Use of Polymeric Agents for the Immobilization of Potential Cr(VI)-Degrading Microorganisms

The widespread discharge of heavy metals, particularly hexavalent chromium [Cr(VI)], into aquatic systems underscores the urgent need for sustainable bioremediation strategies. Microbial immobilization within polymeric matrices such as sodium alginate (ALG-Na) and polyvinyl alcohol (PVA) offers enhanced protection, viability, and controlled contaminant interaction. This study evaluated the encapsulation, spatial distribution, and morphological behavior of Enterobacter hormaechei and Bacillus subtilis —microorganisms with recognized Cr(VI)-reducing potential—using optical, fluorescence, and scanning electron microscopy (SEM). ALG-Ca and ALG-Ca + PVA beads were produced via extrusion and ionic gelation (4:1 ratio) and monitored over 43 days to assess stability and size consistency. A modified Kirby-Bauer assay determined microbial compatibility, while fluorescence labeling with DAPI ( E . hormaechei ) and Rhodamine B ( B . subtilis ) enabled visualization within the polymeric network. Both bead types exhibited structural stability and uniform diameters (1.9–2.0 mm). The antagonism assay indicated bacteriostatic rather than antagonistic activity, supporting dual encapsulation. Fluorescence microscopy confirmed homogeneous microbial distribution, and SEM revealed pores (0.15–12 µm), cracks, and folds that facilitated mass transfer. Single-strain beads showed evident biofilm formation, more pronounced in B . subtilis , whereas consortium beads displayed reduced biofilm development associated with bacteriostatic balance. The puncture assay corroborated microbial entrapment. Overall, encapsulation in ALG-Na/PVA matrices preserved viability and promoted structural configurations favorable for diffusion and activity. These findings demonstrate that polymeric immobilization provides a cost-effective, scalable approach for Cr(VI) bioremediation while elucidating the microstructural and ecological dynamics of encapsulated bacterial systems.