Dual Functionality of Exiguobacterium indicum OMCW-10: Efficient Cr6+ Bioremediation and Induction of Systemic Resistance Against Rice Blast

Abstract

Cr6+ pollution has significant adverse effects on both the environment and the agricultural sector. In contrast, rice blast disease, caused by the pathogen Magnaporthe oryzae, also has major adverse effects on rice cultivation globally. In the present study, Exiguobacterium indicum OMCW-10, which naturally exhibits resistance to chromium and was isolated from chromite mines, acts as a potential biphasic agent in the removal of Cr6+ ions as well as in plant disease control. E. indicum OMCW-10 reduced 88.94% of Cr6+ ions to Cr3+ in soil within 50 days. Advanced analytical techniques, such as SEM-EDX, also validated the deposition of chromium on E. indicum OMCW-10, while ATR-FTIR analysis revealed the involvement of different functional groups in chromium binding and reduction. E. indicum OMCW-10 also released antimicrobial substances capable of inhibiting the radial growth of M. oryzae by 50%, 47%, and 40% on the 3rd, 5th, and 7th days of cocultivation, respectively. Rice seedlings (cultivar Swarna) bioprimed with a density of 10⁸ CFU/mL of the bacterium, when grown in optimised conditions of temperature (25-35°C), day-night cycles (16 h light:8 h darkness), and relative humidity (80-85%), demonstrated increased transcript levels of defence-related genes (OsNPR1, OsWRKY45, and OsPR10). The biopriming led to effective induction of early and high levels of SAR, which in turn resulted in over 83.3% reduction in the size of blast lesions, reduction in cellular damage, protection of chlorophyll content, preservation of membrane integrity, and suppressed invasive growth of mycelium of the pathogen.