Transcriptome analysis of ionic-liquid tolerant Bacillus amyloliquefaciens CMW1 and identification of a novel efflux pump

Bacteria that exhibit ionic-liquid (IL) tolerance are useful in chemical
industries using renewable carbon sources pretreated by ILs to produce
biofuels and fine chemicals. Although an IL, 1-butyl-3-methylimidazolium
chloride ([BMIM]Cl), has a remarkable ability to solubilize wood
components, [BMIM]Cl inhibits the growth of various bacterial hosts useful
for bioconversion. We previously isolated a 10% [BMIM]Cl-tolerant
bacterium Bacillus amyloliquefaciens CMW1. Here we report novel mechanisms
of tolerance to [BMIM]Cl in strain CMW1 and a novel major facilitator
superfamily (MFS) transporter coded by an ionic-liquid tolerance (ILT)
gene. First, using CMW1 cells grown in the presence or absence of 10%
[BMIM]Cl, whole-transcriptome analysis and differentially expressed gene
analysis were performed. Probable mechanisms of tolerance to [BMIM]Cl
include uptake of osmoprotectants from the culture medium toward CMW1
cells and the export of [BMIM] cations that accumulated in CMW1 cells. The
finding represents a first step in elucidation of the mechanisms of IL
resistance in Gram-positive bacteria. Second, we conferred tolerance to 5%
[BMIM]Cl on [BMIM]Cl-susceptible Brevibacillus choshinensis using ILT
gene. This finding provides a notable basis for engineering IL-tolerant
bacterial hosts that are applicable for the effective and sustainable
production of industrially important chemicals.