Enhancing adhesion of yeast brewery strains to chamotte carriers through aminosilane surface modification

Microscopic techniques to evaluate the biofilm formation ability of a marine bacterium Pseudomonas aeruginosa PFL-P1 on different substrata

Biofilm formation in bacteria is strongly affected by the nature of substrata. Different substrata such as glass, polystyrene, steel, ceramic, and rubber were used to assess the biofilm forming ability of a marine bacterium Pseudomonas aeruginosa PFL-P1 using a scanning electron microscope (SEM), atomic force microscope (AFM), and confocal laser scanning microscope (CLSM). The bacterium formed dense biofilms with varied aggregation on different substrata. SEM study revealed small rod-shaped cells with diverse arrangements within the biofilms on all the substrata under study. The AFM study revealed the highest roughness of 545 nm on the ceramic substratum. The biofilms formed on ceramic substratum were characterized with maximum roughness (742 nm), maximum peak height (1,480 nm), and maximum arithmetic mean height (611 nm), significantly higher than all the other substrata (p < .05). AFM studies confirmed that P. aeruginosa PFL-P1 exhibited biofilm heterogeneity on all the substrata. The CLSM study indicated a higher fraction of nucleic acids to α-polysaccharides ratio in the biofilms. COMSTAT analysis revealed the highest biofilm biomass of ~18 μm³ /μm² on the ceramic substratum. The maximum biofilm thickness of ~50 μm in the native state on the ceramic substratum was significantly higher than glass (p = .0015), polystyrene (p = .0001), steel (p = .0035), and rubber substrata (p = .0001). The higher surface roughness of ceramic substratum is accountable for more area for colonization, as evident from higher biomass and thickness of the biofilm. This study provides insight into the substratum properties, which modulate the biofilm forming ability in bacteria.

Beyond Risk: Bacterial Biofilms and Their Regulating Approaches

Bacterial biofilms are complex surface attached communities of bacteria held together by self-produced polymer matrixs mainly composed of polysaccharides, secreted proteins, and extracellular DNAs. Bacterial biofilm formation is a complex process and can be described in five main phases: (i) reversible attachment phase, where bacteria non-specifically attach to surfaces; (ii) irreversible attachment phase, which involves interaction between bacterial cells and a surface using bacterial adhesins such as fimbriae and lipopolysaccharide (LPS); (iii) production of extracellular polymeric substances (EPS) by the resident bacterial cells; (iv) biofilm maturation phase, in which bacterial cells synthesize and release signaling molecules to sense the presence of each other, conducing to the formation of microcolony and maturation of biofilms; and (v) dispersal/detachment phase, where the bacterial cells depart biofilms and comeback to independent planktonic lifestyle. Biofilm formation is detrimental in healthcare, drinking water distribution systems, food, and marine industries, etc. As a result, current studies have been focused toward control and prevention of biofilms. In an effort to get rid of harmful biofilms, various techniques and approaches have been employed that interfere with bacterial attachment, bacterial communication systems (quorum sensing, QS), and biofilm matrixs. Biofilms, however, also offer beneficial roles in a variety of fields including applications in plant protection, bioremediation, wastewater treatment, and corrosion inhibition amongst others. Development of beneficial biofilms can be promoted through manipulation of adhesion surfaces, QS and environmental conditions. This review describes the events involved in bacterial biofilm formation, lists the negative and positive aspects associated with bacterial biofilms, elaborates the main strategies currently used to regulate establishment of harmful bacterial biofilms as well as certain strategies employed to encourage formation of beneficial bacterial biofilms, and highlights the future perspectives of bacterial biofilms.

Yarrowia lipolytica Adhesion and Immobilization onto Residual Plastics

Research in cell adhesion has important implications in various areas, such as food processing, medicine, environmental engineering, biotechnological processes. Cell surface characterization and immobilization of microorganisms on solid surfaces can be performed by promoting cell adhesion, in a relatively simple, inexpensive, and quick manner. The adhesion of Yarrowia lipolytica IMUFRJ 50682 to different surfaces, especially potential residual plastics (polystyrene, poly(ethylene terephthalate), and poly(tetrafluoroethylene)), and its use as an immobilized biocatalyst were tested. Y. lipolytica IMUFRJ 50682 presented high adhesion to different surfaces such as poly(tetrafluoroethylene) (Teflon), polystyrene, and glass, independent of pH, and low adhesion to poly(ethylene terephthalate) (PET). The adhesion of the cells to polystyrene was probably due to hydrophobic interactions involving proteins or protein complexes. The adhesion of the cells to Teflon might be the result not only of hydrophobic interactions but also of acid-basic forces. Additionally, the present work shows that Y. lipolytica cell extracts previously treated by ultrasound waves (cell debris) maintained their enzymatic activity (lipase) and could be attached to polystyrene and PET and used successfully as immobilized biocatalysts in hydrolysis reactions.

Physiological tests for yeast brewery cells immobilized on modified chamotte carrier

In this study yeast cell physiological activity was assessed on the basis of the in situ activity of two important enzymes, succinate dehydrogenase and pyruvate decarboxylase. FUN1 dye bioconversion and cellular ATP content were also taken as important indicators of yeast cell activity. The study was conducted on six brewing yeast strains, which were either free cells or immobilized on a chamotte carrier. The experimental data obtained indicate clearly that, in most cases, the immobilized cells showed lower enzyme activity than free cells from analogous cultures. Pyruvate decarboxylase activity in immobilized cells was higher than in planktonic cell populations only in the case of the Saccharomyces pastorianus 680 strain. However, in a comparative assessment of the fermentation process, conducted with the use of free and immobilized cells, much more favorable dynamics and carbon dioxide productivity were observed in immobilized cells, especially in the case of brewing lager yeast strains. This may explain the higher total cell density per volume unit of the fermented medium and the improved resistance of immobilized cells to environmental changes.