Hepatotoxic Cyanobacteria: A Review of the Biological Importance of Microcystins in Freshwater Environments

Abstract

Cyanobacteria possess many adaptations to develop population maxima or "blooms" in lakes and reservoirs. A potential consequence of freshwater blooms of many cyanobacterial species is the production of potent toxins, including the cyclic hepatotoxins, microcystins (MCs). Approximately 70 MC variants have been isolated. Their toxicity to humans and other animals is well studied, because of public health concerns. This review focuses instead on the production and degradation of MCs in freshwater environments and their effects on aquatic organisms. Genetic research has revealed the existence of MC-related genes, yet the expression of these genes seems to be regulated by complex mechanisms and is influenced by environmental factors. In natural water bodies, the species composition of cyanobacterial communities and the ratio of toxic to nontoxic species and strains are largely responsible for total toxin production. Cyanobacteria play vital roles in aquatic food webs, yet production, accumulation, and toxicity patterns of MCs within aquatic food webs remain obscure.

Mathematical modeling of Microcystis aeruginosa growth and [D-Leu1] microcystin-LR production in culture media at different temperatures

“…Many Microcystis strains can produce the potent hepatotoxin microcystin (MC), of which there are more than 100 variants, causing liver damage as well as nephrotoxicity (Milutinovic et al, 2003;Merel et al, 2013;Niedermeyer, 2013). Harke et al (2016) conclude that the occurrence of Microcystis toxic blooms appears to be expanding, since 108 countries or territories around the world have documented their presence in recent years compared with fewer than 30 countries in earlier years (Zurawell et al, 2005).…”

Tropical cyanobacterial blooms: a review of prevalence, problem taxa, toxins and influencing environmental factors

“…Currently there are two types of cyanotoxins that are particularly problematic to humans: hepatotoxins (cyclic peptides) and neurotoxins (alkaloids) (Sivonen, 1999;Stewart et al, 2008;Wiegand and Pflugmacher, 2005;Zurawell et al, 2005;Chen et al, 2009). Toxin-producing cyanobacteria have been responsible for serious cases of human and livestock poisoning and deaths in a number of countries worldwide (e.g., in Brazil, Australia and North America) (Francis, 1878;Beasley et al, 1989;Azevedo et al, 2002;Cox et al, 2005;Sotero-Santos et al, 2006).…”

Response and recovery of hybrid sturgeon from subchronic oral administration of cyanobacteria

“…However, the harmful effects of MCs on fishes were mainly limited to acute toxic exposure routes and they were based on either oral gavaging, or intraperitoneal injection, or administration via the dorsal aorta of the toxins (Carbis et al, 1996;Bury et al, 1997;Li et al, 2005), which cannot reflect the uptake route under natural environments. More importantly, cyanobacteria are an important dietary component for many fish species (e.g., Tilapia) (Zurawell et al, 2005). In addition, MCs are rarely ingested by human in amount high enough for a lethal acute dose, but the toxicity caused by chronic effect is particularly more probable if there is longterm frequent exposure (Magalhães et al, 2003).…”