Cyano-archive : Cyanobacterial akinete survival and germination from northern Baltic Sea sediment

Cyanobacteria of the order Nostocales, including Baltic Sea bloom-forming species Nodularia spumigena, Aphanizomenon flosaquae, Dolichospermum spp., produce resting stages, known as akinetes, under unfavorable conditions. These akinetes can persist in the sediment and germinate if favorable conditions return, simultaneously representing past blooms and possibly contributing to future bloom formation. The present study characterized cyanobacterial akinete survival, germination, and potential toxin production in 40-to-175- year-old brackish water sediment archives in order to understand historical bloom expansion, akinete persistence, and cyanobacteria life cycles in the northern Baltic Sea. Results showed that cyanobacterial akinetes can persist in and germinate from northern Baltic Sea sediment up to 424 and 174 years old, at coastal and open-sea locations respectively. Akinete abundance and viability decreased with age and depth of vertical sediment layers. Increases in sediment organic matter content and akinete abundance largely corresponded with the historical expansion of anthropogenic eutrophication-fueled blooms of cyanobacteria in the northern Baltic Sea, beginning in the mid-twentieth century. The detection of potential hepatotoxin production from akinetes and revived cultures was minimal and restricted to the coastal sediment core. Phylogenetic analysis of culturable cyanobacteria from the coastal sediment core indicated that the majority of strains likely belonged to benthic genera Anabaena. Findings also supported the notion that, in comparison with Nodularia and Aphanizomenon spp. akinetes, Anabaena/Dolichospermum spp. akinetes play a more significant role in their life cycle and bloom initiation strategies. Further research is recommended to accurately quantify akinetes and create a higher rate of toxin gene detection from brackish water sediment samples in order to further describe species-specific benthic archives of cyanobacteria. Overall, measuring cyanobacterial akinete abundance, germination experiments, and genetic methods can be effectively used to determine akinete persistence, viability, and potential toxin production in brackish water sediment samples. This study highlights the prolonged survival of cyanobacterial akinetes in northern Baltic Sea sediment samples, up to 174 years old