Abstract
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 tRNAAsn. Unlike those two bacteria, B. bacteriovorus encodes only one aspartyl-tRNA synthetase. Here we demonstrate the lone B. bacteriovorus aspartyl-tRNA synthetase catalyzes aspartyl-tRNAAsn formation that GatCAB can then amidate to asparaginyl-tRNAAsn. This non-discriminating aspartyl-tRNA synthetase with GatCAB thus provides B. bacteriovorus a second route for Asn-tRNAAsn 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-tRNAAsn synthesis with only a limited number encoding a second aspartyl-tRNA synthetase.
Highlights
Bdellovibrio bacteriovorus HD100 preys on other Gramnegative bacteria by inserting into the host’s periplasm where B. bacteriovorus grows and replicates, taking advantage of the nutrient rich environment of the host cell [1]
B. bacteriovorus tRNAAsn has a U1-A72 base pair (Table S1) meaning if aspartylated, the tRNA could serve as a substrate for GatCAB
For B. bacteriovorus to encode the two-step pathway for AsntRNAAsn formation, the organism must code for a ND-aspartyl-tRNA synthetase (AspRS) along with GatCAB and tRNAAsn with a U1-A72 base pair
Summary
Bdellovibrio bacteriovorus HD100 preys on other Gramnegative bacteria by inserting into the host’s periplasm where B. bacteriovorus grows and replicates, taking advantage of the nutrient rich environment of the host cell [1]. Because this predatory process kills the host, B. bacteriovorus is being studied as a living antibiotic for therapeutic, agriculture, and waste treatment purposes [2,3,4,5,6]. In bacteria missing an AsnRS to directly ligate Asn to tRNAAsn, Asn is synthesized on tRNAAsn using an indirect two-step pathway by taking advantage of an aspartyl-tRNA synthetase (AspRS) with relaxed tRNA specificity, a non-discriminating AspRS (NDAspRS) [10,11]. GatCAB can be used for Gln-tRNAGln formation in bacteria lacking a GlnRS, about two-thirds of all known bacteria [8,14,15,16,17,18]
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