Biofilm Composition Research Articles

The microbial community of coral reefs: biofilm composition on artificial substrates under different environmental conditions

Artificial reefs are used as tools for the restoration of degrading coral reefs by providing new settlement substrates. The initial recruitment process consists of the formation of microbial biofilms shortly after deployment. The aim of the present study is to compare biofilm composition and development on artificial substrates at two different coral-reef sites. These locations differ in their environmental conditions, including their level of anthropogenic impact. Substrate and seawater samples were collected four times during the first 6 months after deployment, using a new methodology termed ‘tab-by-tab’. DNA was extracted, sequenced, and sorted for both prokaryotic (16s) and eukaryotic (18s) genes. No difference was found between the planktonic communities in the water, yet significant differences were observed in the biofilm communities on the structures at the two sites. Moreover, differences were recorded in coral recruitment rates, which are known to be affected by biofilm composition. Our findings suggest a potential role of environmental conditions in the early biofilm stages (first few months), which in turn may impact the succession and development of coral-reef communities and the success of artificial reefs as restoration tools.

Impact of changes in biofilm composition response following chlorine and chloramine disinfection on nitrogenous disinfection byproduct formation and toxicity risk in drinking water distribution systems

In practical drinking water treatment, chlorine and chloramine disinfection exhibit different mechanisms that affect biofilm growth. This study focused on the influence of biofilm composition changes, especially extracellular polymeric substance (EPS) fractions, on the potential formation and toxicity of nitrogenous disinfection by-products (N-DBP). Significant differences in microbial diversity and community structure were observed between the chlorine and chloramine treatments. Notably, the biofilms from the chloramine-treated group had higher microbial dominance and greater accumulation of organic precursors, as evidenced by the semi-quantitative confocal laser-scanning microscopy assay of more concentrated microbial aggregates and polysaccharide proteins in the samples. Additionally, the chloramine-treated group compared with chlorine had a higher EPS matrix content, with a 13.5 % increase in protein. Furthermore, the protein distribution within the biofilm differed; in the chlorine group, proteins were concentrated in the central region, whereas in the chloramine group, proteins were primarily located at the water–biofilm interface. Notably, functional prediction analyses of protein fractions in biofilms revealed specific functional regulation patterns and increased metabolism-related abundance of proteins in the chlorine-treated group. This increase was particularly pronounced for proteins such as dehydrogenases, reductases, transcription factors, and acyl-CoA dehydrogenases. By combining the Fukui function and density functional calculations to further analyse the effect of biofilm component changes on N-DBP production under chlorine/chloramine and by assessing the toxicity risk potential of N-DBP, it was determined that chloramine disinfection is detrimental to biofilm control and the accumulation of protein precursors has a higher formation potential of N-DBPs and toxicity risk, increasing the health risk of drinking water.

Biofilm rigidity, mechanics and composition in seawater desalination pretreatment employing ultrafiltration and microfiltration membranes

The choice of appropriate biofilm control strategies in membrane systems for seawater desalination pretreatment relies on understanding the properties of the biofilm formed on the membrane. This study reveals how the biofilm composition, including both organic and inorganic, influenced the biofilm behavior under mechanical loading. The investigation was conducted on two Gravity-Driven Membrane reactors employing Microfiltration (MF) and Ultrafiltration (UF) membrane for the pretreatment of raw seawater. After a stabilization period of 20 days (Phase I), a biofilm behavior test was introduced (Phase II) to evaluate (i) biofilm deformation during the absence of permeation (i.e., relaxation) and (ii) biofilm resistance to detachment forces (i.e., air scouring). The in-situ monitoring investigation using Optical Coherence Tomography (OCT) revealed that the biofilms developed on MF and UF membrane presented a rigid structure in absence of filtration forces, limiting the application of relaxation and biofilm expansion necessary for cleaning. Moreover, under shear stress conditions, a higher reduction in biofilm thickness was observed for MF (−60%, from 84 to 34 µm) compared to UF (−30%, from 64 to 45 µm), leading to an increase of permeate flux (+60%, from 9.1 to 14.9 L/m2/h and +20 % from 7.8 to 9.5 L/m2/h, respectively). The rheometric analysis indicated that the biofilm developed on MF membrane had weaker mechanical strength, displaying lower storage modulus (−50 %) and lower loss modulus (−55 %) compared to UF. These differences in mechanical properties were linked to the lower concentration of polyvalent ions and the distribution of organic foulants (i.e., BB, LMW-N) found in the biofilm on the MF membrane. Moreover, in the presence of air scouring led to a slight difference in microbial community between UF and MF.Our findings provide valuable insight for future investigations aimed at engineer biofilm composition to optimize biofilm control strategies in membrane systems for seawater desalination pretreatment.

(131) Predictors of Success with Early Antibiotic Therapy for Penile Implant Infection: Patients from a Prospective Randomized Study Comparing DNA Sequencing versus Traditional Cultures

Abstract Introduction Traditional culture is the current standard-of-care to determine therapeutic antibiotics for patients suffering from penile prosthesis (PP) infections. However, approximately 30% to 50% of PPs removed for infection are culture negative. Next-generation sequencing (NGS) of DNA has proven to be beneficial in its thorough analysis of biofilm composition. However, there are no existing clinical measures for identifying presenting characteristics of patients of successful or failed antibiotic treatments. Objective The purpose of this early dataset is to identify patient characteristics predicting success or failure with early antibiotic therapy in the setting of penile implant infection. Methods Upon institutional review board approval, adult men undergoing treatment for mild to moderate clinical (non-systemic) PP infection are enrolled after providing informed consent. Enrollees are randomized into one of two analytic arms – traditional culture or NGS. Traditional culture and NGS samples are collected upon clinical presentation prior to initiation of antibiotics. Patients are started on set empiric antibiotics and randomized to traditional culture or NGS. Patients follow up within ten days of antibiotic initiation and at six months complete a safety and compliance questionnaire which assesses symptoms, device function, and patient satisfaction. Results Of the 8 patients enrolled in the study, 4 eventually underwent device explantation due to worsening infection within 7 days of initiating empiric antibiotic treatment. The other 4 patients went on to the next step in the protocol. In evaluating these 2 groups: if there was penile shaft tenderness (2/4) this required PP removal prior to 7 days; while if there was no penile tenderness, the patient ended up with the device surviving at least 10 days. Patients on the NGS arm included those that survived the entire 6-month period. Currently, there are 11 active sites already participating; more patients and more centers are being enrolled in the study. Conclusions Penile shaft tenderness was a more common presentation in patients who failed early antibiotic treatment for penile implant infection. Recruitment of additional patients to this prospective, randomized controlled trial will help to identify additional favorable presentations of penile implant infection in addition to comparing the utility and outcomes of NGS and culture. Disclosure Yes, this is sponsored by industry/sponsor: Microgen Dx. Clarification: Industry initiated, executed and funded study. Any of the authors act as a consultant, employee or shareholder of an industry for: Microgen Dx.

Can "Risk-Sharing" Mechanisms Help Clonal Aquatic Plants Mitigate the Stress of Nanoplastics?

Most aquatic plants applied to ecological restoration have demonstrated a clonal growth pattern. The risk-spreading strategy plays a crucial role in facilitating clonal plant growth under external environmental stresses via clonal integration. However, the effects of different concentrations of nanoplastics (NPs) on the growth traits of clonal aquatic plants are not well understood. Therefore, this study aimed to investigate the impact of NPs exposure on seedlings of parent plants and connected offspring ramets. A dose response experiment (0.1, 1, and 10 mg L-1) showed that the growth of Eichhornia crassipes (water hyacinth) was affected by 100 nm polystyrene nanoplastics after 28 days of exposure. Tracer analysis revealed that NPs are accumulated by parent plants and transferred to offspring ramets through stolon. Quantification analysis showed that when the parent plant was exposed to 10 mg L-1 NPs alone for 28 days, the offspring ramets contained approximately 13 ± 2 μg/g NPs. In the case of connected offspring ramets, leaf and root biomass decreased by 24%-51% and 32%-51%, respectively, when exposed to NP concentrations ranging from 0.1 to 10 mg L-1. Excessive enrichment of NPs had a detrimental effect on the photosynthetic system, decreasing the chlorophyll content and nonphotochemical quenching. An imbalance in the antioxidant defense systems, which were unable to cope with the oxidative stress caused by NP concentrations, further damaged various organs. The root system can take up NPs and then transfer them to the offspring through the stolon. Interference effects of NPs were observed in terms of root activity, metabolism, biofilm composition, and the plant's ability to purify water. However, the risk-spreading strategy employed by parent plants (interconnected offspring ramets) offered some relief from NP-induced stress, as it increased their relative growth rate by 1 to 1.38 times compared to individual plants. These findings provide substantial evidence of the high NP enrichment capacity of E. crassipes for ecological remediation. Nevertheless, we must also remain aware of the environmental risk associated with the spread of NPs within the clonal system of E. crassipes, and contaminated cloned individuals need to be precisely removed in a timely manner to maintain normal functions.

Microbial and Monosaccharide Composition of Biofilms Developing on Sandy Loams from an Aquifer Contaminated with Liquid Radioactive Waste.

The development of microbial biofilms increases the survival of microorganisms in the extreme conditions of ecosystems contaminated with components of liquid radioactive waste (LRW) and may contribute to the successful bioremediation of groundwater. The purpose of this work was to compare the composition of the microorganisms and the exopolysaccharide matrix of the biofilms formed on sandy loams collected at the aquifer from a clean zone and from a zone with nitrate and radionuclide contamination. The aquifer is polluted from the nearby surface repository for liquid radioactive waste (Russia). The phylogenetic diversity of prokaryotes forming biofilms on the sandy loams' surface was determined during 100 days using high-throughput sequencing of the V4 region of the 16S rRNA genes. Scanning electron microscopy was used to study the development of microbial biofilms on the sandy loams. The ratio of proteins and carbohydrates in the biofilms changed in the course of their development, and the diversity of monosaccharides decreased, depending on the contamination of the sites from which the rocks were selected. The presence of pollution affects biofilm formation and EPS composition along with the dominant taxa of microorganisms and their activity. Biofilms establish a concentration gradient of the pollutant and allow the microorganisms involved to effectively participate in the reduction of nitrate and sulfate; they decrease the risk of nitrite accumulation during denitrification and suppress the migration of radionuclides. These biofilms can serve as an important barrier in underground water sources, preventing the spread of pollution. Pure cultures of microorganisms capable of forming a polysaccharide matrix and reducing nitrate, chromate, uranyl, and pertechnetate ions were isolated from the biofilms, which confirmed the possibility of their participation in the bioremediation of the aquifer from nonradioactive waste components and the decrease in the radionuclides' migration.

Combined pH ratiometry and fluorescence lectin-binding analysis (pH-FLBA) for microscopy-based analyses of biofilm pH and matrix carbohydrates.

Bacterial biofilms have a complex and heterogeneous three-dimensional architecture that is characterized by chemically and structurally distinct microenvironments. Confocal microscopy-based pH ratiometry and fluorescence lectin-binding analysis (FLBA) are well-established methods to characterize pH developments and the carbohydrate matrix architecture of biofilms at the microscale. Here, we developed a combined analysis, pH-FLBA, to concomitantly map biofilm pH and the distribution of matrix carbohydrates in bacterial biofilms while preserving the biofilm microarchitecture. As a proof of principle, the relationship between pH and the presence of galactose- and fucose-containing matrix components was investigated in dental biofilms grown with and without sucrose. The pH response to a sucrose challenge was monitored in different areas at the biofilm base using the ratiometric pH-sensitive dye C-SNARF-4. Thereafter, the fucose- and galactose-specific fluorescently labeled lectins Aleuria aurantia lectin (AAL) and Morus nigra agglutinin G (MNA-G) were used to visualize carbohydrate matrix components in the same biofilm areas and their immediate surroundings. Sucrose during growth significantly decreased biofilm pH (P < 0.05) and increased the amounts of both MNA-G- and AAL-targeted matrix carbohydrates (P < 0.05). Moreover, it modulated the biofilm composition towards a less diverse community dominated by streptococci, as determined by 16S rRNA gene sequencing. Altogether, these results suggest that the production of galactose- and fucose-containing matrix carbohydrates is related to streptococcal metabolism and, thereby, pH profiles in dental biofilms. In conclusion, pH-FLBA using lectins with different carbohydrate specificities is a useful method to investigate the association between biofilm pH and the complex carbohydrate architecture of bacterial biofilms.IMPORTANCEBiofilm pH is a key regulating factor in several biological and biochemical processes in environmental, industrial, and medical biofilms. At the microscale, microbial biofilms are characterized by steep pH gradients and an extracellular matrix rich in carbohydrate components with diffusion-modifying properties that contribute to bacterial acid-base metabolism. Here, we propose a combined analysis of pH ratiometry and fluorescence lectin-binding analysis, pH-FLBA, to concomitantly investigate the matrix architecture and pH developments in microbial biofilms, using complex saliva-derived biofilms as an example. Spatiotemporal changes in biofilm pH are monitored non-invasively over time by pH ratiometry, while FLBA with lectins of different carbohydrate specificities allows mapping the distribution of multiple relevant matrix components in the same biofilm areas. As the biofilm structure is preserved, pH-FLBA can be used to investigate the in situ relationship between the biofilm matrix architecture and biofilm pH in complex multispecies biofilms.

Characterization of MdpS: an in-depth analysis of a MUC5B-degrading protease from Streptococcus oralis.

Oral biofilms, comprising hundreds of bacteria and other microorganisms on oral mucosal and dental surfaces, play a central role in oral health and disease dynamics. Streptococcus oralis, a key constituent of these biofilms, contributes significantly to the formation of which, serving as an early colonizer and microcolony scaffold. The interaction between S. oralis and the orally predominant mucin, MUC5B, is pivotal in biofilm development, yet the mechanism underlying MUC5B degradation remains poorly understood. This study introduces MdpS (Mucin Degrading Protease from Streptococcus oralis), a protease that extensively hydrolyses MUC5B and offers an insight into its evolutionary conservation, physicochemical properties, and substrate- and amino acid specificity. MdpS exhibits high sequence conservation within the species and also explicitly among early biofilm colonizing streptococci. It is a calcium or magnesium dependent serine protease with strict physicochemical preferences, including narrow pH and temperature tolerance, and high sensitivity to increasing concentrations of sodium chloride and reducing agents. Furthermore, MdpS primarily hydrolyzes proteins with O-glycans, but also shows activity toward immunoglobulins IgA1/2 and IgM, suggesting potential immunomodulatory effects. Significantly, MdpS extensively degrades MUC5B in the N- and C-terminal domains, emphasizing its role in mucin degradation, with implications for carbon and nitrogen sequestration for S. oralis or oral biofilm cross-feeding. Moreover, depending on substrate glycosylation, the amino acids serine, threonine or cysteine triggers the enzymatic action. Understanding the interplay between S. oralis and MUC5B, facilitated by MdpS, has significant implications for the management of a healthy eubiotic oral microenvironment, offering potential targets for interventions aimed at modulating oral biofilm composition and succession. Additionally, since MdpS does not rely on O-glycan removal prior to extensive peptide backbone hydrolysis, the MdpS data challenges the current model of MUC5B degradation. These findings emphasize the necessity for further research in this field.

Tobacco-enhanced biofilm formation by Porphyromonas gingivalis and other oral microbes.

Microbial biofilms promote pathogenesis by disguising antigens, facilitating immune evasion, providing protection against antibiotics and other antimicrobials and, generally, fostering survival and persistence. Environmental fluxes are known to influence biofilm formation and composition, with recent data suggesting that tobacco and tobacco-derived stimuli are particularly important mediators of biofilm initiation and development in vitro and determinants of polymicrobial communities in vivo. The evidence for tobacco-augmented biofilm formation by oral bacteria, tobacco-induced oral dysbiosis, tobacco-resistance strategies, and bacterial physiology is summarized herein. A general overview is provided alongside specific insights gained through studies of the model and archetypal, anaerobic, Gram-negative oral pathobiont, Porphyromonas gingivalis.

Interrogating Salmonella Typhi biofilm formation and dynamics to understand antimicrobial resistance

AimsSalmonella Typhi biofilm-mediated infections are globally rising. Due to the emergence of drug resistance antibiotics did not show effective results against S. Typhi biofilm. Therefore, there is an urgent need for an in-depth interrogation of S. Typhi biofilm to understand its formation kinetics, compositions, and surface charge value. MethodsThis study utilized the S. Typhi MTCC-733 strain from a microbial-type culture collection in India. The S. Typhi biofilm was formed on a glass slide in a biofilm development apparatus. Typhoidal biofilm analysis was done with the help of various assays such as a crystal violet assay, SEM analysis, FTIR analysis, Raman analysis, and zeta potential analysis. Key findingThis article contained a comprehensive assessment of the typhoid biofilm formation kinetics, biofilm compositions, and surface charge which revealed that cellulose was a major molecule in the typhoidal biofilm which can be used as a major biofilm drug target against typhoidal biofilm. SignificanceThis study provided interrogations about typhoidal biofilm kinetics which provided ideas about the biofilm composition. The cellulose molecule showed a major component of S. Typhi biofilm and it could potentially involved in drug resistance, and offer a promising avenue for developing a new antibiofilm therapeutic target to conquer the big obstacle of drug resistance. The obtained information can be instrumental in designing novel therapeutic molecules in the future to combat typhoidal biofilm conditions effectively for overcoming antibiotic resistance against bacterial infection Salmonella.

The Evolving Microbiome of Dental Caries.

Dental caries is a significant oral and public health problem worldwide, especially in low-income populations. The risk of dental caries increases with frequent intake of dietary carbohydrates, including sugars, leading to increased acidity and disruption of the symbiotic diverse and complex microbial community of health. Excess acid production leads to a dysbiotic shift in the bacterial biofilm composition, demineralization of tooth structure, and cavities. Highly acidic and acid-tolerant species associated with caries include Streptococcus mutans, Lactobacillus, Actinomyces, Bifidobacterium, and Scardovia species. The differences in microbiotas depend on tooth site, extent of carious lesions, and rate of disease progression. Metagenomics and metatranscriptomics not only reveal the structure and genetic potential of the caries-associated microbiome, but, more importantly, capture the genetic makeup of the metabolically active microbiome in lesion sites. Due to its multifactorial nature, caries has been difficult to prevent. The use of topical fluoride has had a significant impact on reducing caries in clinical settings, but the approach is costly; the results are less sustainable for high-caries-risk individuals, especially children. Developing treatment regimens that specifically target S. mutans and other acidogenic bacteria, such as using nanoparticles, show promise in altering the cariogenic microbiome, thereby combatting the disease.

Characterization of dual-species biofilms formed by bacteria isolated from milk

This study evaluated biofilm formation of bacteria isolated from raw milk and investigated the composition of extracellular polymeric substances (EPS) using Raman spectroscopy. Biofilms were formed from six isolates on a 96-well microplate at 7 and 25 °C in 1 and 10% reconstituted whole milk. Biofilms were then formed on stainless steel coupons at 7 °C from two isolates identified as strong biofilm producers. Pseudomonas fluorescens, a frequent contaminant of raw milk, forms single or dual-species biofilms with Staphylococcus aureus; however, the sessile cell number of S. aureus remained constant over ten days. Raman spectroscopy identified that EPS composition varied with carbohydrate and protein substrates, the predominant components in P. fluorescens single or dual-species biofilms. Understanding the formation and composition of biofilms at different temperatures and in milk concentrations that simulate the equipment used in the dairy industry is a significant subsidy for establishing adequate sanitary protocols for their mitigation.

Microbial contamination profile on esthetic elastomeric ligatures through the checkerboard DNA-DNA hybridization technique : Arandomized split-mouth study.

The aim of this study is to assess the microbial contamination of three different brands of esthetic elastomeric ligatures. Different brands of esthetic ligatures (Unistick Pearl [American Orthodontics, Sheboygan, WI, USA], Power Sticks Pearl [Ortho Technology, Tampa, FL, USA], and Ease [Obscure, 3M Unitek, Monrovia, CA, USA]) were randomly assigned to permanent canines of 25patients (aged 11-18years) undergoing corrective orthodontic treatment. After 30days, the ligatures were removed, processed, and the biofilm composition was analyzed by checkerboard DNA-DNA hybridization for 40bacterial species. The microbiological data were analyzed using anonparametric mixed model. The ligatures presented intense microbial contamination after 30days, but no statistically significant differences were observed among the three groups (p > 0.05). The levels of the evaluated individual species and proportions of the microbial complexes showed no statistically significant differences among the ligature groups (p > 0.05). Esthetic elastomeric ligatures became multicolonized by several bacterial species after 30days of exposure to the oral cavity. However, no relevant differences were observed among the biofilm composition formed on the different ligature brands.

Saliva biofilm-derived outer membrane vesicles regulate biofilm formation and immune response of oral epithelial cells on titanium surfaces.

While the significant roles of outer membrane vesicles (OMVs) from individual oral bacterial species in bacterial-host interactions are known, the involvement of saliva biofilm-derived OMVs in peri-implant disease pathogenesis remains unclear. This study aimed to investigate the effect of saliva biofilm-derived OMVs on regulating saliva biofilm formation and modulating the immune response of the epithelial cells on titanium surfaces. Saliva derivedbiofilms were cultured on tissue culture plates (TCP) for 4 days using pooled saliva from four healthy donors. OMVs secreted from the TCP bound biofilm (referred to as OMVs or healthy saliva biofilm OMVs) were enriched using the size-exclusion chromatography method. We then evaluated the effects of these OMVs on theviability, metabolic activity, and the presence oforal pathogens in saliva biofilm grownon titanium discs for 24 h and 72 h. Furthermore, the impact of OMVs on the mRNA expression and inflammatory cytokines [interleukin (IL)-6, IL-1α, and monocyte chemoattractant protein-1 (MCP-1)] in human oral epithelial cells (OKF6/TERT-2) was investigated using RT-qPCR and enzyme-linked immunosorbent assay(ELISA), respectively. Healthy saliva biofilm OMVs improved the biomass and activity of saliva biofilm cultured on the titanium surfaces, with inhibited Porphyromonas gingivalis and Fusobacterium nucleatum, and enhanced Streptococcus mutansexpression. Additionally, OMVs increased pro-inflammatory cytokine IL-6 mRNA and IL-6cytokine expression in human oral epithelial cells. However, IL-1α and MCP-1 cytokines were inhibited 24-hour post-incubation with OMVs. Healthy saliva biofilm derivedOMVs regulate the activity and pathogen composition of biofilms formed on titanium, while modulating the secretion of pro-inflammation factors of oral epithelial cells grownon titanium surfaces. Healthy saliva biofilm OMVs may regulate the early biofilm formation on abutment surfaces and modulate epithelial cell immune response, which may alter the peri-implant niche and participate in the pathogenesis of peri-implant disease.

Distinctions in molecular composition of the dental biofilm in a dependence of method of exo/endogeneous caries prevention and cariogenic condition of a patient

Comparative study of changes in the secondary structure of dental biofilm proteins in people with cariesogenic and cariesoprotective status using synchrotron IR microspectroscopy. Dental biofilm samples from 50 patients without caries (group 1) and with carious lesions of tooth enamel (group 2) were studied. The molecular composition of biofilms was studied using IR microspectroscopy. Changes in the secondary structure of dental biofilm proteins were evaluated based on deconvolution of Amide I or Amide II amide bands. using the analysis of variance. Patients of both groups took tablets containing a mineral complex with calcium glycerophosphate. Based on the deconvolution of the IR spectral profile of the Amide I and Amide II bands, the changes occurring in the secondary structure of dental biofilm proteins have been studied. Using a large set of spectra, it was shown that the prediction of the secondary structure of the biofilm protein network is influenced by both the cariesogenic situation in the oral cavity (with initial carious lesions of the enamel) and the fact that patients use a modulator - calcium glycerophosphate (a tableted mineral complex with calcium glycerophosphate). Significant intra-group and intergroup differences in the secondary structure of dental biofilm proteins were established for patients in normal and carisogenic situations in the mouth, including after the use of a tableted mineral complex with calcium glycerophosphate. This allowed us to give a mathematical assessment of shifts in the secondary structure of proteins depending on the activity of caries and external modulation. The results obtained can form the basis of a technique for spectroscopic diagnosis of changes (shifts) in the oral microbiome leading to the development of the carious process, as well as become the basis for choosing the optimal therapeutic ways to treat enamel caries, including through preventive measures aimed at restoring the microflora of the patient's oral cavity.

An apparent lack of synergy between degradative enzymes against Staphylococcus aureus biofilms.

Enzymes combat bacterial infections by degrading biomolecules to disperse Staphylococcus aureus biofilms. Commercial enzyme mixtures, like cellulase and pepsin, show concentration-dependent dispersion, but low concentrations lack synergy. Only the sequential addition of pepsin followed by Arthrobacter luteus zymolyase 20T displays synergy, effectively dispersing biofilms. Purified zymolyase 100T outperforms zymolyase 20T but lacks synergy with pepsin. This study underscores the complexity of enzymatic biofilm dispersal, highlighting the need for tailored approaches based on enzyme properties and biofilm composition.

Enhanced electricity generation of a 1.2-L microbial fuel cell with acclimation of applied voltage

The aim of this study was to investigate the effect of acclimation at different applied voltages on the electricity generation and composition of anodic biofilm in microbial fuel cell (MFC). Single-chamber air-cathode 1.2-L MFCs were acclimated by different applied voltages (i.e., 0.5, 1.0, 1.5 and 2.0 V). The maximum power density of 1587 mW/m2 and maximum current density of 32.2 ± 0.3 A/m2 were obtained in the MFC after the acclimation by 1.0 V, respectively, which were 10.5 and 1610 times that of the unacclimated MFC. The MFC acclimated by 2.0 V could remain in stable operation with an average maximum current density of 7.8 ± 0.1 A/m2 and a maximum power density of 1439 ± 30 mW/m2 within 40 cycles (∼20 d). The average biomass of the anodic biofilms increased from 3.8 ± 0.9 mg/g before the acclimation to 11.3 ± 1.6 mg/g after the acclimation by 2.0 V. Correspondingly, the anode bacterial viability increased from 0.74 ± 0.02 to 0.91 ± 0.02. The relative abundance of Geoalkalibacter decreased from 18.7 % to 36.1 % before the acclimation to 1.3 %–18.0 % after the acclimation by 2.0 V in the bacterial communities of the anodic biofilms in the MFC. Results from this study should provide an easy way to enhance electrochemically active bacteria acclimation and improve electricity generation in the MFC.

Microbial diversity of biofilm in spent nuclear fuel storage pond

Spent nuclear fuel (SNF) storage is a facility requiring careful attention to prevent corrosion, with microbial-induced corrosion (MIC) being a significant contributing factor. While previous investigations have genetically identified total microbes and sulfate-reducing bacteria (SRB) in SNF storage ponds, similar studies have highlighted the dominance of Proteobacteria and Firmicutes in these environments. Therefore, this study aimed to identify the diversity of bacteria biofilm in SNF storage ponds through a metagenomic approach, with a specific focus on those potentially causing MIC. The results showed that the rack had the highest number of taxa based on taxonomic identification. The bacteria community on the rack, at the phylum level, was dominated by Proteobacteria (34.04%), Firmicutes (24.96%), and Chloroflexi (20.52%). Chloroflexi constituted the majority of the bacteria community on the pool floor (91.09%), while on the pool walls, Chloroflexi (45.17%) and Proteobacteria (44.02%) dominated almost equally. Metabolic pathway analysis further confirmed the activity of MIC in biofilm by the presence of MIC-related pathways. These findings contribute novel insights into the microbial composition of biofilms in SNF storage ponds, providing a foundation for future studies on the prevention and management of MIC in such facilities.

Analysis of the quantitative composition of the dental biofilm depending on the state of the hard dental tissues

The microflora of the oral cavity affects not only the development and course of the pathology of the hard dental tissues but also the effectiveness of its treatment and prevention. Therefore, it is equally important for a dentist to determine the species composition of microorganisms and their quantitative characteristics. The aim of the work was to study the quantitative composition of the planktonic form of the dental biofilm of the vestibular surface of the cervical teeth in young patients; its analysis in patients with a wedge-shaped defect, cervical caries and clinically intact teeth. A microbiological study of the dental biofilm of intact premolars of 33 caries-resistant patients (average age [23.90±5.34] years) was conducted. All patients were divided into three groups depending on the condition of the hard dental tissues. The dental biofilm removed from the lesion was additionally examined in patients with wedge-shaped defects. Microorganisms were identified by morphological, tinctorial and biochemical characteristics. A quantitative study of the population level was carried out by counting colony-forming units (CFU) in one gram of biomaterial which was expressed as a decimal logarithm (lg CFU/g). An imbalance between representatives of pathological and normal microflora was determined. Patients with cervical caries had a significantly higher chance of having Str. mutans and Lactobacterium in the dental biofilm, and a lower chance Str. γ-haemolyticus (p&lt;0.05). It confirms the role of Str. mutans and Lactobacterium in the etiology of cervical dental caries. There were no significant differences between the quantitative composition of the dental biofilm of patients of different groups that is probably related to the study of its planktonic component, the criteria for forming groups and the high level of caries resistance of the examined enamel. The obtained results can be useful in prescribing treatment and preventive measures for patients with cervical pathology of the teeth as well as in evaluating their effectiveness. In our opinion, it will contribute to a significant reduction in its prevalence and intensity among young people. Keywords: microorganisms, оral cavity, wedge-shaped defect, cervical caries.

Polyhexamethylene biguanide promotes adaptive cross-resistance to gentamicin in Escherichia coli biofilms.

Antimicrobial resistance is a critical public health issue that requires a thorough understanding of the factors that influence the selection and spread of antibiotic-resistant bacteria. Biocides, which are widely used in cleaning and disinfection procedures in a variety of settings, may contribute to this resistance by inducing similar defense mechanisms in bacteria against both biocides and antibiotics. However, the strategies used by bacteria to adapt and develop cross-resistance remain poorly understood, particularly within biofilms -a widespread bacterial habitat that significantly influences bacterial tolerance and adaptive strategies. Using a combination of adaptive laboratory evolution experiments, genomic and RT-qPCR analyses, and biofilm structural characterization using confocal microscopy, we investigated in this study how Escherichia coli biofilms adapted after 28 days of exposure to three biocidal active substances and the effects on cross-resistance to antibiotics. Interestingly, polyhexamethylene biguanide (PHMB) exposure led to an increase of gentamicin resistance (GenR) phenotypes in biofilms formed by most of the seven E. coli strains tested. Nevertheless, most variants that emerged under biocidal conditions did not retain the GenR phenotype after removal of antimicrobial stress, suggesting a transient adaptation (adaptive resistance). The whole genome sequencing of variants with stable GenR phenotypes revealed recurrent mutations in genes associated with cellular respiration, including cytochrome oxidase (cydA, cyoC) and ATP synthase (atpG). RT-qPCR analysis revealed an induction of gene expression associated with biofilm matrix production (especially curli synthesis), stress responses, active and passive transport and cell respiration during PHMB exposure, providing insight into potential physiological responses associated with adaptive crossresistance. In addition, confocal laser scanning microscopy (CLSM) observations demonstrated a global effect of PHMB on biofilm architectures and compositions formed by most E. coli strains, with the appearance of dense cellular clusters after a 24h-exposure. In conclusion, our results showed that the PHMB exposure stimulated the emergence of an adaptive cross-resistance to gentamicin in biofilms, likely induced through the activation of physiological responses and biofilm structural modulations altering gradients and microenvironmental conditions in the biological edifice.