Morphological and chemical changes in the attached cells of Pseudomonas aeruginosa as primary biofilms develop on aluminium and CaF₂ plates

Aims: To investigate the morphological and chemical changes in attached cells of Pseudomonas aeruginosa (ATCC 14886) at different stages of biofilm development on two different types of substrata. Methods and Results: The development of primary biofilm on aluminium plates representing metals and on CaF₂ discs representing dielectric materials was monitored by FTIR microscopy, ESEM, EDAX and protein analysis by SDS-PAGE. A unique cellular feature similar in morphology to pili was observed on the surface of P. aeruginosa adhering on aluminium but not on CaF₂. Results derived from FTIR analysis confirm on both substrata the successive importance of polysaccharides and proteins during the biofilm development. These results also revealed that the increase of the ratio of carboxylates to amide I was higher with the aluminium plates than with the CaF₂ discs. The number of cells adhered and the amount of oxygen incorporated in adhered cells on the latter materials were, respectively, less and almost nil in comparison with the former. Protein analysis of the lysates of cells by SDS-PAGE revealed that expression of one protein with a molecular weight of 45 kDa, was greatly enhanced in attached cells on both substrata. However, expression of another protein with molecular weight of 35 kDa was up-regulated only in cells adhering on CaF₂ but not in those on aluminium. Conclusion: Depending on the nature of the surface, new proteinaceous complexes and cellular features were formed in the attachment process of P. aeruginosa. Significance and Impact of the Study: The pattern of P. aeruginosa cells adhering onto CaF₂ discs and aluminium plates is different. Formation of biofilm is more difficult on CaF₂ than on aluminium.