Dependent Biofilm Formation Research Articles

The catheterized bladder environment promotes Efg1- and Als1-dependent Candida albicans infection.

Catheter-associated urinary tract infections (CAUTIs) account for 40% of hospital-acquired infections (HAIs). As 20 to 50% of hospitalized patients receive catheters, CAUTIs are one of the most common HAIs, resulting in increased morbidity, mortality, and health care costs. Candida albicans is the second most common CAUTI uropathogen, yet relative to its bacterial counterparts, little is known about how fungal CAUTIs are established. Here, we show that the catheterized bladder environment induces Efg1- and fibrinogen (Fg)-dependent biofilm formation that results in CAUTI. In addition, we identify the adhesin Als1 as the critical fungal factor for C. albicans Fg-urine biofilm formation. Furthermore, we show that in the catheterized bladder, a dynamic and open system, both filamentation and attachment are required, but each by themselves are not sufficient for infection. Our study unveils the mechanisms required for fungal CAUTI establishment, which may aid in the development of future therapies to prevent these infections.

Pseudomonas aeruginosa quorum-sensing molecule N-(3-oxododecanoyl) homoserine lactone induces calcium signaling-dependent crosstalk between autophagy and apoptosis in human macrophages

N-(3-oxododecanoyl) homoserine lactone (3oc) is a Pseudomonas aeruginosa secreted quorum-sensing signal molecule playing a crucial role in regulating quorum-sensing (QS) dependent biofilm formation and secretion of virulence factors. In addition to regulating quorum sensing, 3oc also plays an immunomodulatory role in the host by triggering regulated cell death in immune cells. The molecular mechanisms of 3oc in modulating macrophage pathologies are still unclear. In this study, we hypothesized the novel 3oc mediated crosstalk between autophagy and apoptosis at the interphase of calcium signaling in human macrophages. The study showed that 3oc induces mitochondrial dysfunction and apoptosis in macrophages through elevating cytosolic Ca+2 ([Ca+2]cyt) levels. Pre-treatment with the calcium-specific chelator BAPTA-AM effectively abrogated 3oc-induced apoptotic events, like mitochondrial ROS generation (mROS), mitochondrial membrane potential (MMP) drop, and phosphatidylserine (PS) exposure. The study also showed that 3oc induces autophagy, as assessed by the accumulation of autophagic vacuoles, induction of lysosomal biogenesis, upregulation of autophagy genes (LC3, BECLIN 1, STX17, PINK1, and TFEB), autophagosomes formation, and LC3 lipidation. Mechanistically, our study proved that 3oc-induced autophagy was [Ca+2]cyt dependent as BAPTA-AM pre-treatment reduced autophagosome formation. Furthermore, inhibiting autophagy with chloroquine attenuated 3oc-induced apoptosis, while autophagy induction with rapamycin aggravated cell death, suggesting autophagy plays a role in cell death in 3oc-treated macrophages. In conclusion, our findings indicate that 3oc activates a multifaceted death signaling by activating autophagy and apoptosis through Ca+2 signaling, and we propose pharmacological modulation of Ca+2 signaling may act as a combinatorial therapeutic intervention in patients with Pseudomonas aeruginosa-associated infections.

Stress Dependent Biofilm Formation and Bioactive Melanin Pigment Production by a Thermophilic Bacillus Species from Chilean Hot Spring.

Thermophilic bacteria able to survive extreme temperature stress are of great biotechnological interest due to their extracellular production of bioactive molecules as a part of a survival strategy, or by intracellular modifications. In the present study, thermophilic Bacillus haynesii CamB6, isolated from a Chilean hot spring, was studied for the formation of different stress response molecules. The polymeric pigment produced by the bacterial strain was characterized by different physicochemical techniques. On exposure to ranges of temperature (50–60 °C), pH (5.0–7.0), and sources of nitrogen and carbon (1–5 g·L−1), the bacteria responded with a biofilm network formation in a hydrophobic polystyrene surface. Biofilm formation under fed-batch conditions was also statistically validated. The bacteria showed a planktonic pellicle network formation in the presence of induced hypoxia and salinity stress (19.45 g·L−1) under static conditions. Salinity stress also resulted in the intracellular response of brown pigment production. The pigment was structurally and functionally characterized by UV-Vis absorbance and the presence of different characteristic peaks via FTIR analysis (bacterial pyomelanin fingerprints) were assessed. A high thermal stability and TGA profile indicated the brown pigment was a probable pyomelanin candidate. Micropyrolysis (Py-GC/MS) showed that isoprene, pyrrole, benzene, pyridine, and their derivatives were the major components detected. In addition, acetic acid, indole, phenol, and its derivatives were observed. The absence of sulfocompounds in the pyrolyzed products agreed with those reported in the literature for pyomelanin. The pigment surface morphology was analyzed via SEM, and the elemental composition via EDS also demonstrated the similarity of the brown pigment to that of the melanin family. The pyomelanin pigment was observed to be bioactive with promising antioxidant capacity (H2O2, Fe2+) compared to the standard antioxidant molecules. In conclusion, B. haynesii CamB6 demonstrated the formation of several biomolecules as a stress response mechanism that is bioactive, showing its probable biotechnological applications in future.

The Staphylococcus aureus toxin-antitoxin system YefM-YoeB is associated with antibiotic tolerance and extracellular dependent biofilm formation.

The high antibiotic tolerance of Staphylococcus aureus biofilms is associated with challenges for treating periprosthetic joint infection. The toxin–antitoxin system, YefM–YoeB, is thought to be a regulator for antibiotic tolerance, but its physiological role is unknown. The objective of this study was to determine the biofilm and antibiotic susceptibility phenotypes associated with S. aureus yoeB homologs. We hypothesized the toxin–antitoxin yoeB homologs contribute to biofilm formation and antibiotic susceptibility. Disruption of yoeB1 and yoeB2 resulted in decreased biofilm formation in comparison to Newman and JE2 wild-type (WT) S. aureus strains. In comparison to yoeB mutants, both Newman and JE2 WT strains had higher polysaccharide intercellular adhesin (PIA) production. Treatment with sodium metaperiodate increased biofilm formation in Newman WT, indicating biofilm formation may be increased under conditions of oxidative stress. DNase I treatment decreased biofilm formation in Newman WT but not in the absence of yoeB1 or yoeB2. Additionally, WT strains had a higher extracellular DNA (eDNA) content in comparison to yoeB mutants but no differences in biofilm protein content. Moreover, loss of yoeB1 and yoeB2 decreased biofilm survival in both Newman and JE2 strains. Finally, in a neutropenic mouse abscess model, deletion of yoeB1 and yoeB2 resulted in reduced bacterial burden. In conclusion, our data suggest that yoeB1 and yoeB2 are associated with S. aureus planktonic growth, extracellular dependent biofilm formation, antibiotic tolerance, and virulence.

Biodegradation of polystyrene by deep-sea Bacillus paralicheniformis G1 and genome analysis

Polystyrene (PS) films were subjected to in vitro biodegradation by Bacillus paralicheniformis G1 (MN720578) isolated from 3538 m depth sediments of the Arabian Sea. The growth of the isolate was most favourable at pH 7.5, 30 °C and 4% salinity. A series of batch experiments were conducted to investigate the degradation of PS films up to 60 days. The results of this study indicated that the strain degraded 34% of PS film within 60 days of incubation. The complete genome sequence consists of 4,281,959 bp with 45.88% GC content and encodes 4213 protein coding genes. A high number of genes encoding monooxygenase, dioxygenase, peroxidase, esterase and hydrolase involved in the degradation of synthetic polymers were identified. Also genes associated with flagellum dependent motility, chemotaxis, biofilm formation and siderophores biosynthesis were identified in this deep-sea strain G1. This study suggests that B. paralicheniformis G1 could be a potential species for degradation of PS and its genome analysis provides insight into the molecular basis of biodegradation.

The Transcription Factor SomA Synchronously Regulates Biofilm Formation and Cell Wall Homeostasis in Aspergillus fumigatus.

Polysaccharides are key components of both the fungal cell wall and biofilm matrix. Despite having distinct assembly and regulation pathways, matrix exopolysaccharide and cell wall polysaccharides share common substrates and intermediates in their biosynthetic pathways. It is not clear, however, if the biosynthetic pathways governing the production of these polysaccharides are cooperatively regulated. Here, we demonstrate that cell wall stress promotes production of the exopolysaccharide galactosaminogalactan (GAG)-depend biofilm formation in the major fungal pathogen of humans Aspergillus fumigatus and that the transcription factor SomA plays a crucial role in mediating this process. A core set of SomA target genes were identified by transcriptome sequencing and chromatin immunoprecipitation coupled to sequencing (ChIP-Seq). We identified a novel SomA-binding site in the promoter regions of GAG biosynthetic genes agd3 and ega3, as well as its regulators medA and stuA Strikingly, this SomA-binding site was also found in the upstream regions of genes encoding the cell wall stress sensors, chitin synthases, and β-1,3-glucan synthase. Thus, SomA plays a direct regulation of both GAG and cell wall polysaccharide biosynthesis. Consistent with these findings, SomA is required for the maintenance of normal cell wall architecture and compositions in addition to its function in biofilm development. Moreover, SomA was found to globally regulate glucose uptake and utilization, as well as amino sugar and nucleotide sugar metabolism, which provides precursors for polysaccharide synthesis. Collectively, our work provides insight into fungal adaptive mechanisms in response to cell wall stress where biofilm formation and cell wall homeostasis were synchronously regulated.IMPORTANCE The cell wall is essential for fungal viability and is absent from human hosts; thus, drugs disrupting cell wall biosynthesis have gained more attention. Caspofungin is a member of a new class of clinically approved echinocandin drugs to treat invasive aspergillosis by blocking β-1,3-glucan synthase, thus damaging the fungal cell wall. Here, we demonstrate that caspofungin and other cell wall stressors can induce galactosaminogalactan (GAG)-dependent biofilm formation in the human pathogen Aspergillus fumigatus We further identified SomA as a master transcription factor playing a dual role in both biofilm formation and cell wall homeostasis. SomA plays this dual role by direct binding to a conserved motif upstream of GAG biosynthetic genes and genes involved in cell wall stress sensors, chitin synthases, and β-1,3-glucan synthase. Collectively, these findings reveal a transcriptional control pathway that integrates biofilm formation and cell wall homeostasis and suggest SomA as an attractive target for antifungal drug development.

PelX is a UDP-N-acetylglucosamine C4-epimerase involved in Pel polysaccharide–dependent biofilm formation

Pel is a GalNAc-rich bacterial polysaccharide that contributes to the structure and function of Pseudomonas aeruginosa biofilms. The pelABCDEFG operon is highly conserved among diverse bacterial species, and Pel may therefore be a widespread biofilm determinant. Previous annotation of pel gene clusters has helped us identify an additional gene, pelX, that is present adjacent to pelABCDEFG in >100 different bacterial species. The pelX gene is predicted to encode a member of the short-chain dehydrogenase/reductase (SDR) superfamily, but its potential role in Pel-dependent biofilm formation is unknown. Herein, we have used Pseudomonas protegens Pf-5 as a model to elucidate PelX function as Pseudomonas aeruginosa lacks a pelX homologue in its pel gene cluster. We found that P. protegens forms Pel-dependent biofilms; however, despite expression of pelX under these conditions, biofilm formation was unaffected in a ΔpelX strain. This observation led us to identify a pelX paralogue, PFL_5533, which we designate here PgnE, that appears to be functionally redundant to pelX In line with this, a ΔpelX ΔpgnE double mutant was substantially impaired in its ability to form Pel-dependent biofilms. To understand the molecular basis for this observation, we determined the structure of PelX to 2.1 Å resolution. The structure revealed that PelX resembles UDP-GlcNAc C4-epimerases. Using 1H NMR analysis, we show that PelX catalyzes the epimerization between UDP-GlcNAc and UDP-GalNAc. Our results indicate that Pel-dependent biofilm formation requires a UDP-GlcNAc C4-epimerase that generates the UDP-GalNAc precursors required by the Pel synthase machinery for polymer production.

Antiquorum Sensing Potential of Andrographolide from Andrographis paniculata in Vibrio harveyi

The recently discovered cell–cell communication system through signaling molecules among bacterial pathogens is known as Quorum sensing. It is well known for bacterial virulence, antibiotic resistance and biofilm production. Microbial pathogenicity is reduced by inhibiting the quorum sensing activity in all infections caused by bacteria. In this present study the compound Andrographolide which is present as a secondary metabolite in Andrographis paniculata was assessed for its anti quorum sensing activity against acyl homoserine lactone (AHL)-dependent biofilm formation and bioluminescence production in Vibrio harveyi (MTCC 7771). The Andrographolide showed a concentration dependent (100 µg/ml) reduction in biofilm production to a level of 97% and reduction of bioluminescence at the level of 98% in Vibrio harveyi (MTCC 7771) and compared with the standard Andrographolide (sigma aldrich). Light microscopic analysis and Microtiter plate assay further confirmed the reduction in the biofilm forming ability of Vibrio harveyi (MTCC 7771) when treated with andrographolide. The andrographolide at its standard concentration showed antibacterial effect on Vibrio harveyi(MTCC 7771).

Inhibition of biofilm formation in Serratia marcescens by Andrographolide from Andrographis paniculata

Quorum sensing (QS) is well known for bacterial virulence, antibiotic resistance and biofilm production. Inhibition of quorum sensing can reduce the risk of microbial pathogenicity in all infection. In this present study the compound Andrographolide which is present in Andrographis paniculata leaf extract was assessed for its anti quorum sensing activity against acyl homoserine lactone (AHL)-dependent biofilm formation in Serratia marcescens. The Andrographolide obtained from Andrographis paniculata exhibited a concentration dependent (100 µg/ml) reduction in biofilm production in Serratia marcescens to a level of 90% and compared with the standard Andrographolide (sigma aldrich). Microtiter plate and Light microscopic analysis further confirmed the reduction in the biofilm forming ability of Serratia marcescens when treated with andrographolide. In addition the Andrographolide present in Andrographis paniculata by itself showed no growth inhibitory effect on Serratia marcescens.

High Prevalence of Icaadbc Genes Responsible for Biofilm Formation in Clinical Isolates of Staphylococcus aureus From Hospitalized Children

Background: The icaABCD genes encode a Polysaccharide Intercellular Adhesion (PIA), which is a tight structure protecting Staphylococcus aureus community against adverse environmental conditions. The ica dependent biofilm formation plays an important role in persistent infections in hospitalized patients. Objectives: The aim of this study was to detect icaADBC genes encoding PIA among S. aureus isolates from children in Loghman Hospital of Tehran. Materials and Methods: We collected 22 clinical specimens from hospitalized pediatrics and identified the isolates. Then, we detected mecA gene among Methicillin Resistant S. aureus (MRSA), SCCmec types and icaABCD gens by PCR assay and specific primers. Results: Five isolates (22.7%) were methicillin resistant (MRSA) and mecA gene was detected among them. All the MRSA isolates harbored SCCmec type III. Prevalence of icaA, icaB, icaC and icaD in the isolates were 16 (73%), 14 (63.6%), 16 (73%) and 16 (73%), respectively. Moreover, all the MRSA strains were icaADBC positive. Conclusions: Prevalence of icaADBC genes was relatively high among children and also all the four ica genes were detected among MRSA strains.

Indole inhibits bacterial quorum sensing signal transmission by interfering with quorum sensing regulator folding

Quorum sensing (QS)-dependent biofilm formation and motility were controlled by AqsR in Acinetobacter oleivorans DR1. QS-controlled phenotypes appeared to be inhibited by indole and the aqsR mutant had the same phenotypes. We demonstrated that the turnover rate of AqsR became more rapid without the N-acylhomoserine lactone (AHL) signal, and that indole could increase the expression of many protease and chaperone proteins. The addition of exogenous indole decreased the expression of two AqsR-targeted genes: AOLE_03905 (putative surface adhesion protein) and AOLE_11355 (L-asparaginase). The overexpression of AqsR in Escherichia coli was impossible with the indole treatment. Surprisingly, our [(35)S]methionine pulse-labelling data demonstrated that the stability and folding of AqsR protein decreased in the presence of indole without changing aqsR mRNA expression in E. coli. Interestingly, indole resulted in a loss of TraR-dependent traG expression in an Agrobacterium tumefaciens indicator strain. However, when indole was added after incubation with exogenous AHL, indole could not inhibit the TraR-dependent expression of the traG promoter. This indicated that AHL-bound TraR could be protective against indole, but TraR without AHL could not be active in the presence of indole. Here, we provided evidence for the first time showing that the indole effect on QS-controlled bacterial phenotypes is due to inhibited QS regulator folding and not a reduced QS signal.

Biofilm formation and dispersal of Staphylococcus aureus under the influence of oxacillin

A total of 180 food borne isolates of methicillin resistant Staphylococcus aureus (MRSA) (oxacillin MICs 864 μg/ml) were used in the present study to investigate the effect of oxacillin on biofilm formation and its detachment process. Majority (98.3%) of these isolates were found to carry icaA gene. Out of 180 isolates 35.5% were identified as MRSA and 64.4% were methicillin sensitive S. aureus (MSSA). Biofilm studies by con-red agar and tube methods revealed that 57% of the MRSA isolates were biofilm producers. Polymerase chain reaction studies suggested that all of the biofilm positive MRSA isolates belong to SCCmec type IV and carry agr type II. This showed the strong association of SCCmec IV agr type II and biofilm formation in food borne MRSA. Conversely, only 13.7% of the MSSA isolates were biofilm positive and majority was found to carry agr type II. It has been noticed that oxacillin has regulatory effect on icaA expression and induce the icaA dependent polysaccharide intracellular adhesin (PIA) production and biofilm formation. This was confirmed by Real Time PCR studies of MRSA and MSSA isolates. Quantitative analysis showed that most of the MRSA isolates started biofilm formation after 24 h of incubation in the presence of sub-inhibitory concentration of oxacillin and achieved highest adhesion on glass slide after 48 h. The control in the absence of oxacillin showed slow conversion from planktonic to biofilm mode of growth (Table 1). Another novel feature of most of these biofilm producing isolates is the reduction in (Optical Density) OD, which is noticed after 48 h of incubation. Possibly, after 48 h oxacillin loses its toxicity or consumed the cells re-adapt to the planktonic state, possibly, by the activation of accessory gene regulator A (agrA) which has an important role in biofilm dispersal.

The global repressor FliZ antagonizes gene expression by σ S -containing RNA polymerase due to overlapping DNA binding specificity

FliZ, a global regulatory protein under the control of the flagellar master regulator FlhDC, was shown to antagonize σS-dependent gene expression in Escherichia coli. Thereby it plays a pivotal role in the decision between alternative life-styles, i.e. FlhDC-controlled flagellum-based motility or σS-dependent curli fimbriae-mediated adhesion and biofilm formation. Here, we show that FliZ is an abundant DNA-binding protein that inhibits gene expression mediated by σS by recognizing operator sequences that resemble the −10 region of σS-dependent promoters. FliZ does so with a structural element that is similar to region 3.0 of σS. Within this element, R108 in FliZ corresponds to K173 in σS, which contacts a conserved cytosine at the −13 promoter position that is specific for σS-dependent promoters. R108 as well as C(−13) are also crucial for DNA binding by FliZ. However, while a number of FliZ binding sites correspond to known σS-dependent promoters, promoter activity is not a prerequisite for FliZ binding and repressor function. Thus, we demonstrate that FliZ also feedback-controls flagellar gene expression by binding to a site in the flhDC control region that shows similarity only to a −10 element of a σS-dependent promoter, but does not function as a promoter.

Mapping pilicide anti-virulence effect in Escherichia coli, a comprehensive structure–activity study

Pilicides prevent pili formation and thereby the development of bacterial biofilms in Escherichia coli. We have performed a comprehensive structure activity relationship (SAR) study of the dihydrothiazolo ring-fused 2-pyridone pilicide central fragment by varying all open positions. Orthogonal projections to latent structures discriminant analysis (OPLS-DA) was used to distinguish active from inactive compounds in which polarity proved to be the most important factor for discrimination. A quantitative SAR (QSAR) partial least squares (PLS) model was calculated on the active compounds for prediction of biofilm inhibition activity. In this model, compounds with high inhibitory activity were generally larger, more lipophilic, more flexible and had a lower HOMO. Overall, this resulted in both highly valuable SAR information and potent inhibitors of type 1 pili dependent biofilm formation. The most potent biofilm inhibitor had an EC50 of 400nM.

Inhibition of quorum-sensing-dependent phenotypic expression in Serratia marcescens by marine sediment Bacillus spp. SS4

The role of quorum sensing (QS) is well known for bacterial virulence, antibiotic resistance and biofilm production. Consequently, inhibition of QS may reduce the risk of microbial pathogenicity in systemic and local infections. Hence, in the present study, the marine sediment bacterial isolate Bacillus spp. SS4 (GenBank accession number GU471751) isolated from the Point Calimere coastal region was assessed for its anti-quorum-sensing (anti-QS) activity against acyl homoserine lactone (AHL)-dependent prodigiosin, protease production and biofilm formation in Serratia marcescens (FJ584421). The ethyl acetate extract obtained from SS4 exhibited a concentration-dependent (50–200 μg/ml) reduction in prodigiosin production in S. marcescens to a level of 40–87%. The azocasein-degrading proteolytic activity of S. marcescens was also reduced by up to 60%, when treated with the SS4 extract at a final concentration of 200 μg/ml. Light- and confocal laser scanning-microscopic (CLSM) analysis further confirmed the reduction in the biofilm-forming ability of S. marcescens when treated with this extract. In an antibiotic susceptibility assay, cells of S. marcescens showed increased susceptibility towards antibiotics in the presence of SS4 extract. In addition, SS4 extract by itself showed no growth inhibitory effect on S. marcescens. Thus, the results of present study reveal the anti-QS potential of Bacillus spp. SS4 by notably reducing AHL-dependent behaviors in S. marcescens.

Genetic adaptation of Streptococcus mutans during biofilm formation on different types of surfaces

BackgroundAdhesion and successful colonization of bacteria onto solid surfaces play a key role in biofilm formation. The initial adhesion and the colonization of bacteria may differ between the various types of surfaces found in oral cavity. Therefore, it is conceivable that diverse biofilms are developed on those various surfaces. The aim of the study was to investigate the molecular modifications occurring during in vitro biofilm development of Streptococcus mutans UA159 on several different dental surfaces.ResultsGrowth analysis of the immobilized bacterial populations generated on the different surfaces shows that the bacteria constructed a more confluent and thick biofilms on a hydroxyapatite surface compared to the other tested surfaces. Using DNA-microarray technology we identified the differentially expressed genes of S. mutans, reflecting the physiological state of biofilms formed on the different biomaterials tested. Eight selected genes were further analyzed by real time RT-PCR. To further determine the impact of the tested material surfaces on the physiology of the bacteria, we tested the secretion of AI-2 signal by S. mutans embedded on those biofilms. Comparative transcriptome analyses indicated on changes in the S. mutans genome in biofilms formed onto different types of surfaces and enabled us to identify genes most differentially expressed on those surfaces. In addition, the levels of autoinducer-2 in biofilms from the various tested surfaces were different.ConclusionsOur results demonstrate that gene expression of S. mutans differs in biofilms formed on tested surfaces, which manifest the physiological state of bacteria influenced by the type of surface material they accumulate onto. Moreover, the stressful circumstances of adjustment to the surface may persist in the bacteria enhancing intercellular signaling and surface dependent biofilm formation.

Inhibiting effects of Streptococcus salivarius on competence‐stimulating peptide‐dependent biofilm formation by Streptococcus mutans

The effects of Streptococcus salivarius on the competence-stimulating peptide (CSP)-dependent biofilm formation by Streptococcus mutans were investigated. Biofilms were grown on 96-well microtiter plates coated with salivary components in tryptic soy broth without dextrose supplemented with 0.25% sucrose. Biofilm formations were stained using safranin and quantification of stained biofilms was performed by measuring absorbance at 492 nm. S. mutans formed substantial biofilms, whereas biofilms of S. salivarius were formed poorly in the medium conditions used. Furthermore, in combination cultures, S. salivarius strongly inhibited biofilm formation when cultured with S. mutans. This inhibition occurred in the early phase of biofilm formation and was dependent on inactivation of the CSP of S. mutans, which is associated with competence, biofilm formation, and antimicrobial activity of the bacterium, and is induced by expression of the comC gene. Comparisons between the S. mutans clinical strains FSC-3 and FSC-3DeltaglrA in separate dual-species cultures with S. salivarius indicated that the presence of the bacitracin transport ATP-binding protein gene glrA caused susceptibility to inhibition of S. mutans biofilm formation by S. salivarius, and was also associated with the regulation of CSP production by com gene-dependent quorum sensing systems. It is considered that regulation of CSP by glrA in S. mutans and CSP inactivation by S. salivarius are important functions for cell-to-cell communication between biofilm bacteria and oral streptococci such as S. salivarius. Our results provide useful information for understanding the ecosystem of oral streptococcal biofilms, as well as the competition between and coexistence of multiple species in the oral cavity.

Simultaneous analysis of physiological and electrical output changes in an operating microbial fuel cell with Shewanella oneidensis

Changes in metabolism and cellular physiology of facultative anaerobes during oxygen exposure can be substantial, but little is known about how these changes connect with electrical current output from an operating microbial fuel cell (MFC). A high-throughput voltage based screening assay (VBSA) was used to correlate current output from a MFC containing Shewanella oneidensis MR-1 to carbon source (glucose or lactate) utilization, culture conditions, and biofilm coverage over 250 h. Lactate induced an immediate current response from S. oneidensis MR-1, with both air-exposed and anaerobic anodes throughout the duration of the experiments. Glucose was initially utilized for current output by MR-1 when cultured and maintained in the presence of air. However, after repeated additions of glucose, the current output from the MFC decreased substantially while viable planktonic cell counts and biofilm coverage remained constant suggesting that extracellular electron transfer pathways were being inhibited. Shewanella maintained under an anaerobic atmosphere did not utilize glucose consistent with literature precedents. Operation of the VBSA permitted data collection from nine simultaneous S. oneidensis MR-1 MFC experiments in which each experiment was able to demonstrate organic carbon source utilization and oxygen dependent biofilm formation on a carbon electrode. These data provide the first direct evidence of complex cellular responses to electron donor and oxygen tension by Shewanella in an operating MFC at select time points.