Optimization of theoretical maximal quantity of cells to immobilize on solid supports in the rational design of...

Current worldwide challenges are to increase the food production and decrease the environmental contamination by industrial emissions. For this, bacteria can produce plant growth promoter phytohormones and mediate the bioremediation of sewage by heavy metals removal. We developed a Rational Design of Immobilized Derivatives (RDID) strategy, applicable for protein, spore and cell immobilization and implemented in the RDID_1.0 software. In this work, we propose new algorithms to optimize the theoretical maximal quantity of cells to immobilize (tMQ_Cell) on solid supports, implemented in the RDID_Cell software. The main modifications to the preexisting algorithms are related to the sphere packing theory and exclusive immobilization on the support surface. We experimentally validated the new tMQ_Cell parameter by electrostatic immobilization of ten microbial strains on AMBERJET^® 4200 Cl^- porous solid support. All predicted tMQ_Cell match the practical maximal quantity of cells to immobilize with a 10% confidence. The values predicted by the RDID_Cell software are more accurate than the values predicted by the RDID_1.0 software. 3-indolacetic acid (IAA) production by one bacterial immobilized derivative was higher (~ 2.6 μg IAA-like indoles/10⁸ cells) than that of the cell suspension (1.5 μg IAA-like indoles/10⁸ cells), and higher than the tryptophan amount added as indole precursor. Another bacterial immobilized derivative was more active (22 μg Cr(III)/10⁸ cells) than the resuspended cells (14.5 μg Cr(III)/10⁸ cells) in bioconversion of Cr(VI) to Cr(III). Optimized RDID strategy can be used to synthesize bacterial immobilized derivatives with useful biotechnological applications.