When Beneficial Biofilm on Materials Is Needed: Electrostatic Attachment of Living Bacterial Cells Induces Biofilm Formation

Bacterial attachment is crucial in many biotechnological applications, but many important bacterial strains cannot form biofilms. Biofilms can damage materials, and current strategies to manage biofilms are focused on inhibition and removal of biofilm. Biofilm formation is inevitable when materials are exposed to microbes and instead of biofilm prevention, we propose management of microbial composition by formation of biofilms with beneficial microbes. Since bacteria need to overcome a high repulsive force to attach to the surface and later to grow and multiply on it, electrostatic modification of the surfaces of cells or the material by polyelectrolytes (PE) was used in our approach, enabling efficient attachment of viable bacterial cells. Since highly positively charged PEs are known to be bactericidal, they were acetylated to reduce their toxicity, while preserving their net positive charge and ensuring cell viability. In our study bacterial strains were selected according to their intrinsic capability of biofilm formation, their shape variety and cell wall structure. These strains were tested to compare how the artificially prepared vs. natural biofilms can be used to populate the surface with beneficial bacteria. Using an artificial biofilm constructed of the potentially probiotic isolate Bacillus sp. strain 25.2. M, reduced the attachment and induced complete inhibition of E. coli growth over the biofilm. This study also revealed that the modification of the surfaces of cells or material by polyelectrolytes allows the deposition of bacterial cells, biofilm formation and attachment of biofilm non-forming cells onto surfaces. In this way, artificial biofilms with extended stability can be constructed, leading to selective pressure on further colonization of environmental bacteria.

Hydrogel Containing an Extract of Tormentillae Rhizoma for the Treatment of Biofilm-Related Oral Diseases

In the present study, hydrogels containing the dried extract of tormentil ( Potentilla erecta (L.) Raeusch., Rosaceae) were designed and qualitatively evaluated regarding their viscosity, thixotropy, and texture properties. As mucoadhesiveness is a crucial factor determining drug retention within the oral cavity, mucoadhesive properties expressed as the work of adhesion and maximum detachment force under the presence of porcine buccal mucosa and two different models of mucoadhesive layers: mucin and gelatin discs were evaluated. The fingerprints of the analyzed tormentil extract were established by using a LC-ESI-MS method. The dominating compounds of the tested extract are oligomeric proanthocyanidins and agrimoniin. This study reveals that designed hydrogels are promising semi-solid delivery systems for the dry extract of tormentil with beneficial mucoadhesive, thixotropic, and texture characteristics and may be utilized as platforms for tormentil delivery to the oral cavity in periodontal diseases. In vitro evaluation of the efficacy of the tormentil hydrogel against cariogenic Streptococcus mutans biofilms was also performed. The hydrogel significantly reduced artificial biofilm formation. For all Streptococci, complete inhibition was revealed at a final concentration of the extract of 2 mg/mL. These beneficial characteristics, as well as the anti-biofilm activity, enable its use for dental care, but further clinical studies are required.

Effects of Nutrition on Mild Steel Corrosion by Sulfate Reducing Bacteria under Aerobic Environment

Sulfate reducing bacteria (SRB) are traditionally considered as anaerobic organism. In this paper, the potential of sulfate reducing bacteria to cause mild steel corrosion under aerobic situation was investigated. Natural biopolymer agar and sulfate reducing bacteria cells were used to produce artificial biofilm. Micro-sensors were used to investigate the microenvironment in artificial biofilm. Environmental scanning electron microscopy and energy dispersive spectroscopy were used to study mild steel corrosion covered by artificial biofilm. The results indicated that SRB could grow and reduce sulfate both in suspension and in biofilm. The hydrogen sulfide produced by SRB and mild steel corrosion were influenced by the nutrients in the environment. The concentration of H2S in SRB biofilm exposed to culture medium was as twenty times as that exposed to marine water. The main corrosion product of mild steel in culture medium was iron sulfide, whereas the main product of mild steel in marine water was iron oxide.

Layer-by-layer assembly of a redox enzyme displayed on the surface of elongated bacteria into a hierarchical artificial biofilm based anode

A highly efficient artificial biofilm based anode was constructed by an assembly of an elongatedE. coliwith surface displayed redox-enzyme.