Gkelis, S. | bioRxiv Science

bioRxiv2020

The effects of microcystin-LR in Oryza sativa root cells: F-actin as a new target of cyanobacterial toxicity

O_LIMicrocystins are toxins produced by cyanobacteria, notorious for negatively affecting a wide range of living organisms, among which several plant species. Although microtubules are a well-established target of microcystin toxicity, its effect on filamentous actin (F-actin) in plant cells has not been studied yet. C_LIO_LIThe effects of microcystin-LR (MC-LR) and the extract of a microcystin-producing freshwater cyanobacterial strain (Microcystis flos-aquae TAU-MAC 1510) on the cytoskeleton (F-actin and microtubules) of Oryza sativa (rice) root cells, were studied by light, confocal, and transmission electron microscopy. Considering the role of F-actin in endomembrane system distribution, the endoplasmic reticulum and the Golgi apparatus in extract-treated cells were also examined. C_LIO_LIF-actin in both MC-LR- and extract-treated meristematic and differentiating root cells exhibited time-dependent alterations, ranging from disorientation and bundling to the formation of ring-like structures, eventually resulting to a collapse of the F-actin network at longer treatments. Disorganization and eventual depolymerization of microtubules, as well as abnormal chromatin condensation were observed following treatment with the extract, effects which could be attributed to microcystins and other bioactive compounds. Moreover, cell cycle progression was inhibited in extract-treated roots, specifically affecting the mitotic events. As a consequence of F-actin network disorganization, endoplasmic reticulum elements appeared stacked and diminished, while Golgi dictyosomes appeared aggregated. C_LIO_LIThese results support that F-actin is a prominent target of MC-LR, both in pure form and as an extract ingredient. Endomembrane system alterations can also be attributed to the effects of cyanobacterial bioactive compounds (including microcystins) on F-actin cytoskeleton. C_LI

plant biology↗

bioRxiv2020

Cyano-assassins: Widespread cyanogenic production from cyanobacteria

Cyanobacteria have been linked with hydrogen cyanide, based on their ability to catabolize it by the nitrogenase enzyme, as a part of nitrogen fixation. Nitrogenase can also use hydrogen cyanide instead of its normal substrate, dinitrogen and convert it to methane and ammonia. In this study, we tested whether cyanobacteria are able, not only to reduce, but also to produce HCN. The production of HCN was examined in 78 cyanobacteria strains from all five principal sections of cyanobacteria, both non-heterocytous and heterocytous, representing a variety of lifestyles and habitats. Twenty-eight (28) strains were found positive for HCN production, with universal representation amongst 22 cyanobacterial planktic and epilithic genera inhabiting freshwater, brackish, marine (including sponges), and terrestrial (including anchialine) habitats. The HCN production could be linked with nitrogen fixation, as all of HCN producing strains are considered capable of fixing nitrogen. Epilithic lifestyle, where cyanobacteria are more vulnerable to a number of grazers and accumulate more glycine, had the largest percentage (75%) of HCN-producing cyanobacteria compared to strains from aquatic ecosystems. Further, we demonstrate the isolation and characterisation of taxa like Geitleria calcarea and Kovacikia muscicola, for which no strain existed and Chlorogloea sp. TAU-MAC 0618 which is, to the best of our knowledge, the first bacterium isolate from anchialine ecosystems. Our results highlight the complexity of cyanobacteria secondary metabolism, as well as the diversity of cyanobacteria in underexplored habitats, providing a missing study material for this type of environments.

microbiology↗