Salmonella enterica serovar Typhimurium (S.
Typhimurium) is a common cause of gastroenteritis and diarrhoea,
contributing to significant morbidity and mortality worldwide. In recent years,
the prevalence of antibiotic resistance in S.
Typhimurium has, like many other pathogens, increased, highlighting the need
for new drug targets. Methionine is an essential amino acid required for a
variety of fundamental biochemical processes, including protein synthesis,
translation initiation and as a methyl donor through S-adenosylmethionine. Salmonella, like most other
prokaryotes, is capable of de novo methionine biosynthesis, a process absent
in higher eukaryotes. We aimed to investigate the role of methionine biosynthesis
and transport in virulence of S. Typhimurium strain SL1344. Initially, we constructed
targeted gene knockout mutants for enzymes in the de novo methionine biosynthesis pathway, including genes metA, metB, metC, metE, metF, and metH, and the negative regulatory gene, metJ. Mutants deficient for biosynthetic
enzymes exhibited grossly impaired growth in M9 minimal culture media,
highlighting the essentiality of methionine to Salmonella metabolism. However, in
vivo studies in murine model showed that mutants ΔmetA, ΔmetB, ΔmetC, ΔmetH were not attenuated compared to wild type, suggesting that de novo biosynthesis is not required
during growth in the murine model. Salmonella
import methionine from the environment, via mechanisms including the high
affinity transporter MetD which is encoded by metN, metI and metQ. We generated double mutants that were
deficient in high affinity transport as well as de novo biosynthesis of methionine: ΔmetA:ΔmetNIQ, ΔmetB:ΔmetNIQ,
ΔmetC:ΔmetNIQ. In minimal culture
media, the double mutants exhibited further growth attenuation compared to the
single mutants, suggesting functional cooperation between methionine
biosynthesis and transportation pathways. Ongoing studies aim to establish the
relative importance of these two pathways for Salmonella virulence in the host, and hence their relevance as
antibacterial targets.