Active fluid with Acidithiobacillus ferrooxidans: correlations between swimming and the oxidation route.

To explore engineering platforms towards 'active bacterial baths', we grow and characterize native and commercial strains of Acidithiobacillus ferrooxidans to promote swimming locomotion. Three different energy sources were used, namely elemental sulfur, ferrous sulfate, and pyrite. The characteristics of the culture, such as pH, Eh, and the concentration of cells and ions, are monitored to seek correlations between the oxidation route and the transport mechanism. We found that only elemental sulfur induces swimming mobility in the commercial DSMZ - 24,419 strain, while ferrous sulfate and the sulfide mineral, pyrite, did not activate swimming on any strain. The bacterial mean squared displacement and the mean velocity are measured to provide a quantitative description of the bacterial mobility. We found that, even if the A. ferrooxidans strain is grown in a sulfur-rich environment, it preferentially oxidizes iron when an iron-based material is included in the media. Similar to other species, once the culture pH decreases below 1.2, the active locomotion is inhibited. The engineering control and activation of swimming in bacterial cultures offer fertile grounds towards applications of active suspensions such as energy-efficient bioleaching, mixing, drug delivery, and bio-sensing.

Application of Dimethicone to Prevent Culture Media from Drying in Microbiological Diagnostics.

The search for novel modifications of culture media aimed at culture prolongation is a prerequisite for microbiological diagnostic progress. The aim of the study was to assess the possibilities of applying dimethicone (polymethylsiloxane) as a barrier between the agar surface and atmosphere to prevent drying of solid and semisolid culture medium providing the retention of its useful properties. Materials and Methods: We studied the dynamics of water (volume) loss of culture media used in microbiology, and the effect of dimethicone on the process. Dimethicone was arranged in layers on culture medium surface. The effect of dimethicone on growth and generation of fast-growing (Staphylococcus aureus, Escherichia coli, Salmonella enterica Serovar Typhimurium, Burkholderia cenocepacia) and slow-growing (Mycobacterium avium) bacteria was studied, as well as on bacterial mobility (Pseudomonas aeruginosa and Escherichia coli) in semisolid agars. Results: The dynamics of water loss in culture media showed the weight loss in all media without dimethicone (control) in 24 h to be statistically significant (p<0.05); 7-8 days later, they lost 50% of weight, and 14 days later they lost approximately 70%. The weight of media under dimethicone underwent no significant changes during the observation period. Growth index of fast-growing bacteria (S. aureus, E. coli, S. Typhimurium, B. cenocepacia) on control culture media without applying any substance, and on culture media under dimethicone had no significant differences. Visible M. avium growth on chocolate agar in controls was recorded on day 19, under dimethicone - on days 18-19. The number of colonies on culture day 19 under dimethicone tenfold exceeded the control values. The mobility indices of P. aeruginosa and E. coli on semisolid agar under dimethicone 24 h later were significantly higher than under control conditions (p<0.05 in both cases). Conclusion: The study confirmed marked deterioration of culture media properties under prolonged cultivation. The suggested protection technology of culture media growth properties using dimethicone showed beneficial effects.

Escherichia coli Biofilm Formation, Motion and Protein Patterns on Hyaluronic Acid and Polydimethylsiloxane Depend on Surface Stiffness.

The surface stiffness of the microenvironment is a mechanical signal regulating biofilm growth without the risks associated with the use of bioactive agents. However, the mechanisms determining the expansion or prevention of biofilm growth on soft and stiff substrates are largely unknown. To answer this question, we used PDMS (polydimethylsiloxane, 9-574 kPa) and HA (hyaluronic acid gels, 44 Pa-2 kPa) differing in their hydration. We showed that the softest HA inhibited Escherichia coli biofilm growth, while the stiffest PDMS activated it. The bacterial mechanical environment significantly regulated the MscS mechanosensitive channel in higher abundance on the least colonized HA-44Pa, while Type-1 pili (FimA) showed regulation in higher abundance on the most colonized PDMS-9kPa. Type-1 pili regulated the free motion (the capacity of bacteria to move far from their initial position) necessary for biofilm growth independent of the substrate surface stiffness. In contrast, the total length travelled by the bacteria (diffusion coefficient) varied positively with the surface stiffness but not with the biofilm growth. The softest, hydrated HA, the least colonized surface, revealed the least diffusive and the least free-moving bacteria. Finally, this shows that customizing the surface elasticity and hydration, together, is an efficient means of affecting the bacteria's mobility and attachment to the surface and thus designing biomedical surfaces to prevent biofilm growth.