Polymicrobial Biofilm of Pseudomonas Oryzihabitans GAT2212B and Aspergillus niger KCRE2202F Promotes Root Colonization and Growth of Mangrove Plant Avicennia officinalis L.

Abstract

Mangrove ecosystems are challenged by salinity, heavy metal stress, and nutrient limitations, which hinder natural regeneration and seedling establishment. In this study, a polymicrobial bacterial-fungal inoculum was developed to enhance the growth of Avicennia officinalis L. Among 738 bacterial and 466 fungal isolates, Pseudomonas oryzihabitans GAT2212B and Aspergillus niger KCRE2202F exhibited more compatibility and formed denser 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, in heavy metal stress conditions, this polymicrobial inoculum improved A. officinalis growth by mitigating stress. Greenhouse trials confirmed significant (p < 0.05) plant growth promotion, attributed to root colonization confirmed by SEM and CLSM. Field trials in the Mahanadi delta (Paradip, Odisha) further validated these findings, with consortium-inoculated seedlings achieving 100% survival and growth improvements in plant height (~105.29%), leaf number (~405.08%), and stem diameter (~117.17%) over controls. This study highlights the ecological and biotechnological potential of synergistic bacterial-fungal biofilm as a nature-based strategy for mangrove rehabilitation and sustainable coastal ecosystem management.