# Staphylococcus epidermidis DnaK alters biofilm formation and proteome in Staphylococcus aureus CIP 107093

## TL;DR

This study shows how a protein from Staphylococcus epidermidis affects biofilm formation in Staphylococcus aureus and other strains.

## Contribution

The study reveals the strain-dependent effects of S. epidermidis DnaK on biofilm formation and proteome changes in S. aureus.

## Key findings

- DnaK increases biofilm biomass in commensal strains but reduces it in clinical S. aureus CIP 107093.
- SBD mutations abolish biofilm reduction in CIP 107093, while NBD mutations have a milder effect.
- DnaK alters the S. aureus proteome by stabilizing degradation components and downregulating biofilm regulators.

## Abstract

Staphylococcus aureus and Staphylococcus epidermidis, two Gram-positive bacteria of the human skin microbiota, form biofilms that contribute to dysbiosis and inflammatory skin diseases such as psoriasis and atopic dermatitis. The human calcitonin gene-related peptide (CGRP), involved in skin inflammation, was previously shown to enhance the virulence of S. epidermidis MFP04. We previously observed a significant increase in the level of the molecular chaperone DnaK/Hsp70 in the secretome of CGRP-activated S. epidermidis. Here, we investigated the role of recombinant S. epidermidis DnaK in biofilm formation in both S. aureus and S. epidermidis. DnaK modulates biofilm formation in a strain-dependent manner. In commensal strains (S. aureus MFP03 and S. epidermidis MFP04), it is associated with an increase in biofilm biomass. In contrast, it significantly reduces biofilm formation in the clinical S. aureus strain CIP 107093. Point mutations in the substrate-binding domain (SBD) and nucleotide-binding domain (NBD) of DnaK differentially affect its modulation of biofilm formation. Specifically, only the mutation in the SBD abolishes the biofilm reduction observed in CIP 107093, while the NBD mutation results in a milder effect. Notably, these mutations have no significant impact on DnaK-induced biofilm changes in strains where DnaK promotes biofilm formation. Proteomic analyses of S. aureus CIP 107093 reveal that DnaK alters the S. aureus biofilm proteome, stabilizing protein degradation components and downregulating key biofilm regulators. These findings highlight the cross-species regulatory potential of S. epidermidis extracellular DnaK in the skin microbiota.