Characterization of akinetes from cyanobacterial strains and lake sediment: A study of their resistance and toxic potential

Nostocalean cyanobacteria are known to proliferate abundantly in eutrophic aquatic ecosystems, and to produce several cyanotoxins, including anatoxin-a. In this study, we investigated both the resistance and toxic potential of the akinetes (resistant cells), using cyanobacterial cultures and akinetes extracted from the sediment of Lake Aydat (France) sampled in the winter and spring. Intact and lysed akinetes were differentiated using a double control based on the autofluorescence of akinetes and SYTOX-green staining. The percentage of resistant akinetes found in several different abiotic stress conditions was highly variable, depending on the species and also on the sampling season. Thus, the resistance of akinetes and their ability to germinate seems to follow a species-specific process, and akinetes can undergo physiologic changes during the sedimentary phase of the Nostocale life cycle. This study also revealed the first evidence of anatoxin-a genes in akinetes, with anaC and anaF genes detected in akinetes from all cyanobacterial producer cultures. The low number of anaC genes, almost exclusively detected using nested PCR, in the sediment at Lake Aydat suggests a limited but existent past population of toxic Nostocales in this lake. Given the key role of akinetes in the annual cycle and subsequent summer proliferation, it can be interesting to integrate the surveillance of akinetes in the management of lakes exposed to recurrent cyanobacterial blooms.