Abstract
The impact of cortisol on Flavobacterium columnare biofilm formation was explored. Firstly, the dynamics of biofilm formation by one highly (HV) and one low virulent (LV) F. columnare isolate with and without the stress hormone cortisol under microfluidic flow conditions was characterized. This to confirm that F. columnare cells could form biofilm under cortisol supplementation, and to compare the temporal and structural differences between different treatment groups. One trial revealed that in both isolates cell aggregates resembling biofilms occurred within 7-h post-inoculation. Consequently, cell clusters were sloughed away, followed by a rebuilding of bacterial cell aggregates, suggestive for a high spreading capacity. While the HV isolate revealed cell aggregates formed upstream at all time-points, for the LV isolate this was only seen upon cortisol supplementation. Secondly, the transcriptional effect of genes (gldK, gldL, gldM, gldN, sprA, sprE, sprT, and porV) belonging to the Type IX secretion system involved in gliding motility was investigated in planktonic and biofilm cells of a HV and LV isolate to which no, a low (LD) or high (HD) dose of cortisol was added. Significantly lower expression of gliding genes gldK, gldL, gldM and gldN, and of protein secretion regulator porV was seen in the LV isolate planktonic cells supplemented with a HD-cortisol. The LV isolate biofilm cells treated with the HD-cortisol showed a significant upregulation of sprT, encoding mobile surface adhesion important in bacterial colonization. This is the first evidence for the co-regulatory effect of cortisol on biofilm formation and F. columnare gliding gene expression.
Highlights
Living organisms survive by maintaining an equilibrium, or homeostasis, that is continuously challenged by intrinsic or extrinsic disturbing stimuli [1]
Cell aggregates resembling biofilm filled the entire channel within 7 h pi, starting at the bacterial inlet and building up to the middle to eventually reach the opposite side of the channel
Biofilm formation of a highly virulent (HV) and low virulent (LV) F. columnare isolate was compared in parallel in these microfluidic chambers
Summary
Living organisms survive by maintaining an equilibrium, or homeostasis, that is continuously challenged by intrinsic or extrinsic disturbing stimuli [1]. The latter are called stressors, and are defined as stimuli that trigger a stress response [2]. For the majority of bacterial fish pathogens, chronic stress is considered a key factor in disease outbreaks as is the case for Flavobacterium columnare (F. columnare), the causative agent of columnaris disease [6, 7].
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