Synergistic polymicrobial biofilm of Pseudomonas oryzihabitans GAT2212B and Aspergillus niger KCRE2202F as a blue biotechnological strategy to enhance the growth of mangrove Avicennia officinalis L.

Abstract

Mangrove ecosystems are a foundational pillar of the emerging blue economy. However, environmental stressors such as salinity fluctuations, pollution, and climate change threaten mangrove survival and regeneration. This study aim to evaluate the role of a synergistic polymicrobial bacterial-fungal inoculum as a blue biotechnology strategy to promote seed germination and enhance the growth of Avicennia officinalis L.. Amplicon-based metagenomic analysis revealed 1,372 bacterial and 284 fungal operational taxonomic units (OTUs), indicating a rich and complex mangrove rhizosphere microbiome. Further functional profiling predicted 408 bacterial and 69 fungal metabolic pathways, suggesting their active involvement in essential processes such as nutrient cycling, xenobiotic degradation, biofilm formation, and plant growth promotion. These functional traits highlight their ecological role in maintaining the stability and resilience of the mangrove ecosystem. Among 738 bacterial and 466 fungal isolates, Pseudomonas oryzihabitans GAT2212B and Aspergillus niger KCRE2202F exhibited more compatibility and formed denser biofilm (Biofilm biomass 13.22±7.85 µm3/µm2) than individual cultures. Phytotoxicity assays showed that seeds treated with polymicrobial inoculum had significantly higher seedling vigour (p<0.0001) than those with individual inoculants or controls. Also, under heavy metal stress, this polymicrobial inoculum improved A. o.fficinalis growth by mitigating the stress. Greenhouse trials confirmed significant (p<0.05) plant growth promotion, attributed to root colonization, as confirmed by scanning electron microscopy. Field trials in the Mahanadi delta (Paradip, Odisha) further validated these findings, with consortium-inoculated seedlings achieving 100% survival and improvements in plant height (~105.29%), leaf number (~405.08%), and stem diameter (~117.17%) compared with controls. Moreover, the bacterial-fungal biofilm improved soil binding, mechanical strength, and overall soil stability. This study underscores the ecological and biotechnological potential of synergistic bacterial-fungal biofilms as a nature-based solution for mangrove restoration, coastal resilience, and sustainable blue economy development.