Biotin-mediated growth and gene expression in Staphylococcus aureus is highly responsive to environmental biotin

Abstract

Biotin (Vitamin B7) is a critical enzyme co-factor in metabolic pathways important for bacterial survival. Biotin is obtained either from the environment or by de novo synthesis, with some bacteria capable of both. In certain species, the bifunctional protein BirA plays a key role in biotin homeostasis as it regulates expression of biotin biosynthetic enzymes in response to biotin demand and supply. Here, we compare the effect of biotin on the growth of two bacteria that possess a bifunctional BirA, namely Escherichia coli and Staphylococcus aureus. Unlike E. coli that could fulfill its biotin requirements through de novo synthesis, S. aureus showed improved growth rates in media supplemented with 10 nM biotin. S. aureus also accumulated more radiolabeled biotin from the media highlighting its ability to efficiently scavenge exogenous material. These data are consistent with S. aureus colonizing low biotin microhabitats. We also demonstrate that the S. aureus BirA protein is a transcriptional repressor of BioY, a subunit of the biotin transporter, and an operon containing yhfT and yhfS, the products of which have a putative role in fatty acid homeostasis. Increased expression of bioY is proposed to help cue S. aureus for efficient scavenging in low biotin environments.

Advanced Resistance Studies Identify Two Discrete Mechanisms in Staphylococcus aureus to Overcome Antibacterial Compounds that Target Biotin Protein Ligase

“…This was supported experimentally where the growth rate of S. aureus was enhanced in media containing exogenous biotin, even though the bacteria were capable of biotin synthesis [23]. We propose that this ability is important during infection as S. aureus occupies a variety of niche microhabitats with varying biotin availability [23]. These findings also suggest that pharmacological induction of transcriptional repressor activity may lead to biotin starvation through the dual actions of reduced de novo biotin synthesis and reduced biotin import.…”

“…It is proposed that this mechanism may assist with metabolic adaptation of the bacteria to their environment, as de novo biotin biosynthesis is an energetically expensive process that can be bypassed when exogenous biotin is readily available for import. This was supported experimentally where the growth rate of S. aureus was enhanced in media containing exogenous biotin, even though the bacteria were capable of biotin synthesis [23]. We propose that this ability is important during infection as S. aureus occupies a variety of niche microhabitats with varying biotin availability [23].…”

“…The effect of impaired homodimerization ability on DNA binding and transcriptional repression was then assessed using a combination of in vitro EMSA analysis and a previously established in vivo transcriptional reporter system in E. coli [23]. Both wildtype and SaBPL-D200E demonstrated weak DNA binding activity in their apo states in the EMSA, with unbound bioO and bioY probes observed even at the highest protein concentration tested (i.e., 625 nM; Figure 4A-D).…”

“…Recent in vivo characterization in S. aureus has revealed a hierarchy in the control of these genes by SaBPL. The biotin biosynthesis operon was shown to be the most responsive to treatment with exogenous biotin, being repressed by 10 nM biotin 15 min post-treatment [23]. Transcripts for bioY and yhfT-yhfS persisted longer after biotin treatment than the biotin biosynthesis genes.…”

“…SaBPL also regulates the transcription of three genetic elements, namely the biotin biosynthesis operon (bioO), a gene encoding the substrate-specific subunit of the biotin transport protein BioY, as well as a putative fatty acid ligase operon yhfT-yhfS [22,23]. Recent in vivo characterization in S. aureus has revealed a hierarchy in the control of these genes by SaBPL.…”