Evaluation of a plastic-degrading bacterium – Mesobacillus foraminis SMCD3 for its plant growth promoting activity in Cicer arietinum seedlings exposed to polystyrene

Abstract

The accumulation of polystyrene (PS) in terrestrial ecosystems poses serious environmental and agricultural concerns, necessitating effective and sustainable bioremediation strategies. In this study, a bacterial isolate, MesoBacillus foraminis strain SMCD3, obtained from municipal dumping ground soil, demonstrated significant PS-degrading capability, achieving a 14% reduction in PS weight when cultured in mineral salt medium with PS as the sole carbon source, accompanied by high cell density, indicating efficient metabolic assimilation under nutrient-limited conditions. Enzymatic characterization revealed that PS degradation is primarily mediated through non-classical pathways involving extracellular hydrolases (lipase and esterase) and oxidative enzymes such as alkane hydroxylase and alcohol dehydrogenase. In addition to its biodegradation potential, MesoBacillus foraminis strain SMCD3 exhibited multiple plant growth-promoting (PGP) traits, including indole-3-acetic acid production, ammonia generation, and siderophore secretion, suggesting its potential to enhance nutrient availability and phytohormonal regulation. Exposure of Cicer arietinum to PS nanoparticles and microplastics significantly inhibited germination, growth, and physiological performance. However, inoculation with MesoBacillus foraminis strain SMCD3 effectively mitigated these phytotoxic effects by improving germination parameters, promoting shoot (1.25-2.68-fold) and root (1.00-2.12-fold) elongation, enhancing relative water content (1.01-1.26-fold), and reducing membrane damage (1.60-2.88-fold) compared to PS-MNP-treated seedlings. Moreover, MesoBacillus foraminis strain SMCD3 represents a versatile bacterium with dual functional attributes in PS biodegradation and plant growth promotion, underscoring its potential for integrated applications in bioremediation and sustainable agroecosystems under plastic-contaminated conditions.