CH1 - Factors controlling the structure and microbial composition of biofilms

• Unité de recherche: COST
• Numéro de projet: C98.0014
• Titre du projet anglais: CH1 - Factors controlling the structure and microbial composition of biofilms

Mots-clé (Anglais)

Biofilm; sulfate-reducing bacteria; triangulation

Programme de recherche (Anglais)

COST-Action 520 - Biofouling et matériaux

Description succincte (Anglais)

See abstract

Partenaires et organisations internationales (Anglais)

B, DK, FIN, F, D, GR, H, I, NL, P, RO, SI, E, S, CH, GB

Résumé des résultats (Abstract) (Anglais)

Sulfate reducing bacteria (SRB) enhance steel corrosion when located in anoxic niches within aerobic biofilms. We have performed studies on the adhesion of the SRB Desulfovibrio desulfuricans to stainless steel and its establishment in biofilms of Pseudomonas aeruginosa PAO1. It was investigated how the adhesion of D. desulfuricans and three other bacterial species was influenced by the surface topography of AISI 304 stainless steel. Five types of surface finish with roughness values Ra between 0.03 and 0.89 µm were produced. Adhesion of all bacteria was minimal at Ra = 0.16 µm, whereas smoother and rougher surfaces gave rise to more adhesion. This surface exhibited parallel scratches, in which a high proportion of bacteria of three of the strains aligned. Reduced overall adhesion was attributed to unfavorable interactions of this surface with bacteria oriented other than parallel to the scratches. Energy calculations and considerations of micro-geometry confirmed this mechanism. Rougher surfaces allowed more bacteria to adhere in other orientations, whereas the orientation of cells adhered to the smoothest surface was random. An unexpected result was that D. desulfuricans, adhered over ten times less than the other strains despite similar attraction energies. Percolation experiments were conducted with stainless steel granules. Bacterial adhesion was quantified by spectrophotometry without any manipulation of the steel. As in batch experiments, adhesion of D. desulfuricans was 10 times lower than of P. aeruginosa and P. putida mt2. It indicates that the poor adhesion of D. desulfuricans was indeed due to the low adhesion efficiency of this strain and not to higher reversibility. The reversibility of D. desulfuricans adhesion was much higher (89% recovery of attached cells upon dilution of the liquid medium) than of the other strains (20 - 33%). D. desulfuricans adhesion was enhanced in columns that had previously been exposed to P. aeruginosa. A confocal laser microscopy-based biofilm quantification method was developed that allowed to quantify the biovolume from the visible biomass and to analyze the thickness and porosity of biofilms. Program sequences were developed to automatically process large numbers of micrographs. Interpolation by triangulation visualized the parameter distribution. Moreover, the average biofilm porosity was deduced from the ratio between the biovolume and the biofilm thickness. The lateral biomass distribution on the surfaces of a steel coupon colonized by P. aeruginosa was heterogeneous but the biofilm density was relatively constant. A high number of observation fields is needed to diminish the impact of peculiarities of individual fields on interpolated representations. This is feasible with the developed automated image analysis. Finally, the influence of P. aeruginosa on the establishment of D. desulfuricans on stainless steel was studied. In batch experiments, adhesion of D. desulfuricans was enhanced by a factor 7.6 in mixed suspension with P. aeruginosa. The enhancement appeared to be due to the presence of P. aeruginosa as most adhered SRB were found in direct contact with adhered P. aeruginosa cells. P. aeruginosa biofilms grown under laminar flow retained more than 600 times more D. desulfuricans than clean steel. D. desulfuricans attachment to and invasion of P. aeruginosa biofilms grown under laminar flow showed over 600 times more retention of D. desulfuricans cells than clean steel. Besides ongoing invasion of the biofilms by SRB over many days, the appearance of microcolonies suggested that this strain grew in P. aeruginosa biofilms. This indicates anoxic microniches in the relatively thin P. aeruginosa biofilms.

Références bases de données (Anglais)

Swiss Database: COST-DB of the State Secretariat for Education and Research Hallwylstrasse 4 CH-3003 Berne, Switzerland Tel. [phone] Swiss Project-Number: C98.0014