No abstract

Dip-coated polystyrene layers of sub-micrometre thickness (85-500 nm) have been applied on copper and copper alloys (aluminium brass, copper-nickel 70/30), as well as on stainless steel 304, and produced an effective barrier against corrosion and adhesion of corrosion-relevant microorganisms. According to the dynamic wettability measurements, the coatings exhibited high advancing (103°), receding (79°) and equilibrium (87°) contact angles, low contact angle hysteresis (6°) and surface free energy (31 mJ/m 2 ). The corrosion rate of copper-nickel 70/30 alloy samples in 3.5% NaCl was as low as 3.2 µm/a (44% of that of the uncoated samples), and in artificial seawater was only 0.9 µm/a (29% of that of the uncoated samples). Cell adhesion was studied by fluorescence microscopy, using monoculture of Desulfovibrio alaskensis. The coatings not only decreased the corrosion rate but markedly reduced the number of bacterial cells adhered to the coated surfaces. The PS-coating on copper gave the best result, 2×10 3 cells/cm 2 (1% of that of the uncoated control).

The composition of tightly bound exopolymeric substances (EPS) obtained from biofilm and planktonic cell subpopulations of Stenotrophomonas maltophilia 5426 UKM was analyzed to study an impact of mild steel presence in the cultivation medium. The overall protein production was found to increase in the presence of a steel coupon. Some amino acids such as lysine, valine, iso-leucine, tyrosine and phenylalanine were found to be secreted in higher amounts in the presence of mild steel, while its absence leads to an increase of arginine, asparagine, serine, glutamine, proline, glycine, cysteine, leucine, methionine production levels. Biofilm cells EPS contained more arginine, glycine, cysteine, valine, methionine and leucine, comparing to EPS of planktonic cells. The changes of tightly bound EPS aggregation around the cells induced in the presence of steel coupons were revealed by transmission electron microscopy. The results suggested the transition of S. maltophilia 5426 UKM cells from planktonic to biofilm lifestyle to be a complex process involving more than a single step.