Planktonic Bacterial Populations Research Articles

Initial cyclic-di-GMP upregulation triggers sporadic cellular expansion leading to improved cellular survival.

Bacterial second messenger c-di-GMP upregulation is associated with the transition from planktonic to sessile microbial lifestyle, inhibiting cellular motility, and virulence. However, in-depth elucidation of the cellular processes resulting from c-di-GMP upregulation has not been fully explored. Here, we report the role of upregulated cellular c-di-GMP in promoting planktonic cell growth of Escherichia coli K12 and Pseudomonas aeruginosa PAO1. We found a rapid expansion of cellular growth during initial cellular c-di-GMP upregulation, resulting in a larger planktonic bacterial population. The initial increase in c-di-GMP levels promotes bacterial swarming motility during the growth phase, which is subsequently inhibited by the continuous increase of c-di-GMP, and ultimately facilitates the formation of biofilms. We demonstrated that c-di-GMP upregulation triggers key bacterial genes linked to bacterial growth, swarming motility, and biofilm formation. These genes are mainly controlled by the master regulatory genes csgD and csrA. This study provides us a glimpse of the bacterial behavior of evading potential threats through adapting lifestyle changes via c-di-GMP regulation.

Hybrid donor-acceptor polymer nanoparticles and combination antibiotic for mitigation of pathogenic bacteria and biofilms

Biofilms pose a significant clinical problem in skin and soft tissue infections. Their resistance to antibiotics has spurred investigations into alternative treatments, such as nanoparticle-mediated photothermal ablation. Non-toxic Hybrid Donor- Acceptor (DA) Polymer nanoParticles (H-DAPPs) were developed for fluorescence imaging (using poly(3-hexylthiophene-2,5 diyl) (P3HT)) and rapid, near-infrared photothermal ablation (NIR- PTA) (using poly[4,4-bis(2-ethylhexyl)-cyclopenta[2,1-b;3,4-b’]dithiophene-2,6-diyl-alt−2,1,3-benzoselenadiazole-4,7-diyl] (PCPDTBSe)). H-DAPPs were evaluated alone, and in combination with antibiotics, against planktonic S. aureus and S. pyogenes, and S. aureus biofilms. H-DAPPs NIR-PTA (15–700 μg/ mL) can generate rapid temperature changes of 27.6–73.1 °C, which can eradicate planktonic bacterial populations and reduce biofilm bacterial viability by more than 4- log (> 99.99%) with exposure to 60 s of 800 nm light. Reductions were confirmed via confocal analysis, which suggested that H-DAPPs PTA caused bacterial inactivation within the biofilms, but did not significantly reduce biofilm polysaccharides. SEM imaging revealed structural changes in biofilms after H-DAPPs PTA. S. aureus biofilms challenged with 100 μg/mL of H-DAPPs (H-DAPPs-100) to induce an average temperature of 55.1 °C, and the minimum biofilm eradication concentration (MBEC) of clindamycin, resulted in up to ~3- log decrease in bacterial viability compared to untreated biofilms and those administered H-DAPPs-100 PTA only, and up to ~2- log compared to biofilms administered only clindamycin. This study demonstrates that polymer nanoparticle PTA can mitigate biofilm infection and may improve antimicrobial efficacy.

Exploiting Covalent, H-Bonding, and π-π Interactions to Design Antibacterial PDMS Interfaces That Load and Release Salicylic Acid.

Smart antimicrobial surfaces are a powerful tool to prevent bacterial colonization at surfaces. In this work, we report a successful strategy for the functionalization of polydimethylsiloxane (PDMS) surfaces, widely used in medical devices, with salicylic acid (SA), a biocide approved for use in humans. Antimicrobial PDMS surfaces were fabricated via a rational design in which bifunctional silane linker molecules were covalently grafted onto the PDMS via one end, while soft intermolecular interactions with SA were generated at the other end to enable reversible load and release of the biocide. A molecular level understanding of the interface was obtained using attenuated total reflectance Fourier transform infrared, Raman, and X-ray photoelectron spectroscopies, alongside density functional theory calculations. These reveal that the linker molecules dock the SA molecules at the surface via a 1:1 complexation interaction. Furthermore, each 1:1 complex acts as a nucleation point onto which multiple stacks of the biocide are subsequently stabilized via a combination of H-bonding and π-π stacking interactions, thus significantly enhancing SA uptake at the interface. The antimicrobial activity of these surfaces against model Gram-negative and Gram-positive bacteria represented by Escherichia coli, Staphylococcus aureus, and Staphylococcus epidermidis is demonstrated by a log 6 reduction of planktonic bacterial populations and an efficient anti-biofilm activity at the surface.

A Multiscale Agent-Based Model for the Investigation of E. coli K12 Metabolic Response During Biofilm Formation.

Bacterial biofilm formation is an organized collective response to biochemical cues that enables bacterial colonies to persist and withstand environmental insults. We developed a multiscale agent-based model that characterizes the intracellular, extracellular, and cellular scale interactions that modulate Escherichia coli MG1655 biofilm formation. Each bacterium's intracellular response and cellular state were represented as an outcome of interactions with the environment and neighboring bacteria. In the intracellular model, environment-driven gene expression and metabolism were captured using statistical regression and Michaelis-Menten kinetics, respectively. In the cellular model, growth, death, and type IV pili- and flagella-dependent movement were based on the bacteria's intracellular state. We implemented the extracellular model as a three-dimensional diffusion model used to describe glucose, oxygen, and autoinducer 2 gradients within the biofilm and bulk fluid. We validated the model by comparing simulation results to empirical quantitative biofilm profiles, gene expression, and metabolic concentrations. Using the model, we characterized and compared the temporal metabolic and gene expression profiles of sessile versus planktonic bacterial populations during biofilm formation and investigated correlations between gene expression and biofilm-associated metabolites and cellular scale phenotypes. Based on our in silico studies, planktonic bacteria had higher metabolite concentrations in the glycolysis and citric acid cycle pathways, with higher gene expression levels in flagella and lipopolysaccharide-associated genes. Conversely, sessile bacteria had higher metabolite concentrations in the autoinducer 2 pathway, with type IV pili, autoinducer 2 export, and cellular respiration genes upregulated in comparison with planktonic bacteria. Having demonstrated results consistent with in vitro static culture biofilm systems, our model enables examination of molecular phenomena within biofilms that are experimentally inaccessible and provides a framework for future exploration of how hypothesized molecular mechanisms impact bulk community behavior.

Differential Activity of the Combination of Vancomycin and Amikacin on Planktonic vs. Biofilm-Growing Staphylococcus aureus Bacteria in a Hollow Fiber Infection Model.

Combining currently available antibiotics to optimize their use is a promising strategy to reduce treatment failures against biofilm-associated infections. Nevertheless, most assays of such combinations have been performed in vitro on planktonic bacteria exposed to constant concentrations of antibiotics over only 24 h and the synergistic effects obtained under these conditions do not necessarily predict the behavior of chronic clinical infections associated with biofilms. To improve the predictivity of in vitro combination assays for bacterial biofilms, we first adapted a previously described Hollow-fiber (HF) infection model by allowing a Staphylococcus aureus biofilm to form before drug exposure. We then mimicked different concentration profiles of amikacin and vancomycin, similar to the free plasma concentration profiles that would be observed in patients treated daily over 5 days. We assessed the ability of the two drugs, alone or in combination, to reduce planktonic and biofilm-embedded bacterial populations, and to prevent the selection of resistance within these populations. Although neither amikacin nor vancomycin exhibited any bactericidal activity on S. aureus in monotherapy, the combination had a synergistic effect and significantly reduced the planktonic bacterial population by -3.0 to -6.0 log10 CFU/mL. In parallel, no obvious advantage of the combination, as compared to amikacin alone, was demonstrated on biofilm-embedded bacteria for which the addition of vancomycin to amikacin only conferred a further maximum reduction of 0.3 log10 CFU/mL. No resistance to vancomycin was ever found whereas a few bacteria less-susceptible to amikacin were systematically detected before treatment. These resistant bacteria, which were rapidly amplified by exposure to amikacin alone, could be maintained at a low level in the biofilm population and even suppressed in the planktonic population by adding vancomycin. In conclusion, by adapting the HF model, we were able to demonstrate the different bactericidal activities of the vancomycin and amikacin combination on planktonic and biofilm-embedded bacterial populations, suggesting that, for biofilm-associated infections, the efficacy of this combination would not be much greater than with amikacin monotherapy. However, adding vancomycin could reduce possible resistance to amikacin and provide a relevant strategy to prevent the selection of antibiotic-resistant bacteria during treatments.

Application of nanoparticles in oral hygiene

Many of more than 700 bacterial species inhabiting the oral cavity are opportunistic pathogens causing systemic infections in addition to dental and periodontal diseases. This renders oral hygiene a much serious issue, which is further exacerbated with the emergence of multiple antibiotic resistance in oral bacteria. The role of nanoparticles based materials especially metal and metal oxide nanoparticles as an effective and alternative/supplementary antimicrobial agent is now well established. These nanoparticles could be a healthier, innocuous and effective alternative for controlling both the dental biofilms and oral planktonic bacterial population with lesser side effects or antibiotic resistance. Antimicrobial activity of these nanoparticles against a number of oral pathogens has already been demonstrated. When added to artificial dental materials and implants these nanoparticles improve the desirable physico-chemical properties of the materials in addition to improving their antimicrobial activity. Besides a few studies, biochemical processes underlying the antimicrobial activity of the nanoparticles against both planktonic cells and oral biofilms is not understood. Through our literature survey it is envisaged that ZnO nanoparticles and TiO2 nanoparticles are the most suitable nanoantibiotic for the development of dental pastes, mouthwashes, and other oral hygiene materials. However in vivo studies on nanotoxicity of these nanoparticles are missing and need a careful and balanced evaluation before successful clinical translations.

남극 해양에서 생물막 생성 초기 단계의 세균 군집 구조 변화

Compared to planktonic bacterial populations, biofilms have distinct bacterial community structures and play important ecological roles in various aquatic environments. Despite their ecological importance in nature, bacterial community structure and its succession during biofilm development in the Antarctic marine environment have not been elucidated. In this study, the succession of bacterial community, particularly during the early stage of biofilm development, in the Antarctic marine environment was investigated by pyrosequencing of the 16S rRNA gene. Overall bacterial distribution in biofilms differed considerably from surrounding seawater. Relative abundance of Gammaproteobacteria and Bacteroidetes which accounted for 78.9–88.3% of bacterial community changed drastically during biofilm succession. Gammaproteobacteria became more abundant with proceeding succession (75.7% on day 4) and decreased to 46.1% on day 7. The relative abundance of Bacteroidetes showed opposite trend to Gammaproteobacteria, decreasing from the early days to the intermediate days and becoming more abundant in the later days. There were striking differences in the composition of major OTUs (≥ 1%) among samples during the early stages of biofilm formation. Gammaproteobacterial species increased until day 4, while members of Bacteroidetes, the most dominant group on day 1, decreased until day 4 and then increased again. Interestingly, Pseudoalteromonas prydzensis was predominant, accounting for up to 67.4% of the biofilm bacterial community and indicating its important roles in the biofilm development.

Evaluating the Metal Tolerance Capacity of Microbial Communities Isolated from Alberta Oil Sands Process Water.

Anthropogenic activities have resulted in the intensified use of water resources. For example, open pit bitumen extraction by Canada’s oil sands operations uses an estimated volume of three barrels of water for every barrel of oil produced. The waste tailings–oil sands process water (OSPW)–are stored in holding ponds, and present an environmental concern as they are comprised of residual hydrocarbons and metals. Following the hypothesis that endogenous OSPW microbial communities have an enhanced tolerance to heavy metals, we tested the capacity of planktonic and biofilm populations from OSPW to withstand metal ion challenges, using Cupriavidus metallidurans, a known metal-resistant organism, for comparison. The toxicity of the metals toward biofilm and planktonic bacterial populations was determined by measuring the minimum biofilm inhibitory concentrations (MBICs) and planktonic minimum inhibitory concentrations (MICs) using the MBEC ™ assay. We observed that the OSPW community and C. metallidurans had similar tolerances to 22 different metals. While thiophillic elements (Te, Ag, Cd, Ni) were found to be most toxic, the OSPW consortia demonstrated higher tolerance to metals reported in tailings ponds (Al, Fe, Mo, Pb). Metal toxicity correlated with a number of physicochemical characteristics of the metals. Parameters reflecting metal-ligand affinities showed fewer and weaker correlations for the community compared to C. metallidurans, suggesting that the OSPW consortia may have developed tolerance mechanisms toward metals present in their environment.

Identification and characterization of microbial biofilm communities associated with corroded oil pipeline surfaces

Microbially influenced corrosion (MIC) has long been implicated in the deterioration of carbon steel in oil and gas pipeline systems. The authors sought to identify and characterize sessile biofilm communities within a high-temperature oil production pipeline, and to compare the profiles of the biofilm community with those of the previously analyzed planktonic communities. Eubacterial and archaeal 16S rRNA sequences of DNA recovered from extracted pipeline pieces, termed ‘cookies,’ revealed the presence of thermophilic sulfidogenic anaerobes, as well as mesophilic aerobes. Electron microscopy and elemental analysis of cookies confirmed the presence of sessile cells and chemical constituents consistent with corrosive biofilms. Mass spectrometry of cookie acid washes identified putative hydrocarbon metabolites, while surface profiling revealed pitting and general corrosion damage. The results suggest that in an established closed system, the biofilm taxa are representative of the planktonic eubacterial and archaeal community, and that sampling and monitoring of the planktonic bacterial population can offer insight into biocorrosion activity. Additionally, hydrocarbon biodegradation is likely to sustain these communities. The importance of appropriate sample handling and storage procedures to oilfield MIC diagnostics is highlighted.

The impact of natural transformation on adaptation in spatially structured bacterial populations.

BackgroundRecent studies have demonstrated that natural transformation and the formation of highly structured populations in bacteria are interconnected. In spite of growing evidence about this connection, little is known about the dynamics of natural transformation in spatially structured bacterial populations.ResultsIn this work, we model the interdependency between the dynamics of the bacterial gene pool and those of environmental DNA in space to dissect the effect of transformation on adaptation. Our model reveals that even with only a single locus under consideration, transformation with a free DNA fragment pool results in complex adaptation dynamics that do not emerge in previous models focusing only on the gene shuffling effect of transformation at multiple loci. We demonstrate how spatial restriction on population growth and DNA diffusion in the environment affect the impact of transformation on adaptation. We found that in structured bacterial populations intermediate DNA diffusion rates predominantly cause transformation to impede adaptation by spreading deleterious alleles in the population.ConclusionOverall, our model highlights distinctive evolutionary consequences of bacterial transformation in spatially restricted compared to planktonic bacterial populations.

Influence of transgenic Bt176 and non-transgenic corn silage on the structure of rumen bacterial communities

The aim of the present study was to investigate the possible effects of a diet containing transgenic corn (Zea mays), cultivar Bt176 expressing the insecticidal protein CryIA(b), on bacterial diversity of the cow rumen in vivo. Silage prepared with Bt176 corn and its parental non-transgenic cultivar showed no significant differences in either composition or in vivo degradability. Four cows were fed for 35 days with the different silage in a cross-over feeding experiment. The overall structure of rumen bacterial populations was analyzed using a cultivation-independent approach—ribosomal intergenic spacer analysis (RISA)—during 3 consecutive days of each feeding trial in all cows. Planktonic bacterial populations present in the rumen fluid and biofilm grown directly on the silage were analyzed separately. Statistical analysis of RISA fingerprints did not reveal significant differences in bacterial community structure between different feedings. Small differences were nevertheless observed between individuals on the structure of bacterial communities directly colonizing the silage material. A diet constituted by transgenic Bt-corn silage was demonstrated not to be substantially different from non-transgenic corn silage in terms of composition, digestibility and impact on the overall rumen microbiota.

New antibiotic agents and approaches to treat biofilm-associated infections

Importance of the field: Current antibiotics have classically been developed to treat infections involving planktonic bacterial populations in acute infection settings and are typically ineffective in the eradication of bacteria in biofilm-associated, persistent infections. The paucity of effective current treatment options and the growing population of susceptible patients with indwelling medical devices and materials are key factors that substantiate the need for new agents effective in the prevention or eradication of biofilms.Areas covered in this review: Published patents relating to biofilm-active agents were identified in SciFinder® for the period January 2005 through March 2010 and representative patents selected with an emphasis on agents claimed for the prophylaxis or treatment of bacterial biofilm infections.What the reader will gain: The review provides a basic understanding of the medical challenges posed by biofilm-associated infections, and summarizes claims describing novel therapeutic approaches in the management of biofilm infections.Take home message: Treatment of biofilm-associated infections with existing approved therapies remains a significant medical challenge. In the near term, new agents demonstrating bactericidal activity against bacteria within biofilms will be most readily incorporated into existing treatment paradigms. Alternative approaches that impact biofilm formation or dispersion are promising, but remain to be validated clinically.

Incorporating toxin hypothesis into a mathematical model of persister formation and dynamics

Biofilms are well known for their extreme tolerance to antibiotics. Recent experimental evidence has indicated the existence of a small fraction of specialized persister cells may be responsible for this tolerance. Although persister cells seem to exist in planktonic bacterial populations, within a biofilm the additional protection offered by the polymeric matrix allows persister cells to evade elimination and serve as a source for re-population. Whether persister cells develop through interactions with toxin/antitoxin modules or are senescent bacteria is an open question. In this investigation we contrast results of the analysis of a mathematical model of the toxin/antitoxin hypothesis for bacteria in a chemostat with results incorporating the senescence hypothesis. We find that the persister fraction of the population as a function of washout rate provides a viable distinction between the two hypotheses. We also give simulation results that indicate that a strategy of alternating dose/withdrawal disinfection can be effective in clearing the entire persister and susceptible populations of bacteria. This strategy was considered previously in analysis of a generic model of persister formation. We find that extending the model of persister formation to include the toxin/antitoxin interactions in a chemostat does not alter the qualitative results that success of the dosing strategy depends on the withdrawal time. While this treatment is restricted to planktonic bacterial populations, it serves as a framework for including persister cells in a spatially dependent biofilm model.

Planktonic Bacterial Population Dynamics with Environmental Changes in Coastal Areas of Suruga Bay

We studied planktonic bacterial population dynamics in response to the changing environment in a coastal system during an observation period of over 5 years using fluorescence in situ hybridization. To estimate the environmental constraint on the bacterial community, we focused on temperature, salinity, abundance of photoplankton (chlorophyll a), and dissolved organic carbon (DOC). The total number of bacteria (TDC) amounted to 3.0×105 to 5.0×106 cells mL-1, with 1.0×105 to 1.0×106 cells mL-1 for Bacteria, accounting for 11.8 to 74.8% of TDC, and 1.0×104 to 1.0×105 cells mL-1 for Gammaproteobacteria, 1.0 to 20.8% of TDC. The abundance of Archaea, which contributed from 0.1 to 12% to TDC, ranged from 2.0×103 to 3.0×104 cells mL-1. We found a positive relationship between environmental parameters such as temperature, salinity, chlorophyll a, and DOC and the abundance of total bacteria and Bacteria. The number of Gammaproteobacteria correlated with temperature, salinity, and chlorophyll a, but not with DOC. We suggest that increasing the temperature under eutrophic conditions will lead to high bacterial abundance and probably a change in the bacterial community.

Die-Away Kinetic Analysis of the Capacity of Epilithic and Planktonic Bacteria from Clean and Polluted River Water To Biodegrade Sodium Dodecyl Sulfate

The capacities of epilithic and planktonic river bacterial populations to degrade sodium dodecyl sulfate (SDS) in samples taken at two times during 1987 from one clean and four polluted sites in a South Wales river were estimated in die-away tests under simulated environmental conditions. There was a relatively slow disappearance of SDS in die-away tests for both planktonic and epilithic populations taken from the clean source site, as compared with those taken from the downstream polluted sites, for which the rate of biodegradation was accelerated, sometimes after an apparent initial lag period. The kinetic components contributing to the die-away curves were quantified by nonlinear regression analysis in which the experimental data were fitted to a variety of possible kinetic models. All samples except for one from the polluted sites best fitted a model which describes the biodegradation of SDS at concentrations well below its K(m) by bacteria whose growth is exponential and unaffected by the addition of a test substrate. Each sample from the clean source site fitted a different model, but there was generally little or no growth on endogenous carbon. A consideration of the numerical values of constants derived from the modeling of epilithic and planktonic populations from polluted sites indicated clearly that the biodegradative capacity of epilithic bacterial populations towards SDS is more stable than that of planktonic bacterial populations.

The use of planktonic bacterial populations in open and closed recirculating water cooling systems for the evaluation of biocides

Uncontrolled microbiological growth in recirculating water cooling towers results in biofouling and sludge formation with subsequent fouling of the system and microbiologically-induced corrosion. Biocides have therefore been used and are still being used to control such microbiological fouling. The problem has, however, been to find suitable methods for evaluating these biocides. During this study, planktonic bacterial numbers and population structure studies were used to evaluate biocides in situ. The results indicate that this method could be used to evaluate biocides objectively.

Loss processes influencing growth of planktonic bacterial populations in Lake Constance

Loss processes influencing growth of planktonic bacterial populations in Lake Constance

Development of planktonic bacterial populations in a water column of Lake Constance (Bodensee-Obersee)

Development of planktonic bacterial populations in a water column of Lake Constance (Bodensee-Obersee)

Seasonal Variations in Four Bacterial Size Fractions from a Hypertrophic Pond in Tokyo, Japan

AbstractThe planktonic bacterial populations in the surface water of the hypertrophic Himon‐ya Pond were separated into four fractions (>35 μm, 35‐5 μm, 5–1 μm, and <1 μm) by size fractionation of suspended particles in the water. The seasonal variations in bacterial numbers over a two year period differed for each of the four fractions. The bacterial counts in the >35 μm fraction were mainly dependent on the biomass of Microcystis colonies. Their peaks were observed in summer. In the 35‐5 μm and 5–1 μm fractions, several peaks in bacterial numbers were observed, influenced by the quality and quantity of the particles associated with the bacteria. The bacterial counts in the <1 μm fraction contributed a high proportion of the total throughout all seasons except summer.