Akinetes May Be Representative of Past Nostocalean Blooms: a Case Study of Their Benthic Spatiotemporal Distribution and Potential for Germination in a Eutrophic Lake

Abstract

Monitoring of water and surface sediment in a French eutrophic lake (Lake Aydat) was carried out over a 2-year period in order to determine whether akinetes in sediment could be representative of the most recent bloom and to estimate their germination potential. Sediment analysis revealed two akinete species, and, present in the same proportions as observed for the pelagic populations. Moreover, similar spatial patterns observed for vegetative cells in the water column and akinete distributions in the sediment suggest that akinetes in the sediment may be representative of the previous bloom. However, the relationship between akinetes in the sediment and vegetative cells in the water column was not linear, and other factors may interfere. For example, our results highlighted horizontal transport of akinetes during the winter. The benthic overwinter phase did not seem to influence the percentages of intact akinetes, which remained stable at approximately 7% and 60% for and, respectively. These percentages may thus be the result of processes that occurred in the water column. The intact overwintering akinetes showed germination rates of up to 90% after 72 h for or 144 h for The difference in akinete germination rates between these two species demonstrates different ecological strategies, which serve to expand the window for germination in time and space and thus optimize colonization of the water column by nostocalean cyanobacteria. Cyanobacteria have the ability to proliferate and to form blooms. These blooms can then affect the local ecology, health, and economy. The akinete, a resistant cell type that persists in sediment, is an important intermediate phase between previous and future blooms. We monitored the water column and the surface sediment of a French eutrophic lake (Lake Aydat) to investigate the relationship between vegetative cells in the water column and akinetes in the sediment. This study focused on the characterization of spatiotemporal akinete distributions, cellular integrity, and germination potential. Species-specific ecological strategies were highlighted and may partly explain the temporal succession of species in the water column. Akinetes may also be used to understand past nostocalean blooms and to predict future ones.

Benthic Archives Reveal Recurrence and Dominance of Toxigenic Cyanobacteria in a Eutrophic Lake over the Last 220 Years

“…In the uppermost 30 cm, D. macropsorum akinetes were characterized by a low integrity whereas a high one was measured for D. flos-aquae . The same applies in the surface sediment of Lake Aydat, where the percentage of intact akinetes varied from 7 to 60% for D. macroporum and D. flos-aquae respectively [ 27 ]. This high species-dependent variability may be explained by a species-specific sensitivity to ecological factors both in the water column and in sediment [ 21 , 27 ].…”

A Review on the Study of Cyanotoxins in Paleolimnological Research: Current Knowledge and Future Needs

“…Under unfavorable conditions, selected toxin producers can form dormant cells known as akinetes, and deposit them in sediments. Whether these akinetes contain cyanotoxins has not been subject to investigation; but it was demonstrated that in some cases, up to several thousands of intact akinetes per g of sediment can be deposited [43]. If these cells contain selected toxins of interest, they would highly contribute to the sedimentary cyanotoxin pool.…”

“…Very few studies have attempted to reconstruct MC production prior to recent human development around lake systems (pre-150 years); most studies have utilized a variety of extraction techniques, and one of two analytical techniques: liquid chromatography-mass spectrometry (LC-MS), or gas chromatography-mass spectrometry (GC-MS) ( Tables 1 and 2). Recently, a longer history of potential MC production was constructed from akinetes, and by sequencing genes related to MC synthesis isolated from a sediment core from Lake Aydat, France [43]. While records of historic MC production are slowly being produced and timelines are being extended, a comprehensive extraction technique and a detailed understanding of MC degradation and transformation post-deposition have yet to be established.…”

“…So far, this has not been a subject of any study. However, paleolimnological investigations have already demonstrated that akinetes can be found in sediments, their characteristic morphological features can be used to identify the species they originated from, and toxin biosynthesis genes can be successfully amplified from their DNA [43,56,112]. If akinetes of toxin-producing strains contain cyanotoxins, then they may make a significant contribution to the sedimentary pool of these compounds, given the fact that in some cases, a high number of these cells can be identified in sediment layers.…”

“…If akinetes of toxin-producing strains contain cyanotoxins, then they may make a significant contribution to the sedimentary pool of these compounds, given the fact that in some cases, a high number of these cells can be identified in sediment layers. For example, Legrand et al [43] reported up to 705,000 and 36,400 akinetes of Dolichospermum macrosporum and D. flos-aquae per g of dried sediment, respectively.…”