# Cutibacterium acnes inhibits Staphylococcus lugdunensis biofilm formation through inhibition of autolysis and purine biosynthesis

## TL;DR

Cutibacterium acnes prevents Staphylococcus lugdunensis from forming biofilms by inhibiting purine biosynthesis and autolysis, offering insights into microbial interactions on the skin.

## Contribution

The study reveals a novel mechanism by which C. acnes inhibits S. lugdunensis biofilm formation through guanine depletion and autolysis repression.

## Key findings

- C. acnes supernatants inhibit S. lugdunensis biofilm formation in a dose-dependent manner.
- C. acnes-derived molecules repress purine biosynthesis and induce autolysis regulators lrgA and lrgB in S. lugdunensis.
- Exogenous guanine reverses the inhibitory effects of C. acnes on biofilm formation and gene expression.

## Abstract

Cutibacterium acnes is a predominant member of the human skin microbiome that plays a pivotal role in maintaining homeostasis and protecting the host against pathogen colonization. Staphylococcus lugdunensis, while also a resident of the skin microbiota, is an opportunistic pathogen capable of causing severe infections, associated with its ability to form biofilms. Building on our previous observation that C. acnes secretes molecules capable of inhibiting S. lugdunensis biofilm formation without inhibiting planktonic growth, we investigated the underlying molecular mechanisms of this phenomenon and its impact on pathogenicity. Here, we demonstrate that cell-free supernatants from various C. acnes strains exhibit dose-dependent antibiofilm activity targeting the initial stages of S. lugdunensis biofilm development. Additionally, extracellular molecules from C. acnescultures significantly reduced the ability of S. lugdunensis to adhere to and invade human epithelial cells (A549) and to adhere to keratinocytes (HaCaT). Transcriptomic analysis revealed that C. acnes-derived molecules significantly repressed the expression of genes involved in purine biosynthesis in S. lugdunensis, while inducing the expression of the negative regulators of autolysis, lrgA and lrgB. Functional assays confirmed that C. acnes-derived molecules inhibit autolysis and extracellular DNA (eDNA) release by S. lugdunensis. Crucially, the addition of exogenous guanine suppressed the effect of C. acnes molecules on both biofilm formation and lrgA gene expression. Collectively, our data indicate that C. acnes molecules inhibit S. lugdunensisbiofilm formation by depleting the intracellular guanine pool, which leads to repression of autolysis, thereby reducing the release of eDNA essential for biofilm structural integrity. These findings underscore the potential of exploiting interspecies microbiome interactions to better understand their role in pathogen exclusion.