In my recent study in five farm ponds and five swine facilities served by these ponds as water sources in the Midwestern United States, it was found that the abundances of toxic Microcystis spp. and Anabaena spp., and levels of microcystin and anatoxin-a had no significant differences (p > 0.05 by paired t-tests) in water between ponds and facilities with a few chlorinated samples in one facility for detoxification (Figure 1). Although all the quantities were far below the warning levels for an HAB or a toxicosis, chronical effects may occur on swine due to accumulation of toxic cyanobacteria and/or toxins. More crucially, swine can easily be poisoned once toxins are rapidly accumulated in an unpredictable HAB event. Furthermore, the failure of decontamination of cyanotoxins by chlorination suggests an option of effective detoxification.
Figure 1: Abundances of toxic Microcystis spp. and Anabaena spp, and levels of microcystin and anatoxin-a in 105 water samples from five farm ponds and five swine facilities in the Midwestern United States. Toxic Microcystis spp. and Anabaena spp. are represented by one synthetase gene for microcystin and anatoxins-a (mcyC and anaG), respectively. MCY and ATX are abbreviations for microcystin and anatoxins-a, respectively. Ponds and facilities are indicated by BWE, B,O,P, and W. Black, red, and blue squares refer to pond water, facility unprocessed water, and chlorinated water, respectively..
In farm ponds as water resources to facilities lies a potential threat of livestock poisoning by cyanotoxins produced by toxic cyanobacteria. Therefore, accurate and prompt detection approaches for toxins and their producers are highly necessary. Nowadays, detection of toxic cyanobacteria and cyanotoxins is a component of routine water monitoring programs for large and important waterbodies like lakes and reservoirs. However, such a program doesn’t exist for small farm ponds that are prone to eutrophication (over enrichment of nutrients) causing HABs. As they are vital for livestock health as water sources, it is strongly suggested monitoring of toxic cyanobacteria and cyanotoxins should be set up in these farm ponds as a diagnostic or prewarning tool for veterinarians, producers, and stakeholders.
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