Effect of Hydrogen Peroxide on Cyanobacterial Biofilms

Abstract

Although a range of disinfecting formulations is commercially available, hydrogen peroxide is one of the safest chemical agents used for disinfection in aquatic environments. However, its effect on cyanobacterial biofilms is poorly investigated. In this work, biofilm formation by two filamentous cyanobacterial strains was evaluated over seven weeks on two surfaces commonly used in marine environments: glass and silicone-based paint (Sil-Ref) under controlled hydrodynamic conditions. After seven weeks, the biofilms were treated with a solution of hydrogen peroxide (H₂O₂) to assess if disinfection could affect long-term biofilm development. The cyanobacterial biofilms appeared to be tolerant to H₂O₂ treatment, and two weeks after treatment, the biofilms that developed on glass by one of the strains presented higher biomass amounts than the untreated biofilms. This result emphasizes the need to correctly evaluate the efficiency of disinfection in cyanobacterial biofilms, including assessing the possible consequences of inefficient disinfection on the regrowth of these biofilms.

Keywords: antifouling strategies; chemical disinfection; cyanobacterial biofilms; hydrogen peroxide; marine biofouling; resistance; virulence.

Figure 1

Romeriopsis sp. LEGE 11469 and cf. Phormidesmis sp. LEGE 10370 biofilm development on different surfaces (glass—white bars and Sil-Ref—black bars). The parameters analyzed refer to biofilm wet weight (a,b), thickness (c,d), biovolume (e,f), average size of non-connected pores (g,h), and contour coefficient (i,j). Mean values and SD from two biological assays with two technical replicates each are represented. For each sampling day, the asterisk (*) indicates significant differences between surfaces (p ≤ 0.1; unpaired, non-parametric Mann–Whitney test).

Figure 2

Romeriopsis sp. LEGE 11469 and cf. Phormidesmis sp. LEGE 10370 biofilm development on different surfaces (glass—white bars and Sil-Ref—black bars) after H₂O₂ disinfection treatment (left side) and regrowth for two weeks after the H₂O₂ disinfection treatment (right side). The parameters analyzed refer to biofilm wet weight (a,b), thickness (c,d), biovolume (e,f), average size of non-connected pores (g,h), and contour coefficient (i,j). Mean values and SD from two biological assays with two technical replicates each are represented. For each comparison Control vs. H₂O₂ treatment, the asterisk (*) indicates significant differences between conditions (p ≤ 0.1; unpaired, non-parametric Mann–Whitney test).

Figure 3

Representative 3D OCT images of Romeriopsis sp. LEGE 11469 and cf. Phormidesmis sp. LEGE 10370 biofilms formed on glass and Sil-Ref after (a) H₂O₂ disinfection treatment and (b) regrowth for two weeks after the H₂O₂ disinfection treatment. The color scale shows the biofilm thickness (µm).

Figure 4

Diagram of the experimental stages of the current study.