Abstract Cyanobacteria have long been considered promising biofertilizers with significant potential to enhance crop production while improving soil quality. These microorganisms form symbiotic relationships with bacteria, which can further boost their growth and productivity. However, the specific role of these associated bacteria in biofertilizer applications remains largely unexplored. In this study, we addressed this gap by investigating, the biofertilizer potential of bacteria associated with Chroococcidiopsis sp. QUCCCM26, Euhalothece sp. QUCCCM77, and Halospirulina sp. QUCCCM155. The associated bacteria were isolated and identified as Alloalcanivorax xenomutans , Bacillus stercoris , and Vreelandella piezotolerans , respectively. Assessment of their plant growth-promoting (PGP) traits revealed notable nitrogen-fixing capacities and siderophore production in (A) xenomutans and (B) stercoris . Quantification of the iron-chelating capacity of the three Cyanobacteria isolates and their associated bacteria evidenced significant for both microorganisms. In addition, associated bacteria and Cyanobacteria showed interesting capability to produce IAA, in contrast to the cyanobacteria aqueous crude extracts. Lastly, in vivo assays on tomato seeds showed significant phytostimulation effects from both biomass and extract of Euhalothece sp. QUCCCM77 and Halospira sp QUCCCM155. However, A. xenomutans QUCCCM26B showed greater activity compared to its host. To conclude, the plant growth promoting potential of cyanobacteria is linked to the interplay and synergetic activities of all three components: cyanobacterial biomass, crude extracts and associated bacteria, with the effects being strain specific.
Siddiqui et al. (Wed,) studied this question.