Biostimulatory effects of Limnospira indica on the modulation of rhizosphere and endosphere microbiota and its impact on plant growth

Abstract Cyanobacteria-derived biostimulants can improve plant performance through microbiota modulation. We tested culture fractions of Limnospira indica on tomato ( Solanum lycopersicum ), focusing on growth and root-associated communities. Nitrogen deprivation in L. indica cultures increased significantly the polysaccharide content, including EPS (EPS 0.05% in N + to 0.15% in N − ; protein/polysaccharide ratio: 8 in N + to 0.5 in N − ). Residual culture medium (CM) and biomass extract (BME) from nitrate-rich and nitrate-deficient cultures, were applied as soil amendments or foliar sprays. EPS-rich CM N − significantly enhanced flower production (49.8%, p -value = 0.005), while foliar BME N − increased fruit yield ( p -value = 0.008). 16S rRNA profiling revealed distinct rhizosphere and endosphere shifts, including enrichment of plant growth-promoting genera (Acidovorax, Devosia, Massalia). Notably, foliar CM N − reshaped root microbiota, suggesting EPS-mediated systemic effects on plant metabolism and root microbiome assembly. This highlights the residual culture media as a biostimulant, offering new economic advantages.