Browsing by Author "Purevdorj, B."

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Biofilm structure, behavior, and hydrodynamics
(2004) Purevdorj, B.; Stoodley, Paul
Hexavalent uranium [U(VI)] was immobilized using biofilms of the sulfate-reducing bacterium (SRB) Desulfovibrio desulfuricans G20. The biofilms were grown in flat-plate continuous-flow reactors using lactate as the electron donor and sulfate as the electron acceptor. U(VI)was continuously fed into the reactor for 32 weeks at a concentration of 126 microM. During this time, the soluble U(VI) was removed (between 88 and 96% of feed) from solution and immobilized in the biofilms. The dynamics of U immobilization in the sulfate-reducing biofilms were quantified by estimating: (1) microbial activity in the SRB biofilm, defined as the hydrogen sulfide (H2S) production rate and estimated from the H2S concentration profiles measured using microelectrodes across the biofilms; (2) concentration of dissolved U in the solution; and (3) the mass of U precipitated in the biofilm. Results suggest that U was immobilized in the biofilms as a result of two processes: (1) enzymatically and (2) chemically, by reacting with microbially generated H2S. Visual inspection showed that the dissolved sulfide species reacted with U(VI) to produce a black precipitate. Synchrotron-based U L3-edge X-ray absorption near edge structure (XANES) spectroscopy analysis of U precipitated abiotically by sodium sulfide indicated that U(VI) had been reduced to U(IV). Selected-area electron diffraction pattern and crystallographic analysis of transmission electron microscope lattice-fringe images confirmed the structure of precipitated U as being that of uraninite.
Clinical significance of seeding dispersal in biofilms: A response
(2005-11) Stoodley, Paul; Purevdorj, B.; Costerton, J. William
We welcome the dialogue concerning the potential clinical significance of seeding dispersal (Purevdorj-Gage et al., 2005) in the life cycle of mucoid Pseudomonas aeruginosa biofilms. We had based our hypothesis that the seeding dispersal phenomenon may be more relevant for non-mucoid, environmental strains on (1) the propensity of diseases associated with reduced mucociliary clearance in the lung, such as cystic fibrosis (CF) or chronic obstructive pulmonary disease (COPD), to select for mucoid P. aeruginosa phenotypes, and (2) that conversion to mucoidy is usually associated with a concomitant down-regulation of flagella production and loss of swimming motility (see Garrett et al., 1999). However, as Kirov et al. discuss above, there may be greater diversity in mucoid CF isolates than generally acknowledged, and the perceived dichotomy between mucoidy and swimming phenotypes should be a topic for debate. More recently it has been shown that expression of flagellum genes in response to oxygen limitation precedes loss of mucoidy and is reversible during this state of transition (Wyckoff et al., 2002). Further, in an ongoing screen of mucoid CF isolates it was found that 6 out of 20 were motile (D.J. Wozniak, personal communication). However, it was suspected that growth medium may also play a role in the outcome of the motility assay and exact proportions may vary depending on culture conditions. The growth-condition-dependent transient switching between mucoid and swimming phenotypes is problematic when relating a particular biofilm behaviour with phenotype and stresses the importance of attempting to characterize the phenotypic state at various time points during biofilm development. Broadly though, the finding of Dr Wozniak is in agreement with that of Kirov et al. We agree that to fully assess the role of seeding dispersal (and other yet unidentified behavioural developmental phenotypes) in the context of lung infections, biofilm studies should include greater diversity in strains, growth conditions and be conducted over longer time scales. The interesting observation that seeding motility occurred in a mucoid CF isolate clearly demonstrates that the phenomenon may have clinical relevance.
The influence of fluid shear and AlCl3 on the material properties of Pseudomonas aeruginosa PAO1 and Desulfovibrio sp. EX265 biofilms
(2001) Stoodley, Paul; Jacobsen, A.; Dunsmore, B. C.; Purevdorj, B.; Wilson, Suzanne; Lappin-Scott, H. M.; Costerton, J. William
An understanding of the material properties of biofilms is important when describing how biofilms physically interact with their environment. In this study, aerobic biofilms of Pseudomonas aeruginosa PAO1 and anaerobic sulfate-reducing bacteria (SRB) biofilms of Desulfovibrio sp. EX265 were grown under different fluid shear stresses (tg) in a chemostat recycle loop. Individual biofilm microcolonies were deformed by varying the fluid wall shear stress (tw). The deformation was quantified in terms of strain (e), and the relative strength of the biofilms was assessed using an apparent elastic coefficient (Eapp) and residual strain (er) after three cycles of deformation. Aluminum chloride (AlCl3) was then added to both sets of biofilm and the tests repeated. Biofilms grown under higher shear were more rigid and had a greater yield shear stress than those grown under lower shear. The addition of AlCl3 resulted in a significant increase in Eapp and also increased the yield point. We conclude that the strength of the biofilm is in part dependent on the shear under which the biofilm was grown and that the material properties of the biofilm may be manipulated through cation cross-linking of the extracellular polysaccharide (EPS) slime matrix.
Influence of hydrodynamics and cell signaling on the structure and behavior of Pseudomonas aeruginosa biofilms
(2002-09) Purevdorj, B.; Costerton, J. William; Stoodley, Paul
Biofilms were grown from wild-type (WT) Pseudomonas aeruginosa PAO1 and the cell signaling lasI mutant PAO1-JP1 under laminar and turbulent flows to investigate the relative contributions of hydrodynamics and cell signaling for biofilm formation. Various biofilm morphological parameters were quantified using Image Structure Analyzer software. Multivariate analysis demonstrated that both cell signaling and hydrodynamics significantly (P < 0.000) influenced biofilm structure. In turbulent flow, both biofilms formed streamlined patches, which in some cases developed ripple-like wave structures which flowed downstream along the surface of the flow cell. In laminar flow, both biofilms formed monolayers interspersed with small circular microcolonies. Ripple-like structures also formed in four out of six WT biofilms, although their velocity was approximately 10 times less than that of those that formed in the turbulent flow cells. The movement of biofilm cell clusters over solid surfaces may have important clinical implications for the dissemination of biofilm subject to fluid shear, such as that found in catheters. The ability of the cell signaling mutant to form biofilms in high shear flow demonstrates that signaling mechanisms are not required for the formation of strongly adhered biofilms. Similarity between biofilm morphologies in WT and mutant biofilms suggests that the dilution of signal molecules by mass transfer effects in faster flowing systems mollifies the dramatic influence of signal molecules on biofilm structure reported in previous studies.
Influence of the hydrodynamic environment on quorum sensing in pseudomonas aeruginosa biofilms
(2007-08) Kirisits, Mary J.; Margolis, Jeffrey J.; Purevdorj, B.; Chopp, David L.; Stoodley, Paul; Parsek, Matthew R.
We provide experimental and modeling evidence that the hydrodynamic environment can impact quorum sensing (QS) in a Pseudomonas aeruginosa biofilm. The amount of biofilm biomass required for full QS induction of the population increased as the flow rate increased.
Phenotypic differentiation and seeding dispersal in non-mucoid and mucoid Pseudomonas aeruginosa biofilms
(2005-05) Purevdorj, B.; Costerton, J. William; Stoodley, Paul
There is growing evidence that Pseudomonas aeruginosa biofilms exhibit a multicellular developmental life cycle analogous to that of the myxobacteria. In non-mucoid PAO1 biofilms cultured in glass flow cells the phenotypic differentiation of microcolonies into a motile phenotype in the interior of the microcolony and a non-motile surrounding 'wall phenotype' are described. After differentiation the interior cells coordinately evacuated the microcolony from local break out points and spread over the wall of the flow cell, suggesting that the specialized microcolonies were analogous to crude fruiting bodies. A microcolony diameter of approximately 80 microns was required for differentiation, suggesting that regulation was related to cell density and mass transfer conditions. This phenomenon was termed 'seeding dispersal' to differentiate it from 'erosion' which is the passive removal of single cells by fluid shear. Using the flow cell culturing method, in which reproducible seeding phenotype in PAO1 wild-type was demonstrated, the effects of quorum sensing (QS) and rhamnolipid production (factors previously identified as important in determining biofilm structure) on seeding dispersal using knockout mutants isogenic with PAO1 was investigated. Rhamnolipid (rhlA) was not required for seeding dispersal but las/rhl QS (PAO1-JP2) was, in our system. To assess the clinical relevance of these data, mucoid P. aeruginosa cystic fibrosis isolate FRD1 was also investigated and was seeding-dispersal-negative.
Pseudomonas aeruginosa biofilm structure, behavior and hydrodynamics
(Montana State University - Bozeman, College of Letters & Science, 2004) Purevdorj, B.; Chairperson, Graduate Committee: William J. Costerton
Biofilm formation by bacterial pathogens is an important factor in the progression and treatment of many infectious diseases. Biofilm structural development is a dynamic process dependent on many cellular and environmental parameters including Quorum Sensing (QS) and hydrodynamics. Since QS is dependent on a threshold autoinducer concentration, it was hypothesized that the flow dynamics in the bulk fluid surrounding the biofilm would play an important role in expression of QS and the genes that are under its control. In order to investigate the relative contribution of hydrodynamics and QS on biofilm development, biofilms were grown from wild type Pseudomonas aeruginosa PAO1 and the cell signaling lasI mutant PAO1-JP1 under laminar and turbulent flows. When morphology of the biofilms were quantified using Image Structure Analyzer (ISA) software, a multivariate analysis demonstrated that both QS and hydrodynamics influenced biofilm structure, suggesting that QS was not required for biofilm development but affected structural heterogeneity in biofilms. GFP reporter based gene expression analysis of QS regulated lasB (coding for elastase) expression during biofilm development in laminar flow further supported these results. Detachment has been recognized as another factor that may define structural morphology of biofilms. Under flow conditions hollow biofilm clusters were formed as a result of active detachment process, termed as "seeding dispersal". A differentiation of a "seeding" microcolony into an interior motile, swarming, phenotype and a non-motile surrounding, "wall phenotype" formed as a prelude to the dispersal process in which the interior cells swarmed out of the microcolony from local break out points and spread over the wall of the flow cell. A critical microcolony diameter of approximately 100 æm was required for differentiation suggesting that regulation was related to cell density and mass transfer conditions. It was found that rhamnolipid (rhlA-) biosurfactant was not required and QS system (PAO1-JP2) was shown to be important in this process, possibly by sensing nutrient limitation within the biofilm microcolonies. These results strengthen a current view of multi-cellularity and coordinated behavior in prokaryotes as well as a dynamic network of overlapping pathways and cellular mechanisms that act on biofilm development in a complex interrelated manner.
The role of FLO11 in Saccharomyces cerevisiae biofilm development in a laboratory based flow-cell system
(2007-05) Purevdorj, B.; Orr, Miranda E.; Stoodley, Paul; Sheehan, Kathy B.; Hyman, Linda E.
A role of the FLO11 in Saccharomyces cerevisiae biofilm development in a flow cell system was examined. We carried out an ectopic FLO11 expression in the wild type (wt) BY4741 strain that has low levels of endogenous FLO11 transcript. In contrast to the nonadhesive wt, the FLO11 overexpression strain (BY4741 FLO111) readily adhered to both liquid-hydrophobic and liquid-hydrophilic solid interfaces and was able to grow as a biofilm monolayer in a flow system. Cellular features associated with FLO11 were examined and found to be consistent with the previous studies conducted in different strains of S. cerevisiae. When grown in suspended liquid culture, BY4741 FLO111 formed larger cellular aggregates (clumps), consisting of from five to 60 cells, and displayed an increased cell surface hydrophobicity, without changes in the cell size or growth rate, compared to wt. However, the invasive growth associated with FLO11 expression was not observed in BY4741 FLO111. The significance of these findings is discussed in the context of clinically and industrially relevant biofilms.This paper was not supported by the CBE, however the corresponding author has given us permission to post this on the CBE website because of the biofilm topic and the CBE affiliated authors.
Viscoelastic fluid description of bacterial biofilm material properties
(2002-09) Klapper, Isaac; Rupp, Cory J.; Cargo, R.; Purevdorj, B.; Stoodley, Paul
A mathematical model describing the constitutive properties of biofilms is required for predicting biofilm deformation, failure and detachment in response to mechanical forces. Laboratory observations indicate that biofilms are viscoelastic materials. Likewise, current knowledge of biofilm internal structure suggests modeling biofilms as associated polymer viscoelastic systems. Supporting experimental results and a system of viscoelastic fluid equations with a linear Jeffreys viscoelastic stress-strain law are presented here. This system of equations is based on elements of associated polymer physics and is also consistent with presented and previous experimental results. A number of predictions can be made. One particularly interesting result is the prediction of an elastic relaxation time on the order of a few minutes: biofilm disturbances on shorter time scales produce an elastic response, biofilm disturbances on longer time scales result in viscous flow, i.e., non-reversible biofilm deformation. Although not previously recognized, evidence of this phenomenon is in fact present in recent experimental results.