Exploring the functional resilience of cyanobacterial multifunctional biofilms and their use as seed coatings under...

Cyanobacteria possessing both carbon-concentrating and nitrogen-fixing mechanisms, offer a unique platform to explore their biofertilizing and elevated CO₂ (eCO₂) ameliorating potential, simultaneously towards enriching soil and improving plant vigour. Multispecies biofilms combining Anabaena torulosa (An) with Trichoderma viride (Tr), and either Providencia sp. (PW5) or Pseudomonas nitroreducens (B3), exhibit additional functional traits, which can also be explored as climate resilient inoculation strategies in rice. This was illustrated in terms of enhancement in chlorophyll (1.82-fold) in An-Tr-PW5, An-Tr showing increased glutamine synthetase (0.92-fold) activity, respectively over An under eCO₂. Fatty Acid Methyl Ester (FAME) profiles revealed that multispecies biofilms actively remodel membrane composition to buffer eCO₂-induced stress, with Tr showing saturated fatty acid spikes (19.68-61.43%), while multispecies biofilms selectively enriched branched fatty acids, optimally in An-Tr-B3 (+ 8.9%). Laboratory-grown and CO₂-acclimatized biofilms used as rice seed coatings exhibited response patterns consistent with a carry-over effect associated with prior environmental conditioning. In soil mesocosms, An-Tr-B3 outperformed An, yielding 5.6-, 3.6-, and 1.6-fold increases in β-glucosidase, urease and acetylene reduction activities, respectively, along with highest seedling vigour index I (SVI; germination × seedling length) (2541) and total leaf pigments (0.91 mg/g). Furthermore, seeds coated with eCO₂ grown biofilms displayed distinct trait-dependent acclimatization, with An-Tr-B3 yielding maximal seedling vigour index II (SVII; germination × seedling dry weight) (37,560) and pigments (0.170 mg/g). Overall, cyanobacterial multispecies biofilms exhibited functional specialization and trait-dependent acclimatization under eCO₂, highlighting their immense potential as a climate-resilient strategy for enriching vegetation, thereby promoting sustainable agriculture.