Abstract:
As photosynthetic organisms, Cyanobacteria play a crucial role in ecosystems. They are highly
adaptable and can be found in various habitats. During summer, cyanobacterial blooms, often with
toxin-producing species, pose a threat to humans and animals.
As primary producers, cyanobacteria are attractive prey for predators. Research on predatory
bacteria has gained increasing importance in recent years. However, only a few predatory bacteria
that prey on cyanobacteria are known, and their properties are poorly characterized. The defense
mechanisms of cyanobacteria against predatory bacteria are also unknown.
This work describes the interaction of the filamentous cyanobacterium Anabaena variabilis with
predatory bacteria. Initially, freshwater isolates were screened for predatory bacteria. Six isolates
were selected and examined in more detail using metagenome analysis and microscopy. Lysobacter
brunescens and Candidatus Venantispira tubingensis, a newly discovered bacterium, have been
identified as predatory bacteria of A. variabilis.
Candidatus Venantispira tubingensis belongs to the phylum Bacteroidota and is a representative of
a new genus in the family Saprospiraceae. It forms spiral, multicellular filaments up to 50 µm long
and it and close relatives have been found in Germany, Italy, New Mexico, and Costa Rica.
Venantispira preys on filamentous and unicellular cyanobacteria.
The cell surface of Venantispira carries outer membrane vesicle chains and smaller, possibly
adhesive filaments, which could play a role in the lysis mechanism. Venantispira moves along the
prey filament by alternating forward and backward movements until the prey cells finally lyse. This
mechanism has not yet been described for predatory bacteria.
Venantispira only lyses vegetative cells, while akinetes are not lysed. Therefore, akinetes play a role
in the defense A. variabilis against bacterial predators.
Further research is needed to fully understand the potential of the newly discovered bacterium
Candidatus Venantispira tubingensis. It has a broad prey spectrum and could thus provide a natural
way to control cyanobacterial blooms in freshwater. This could help reduce ecological damage
caused by toxin-producing blooms and protect drinking water reservoirs.
cyanobacteria