Three types of taxis used in the response of Acidovorax sp. strain JS42 to 2-nitrotoluene

Acidovorax sp. strain JS42 is able to utilize 2-nitrotoluene (2NT) as its sole carbon, nitrogen, and energy source. We report here that strain JS42 is chemotactic to 2NT and that the response is increased when cells are grown on compounds such as 2NT that are known to induce the first step of 2NT degradation. Assays with JS42 mutants unable to oxidize 2NT showed that the first step of 2NT metabolism was required for the induced response, but not for a portion of the constitutive response, indicating that 2NT itself is an attractant. The 2NT metabolite nitrite was shown to be a strong attractant for strain JS42, and sufficient nitrite was produced during the taxis assay to account for a large part of the induced response. A mutant with an inactivated ntdY gene, which is located adjacent to the 2NT degradation genes and codes for a putative methyl-accepting chemotaxis protein, showed a defect in taxis toward 2NT that may involve a reduced response to nitrite. Responses of a mutant defective for the energy-taxis receptor, Aer, indicated that a functional aer gene is required for a substantial part of the wild-type induced response to 2NT. In summary, strain JS42 utilizes three types of taxis to sense and respond to 2NT: constitutive 2NT-specific chemotaxis to directly sense 2NT, metabolism-dependent nitrite-specific chemotaxis that may be mediated by NtdY, and energy taxis mediated by Aer.