Effects of calcium on development of anaerobic acidogenic biofilms

Assessment of multispecies biofilm growth on root canal dentin under different radiation therapy regimens

OBJECTIVES

To assess the growth of a multispecies biofilm on root canal dentin under different radiotherapy regimens.

MATERIALS AND METHODS

Sixty-three human root dentin cylinders were distributed into six groups. In three groups, no biofilm was formed (n = 3): NoRT) non-irradiated dentin; RT55) 55 Gy; and RT70) 70 Gy. In the other three groups (n = 18), a 21-day multispecies biofilm (Enterococcus faecalis, Streptococcus mutans, and Candida albicans) was formed in the canal: NoRT + Bio) non-irradiated + biofilm; RT55 + Bio) 55 Gy + biofilm; and RT70 + Bio) 70 Gy + biofilm. The biofilm was quantified (CFUs/mL). Biofilm microstructure was assessed under SEM. Microbial penetration into dentinal tubules was assessed under CLSM. For the biofilm biomass and dentin microhardness pre- and after biofilm growth assessments, 45 bovine dentin specimens were distributed into three groups (n = 15): NoRT) non-irradiated + biofilm; RT55 + Bio) 55 Gy + biofilm; and RT70 + Bio) 70 Gy + biofilm.

RESULTS

Irradiated specimens (70 Gy) had higher quantity of microorganisms than non-irradiated (p = .010). There was gradual increase in biofilm biomass from non-irradiated to 55 Gy and 70 Gy (p < .001). Irradiated specimens had greater reduction in microhardness after biofilm growth. Irradiated dentin led to the growth of a more complex and irregular biofilm. There was microbial penetration into the dentinal tubules, regardless of the radiation regimen.

CONCLUSION

Radiotherapy increased the number of microorganisms and biofilm biomass and reduced dentin microhardness. Microbial penetration into dentinal tubules was noticeable.

CLINICAL RELEVANCE

Cumulative and potentially irreversible side effects of radiotherapy affect biofilm growth on root dentin. These changes could compromise the success of endodontic treatment in oncological patients undergoing head and neck radiotherapy.

Variability of Micro- and Macro-Elements in Anaerobic Co-Digestion of Municipal Sewage Sludge and Food Industrial By-Products

The main aim of this study was to evaluate the effect of the addition of selected industrial food wastes on the fate of micro- and macro-elements within an anaerobic digestion process (AD), as well as define the relationship between their content and AD efficiency. Orange peels, (OP), orange pulp (PL) and brewery spent grain (BSG) were used as co-substrates, while municipal sewage sludge (SS) was applied as the main component. The introduction of co-substrates resulted in improvements in feedstock composition in terms of macro-elements, with a simultaneous decrease in the content of HMs (heavy metals). Such beneficial effects led to enhanced methane production, and improved process performance at the highest doses of PL and BSG. In turn, reduced biogas and methane production was found in the three-component digestion mixtures in the presence of OP and BSG; therein, the highest accumulation of most HMs within the process was also revealed. Considering the agricultural application of all digestates, exceedances for Cu, Zn and Hg were recorded, thereby excluding their further use for that purpose.

Effect of Calcium Ion Supplementation on Oral Microbial Composition and Biofilm Formation In Vitro

The oral cavity contains a variety of ecological niches with very different environmental conditions that shape biofilm structure and composition. The space between the periodontal tissue and the tooth surface supports a unique anaerobic microenvironment that is bathed in the nutrient-rich gingival crevicular fluid (GCF). During the development of periodontitis, this environment changes and clinical findings reported a sustained level of calcium ion concentration in the GCF collected from the periodontal pockets of periodontitis patients. Here, we report the effect of calcium ion supplementation on human oral microbial biofilm formation and community composition employing an established SHI medium-based in vitro model system. Saliva-derived human microbial biofilms cultured in calcium-supplemented SHI medium (SHICa) exhibited a significant dose-dependent increase in biomass and metabolic activity. The effect of SHICa medium on the microbial community composition was evaluated by 16S rRNA gene sequencing using saliva-derived microbial biofilms from healthy donors and periodontitis subjects. In this study, intracellular microbial genomic DNA (iDNA) and extracellular DNA (eDNA) were analyzed separately at the genus level. Calcium supplementation of SHI medium had a differential impact on iDNA and eDNA in the biofilms derived from healthy individuals compared to those from periodontitis subjects. In particular, the genus-level composition of the eDNA portion was distinct between the different biofilms. This study demonstrated the effect of calcium in a unique microenvironment on oral microbial complex supporting the dynamic transformation and biofilm formation.

Salinity effect on freshwater Anammox bacteria: Ionic stress and ion composition

The biggest challenge to apply Anammox to treat wastewater with elevated salt content is the inhibitory effect of salinity on freshwater Anammox bacteria (FAB). Most of the research into salinity inhibition has focused on the osmotic pressure effect, while the inhibitory effect and its mechanisms induced by ion composition are poorly understood. In this study, the individual and combined effect of NaCl, KCl and Na₂SO₄ on FAB (>99% belonging to Ca. Brocadia genera) were systematically investigated by batch tests. The corresponding responses of mRNA abundance of three functional genes (including nitrite reductase gene (nirS), hydrazine synthase gene (hzsB) and hydrazine dehydrogenase gene (hdh)) under different salt conditions were analyzed. The results indicated that NaCl, KCl and Na₂SO₄ have different inhibition effects, with the 50% inhibition at 0.106, 0.096 and 0.063 M, respectively. The combined inhibition of NaCl+KCl and NaCl+Na₂SO₄ on FAB were both synergistic; while the combined inhibition of NaCl+KCl+Na₂SO₄ was additive. The responses of mRNA (of genes: nirS, hzsB and hdh) suggested NaCl inhibited the transport of ammonium; Na₂SO₄ inhibited both nitrite and ammonium transport; high salinity inhibited functional enzyme activity. These results suggest both ionic stress and ion composition contributed to the observed inhibition.

Enhanced anaerobic co-digestion of fat, oil, and grease by calcium addition: Boost of biomethane production and microbial community shift

This work focused on the application of calcium (0.1-1% w/v) to overcome the inhibition caused by the high loadings (2% v/v) of fat, oil, and grease (FOG) in the context of biomethane production, organic removal, and microbial community shift. Addition of 0.5% calcium showed maximum biomethane production (6-fold increase); biomethane production decreased following the addition of calcium (>0.5%). The highest organic removal rates were 83 and 89% upon the addition of 0.3 and 0.5% calcium, respectively. Addition of calcium facilitated the growth of bacteria of phylum Firmicutes from the Clostridium, Syntrophomonas, and Sedimentibacter genera. The population of members from the genus Methanosaeta increased after the addition of 0.5% calcium, which is one of the factors responsible for high biomethane production. This study demonstrated that addition of calcium is an attractive strategy to avoid the inhibition of the growth of anaerobic microflora due to the presence of high FOG concentrations.

Nanoantibiotics: A Novel Rational Approach to Antibiotic Resistant Infections

Background:

The main drawbacks for using conventional antimicrobial agents are the development of multiple drug resistance due to the use of high concentrations of antibiotics for extended periods. This vicious cycle often generates complications of persistent infections, and intolerable antibiotic toxicity. The problem is that while all new discovered antimicrobials are effective and promising, they remain as only short-term solutions to the overall challenge of drug-resistant bacteria.

Objective:

Recently, nanoantibiotics (nAbts) have been of tremendous interest in overcoming the drug resistance developed by several pathogenic microorganisms against most of the commonly used antibiotics. Compared with free antibiotic at the same concentration, drug delivered via a nanoparticle carrier has a much more prominent inhibitory effect on bacterial growth, and drug toxicity, along with prolonged drug release. Additionally, multiple drugs or antimicrobials can be packaged within the same smart polymer which can be designed with stimuli-responsive linkers. These stimuli-responsive nAbts open up the possibility of creating multipurpose and targeted antimicrobials. Biofilm formation still remains the leading cause of conventional antibiotic treatment failure. In contrast to conventional antibiotics nAbts easily penetrate into the biofilm, and selectively target biofilm matrix constituents through the introduction of bacteria specific ligands. In this context, various nanoparticles can be stabilized and functionalized with conventional antibiotics. These composites have a largely enhanced bactericidal efficiency compared to the free antibiotic.

Conclusion:

Nanoparticle-based carriers deliver antibiotics with better biofilm penetration and lower toxicity, thus combating bacterial resistance. However, the successful adaptation of nanoformulations to clinical practice involves a detailed assessment of their safety profiles and potential immunotoxicity.

Effect of calcium chloride on abating inhibition due to volatile fatty acids during the start-up period in anaerobic digestion of municipal solid waste

Biomethanation of municipal solid waste (MSW) is a slow process and the yield of biogas is usually low. The present study was carried out to examine the effect of calcium chloride (CaCl2) on anaerobic digestion of MSW. Three anaerobic digesters with different concentrations of CaCl2, namely sample without additives (Control), sample with 2.5 g/L CaCl2 (R1) and sample with 5 g/L CaCl2 (R2) were studied separately and the significant results are presented. From the experimental results, it was observed that pH decreased with an increase in the dosage of CaCl2. Total solids and volatile solids reduction percentage in digester R2 was considerably lower than Control and R1 digesters. The significant positive correlation with small increments in volatile solids and chemical oxygen demand (COD) reduction were observed with an increase in pH. The cumulative biogas production in all the three digesters (Control, R1 and R2) were observed to be 35.38, 46.46 and 37.56 L, respectively. It was also observed that the volatile fatty acids (VFAs) removal efficiency in digester R1 was the best among all the three digesters. A comparison of the effluent characteristics revealed improvement in the overall performance of the digester R1 amended with 2.5 g/L CaCl2 over the other two digesters.

Role of biofilm roughness and hydrodynamic conditions in Legionella pneumophila adhesion to and detachment from simulated drinking water biofilms

Biofilms in drinking water distribution systems (DWDS) could exacerbate the persistence and associated risks of pathogenic Legionella pneumophila (L. pneumophila), thus raising human health concerns. However, mechanisms controlling adhesion and subsequent detachment of L. pneumophila associated with biofilms remain unclear. We determined the connection between L. pneumophila adhesion and subsequent detachment with biofilm physical structure characterization using optical coherence tomography (OCT) imaging technique. Analysis of the OCT images of multispecies biofilms grown under low nutrient condition up to 34 weeks revealed the lack of biofilm deformation even when these biofilms were exposed to flow velocity of 0.7 m/s, typical flow for DWDS. L. pneumophila adhesion on these biofilm under low flow velocity (0.007 m/s) positively correlated with biofilm roughness due to enlarged biofilm surface area and local flow conditions created by roughness asperities. The preadhered L. pneumophila on selected rough and smooth biofilms were found to detach when these biofilms were subjected to higher flow velocity. At the flow velocity of 0.1 and 0.3 m/s, the ratio of detached cell from the smooth biofilm surface was from 1.3 to 1.4 times higher than that from the rough biofilm surface, presumably because of the low shear stress zones near roughness asperities. This study determined that physical structure and local hydrodynamics control L. pneumophila adhesion to and detachment from simulated drinking water biofilm, thus it is the first step toward reducing the risk of L. pneumophila exposure and subsequent infections.

Biofilm-related infections: bridging the gap between clinical management and fundamental aspects of recalcitrance toward antibiotics

Surface-associated microbial communities, called biofilms, are present in all environments. Although biofilms play an important positive role in a variety of ecosystems, they also have many negative effects, including biofilm-related infections in medical settings. The ability of pathogenic biofilms to survive in the presence of high concentrations of antibiotics is called "recalcitrance" and is a characteristic property of the biofilm lifestyle, leading to treatment failure and infection recurrence. This review presents our current understanding of the molecular mechanisms of biofilm recalcitrance toward antibiotics and describes how recent progress has improved our capacity to design original and efficient strategies to prevent or eradicate biofilm-related infections.

Potential of calcium to scaffold an endodontic biofilm, thus protecting the micro-organisms from disinfection

Biofilms in the root canal of a tooth (endodontic biofilm) can induce and sustain apical periodontitis which is an oral inflammatory disease. Still, little is known about the composition of the endodontic biofilm. Studies on biofilms in root canals focus on the identification of the microbial species, but the majority of the biofilm consists of matrix material. Environmental aspects determine the structure of the biofilm and extracellular matrix. Calcium is involved in biofilm formation and activity at three levels. Firstly in cell-environment; calcium may 'condition' the surfaces of support and bacterial cells. Secondly, in cell-cell interaction; calcium plays a role in build up of biofilm structures. Typically, calcium ions act as 'cation bridges' between polysaccharides originating from different cells. Thirdly, within cells, calcium is required for certain biochemical reactions in bacteria and some bacterial physiological activities. Because calcium is present in the root canal, it could play a significant role in the organization of the biofilm. Chelators, already used in endodontics to remove the smear layer by disintegration of the structural cohesion calcium bonds, could weaken the biofilm matrix by removing calcium from the extracellular matrix thus disturbing its coherence. Subsequently, this disruption could increase the efficacy of disinfecting agents.

Effect of calcium on moving-bed biofilm reactor biofilms

The effect of calcium concentration on the biofilm structure, microbiology, and treatment performance was evaluated in a moving-bed biofilm reactor. Three experiments were conducted in replicate laboratory-scale reactors to determine if wastewater calcium is an important variable for the design and optimization of these reactors. Biofilm structural properties, such as thickness, oxygen microprofiles, and the composition of extracellular polymeric substances (EPS) were affected by increasing calcium concentrations. Above a threshold concentration of calcium between 1 and 50 mg/L, biofilms became thicker and denser, with a shift toward increasingly proteinaceous EPS at higher calcium concentrations up to 200 mgCa2+/L. At 300 mgCa2+/L, biofilms were found to become primarily composed of inorganic calcium precipitates. Microbiology was assessed through microscopy, denaturing grade gel electrophoresis, and enumeration of higher organisms. Higher calcium concentrations were found to change the bacterial community and promote the abundant growth of filamentous organisms and various protazoa and metazoan populations. The chemical oxygen demand removal efficiency was improved for reactors at calcium concentrations of 50 mg/L and above. Reactor effluents for the lowest calcium concentration (1 mgCa2+/L) were found to be turbid (>50 NTU), as a result of the detachment of small and poorly settling planktonic biomass, whereas higher concentrations promoted settling of the suspended phase. In general, calcium was found to be an important variable causing significant changes in biofilm structure and reactor function.

Evaluation and elimination of inhibitory effects of salts and heavy metal ions on biodegradation of Congo red by Pseudomonas sp. mutant

In this study, it was attempted to evaluate the influences and also recommended some elimination methods for inhibitory effects offered by salts and heavy metal ions. Congo red dye solution treated with mutant Pseudomonas sp. was taken as a model system for study. The salts used in this study are NaCl, CaCl(2) and MgSO(4)· 7H(2)O. Though the growth was inhibited at concentrations above 4 g/l, toleration was achieved by acclimatization process. In case of heavy metal ions, Cr (VI) showed low inhibition up to 500 mg/l of concentration, compared to Zn (II) and Cu (II). It was due to the presence of chromium reductase enzyme which was confirmed by SDS-PAGE. Zn (II) and Cu (II) ion inhibitions were eliminated by chelation with EDTA. The critical ion concentrations obtained as per Han-Levenspiel model for Cr (VI), Zn (II) and Cu (II) were 0.8958, 0.3028 and 0.204 g/l respectively.

Pellicle formation in Shewanella oneidensis

Background

Although solid surface-associated biofilm development of S. oneidensis has been extensively studied in recent years, pellicles formed at the air-liquid interface are largely overlooked. The goal of this work was to understand basic requirements and mechanism of pellicle formation in S. oneidensis.

Results

We demonstrated that pellicle formation can be completed when oxygen and certain cations were present. Ca(II), Mn(II), Cu(II), and Zn(II) were essential for the process evidenced by fully rescuing pellicle formation of S. oneidensis from the EDTA treatment while Mg (II), Fe(II), and Fe(III) were much less effective. Proteins rather than DNA were crucial in pellicle formation and the major exopolysaccharides may be rich in mannose. Mutational analysis revealed that flagella were not required for pellicle formation but flagellum-less mutants delayed pellicle development substantially, likely due to reduced growth in static media. The analysis also demonstrated that AggA type I secretion system was essential in formation of pellicles but not of solid surface-associated biofilms in S. oneidensis.

Conclusion

This systematic characterization of pellicle formation shed lights on our understanding of biofilm formation in S. oneidensis and indicated that the pellicle may serve as a good research model for studying bacterial communities.

Environmental influences on the partitioning and diffusion of hydrophobic organic contaminants in microbial biofilms

A biofilm reactor was used to investigate kinetic and thermodynamic aspects of the sorption of polycyclic aromatic hydrocarbons (PAH) as model compounds for hydrophobic organic contaminants (HOC) to intact microbial biofilms. Effective diffusion coefficients are in the range of 10(-10) cm2 x s(-1) resulting in equilibration times of more than 3 days for a biofilm of 100 microm thickness. Diffusion in the biofilm was strongly temperature-dependent and increased by a factor of 3 (phenanthrene) to 6 (fluoranthene, pyrene) between 5 and 35 degrees C. Drying and rewetting of the biofilm as well as the inclusion of Ca2+ ions and of humic acids all strengthened the biofilm rigidity and slowed down the diffusion of PAH. The later two factors also influenced the thermodynamics of the process as they supported the partitioning of PAH into the biofilm. Humic acid inclusion from solution into the biofilm illustrates that a microbial biofilm can act as a primer allowing for the buildup of a particulate organic phase from dissolved organic matter. PAH metabolites (3-hydroxy-phenanthrene and 1-hydroxy-2-naphthoic acid) showed lower partition coefficients as compared to their parent compounds and 3-hydroxy-phenanthrene also showed a higher diffusion constant, indicating that these transformation products would be easily released into the water phase upon formation during PAH biodegradation in a biofilm. These results allow the quantification of the influence of environmental conditions on a biofilm's function as a sink or as a diffusion barrier for PAH from aqueous solution, and they indicate the importance of kinetic aspects of this partitioning process.

Mechanism of calcium accumulation in acetate-fed aerobic granule

High calcium content has been widely reported in acetate-fed aerobic granules, but the reason behind this is unclear yet. By SEM-energy dispersive X-ray mapping analysis, this study showed that the majority of calcium was presented in the central part of the acetate-fed aerobic granule, and the granule shell part was nearly calcium-free. The elemental analysis of calcium ions coupled with the chemical titration of carbonate further revealed that the calcium ions that accumulated in the acetate-fed aerobic granule mainly existed in the form of calcium carbonate (CaCO3). The formation of the CaCO3 appeared to be highly dependent on the size of the aerobic granule, i.e., the CaCO3 precipitation was found only in aerobic granules with radiuses larger than 0.5 mm. These experimental observations with regard to the formation of CaCO3 in the acetate-fed aerobic granule were further confirmed by the model simulation, which was based on the principles of mass diffusion and carbonate dissociation in liquid phase. This study for the first time showed that the size of the acetate-fed aerobic granule would indeed play an essential role in the CaCO3 formation, and provided experimental evidence that a crystal CaCO3 core was not necessarily required for granulation.

Removal of toluene vapour using agro-waste as biofilter media

Biodegradation of toluene vapour was investigated in a laboratory scale biofilter packed with cylindrical pieces of yellow-gram (Cajanus cajan) stalk. Inlet concentrations and volumetric flow rates of toluene were varied from 2.56 to 34.73 g/m3 and 0.18 to 0.24 m3/h, respectively. The steady state was achieved within seven days and the degradation of toluene followed an exponential behaviour with time. Elimination capacity increased and tended towards a constant value but removal efficiency decreased with increase in inlet toluene loading. Depending upon loading rate, the process was either mass transfer or reaction-controlled.

Chelator-induced dispersal and killing of Pseudomonas aeruginosa cells in a biofilm

Biofilms consist of groups of bacteria attached to surfaces and encased in a hydrated polymeric matrix. Bacteria in biofilms are more resistant to the immune system and to antibiotics than their free-living planktonic counterparts. Thus, biofilm-related infections are persistent and often show recurrent symptoms. The metal chelator EDTA is known to have activity against biofilms of gram-positive bacteria such as Staphylococcus aureus. EDTA can also kill planktonic cells of Proteobacteria like Pseudomonas aeruginosa. In this study we demonstrate that EDTA is a potent P. aeruginosa biofilm disrupter. In Tris buffer, EDTA treatment of P. aeruginosa biofilms results in 1,000-fold greater killing than treatment with the P. aeruginosa antibiotic gentamicin. Furthermore, a combination of EDTA and gentamicin results in complete killing of biofilm cells. P. aeruginosa biofilms can form structured mushroom-like entities when grown under flow on a glass surface. Time lapse confocal scanning laser microscopy shows that EDTA causes a dispersal of P. aeruginosa cells from biofilms and killing of biofilm cells within the mushroom-like structures. An examination of the influence of several divalent cations on the antibiofilm activity of EDTA indicates that magnesium, calcium, and iron protect P. aeruginosa biofilms against EDTA treatment. Our results are consistent with a mechanism whereby EDTA causes detachment and killing of biofilm cells.

Long-term persistence of a nutrient-starved biofilm in a limestone fracture

The persistence of biofilms is a key element of the biobarrier concept applied to fractured rock. After a 43-day biostimulation with molasses for the biofilm growth (phase I), the effects of a 179-day starvation on the persistence of the biofilm (phase II) were investigated in a single-fractured limestone apparatus equipped to detect small changes in hydraulic conductivity (K) (cm min(-1)). The K in the central fracture section (Kf) decreased by 4.6 logs between days 0 and 167 and increased by 1.3 logs between days 167 and 222, leading to an overall 3.3-logs reduction for the 222-day experiment. Accumulation of rod- and filamentous-shaped bacteria and deposition of minerals were thought to account for the decrease in Kf. Even though the filamentous bacterial cells possibly enhanced the stability of the developing biofilm, increases in Kf became more frequent after 100 days of operation. This decrease in stability was presumably related to sloughing events, which were in turn attributed to a combination of processes, including nutrient deprivation, the release of deposited minerals, decreasing fluid flowrate, and endogenous decay as part of biofilm ageing. This study indicates that biofilms developed in fractures can persist for extended periods at reduced K when exposed to a long-term starvation.

The role of calcium in oral streptococcal aggregation and the implications for biofilm formation and retention

Much work on bacterial adhesion has focussed on the colonisation of surfaces and the removal of mature biofilms. Little attention has been devoted to interactions within mature biofilms and how these might be manipulated in the cause of novel therapies. Calcium binding to oral streptococci displays characteristics of positive cooperativity and calcium uptake does not follow the same mechanism as calcium release [Rose et al., J. Dent. Res. 72 (1993) 78-84]. An investigation of the variation in dissociation constants found with respect to cell concentration (from 2.77+/-0.66 mmol/l at 5 g/l [cell] to 1.28+/-0.37 mmol/l at 20 g/l), and in particular the non-zero value of the apparent binding constant (K(app)) on extrapolation to zero cell concentration, revealed that calcium uptake could be explained by a ligand-facilitated mechanism of cell association. Hence, cell association follows a route that starts with essentially irreversible long-range interactions between the cells, mediated by as yet unidentified macromolecules, followed by reversible calcium bridging. This suggests that cells are held in place within biofilms by a web of polymers, but that proximity to neighbouring cells is dependent on calcium bridging and that this may be manipulated to allow increased penetration of therapeutic agents.

Quantification of Dehalospirillum multivorans in Mixed-Culture Biofilms with an Enzyme-Linked Immunosorbent Assay

A fast, highly selective and sensitive method to quantify specific biomasses in mixed-culture biofilms is described. It consists of detachment of a biofilm from its support material, resolution of the detached biofilm flocs in order to separate the enclosed cells and antigens, and quantification of specific biomass by an enzyme-linked immunosorbent assay.