Isolation and Screening of Thermophilic Bacilli from Compost for Electrotransformation and Fermentation: Characterization of Bacillus smithii ET 138 as a New Biocatalyst

Abstract

ABSTRACTThermophilic bacteria are regarded as attractive production organisms for cost-efficient conversion of renewable resources to green chemicals, but their genetic accessibility is a major bottleneck in developing them into versatile platform organisms. In this study, we aimed to isolate thermophilic, facultatively anaerobic bacilli that are genetically accessible and have potential as platform organisms. From compost, we isolated 267 strains that produced acids from C5and C6sugars at temperatures of 55°C or 65°C. Subsequently, 44 strains that showed the highest production of acids were screened for genetic accessibility by electroporation. TwoGeobacillus thermodenitrificansisolates and oneBacillus smithiiisolate were found to be transformable with plasmid pNW33n. Of these,B. smithiiET 138 was the best-performing strain in laboratory-scale fermentations and was capable of producing organic acids from glucose as well as from xylose. It is an acidotolerant strain able to produce organic acids until a lower limit of approximately pH 4.5. As genetic accessibility ofB. smithiihad not been described previously, six otherB. smithiistrains from the DSMZ culture collection were tested for electroporation efficiencies, and we found the type strain DSM 4216Tand strain DSM 460 to be transformable. The transformation protocol forB. smithiiisolate ET 138 was optimized to obtain approximately 5 × 103colonies per μg plasmid pNW33n. Genetic accessibility combined with robust acid production capacities on C5and C6sugars at a relatively broad pH range makeB. smithiiET 138 an attractive biocatalyst for the production of lactic acid and potentially other green chemicals.