The Predatory Bacterium Bdellovibrio bacteriovorus Aspartyl-tRNA Synthetase Recognizes tRNA(Asn) as a Substrate

The predatory bacterium Bdellovibrio bacteriovorus preys on other Gram-negative bacteria and was predicted to be an asparagine auxotroph. However, despite encoding asparaginyl-tRNA synthetase and glutaminyl-tRNA synthetase, B. bacteriovorus also contains the amidotransferase GatCAB. Deinococcus radiodurans, and Thermus thermophilus also encode both of these aminoacyl-tRNA synthetases with GatCAB. Both also code for a second aspartyl-tRNA synthetase and use the additional aspartyl-tRNA synthetase with GatCAB to synthesize asparagine on tRNA(Asn). Unlike those two bacteria, B. bacteriovorus encodes only one aspartyl-tRNA synthetase. Here we demonstrate the lone B. bacteriovorus aspartyl-tRNA synthetase catalyzes aspartyl-tRNA(Asn) formation that GatCAB can then amidate to asparaginyl-tRNA(Asn). This non-discriminating aspartyl-tRNA synthetase with GatCAB thus provides B. bacteriovorus a second route for Asn-tRNA(Asn) formation with the asparagine synthesized in a tRNA-dependent manner. Thus, in contrast to a previous prediction, B. bacteriovorus codes for a biosynthetic route for asparagine. Analysis of bacterial genomes suggests a significant number of other bacteria may also code for both routes for Asn-tRNA(Asn) synthesis with only a limited number encoding a second aspartyl-tRNA synthetase.