Escherichia coli utilizes methanesulfonate and L-cysteate as sole sulfur sources for growth

Twenty-three Escherichia coli strains were tested for their ability to use taurine, methanesulfonate, L-cysteate and other alkanesulfonates as sole sulfur sources for growth. One strain was unable to use any of the alkanesulfonates offered as sole sulfur sources for growth but grew with sulfate. Seven strains (class I) used alkanesulfonates for this purpose, but not methanesulfonate or L-cysteate. A further seven strains (class II) grew with all compounds tested, except with L-cysteate, and eight strains (class III) utilized all compounds tested as sulfur sources. Sulfur assimilation from methanesulfonate and L-cysteate was absolutely dependent on the ssuEADCB operon that encodes an alkanesulfonate uptake system (SsuABC) and a two-component monooxygenase (SsuDE) involved in the release of sulfite from alkanesulfonates. Long-term exposure of class I strains to methanesulfonate and of class II strains to L-cysteate selected for derivatives that utilized these two sulfur sources as efficiently as sulfate. The nucleotide sequence of the ssuEADCB operon in the methanesulfonate- and L-cysteate-utilizing derivative EC1250Me+ was identical to that in the class I wild-type EC1250. Gain of the ability to utilize methanesulfonate and L-cysteate as sulfur sources thus appears to result from increased expression of ssu genes rather than from a change in the quality of one or several of the Ssu proteins.