Calcineurin signaling pathway influences biofilm formation by affecting hydrophobicity and cell wall integrity.

Background: Biofilms, as a kind of fixed-cell community, can greatly improve industrial fermentation efficiency in immobilized fermentation, but the regulation process is still unclear, which restricts their application. Ca was reported to be a key factor affecting biofilm formation. However, the effect of Ca on biofilm structure and microbiology was yet only studied in bacteria. How Ca-mediated calcineurin signaling pathway (CSP) alters biofilm formation in bacteria and fungi has rarely been reported. On this basis, we investigated the regulation of CSP on the formation of biofilm in .

Results: Deletion of the key genes , , or in the CSP lowered the Ca concentration in the mycelium to a different extent, inhibited the formation of biofilm, reduced the hydrophobicity and adhesion of spores, destroyed the cell wall integrity of hyphae, and reduced the flocculation ability of hyphae. qRT-PCR results showed that the expression of spore hydrophobic protein , galactosaminogalactan (GAG) biosynthesis genes (, , , ), and α-1,3-glucan biosynthesis genes (, ) in the ∆, ∆, ∆, ∆ strains were significantly down-regulated compared with those of the wild type (WT). In addition, the transcription levels of the chitin synthesis gene (, ) and β-1,3-glucan synthesis gene () were consistent with the change in chitin and β-1,3-glucan contents in mutant strains.

Conclusion: These results indicated that CSP affected the hydrophobicity and adhesion of spores, the integrity of mycelial cell walls and flocculation by affecting Ca levels in mycelium, which in turn affected biofilm formation. This work provides a possible explanation for how CSP changes the formation of biofilm, and reveals a pathway for controlling biofilm formation in industrial immobilized fermentation.