The bacterial planktonic growth and the removal of bacterial cells grown on polypropylene surface coated with covalently immobilized proteases (subtilisin Carlsberg or α-chymotrypsin) was investigated for Enterococcus hirae, Staphyloccocus epidermidis and Eschericha coli. Immobilization of both proteases on plasma-treated polypropylene was carried out using as cross-linking agent i) glutaraldehyde or ii) N'-diisopropylcarbodiimide and N-hydroxysuccinimide. In the presence of immobilized proteases a higher bacterial planktonic growth (up to 40 %) was observed. Instead, a different effect was observed on cell removal, and it varied according to the bacteria strain, the immobilized protease and the immobilization procedure. In particular, the presence of subtilisin in the polypropylene coating increased the cell removal of E. hirae by simple washing of the polypropylene surface and both subtilisin and α-chymotrypsin immobilized by N'-diisopropylcarbodiimide and N-hydroxysuccinimide favored the removal of S. epidermidis after sonication. No significant differences compared to the control where observed in all the other cases. In conclusion this study indicates that proteases can be an enhancer of microbial biomass (a phenomena that could be exploited for industrial fermentation) and can affect the strength of cell adhesion for some bacteria.
Changes in surface roughness and topography on the macroscopic scale are known to affect bacterial attachment and retention. Little quantitative information is available as to how changes in surface topography on the micron and submicron scale affect the strength of bacterial attachment to substrata. A novel method is described using the atomic force microscope where a varying shear/lateral force (in nanonewtons) is used to detach individual bacterial cells from various substrata of different surface topographies. Lateral changes of 0.1 µm in the surface topography are sufficient to affect the strength of bacterial attachment. An increase in applied force from 4 to 8 nN was necessary to move bacteria retained in surface defects of approximately 1 µm wide and 0.2 µm deep compared with cells attached on smooth surfaces.
The interactions of purified staphylococcal delta-lysin and melittin with various phospholipid monolayers containing different polar head groups and fatty acid moieties and with monolayers of cod and sheep erythrocyte lipids at various initial film pressures (pi i) were studied by using the Wilhelmy plate method. In each case the final increase in surface pressure (delta pi) was a linear function of pi i. In the case of delta-lysin, the critical pressures (pi c, the extrapolated values of pi i at delta pi = 0) for phosphatidylcholines with different fatty acid chain length, dipalmitoylphospholipids with different polar head groups, and cod or sheep erythrocyte total lipids fell within a relatively narrow range whereas melittin showed a much wider range. The collapse pressures of the delta-lysin and melittin films at the air-water interface when adsorbed from the hypophase were very similar. delta-Lysin showed little or no specificity in its interactions with all types of lipid films studied, whereas melittin showed preferential interaction with films of acidic lipid, similar to the specificity reported for cardiotoxins of Naja mossambica mossambica described by other workers.
The free fatty acid and phospholipid composition of 5 psychrotrophic marine Pseudomonas spp. have been determined in chemostat culture with glucose as the limiting substrate over the range 0--20 degrees C. The predominant fatty acid present in all the isolates was hexadecenoic acid (C 16:1) together with lesser quantities of octadecenoic acid (C 18:1) whilst none contained acids with chain lengths exceeding 18 carbon atoms. Decreasing the growth temperature from 20 degrees C to 0 degrees C resulted in little significant change in fatty acid composition. The principal phospholipid components of the five psychrotrophic pseudomonads have been identified as phosphatidylserine, phosphatidylglycerol, phosphatidylethanolamine and diphosphatidylglycerol. Decreasing the growth temperature did not elicit significant changes either in the total quantities of phospholipid synthesized or in the concentration of individual phospholipid components in any of the isolates. All the psychrotrophs showed maximum glucose uptake between 15 degrees C and 20 degrees C and the rate decreased rapidly as the temperature was decreased towards 0 degrees C.
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