The impact of some microcystins on the growth of heterotrophic bacteria from Portuguese freshwater reservoirs

Abstract

The impact of some microcystins on the growth of heterotrophic bacteria from Portuguese freshwater reservoirs Microcystins (MCs) are hepatotoxins that are abundantly produced by cyanobacteria. Studies have shown that these toxins affect many multicellular organisms that inhabit aquatic ecosystems; however, their impact on bacteria that co-occur with freshwater cyanobacteria is still unclear. In this study, the impact of the three most common variants of MCs (MCLR, MCRR, and MCYR) on the growth of heterotrophic bacteria isolated from four Portuguese reservoirs was evaluated. Some isolates were derived from freshwater sources where blooms of cyanobacteria that often contain microcystin-producing strains are frequently observed and from a reservoir where these phenomena do not occur. Morphological and molecular characterisation of the bacterial isolates was performed, and these bacteria were exposed to three different concentrations of each MC variant. The effect of MCs on bacterial growth was then evaluated. This study showed that MCLR, MCRR and MCYR can reduce the growth of some heterotrophic bacteria isolated from freshwater sources. To our knowledge, this is the first study in which the impact of several variants of MCs was evaluated in a diverse group of freshwater heterotrophic bacteria.

The Effect of Microcystis on the Monitoring of Faecal Indicator Bacteria

“…In addition, when Chlorella was present in the absence of the Microcystis species in lake water, there was no deleterious effect on E. coli, further supporting the notion that toxin from cyanobacteria played an important role in reducing survival of the tested FIB. It is known that Microcystis can alter native bacterial assemblages in lakes [7], that microcystins modify bacterial communities in sediments [8] and affect bacterial growth in freshwater reservoirs [6].…”

“…Cyanotoxins such as microcystins that are produced by cyanobacteria, most notably Microcystis species, are known to cause numerous toxic effects in mammals, other animals and plants [2]. Although these compounds can negatively impact the growth and carbon fixation of photosynthetic prokaryotes [3], there is little information concerning their effects on heterotrophic prokaryotes [4][5][6]. Even though changes in bacterial assemblages have been detected in response to Microcystis colonies [7] and microcystins [8], there are no available reports addressing directly the dynamics of cyanobacteria and E. coli or other coliform bacteria, especially from the point of view of the effectiveness of faecal indicator bacteria (FIB) to indicate water quality when there is a risk of HABs being present.…”