Expression of Heterologous Sigma Factor Expands the Searchable Space for Biofuel Tolerance Mechanisms.
Microorganisms can produce hydrocarbons that can serve as replacements or additions to conventional liquid fuels for use in the transportation sector. However, a common problem in the microbial synthesis of biofuels is that these compounds often have toxic effects on the cell. In this study, we focused on mitigating the toxicity of the biojet fuel precursor pinene on Escherichia coli. We used genomic DNA from Pseudomonas putida KT2440, which has innate solvent-tolerance properties, to create transgenic libraries in an E. coli host. We exposed cells containing the library to pinene, selecting for genes that improved tolerance. Importantly, we found that expressing the sigma factor RpoD from P. putida greatly expanded the diversity of tolerance genes recovered. With low expression of rpoDP.putida, we isolated a single pinene tolerance gene; with increased expression of the sigma factor our selection experiments returned multiple distinct tolerance mechanisms, including some that have been previously documented and also new mechanisms. Interestingly, high levels of rpoDP.putidainduction resulted in decreased diversity. We found that the tolerance levels provided by some genes are highly sensitive to the level of induction of rpoDP.putida, while others provide tolerance across a wide range of rpoDP.putidalevels. This method for unlocking diversity in tolerance screening using heterologous sigma factor expression was applicable to both plasmid and fosmid-based transgenic libraries. These results suggest that by controlling the expression of appropriate heterologous sigma factors, we can greatly increase the searchable genomic space within transgenic libraries.
College of Engineering and Mathematical Sciences, University of Vermont , 33 Colchester Avenue, Burlington, Vermont 05405, United States.
Timothy A
TA
Tomko
College of Engineering and Mathematical Sciences, University of Vermont , 33 Colchester Avenue, Burlington, Vermont 05405, United States.|Biomedical Engineering Department, Boston University , 44 Cummington Mall, Boston, Massachusetts 02215, United States.
Mary J
0000-0002-9261-8216
MJ
Dunlop
D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D056804:Biofuels; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D010957:Plasmids / Q000235:genetics; D016958:Pseudomonas putida / Q000235:genetics / Q000378:metabolism; D012808:Sigma Factor / Q000235:genetics / Q000378:metabolism*
D001426:Bacterial Proteins; D056804:Biofuels; D012808:Sigma Factor
Pseudomonas putida; RpoD; biofuel tolerance; monoterpene; pinene; transgenic library