Phenoxyalkanoic acid
(PAA) herbicides are mainly metabolized by
microorganisms in soils, but the degraders that perform well under
alkaline environments are rarely considered. Herein, we report Cupriavidus oxalaticus strain X32, which showed encouraging
PAA-degradation abilities, PAA tolerance, and alkali tolerance. In
liquid media, without the addition of exogenous carbon sources, X32
could completely remove 500 mg/L 2,4-dichlorophenoxyacetic acid (2,4-D)
or 4-chloro-2-methylphenoxyacetic acid within 3 days, faster than
that with the model degrader Cupriavidus necator JMP134. Particularly, X32 still functioned at pH 10.5. Of note,
with X32 inoculation, we observed 2,4-D degradation in soils and diminished
phytotoxicity to maize (Zea mays).
Furthermore, potential mechanisms underlying PAA biodegradation and
alkali tolerance were then analyzed by whole-genome sequencing. Three
modules of tfd gene clusters involved in 2,4-D catabolism
and genes encoding monovalent cation/proton antiporters involved in
alkali tolerance were putatively identified. Thus, X32 could be a
promising candidate for the bioremediation of PAA-contaminated sites,
especially in alkaline surroundings.