Fermentation with continuous ball milling: Effectiveness at enhancing solubilization for several cellulosic feedstocks and comparative tolerance of several microorganisms

Mechanical disruption of lignocellulose during fermentation, cotreatment, is a nascent approach to increase biologically-mediated carbohydrate solubilization without exposure to high temperatures or chemicals. However, ability to tolerate the presence of milling at intensities sufficient to allow high lignocellulose solubilization yields has to date only been evaluated for Clostridium thermocellum and Saccharomyces cerevisiae, and demonstration of high carbohydrate solubilization has only been reported for switchgrass at the time of submission. Continuous ball milling during fermentation by C. thermocellum was found to be sufficient to allow high (>85%) total carbohydrate solubilization of corn stover and poplar as well as switchgrass. Under the conditions tested, ball milling had no apparent effect on soluble sugar fermentation by Escherichia coli and Thermoanaerobacterium saccharolyticum but completely inhibited carbohydrate fermentation by Zymomonas mobilis and Bacillus subtilis. Our results are consistent with the stress of milling being sufficient to overwhelm the inefficient fermentative metabolism of Z. mobilis and B. subtilis, but not to the other microorganisms tested in this work for which fermentation is more efficient and robust. •Cotreatment was tested on three lignocellulosic feedstocks and four microorganisms.•Carbohydrate solubilization is improved with cotreatment on all feedstocks tested.•Solubilization was found to be high for both woody and herbaceous angiosperms.•Growth of some microorganisms is affected by milling but for others it is not.