Modeling and optimization of a continuous bead milling process for bacterial cell lysis using response surface methodology

Abstract

Efficient cell lysis for intracellular protein recovery is a major bottleneck in the economics and commercial feasibility of any biotechnological process. Grinding of cells with abrasive beads, also known as bead milling remains a method of choice, as it can handle a large volume of cells. Bead mills when operated in a continuous mode substantiate to be economical, and more productive as compared to a batch mode process. In this study, the recovery of recombinant cholesterol oxidase (COD) was investigated and optimized using response surface methodology (RSM) based on Central Composite Design (CCD) in a continuous bead milling process. Process parameters, viz. slurry feed rate (A), bead loading (B), cell loading (C) and process time (D) were found to be significant during the continuous bead milling process. A polynomial model was developed to correlate the participating factors for efficient cell disruption. Optimized conditions yielded 3.20 g L⁻¹ (∼90%) of COD with A = 300.6 mL h⁻¹, B = 77.5% (v/v), C = 69.9 (OD_{600 nm}) and D = 29.7 (min), when compared to existing batch mode operations (3.56 g L⁻¹). This is the very first study that attempts to optimize a continuous bead milling process using RSM to maximize the intracellular protein (COD in this case) recovery with minimum inputs to make the process economical and scalable to industrial levels. The developed model in this study can be scaled-up to large-scale for efficient recovery of intracellular proteins in similar expression systems.