Identification of Bacterial Species That Can Utilize Fructose-Asparagine.

serovar Typhimurium is the only organism demonstrated to utilize fructose-asparagine (F-Asn) as a source of carbon and nitrogen. In this report, we first used a bioinformatics approach to identify other microorganisms that encode homologs of the F-Asn utilization enzymes FraB (deglycase), FraD (kinase), and FraE (asparaginase). These candidate organisms were then tested with up to four different methods to confirm their ability to utilize F-Asn. The easiest and most broadly applicable method utilized a biological toxicity assay, which is based on the observation that F-Asn is toxic to a mutant. Candidate organisms were grown in a rich medium containing F-Asn, and depletion of F-Asn from the medium was inferred by the growth of a mutant in that same medium. For select organisms, the toxicity assay was cross-validated by direct mass spectrometry-aided measurement of F-Asn in the spent-culture media and through demonstration of FraB and FraD enzyme activity in cellular extracts. For prototrophs, F-Asn utilization was additionally confirmed by growth in a minimal medium containing F-Asn as the sole carbon source. Collectively, these studies established that , , and can utilize F-Asn, but cannot; and some subspecies can utilize F-Asn; and some and strains can also utilize F-Asn. Within , the host-adapted serovars Typhi and Paratyphi A have lost the ability to utilize F-Asn. Fructose-asparagine (F-Asn) is a precursor to acrylamide that is found in human foods, and it is also a nutrient source for , a foodborne pathogen. Here, we determined that among the normal intestinal microbiota, there are species of that encode the enzymes required for F-Asn utilization. Using complementary experimental approaches, we have confirmed that three members of , two members of , and two members of can indeed utilize F-Asn. The spp. likely compete with for F-Asn in the gut and contribute to competitive exclusion. FraB, one of the enzymes in the F-Asn utilization pathway, is a potential drug target because inhibition of this enzyme leads to the accumulation of a toxic metabolite that inhibits the growth of species. This study identifies the potential off-target organisms that need to be considered when developing therapeutics directed at FraB.

Copyright © 2018 American Society for Microbiology.