A new cyanobacterial species with a protective effect on lettuce grown under salinity stress: Envisaging sustainable agriculture practices

In this work, a new terrestrial cyanobacterial species, Oculatella lusitanica LEGE 161147, was isolated and characterized using a polyphasic approach. Morphologically, O . lusitanica shares characteristics with different Oculatella species (mainly with O . crustae - formantes ), lacking distinctive features. However, the phylogeny based on the 16S rRNA gene sequence and the 16S-23S ITS secondary structures support the establishment of this isolate as a new species. O. lusitanica is placed within a clade mainly composed by other Oculatella terrestrial strains; however, it forms a separate lineage. In addition, our species differs from the other Oculatella described so far by lacking the V2 helix within the ITS region. Since cyanobacteria are known to release compounds that promote plant growth and/or increase their tolerance to stresses, the effect of this newly described cyanobacterial species on Lactuca sativa (lettuce) plants development and salinity stress resistance was evaluated. Our results showed that, although the cyanobacterium had no impact on plant growth under the conditions tested, it was able to mitigate the deleterious salinity stress effects on plant size, root and aerial part fresh weight, by eliciting the non-enzymatic antioxidant response system (proline, H 2 O 2 and reduced glutathione). In addition, the microorganism was able to induce a priming effect on lettuce plants by stimulating defensive mechanisms under non-stress conditions, and enhances the activity of nitrogen metabolism-related enzymes glutamate dehydrogenase, glutamine synthetase and nitrate reductase. These results indicate that this native terrestrial cyanobacterial species could be employed as a tool in sustainable agricultural practices.