Phosphonate catabolism by Campylobacter spp.

Abstract

The catabolism of phosphonates (Phn) by Campylobacter spp. was investigated employing nuclear magnetic resonance spectroscopy and cell culture techniques. The bacteria were capable of cleaving the Phn bonds of different compounds, including α-aminomethylphosphonate, phosphonoacetate and phenylphosphonate (PhePhn). The kinetic parameters of these activities were determined in vivo in intact cells and in situ in whole-cell lysates. Cleavage of Phn-bearing compounds was associated with the cell-wall and cytosolic fractions. Results from substrate competition experiments suggested that at least two enzyme activities appeared to be involved in the cleavage of carbon–phosphate (C–P) bonds. In silico analyses indicated that no genes orthologous to those encoding C–P bond-cleaving enzymes in other bacteria were present in the Campylobacter jejuni genome. In most bacteria studied, Phn catabolism is induced under conditions of phosphate limitation; however, in Campylobacter spp. these activities were expressed in cells grown in media rich in phosphate. In chemically defined media, PhePhn supported bacterial growth and proliferation at concentrations above 100 μM in the absence of phosphate. Thus, Phn utilisation may be a survival mechanism of Campylobacter spp. in milieux lacking sufficient phosphate. The expression of these enzyme activities in media abundant in phosphate suggested also that they may have other physiological roles.