Bacterial surface adhesives and biofilm matrix polymers of marine and freshwater bacteria†

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Abstract
The initial adhesive polymers and biofilm matrix polymers of a mat colony phenotype of Pseudomonas sp. NCIMB2021 were investigated in situ using two optical techniques, interference reflection microscopy (IRM) and light section microscopy (LSM). Newly attached cells and bacterial biofilms were tested with various chemical treatments that might be expected to alter the integrity of specific intrapolymer or polymer‐substratum interactions, e.g. electrostatic, hydrophobic interactions, or hydrogen bonding, to determine whether the two types of adhesive polymer responded in the same way. A contraction or expansion of initial adhesive polymer was evaluated by IRM, whereas thickness changes in biofilms, dominated by matrix polymers, were measured by LSM. The test chemicals were solutions of Tween 20, ethylene glycol‐bis(p‐aminoethylether)N,N,N'N'‐tetraacetic acid (EGTA), ethylenediaminetetraacetic acid (EDTA), guanidine thiocyanate (GT), dimethyl sulphoxide (DMSO), all in an artificial seawater, 0–4 M NaCl, and 5 mM LaCl, in 0–4 M NaCl. None of the test chemicals affected thickness of biofilms measured by LSM. With newly attached cells, treatment with GT caused detachment of cells, whereas treatment with LaCl, produced various changes in image brightness, indicating changes in adhesive polymer thickness. These results are discussed in the context of previous studies with freshwater and estuarine isolates, in which polymers of freshwater strains were affected by electrolytes, Tween 20, and DMSO. Taken together, these results suggest that there are differences between the initial adhesive polymers and biofilm matrix polymers of the tested bacteria. Also, results indicated that there may be differences between polymers of freshwater bacteria and those adapted to saline environments, suggested by their different responses to change in total electrolyte.