Frontiers in Microbiology· 2026Q1
Metabolic versatility of Acinetobacter baumannii: distinct pathways for the utilization of short-, medium- and long-chain acyl-L-carnitines
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- Q1SCImago
- 2026year
Short summary
Acinetobacter baumannii employs two distinct hydrolases to metabolize short-, medium-, and long-chain acyl-L-carnitines, enabling its growth on these host-derived nutrients.
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Key points
- Acinetobacter baumannii uses a cytoplasmic hydrolase (ACH) for short- and medium-chain acyl-L-carnitines.
- A distinct secreted hydrolase (ACHS) is responsible for cleaving long-chain acyl-L-carnitines.
- The betaine/choline/carnitine transporter (BCCT) is involved in the uptake of short- and medium-chain variants.
- Growth experiments with wild-type and Δbcct, Δach mutant strains confirmed the roles of these enzymes and transporters.
AI-generated from the title and abstract; the full text is not read.
Abstract
Acinetobacter baumannii is a multidrug-resistant pathogen capable of metabolizing host-derived acyl-L-carnitines, which contributes to its virulence. During A. baumannii growth on acetyl-L-carnitine, L-carnitine was initially released into the growth medium suggesting that acetate is metabolized first. The subsequent uptake of L-carnitine at the end of the exponential phase then facilitates the catabolism of L-carnitine. Involvement of the betaine/choline/carnitine transporter (BCCT) in the uptake of short- and medium-chain acyl-L-carnitines was confirmed through growth experiments using the Δ bcct mutant strain. An uncharacterized hydrolase (HMPREF0010_01348) encoded by the L-carnitine degradation gene operon (HMPREF0010_01345 – HMPREF0010_01351) was biochemically identified as a short- and medium-chain acyl-L-carnitine hydrolase (ACH). Its cellular localization in the cytoplasm was demonstrated. The purified ACH exhibited no enzymatic activity toward long-chain acyl-L-carnitines. However, growth experiments revealed that both the wild type and the Δ ach mutant were able to grow clearly on these substrates, providing evidence for the involvement of an additional, as-yet-uncharacterized enzyme. The cell culture supernatant was used for the chromatographic enrichment of a protein fraction showing robust enzyme activity for the hydrolysis of long-chain acyl-L-carnitines. Proteomic analysis of a partially purified hydrolase fraction and of the A. baumannii secretome revealed the gene product of open reading frame HMPREF0010_02333 as a hydrolase candidate. The respective protein was recombinantly overproduced and purified and its ability to cleave various long-chain acyl-L-carnitines was demonstrated. Based on the substrate specificity of the characterized ACH from the cytosol and the acyl-L-carnitine hydrolase present in the culture supernatant (ACHS), a metabolic model for the versatile utilization of small- medium- and long-chain acyl-L-carnitines by A. baumannii was proposed.
The authors' abstract, as published at the source. Frontiers in Microbiology, 2026 · DOI ↗
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