Combined chemical and mechanical processes for the disruption of bacteria

Mechanical cell disruption by high pressure homogenisation or high speed bead mills is currently the general method of choice for the large scale disruption of micro-organisms; however, deleterious effects include the high energy requirement, the need for efficient cooling to prevent the excessive heating of the product and the micronisation of cell debris. Certain chemical treatments for microbial cell disruption alter the permeability of bacteria and yeasts, allowing partial release of soluble products. Such treatments are insufficient for the recovery of granular intracellular products. As cell wall strength has been cited as a major factor influencing the requirements for efficient mechanical disruption, the use of chemical pretreatment to decrease cell wall strength prior to mechanical breakage by homogenisation has been considered. The following treatments were shown to increase the sensitivity of the Gram-negative bacterium, Alcaligenes eutrophus, to disruption: alkaline pH shock, the addition of an anionic detergent, increase of the monovalent cation concentration, the addition of EDTA and enzymic lysis by lysozyme. These pretreatments allow equivalent disruption to be achieved at lower operating pressures or fewer passes through the homogeniser. Alkaline pH pretreatment at pH 10.5 allowed a 37.5% increase in soluble protein release on subsequent homogenisation. An increase of some 30% in soluble protein release was found following prior addition of 0.137 M monovalent cations (Na+ or K+) at 60 degrees C. Treatment with an anionic detergent showed a considerable decrease in the number of passes required through the homogeniser. Maximum cell rupture can thus be accomplished at reduced energy inputs.