The short-chain fatty acid crotonate reduces invasive growth and immune escape of
Candida albicans
by regulating hyphal gene expression
Authors: McCrory Christopher , Verma Jiyoti , Tucey Timothy M. , Turner Rachael , Weerasinghe Harshini , Beilharz Traude H. , Traven Ana 
Published: November 2023

Microbes are exposed to nutritional and stress challenges in their environmental and host niches. To rise to these challenges, they regulate transcriptional programs that enable cellular adaptation. For instance, metabolite concentrations regulate post-translational modifications of chromatin, such as histone acetylation. In this way, metabolic signals are integrated with transcription. Over the last decade, several histone acylations have been discovered, including histone crotonylation. Their roles in microbial biology, environmental adaptation, and microbe-host interactions are incompletely defined. Here we show that the short-chain fatty acid crotonate, which is used to study histone crotonylation, changes cell morphology and immune interactions of
Candida albicans
. Crotonate reduces invasive hyphal morphogenesis of
C. albicans
within macrophages, thereby delaying macrophage killing and pathogen escape, as well as reducing inflammatory cytokine maturation. Crotonate’s ability to reduce hyphal growth is environmentally contingent and pronounced within macrophages. Moreover, crotonate is a stronger hyphal inhibitor than butyrate under the conditions that we tested. Crotonate causes increased histone crotonylation in
C. albicans
under hyphal growth conditions and reduces transcription of hyphae-induced genes in a manner that involves the Nrg1 repressor pathway. Increasing histone acetylation by histone deacetylase inhibition partially rescues hyphal growth and gene transcription in the presence of crotonate. These results indicate that histone crotonylation might compete with acetylation in the regulation of hyphal morphogenesis. Based on our findings, we propose that diverse acylations of histones (and likely also non-histone proteins) enable
C. albicans
to respond to environmental signals, which in turn regulate its cell morphology and host-pathogen interactions.

IMPORTANCE

Macrophages curtail the proliferation of the pathogen
Candida albicans
within human body niches. Within macrophages,
C. albicans
adapts its metabolism and switches to invasive hyphal morphology. These adaptations enable fungal growth and immune escape by triggering macrophage lysis. Transcriptional programs regulate these metabolic and morphogenetic adaptations. Here we studied the roles of chromatin in these processes and implicate lysine crotonylation, a histone mark regulated by metabolism, in hyphal morphogenesis and macrophage interactions by
C. albicans
. We show that the short-chain fatty acid crotonate increases histone crotonylation, reduces hyphal formation within macrophages, and slows macrophage lysis and immune escape of
C. albicans
. Crotonate represses hyphal gene expression, and we propose that
C. albicans
uses diverse acylation marks to regulate its cell morphology in host environments. Hyphal formation is a virulence property of
C. albicans
. Therefore, a further importance of our study stems from identifying crotonate as a hyphal inhibitor.