Characterization of the major autolysin (AtlC) of Staphylococcus carnosus.

BMC Microbiol

Chair of Microbiology, Technical University of Munich, Gregor-Mendel-Straße 4, 85354, Freising, Germany.

Published: March 2024

AI Article Synopsis

  • Autolysis in bacteria, specifically in Staphylococcus carnosus, plays a significant role in food fermentation, enhancing processes like nitrate reduction and flavor formation.
  • Mutant strains of S. carnosus lacking the major autolysin (AtlC) showed reduced growth and autolysis, resulting in clumped cells with rough surfaces, unlike the smooth, well-separated wild-type cells.
  • The study identified changes over time in the lytic enzymes produced by these strains, indicating that AtlC degrades into smaller fragments and revealing additional lytic bands not previously described, which suggests a complex autolytic process that varies with growth stages.

Article Abstract

Background: Autolysis by cellular peptidoglycan hydrolases (PGH) is a well-known phenomenon in bacteria. During food fermentation, autolysis of starter cultures can exert an accelerating effect, as described in many studies on cheese ripening. In contrast, very little is known about autolysis of starter cultures used in other fermentations. Staphylococcus (S.) carnosus is often used in raw sausage fermentations, contributing to nitrate reduction and flavor formation. In this study, we analyzed the influence of PGHs of the strains S. carnosus TMW 2.146 and S. carnosus TMW 2.2525 on their autolytic behavior. The staphylococcal major autolysin (Atl), a bifunctional enzyme with an N-acetylmuramoyl-L-alanine amidase and a glucosaminidase as an active site, is assumed to be the enzyme by which autolysis is mainly mediated.

Results: AtlC mutant strains showed impaired growth and almost no autolysis compared to their respective wild-type strains. Light microscopy and scanning electron microscopy showed that the mutants could no longer appropriately separate from each other during cell division, resulting in the formation of cell clusters. The surface of the mutants appeared rough with an irregular morphology compared to the smooth cell surfaces of the wild-types. Moreover, zymograms showed that eight lytic bands of S. carnosus, with a molecular mass between 140 and 35 kDa, are processed intermediates of AtlC. It was noticed that additional bands were found that had not been described in detail before and that the banding pattern changes over time. Some bands disappear entirely, while others become stronger or are newly formed. This suggests that AtlC is degraded into smaller fragments over time. A second knockout was generated for the gene encoding a N-acetylmuramoyl-L-alanine amidase domain-containing protein. Still, no phenotypic differences could be detected in this mutant compared to the wild-type, implying that the autolytic activity of S. carnosus is mediated by AtlC.

Conclusions: In this study, two knockout mutants of S. carnosus were generated. The atlC mutant showed a significantly altered phenotype compared to the wild-type, revealing AtlC as a key factor in staphylococcal autolysis. Furthermore, we show that Atl is degraded into smaller fragments, which are still cell wall lytic active.

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Source
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC10921637PMC
http://dx.doi.org/10.1186/s12866-024-03231-6DOI Listing

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