Abstract
The capacity to form biofilms is a common trait among many
microorganisms present on Earth. In this study, we demonstrate for the
first time that the fatal pine pitch canker agent, Fusarium circinatum,
can lead a biofilm-like lifestyle with aggregated hyphal bundles wrapped
in extracellular matrix (ECM). Our study suggests that F. circinatum
biofilms respond to a changing environment, demonstrated by poor and
optimal biofilm development under particular abiotic conditions,
including temperature and pH. Further analysis revealed that while
planktonic cells produced small amounts of ECM per unit of the biomass,
heat- and azole-exposed biofilms produced significantly more ECM than
non-exposed biofilms. The increased synthesis of ECM in biofilms due to
these abiotic factors underscores biofilm importance in response to
various stress conditions, demonstrating the adaptability of F.
circinatum to changing environments. Interestingly, azole exposure also
led to biofilms that were resistant to DNase, which typically uncouples
biofilms by penetrating the biofilm and degrading its extracellular DNA;
we propose that DNases were likely hindered from reaching target cells
by the ECM barricade. The interplay between antifungal treatment and
DNase enzyme suggests a complex relationship between eDNA, ECM, and
antifungal agents in F. circinatum biofilms. Therefore, our results show
how a phytopathogen’s sessile (biofilm) lifestyle could influence its
response to the surrounding environment.