Light and Electron Microscopic Studies of Microorganisms Growing in Rotating Biological Contactor Biofilms

The biofilms growing in the first compartments of two rotating biological contactors used to treat municipal wastewater were examined by light and electron microscopy. The biofilms were found to contain a complex and varied microbial community that included filamentous and unicellular bacteria, protozoa, metazoa, and (possibly) bacteriophage. The predominant microorganism among these appeared to be a filamentous bacterium that was identical to Sphaerotilus in both morphological and ultrastructural characteristics. It was possible to isolate a Sphaerotilus-like bacterium from each contactor. Both the Sphaerotilus filaments and the wide variety of unicellular bacteria present tended to contain poly-β-hydroxybutyrate inclusions, a probable indication that these organisms were removing carbon from the wastewater and storing it. The microbial population of the biofilms appeared to be metabolically active, as evidenced by the presence of microcolonies and dividing cells.     

Characterisation of the bacteria associated with barnacle,Balanus amphitrite,shell and their role in gregarious settlement of cypris larvae

The acorn barnacle Balanus amphitrite (syn. Amphibalanus amphitrite) is a model organism to investigate pelago-benthic transitions in marine invertebrates. A driver for larval settlement in this organism is the need to attach close to conspecifics, to allow reproduction to take place. Adult barnacles are covered by microbial biofilms and the contribution of these biofilms to conspecific recognition is not fully understood. Little information is available on microbial communities associated with B. amphitrite. We compared biofilm communities from the barnacle shell surface with those from the surrounding rocks using the culture-independent methods of quantitative PCR and denaturing gradient gel electrophoresis. Quantification of the relative abundances of higher bacterial taxa showed that barnacles hosted a greater proportion of α-Proteobacteria compared to rock-associated biofilms (p < 0.01). Differences in relative abundances of other taxa were not observed but DGGE profiling suggested that differences were present at lower taxonomic levels. The capacity of these communities to influence larval settlement was assessed by growing multispecies biofilms on artificial medium, obtained by extracting nutrients from adult barnacles. Biofilms composed of shell-associated bacteria were capable of promoting conspecific settlement by 67% compared to control surfaces (p < 0.05), while rock-associated communities showed contrasting effects. A taxonomic comparison of settlement-stimulating and -inhibiting bacteria was performed by DGGE and band sequencing. All partial 16S rRNA genes sequenced were similar to members of the Vibrio and Pseudoalteromonas genera, suggesting that larvae can detect and respond to variations in the composition of microbial biofilms at low taxonomic levels. Our results indicate that barnacle larvae may be able to detect parentally-associated biofilms and use this information to settle close to members of its own species.     

New Methods for Analysis of Spatial Distribution and Coaggregation of Microbial Populations in Complex Biofilms

In biofilms, microbial activities form gradients of substrates and electron acceptors, creating a complex landscape of microhabitats, often resulting in structured localization of the microbial populations present. To understand the dynamic interplay between and within these populations, quantitative measurements and statistical analysis of their localization patterns within the biofilms are necessary, and adequate automated tools for such analyses are needed. We have designed and applied new methods for fluorescence in situ hybridization (FISH) and digital image analysis of directionally dependent (anisotropic) multispecies biofilms. A sequential-FISH approach allowed multiple populations to be detected in a biofilm sample. This was combined with an automated tool for vertical-distribution analysis by generating in silico biofilm slices and the recently developed Inflate algorithm for coaggregation analysis of microbial populations in anisotropic biofilms. As a proof of principle, we show distinct stratification patterns of the ammonia oxidizers Nitrosomonas oligotropha subclusters I and II and the nitrite oxidizer Nitrospira sublineage I in three different types of wastewater biofilms, suggesting niche differentiation between the N. oligotropha subclusters, which could explain their coexistence in the same biofilms. Coaggregation analysis showed that N. oligotropha subcluster II aggregated closer to Nitrospira than did N. oligotropha subcluster I in a pilot plant nitrifying trickling filter (NTF) and a moving-bed biofilm reactor (MBBR), but not in a full-scale NTF, indicating important ecophysiological differences between these phylogenetically closely related subclusters. By using high-resolution quantitative methods applicable to any multispecies biofilm in general, the ecological interactions of these complex ecosystems can be understood in more detail.     

Molecular Analysis of Shower Curtain Biofilm Microbes

Households provide environments that encourage the formation of microbial communities, often as biofilms. Such biofilms constitute potential reservoirs for pathogens, particularly for immune-compromised individuals. One household environment that potentially accumulates microbial biofilms is that provided by vinyl shower curtains. Over time, vinyl shower curtains accumulate films, commonly referred to as “soap scum,” which microscopy reveals are constituted of lush microbial biofilms. To determine the kinds of microbes that constitute shower curtain biofilms and thereby to identify potential opportunistic pathogens, we conducted an analysis of rRNA genes obtained by PCR from four vinyl shower curtains from different households. Each of the shower curtain communities was highly complex. No sequence was identical to one in the databases, and no identical sequences were encountered in the different communities. However, the sequences generally represented similar phylogenetic kinds of organisms. Particularly abundant sequences represented members of the α-group of proteobacteria, mainly Sphingomonas spp. and Methylobacterium spp. Both of these genera are known to include opportunistic pathogens, and several of the sequences obtained from the environmental DNA samples were closely related to known pathogens. Such organisms have also been linked to biofilm formation associated with water reservoirs and conduits. In addition, the study detected many other kinds of organisms at lower abundances. These results show that shower curtains are a potential source of opportunistic pathogens associated with biofilms. Frequent cleaning or disposal of shower curtains is indicated, particularly in households with immune-compromised individuals.     

Pseudomonas aeruginosa and Saccharomyces cerevisiae Biofilm in Flow Cells

Many microbial cells have the ability to form sessile microbial communities defined as biofilms that have altered physiological and pathological properties compared to free living microorganisms. Biofilms in nature are often difficult to investigate and reside under poorly defined conditions¹. Using a transparent substratum it is possible to device a system where simple biofilms can be examined in a non-destructive way in real-time: here we demonstrate the assembly and operation of a flow cell model system, for in vitro 3D studies of microbial biofilms generating high reproducibility under well-defined conditions^2,3.The system consists of a flow cell that serves as growth chamber for the biofilm. The flow cell is supplied with nutrients and oxygen from a medium flask via a peristaltic pump and spent medium is collected in a waste container. This construction of the flow system allows a continuous supply of nutrients and administration of e.g. antibiotics with minimal disturbance of the cells grown in the flow chamber. Moreover, the flow conditions within the flow cell allow studies of biofilm exposed to shear stress. A bubble trapping device confines air bubbles from the tubing which otherwise could disrupt the biofilm structure in the flow cell.The flow cell system is compatible with Confocal Laser Scanning Microscopy (CLSM) and can thereby provide highly detailed 3D information about developing microbial biofilms. Cells in the biofilm can be labeled with fluorescent probes or proteins compatible with CLSM analysis. This enables online visualization and allows investigation of niches in the developing biofilm. Microbial interrelationship, investigation of antimicrobial agents or the expression of specific genes, are of the many experimental setups that can be investigated in the flow cell system.     

药物外排泵与生物被膜在微生物耐药机制中的相关性研究进展

生物被膜是介导微生物耐药与多重耐药的一大热点机制,涉及微生物的生长代谢、耐药基因等基因表型改变、群体感应系统的调控及药物外排泵等多重因素。耐药基因、药物外排泵与生物被膜在微生物耐药机制中,具有复杂而密切的相互影响。分别从生物被膜对药物外排泵、耐药基因的影响,药物外排泵对生物被膜的影响,以及药物外排泵和微生物生物被膜共同的调节因素,对近年来的相关研究进展作一综述。     

Pseudomonas fluorescens' view of the periodic table

Growth in a biofilm modulates microbial metal susceptibility, sometimes increasing the ability of microorganisms to withstand toxic metal species by several orders of magnitude. In this study, a high-throughput metal toxicity screen was initiated with the aim of correlating biological toxicity data in planktonic and biofilm cells to the physiochemical properties of metal ions. To this end, Pseudomonas fluorescens ATCC 13525 was grown in the Calgary Biofilm Device (CBD) and biofilms and planktonic cells of this microorganism were exposed to gradient arrays of different metal ions. These arrays included 44 different metals with representative compounds that spanned every group of the periodic table (except for the halogens and noble gases). The minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and minimum biofilm eradication concentration (MBEC) values were obtained after exposing the biofilms to metal ions for 4 h. Using these values, metal ion toxicity was correlated to the following ion-specific physicochemical parameters: standard reduction-oxidation potential, electronegativity, the solubility product of the corresponding metal–sulfide complex, the Pearson softness index, electron density and the covalent index. When the ions were grouped according to outer shell electron structure, we found that heavy metal ions gave the strongest correlations to these parameters and were more toxic on average than the other classes of the ions. Correlations were different for biofilms than for planktonic cells, indicating that chemical mechanisms of metal ion toxicity differ between the two modes of growth. We suggest that biofilms can specifically counter the toxic effects of certain physicochemical parameters, which may contribute to the increased ability of biofilms to withstand metal toxicity.     

Complex bacterial diversity in the white biofilms of the Catacombs of St. Callixtus in Rome evidenced by different investigation strategies

Roman Catacombs are affected by different kinds of biofilms that were extensively investigated in the last 14 years. In particular, the areas far from the lamps are often covered by white biofilms of different extension, consistency and nature. The aim of this paper is to describe the profile of the microbial community present in two areas of the Ocean's Cubiculum (CSC13), characterized by similar alterations described as white biofilms, by using a multistep approach that included direct microscopy observations, culture‐dependent and culture‐independent methodologies through the extraction of DNA and RNA directly from the sampled areas. In addition to this, we extracted the DNA directly from the Petri dishes containing R2A and B4 media after incubation and growth of bacteria. Our results evidenced that a complex bacterial community (mainly constituted by filamentous Actinobacteria, as well as Firmicutes and Proteobacteria) colonizes the two different white biofilms, and its detection, quantitative and qualitative, could be revealed only by different approaches, each method giving different information that only partially overlap.     

Diversity of Bacterial Biofilm Communities on Sprinklers from Dairy Farm Cooling Systems in Israel

On dairy farms in hot climates worldwide, cows suffer from heat stress, which is alleviated by the use of water cooling systems. Sprinklers and showerheads are known to support the development of microbial biofilms, which can be a source of infection by pathogenic microorganisms. The aim of this study was to investigate the presence of microbial biofilms in dairy cooling systems, and to analyze their population compositions using culture-independent technique, 16S rRNA gene sequencing. Biofilm samples were collected on eight dairy farms from 40 sprinklers and the microbial constituents were identified by deep sequencing of the 16S rRNA gene. A total of 9,374 operational taxonomic units (OTUs) was obtained from all samples. The mean richness of the samples was 465 ± 268 OTUs which were classified into 26 different phyla; 76% of the reads belonged to only three phyla: Proteobacteria, Actinobacteria and Firmicutes. Although the most prevalent OTUs (Paracoccus, Methyloversatilis, Brevundimonas, Porphyrobacter, Gp4, Mycobacterium, Hyphomicrobium, Corynebacterium and Clostridium) were shared by all farms, each farm formed a unique microbial pattern. Some known potential human and livestock pathogens were found to be closely related to the OTUs found in this study. This work demonstrates the presence of biofilm in dairy cooling systems which may potentially serve as a live source for microbial pathogens.     

Metamorphosis of a Scleractinian Coral in Response to Microbial Biofilms

Microorganisms have been reported to induce settlement and metamorphosis in a wide range of marine invertebrate species. However, the primary cue reported for metamorphosis of coral larvae is calcareous coralline algae (CCA). Herein we report the community structure of developing coral reef biofilms and the potential role they play in triggering the metamorphosis of a scleractinian coral. Two-week-old biofilms induced metamorphosis in less than 10% of larvae, whereas metamorphosis increased significantly on older biofilms, with a maximum of 41% occurring on 8-week-old microbial films. There was a significant influence of depth in 4- and 8-week biofilms, with greater levels of metamorphosis occurring in response to shallow-water communities. Importantly, larvae were found to settle and metamorphose in response to microbial biofilms lacking CCA from both shallow and deep treatments, indicating that microorganisms not associated with CCA may play a significant role in coral metamorphosis. A polyphasic approach consisting of scanning electron microscopy, fluorescence in situ hybridization (FISH), and denaturing gradient gel electrophoresis (DGGE) revealed that coral reef biofilms were comprised of complex bacterial and microalgal communities which were distinct at each depth and time. Principal-component analysis of FISH data showed that the Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, and Cytophaga-Flavobacterium of Bacteroidetes had the largest influence on overall community composition. A low abundance of Archaea was detected in almost all biofilms, providing the first report of Archaea associated with coral reef biofilms. No differences in the relative densities of each subdivision of Proteobacteria were observed between slides that induced larval metamorphosis and those that did not. Comparative cluster analysis of bacterial DGGE patterns also revealed that there were clear age and depth distinctions in biofilm community structure; however, no difference was detected in banding profiles between biofilms which induced larval metamorphosis and those where no metamorphosis occurred. This investigation demonstrates that complex microbial communities can induce coral metamorphosis in the absence of CCA.     

Automated Confocal Laser Scanning Microscopy and Semiautomated Image Processing for Analysis of Biofilms

The purpose of this study was to develop and apply a quantitative optical method suitable for routine measurements of biofilm structures under in situ conditions. A computer program was designed to perform automated investigations of biofilms by using image acquisition and image analysis techniques. To obtain a representative profile of a growing biofilm, a nondestructive procedure was created to study and quantify undisturbed microbial populations within the physical environment of a glass flow cell. Key components of the computer-controlled processing described in this paper are the on-line collection of confocal two-dimensional (2D) cross-sectional images from a preset 3D domain of interest followed by the off-line analysis of these 2D images. With the quantitative extraction of information contained in each image, a three-dimensional reconstruction of the principal biological events can be achieved. The program is convenient to handle and was generated to determine biovolumes and thus facilitate the examination of dynamic processes within biofilms. In the present study, Pseudomonas fluorescens or a green fluorescent protein-expressing Escherichia coli strain, EC12, was inoculated into glass flow cells and the respective monoculture biofilms were analyzed in three dimensions. In this paper we describe a method for the routine measurements of biofilms by using automated image acquisition and semiautomated image analysis.     

Ratiometric Imaging of Extracellular pH in Bacterial Biofilms with C-SNARF-4

pH in the extracellular matrix of bacterial biofilms is of central importance for microbial metabolism. Biofilms possess a complex three-dimensional architecture characterized by chemically different microenvironments in close proximity. For decades, pH measurements in biofilms have been limited to monitoring bulk pH with electrodes. Although pH microelectrodes with a better spatial resolution have been developed, they do not permit the monitoring of horizontal pH gradients in biofilms in real time. Quantitative fluorescence microscopy can overcome these problems, but none of the hitherto employed methods differentiated accurately between extracellular and intracellular microbial pH and visualized extracellular pH in all areas of the biofilms. Here, we developed a method to reliably monitor extracellular biofilm pH microscopically with the ratiometric pH-sensitive dye C-SNARF-4, choosing dental biofilms as an example. Fluorescent emissions of C-SNARF-4 can be used to calculate extracellular pH irrespective of the dye concentration. We showed that at pH values of <6, C-SNARF-4 stained 15 bacterial species frequently isolated from dental biofilm and visualized the entire bacterial biomass in in vivo-grown dental biofilms with unknown species composition. We then employed digital image analysis to remove the bacterial biomass from the microscopic images and adequately calculate extracellular pH values. As a proof of concept, we monitored the extracellular pH drop in in vivo-grown dental biofilms fermenting glucose. The combination of pH ratiometry with C-SNARF-4 and digital image analysis allows the accurate monitoring of extracellular pH in bacterial biofilms in three dimensions in real time and represents a significant improvement to previously employed methods of biofilm pH measurement.     

High-Throughput Screening of Multispecies Biofilm Formation and Quantitative PCR-Based Assessment of Individual Species Proportions,Useful for Exploring Interspecific Bacterial Interactions

Multispecies biofilms are predominant in almost all natural environments, where myriads of resident microorganisms interact with each other in both synergistic and antagonistic manners. The interspecies interactions among different bacteria are, despite the ubiquity of these communities, still poorly understood. Here, we report a rapid, reproducible and sensitive approach for quantitative screening of biofilm formation by bacteria when cultivated as mono- and multispecies biofilms, based on the Nunc-TSP lid system and crystal violet staining. The relative proportion of the individual species in a four-species biofilm was assessed using quantitative PCR based on SYBR Green I fluorescence with specific primers. The results indicated strong synergistic interactions in a four-species biofilm model community with a more than 3-fold increase in biofilm formation and demonstrated the strong dominance of two strains, Xanthomonas retroflexus and Paenibacillus amylolyticus. The developed approach can be used as a standard procedure for evaluating interspecies interactions in defined microbial communities. This will be of significant value in the quantitative study of the microbial composition of multispecies biofilms both in natural environments and infectious diseases to increase our understanding of the mechanisms that underlie cooperation, competition and fitness of individual species in mixed-species biofilms.     

Heterotrophic Archaea Contribute to Carbon Cycling in Low-pH,Suboxic Biofilm Communities

Archaea are widely distributed and yet are most often not the most abundant members of microbial communities. Here, we document a transition from Bacteria- to Archaea-dominated communities in microbial biofilms sampled from the Richmond Mine acid mine drainage (AMD) system (∼pH 1.0, ∼38°C) and in laboratory-cultivated biofilms. This transition occurs when chemoautotrophic microbial communities that develop at the air-solution interface sink to the sediment-solution interface and degrade under microaerobic and anaerobic conditions. The archaea identified in these sunken biofilms are from the class Thermoplasmata, and in some cases, the highly divergent ARMAN nanoarchaeal lineage. In several of the sunken biofilms, nanoarchaea comprise 10 to 25% of the community, based on fluorescent in situ hybridization and metagenomic analyses. Comparative community proteomic analyses show a persistence of bacterial proteins in sunken biofilms, but there is clear evidence for amino acid modifications due to acid hydrolysis. Given the low representation of bacterial cells in sunken biofilms based on microscopy, we infer that hydrolysis reflects proteins derived from lysed cells. For archaea, we detected ∼2,400 distinct proteins, including a subset involved in proteolysis and peptide uptake. Laboratory cultivation experiments using complex carbon substrates demonstrated anaerobic enrichment of Ferroplasma and Aplasma coupled to the reduction of ferric iron. These findings indicate dominance of acidophilic archaea in degrading biofilms and suggest that they play roles in anaerobic nutrient cycling at low pH.     

Lipoic Acid Does Not Affect The Growth of Mycoplasma hominis Cells In Vitro

Mycoplasma hominis is associated with various infections, for which the treatment can be complex. Lipoic acid (LA) plays a role as a cofactor in eukaryotes, most Bacteria, and some Archea. Research of recent years has increasingly pointed to the therapeutic properties of exogenously supplemented LA. The present study was conducted on 40 strains of M. hominis cultured with the following LA concentrations: 1,200 μg/ml, 120 μg/ml, and 12 μg/ml. The bacterial colonies of each strain were counted and expressed as the number of colony-forming units/ml (CFU). The number of CFU in M. hominis strains obtained in the presence of LA was compared with the number of CFU in the strains grown in the media without LA. The obtained results indicated that the presence of LA in the medium did not affect the growth of M. hominis. The investigation of the influence of LA on the growth and survival of microbial cells not only allows for obtaining an answer to the question of whether LA has antimicrobial activity and, therefore, can be used as a drug supporting the treatment of patients infected with a given pathogenic microorganism. Such studies are also crucial for a better understanding of LA metabolism in the microbial cells, which is also important for the search for new antimicrobial drugs. This research is, therefore, an introduction to such further studies.     

Differential Effects of Distinct Bacterial Biofilms in a Cave Environment

Current microbial surveys using molecular methods provide us with critical information on the major components of natural bacterial communities. However, limited investigation has been performed on the influence of bacterial metabolism on the environment. In this study, we analyzed the pH generated by distinct bacterial communities in a cave environment. Different bacterial biofilms developing on the walls of the cave were visually distinguished by their colorations (e.g., white, yellow, and gray) and mineral depositions, and previous studies have reported on their bacterial diversity and distribution. Using pH microelectrodes, we carried out in situ measurements and were able to detect differences among these bacterial biofilms. White biofilms and carbonate depositions resulted in alkaline pH values. Gray biofilms also increased the pH although these values remained lower than in white biofilms. A combination of gray–white biofilms resulted in alkaline pH values with highest values at the white edge of the colonies. Yellow biofilms generated a slightly acid pH. These results suggest that different bacterial communities can lead to distinct effects on their environment, for instance, precipitation or dissolution of carbonates in caves. These results add information about metabolic response to current knowledge from bacterial diversity surveys, providing information on the interaction between complex bacterial communities and the geological substrate.     

Discriminating multi-species populations in biofilms with peptide nucleic acid fluorescence in situ hybridization (PNA FISH)

Background

Our current understanding of biofilms indicates that these structures are typically composed of many different microbial species. However, the lack of reliable techniques for the discrimination of each population has meant that studies focusing on multi-species biofilms are scarce and typically generate qualitative rather than quantitative data.

Methodology/Principal Findings

We employ peptide nucleic acid fluorescence in situ hybridization (PNA FISH) methods to quantify and visualize mixed biofilm populations. As a case study, we present the characterization of Salmonella enterica/Listeria monocytogenes/Escherichia coli single, dual and tri-species biofilms in seven different support materials. Ex-situ, we were able to monitor quantitatively the populations of ∼56 mixed species biofilms up to 48 h, regardless of the support material. In situ, a correct quantification remained more elusive, but a qualitative understanding of biofilm structure and composition is clearly possible by confocal laser scanning microscopy (CLSM) at least up to 192 h. Combining the data obtained from PNA FISH/CLSM with data from other established techniques and from calculated microbial parameters, we were able to develop a model for this tri-species biofilm. The higher growth rate and exopolymer production ability of E. coli probably led this microorganism to outcompete the other two [average cell numbers (cells/cm²) for 48 h biofilm: E. coli 2,1×10⁸ (±2,4×10⁷); L. monocytogenes 6,8×10⁷ (±9,4×10⁶); and S. enterica 1,4×10⁶ (±4,1×10⁵)]. This overgrowth was confirmed by CSLM, with two well-defined layers being easily identified: the top one with E. coli, and the bottom one with mixed regions of L. monocytogenes and S. enterica.

Significance

While PNA FISH has been described previously for the qualitative study of biofilm populations, the present investigation demonstrates that it can also be used for the accurate quantification and spatial distribution of species in polymicrobial communities. Thus, it facilitates the understanding of interspecies interactions and how these are affected by changes in the surrounding environment.     

Growth of Mycobacterium tuberculosis Biofilms

Mycobacterium tuberculosis, the etiologic agent of human tuberculosis, has an extraordinary ability to survive against environmental stresses including antibiotics. Although stress tolerance of M. tuberculosis is one of the likely contributors to the 6-month long chemotherapy of tuberculosis ¹, the molecular mechanisms underlying this characteristic phenotype of the pathogen remain unclear. Many microbial species have evolved to survive in stressful environments by self-assembling in highly organized, surface attached, and matrix encapsulated structures called biofilms ^2-4. Growth in communities appears to be a preferred survival strategy of microbes, and is achieved through genetic components that regulate surface attachment, intercellular communications, and synthesis of extracellular polymeric substances (EPS) ^5,6. The tolerance to environmental stress is likely facilitated by EPS, and perhaps by the physiological adaptation of individual bacilli to heterogeneous microenvironments within the complex architecture of biofilms ⁷.In a series of recent papers we established that M. tuberculosis and Mycobacterium smegmatis have a strong propensity to grow in organized multicellular structures, called biofilms, which can tolerate more than 50 times the minimal inhibitory concentrations of the anti-tuberculosis drugs isoniazid and rifampicin ^8-10. M. tuberculosis, however, intriguingly requires specific conditions to form mature biofilms, in particular 9:1 ratio of headspace: media as well as limited exchange of air with the atmosphere ⁹. Requirements of specialized environmental conditions could possibly be linked to the fact that M. tuberculosis is an obligate human pathogen and thus has adapted to tissue environments. In this publication we demonstrate methods for culturing M. tuberculosis biofilms in a bottle and a 12-well plate format, which is convenient for bacteriological as well as genetic studies. We have described the protocol for an attenuated strain of M. tuberculosis, mc²7000, with deletion in the two loci, panCD and RD1, that are critical for in vivo growth of the pathogen ⁹. This strain can be safely used in a BSL-2 containment for understanding the basic biology of the tuberculosis pathogen thus avoiding the requirement of an expensive BSL-3 facility. The method can be extended, with appropriate modification in media, to grow biofilm of other culturable mycobacterial species.Overall, a uniform protocol of culturing mycobacterial biofilms will help the investigators interested in studying the basic resilient characteristics of mycobacteria. In addition, a clear and concise method of growing mycobacterial biofilms will also help the clinical and pharmaceutical investigators to test the efficacy of a potential drug.     

重度火烧迹地微地形对土壤微生物特性的影响——以坡度和坡向为例

通过对大兴安岭重度火烧迹地不同坡度和坡向的土壤微生物群落进行调查研究,旨在揭示重度火烧迹地过火6a后森林恢复过程土壤微生物群落的变化规律与影响因素.研究结果表明:平地土壤微生物生物量碳含量(MBC)和土壤微生物生物量碳氮比(MBC/MBN)均高于坡地,其中MBC/MBN达到差异极显著水平.平地土壤微生物的代谢活性AWCD值、对31种4类碳源(糖类、脂类、氨基酸、代谢物)的利用能力和Shannon-Winner多样性指数(H')均极显著低于坡地.西坡土壤微生物AWCD值和H'高于南坡,但AWCD和H'与土壤养分、pH值、EC无显著相关关系,说明坡向可能与土壤微生物代谢活性和多样性的关系并不密切,反映了两坡向土壤微生物群落结构的相似性.坡度由于影响了土壤养分和水分条件,进而影响了土壤微生物的生物量、群落结构、物种多样性和碳源利用能力.火烧迹地恢复初期平地土壤微生物量碳高于坡地,西坡高于南坡;恢复6a后,土壤微生物量碳的差异己不显著,但土壤微生物群落结构、物种多样性以及代谢特性仍具有显著差异,这可能与地形坡度仍然显著影响土壤水分含量的因素有关.     

Probabilistic Models to Describe the Dynamics of Migrating Microbial Communities

In all but the most sterile environments bacteria will reside in fluid being transported through conduits and some of these will attach and grow as biofilms on the conduit walls. The concentration and diversity of bacteria in the fluid at the point of delivery will be a mix of those when it entered the conduit and those that have become entrained into the flow due to seeding from biofilms. Examples include fluids through conduits such as drinking water pipe networks, endotracheal tubes, catheters and ventilation systems. Here we present two probabilistic models to describe changes in the composition of bulk fluid microbial communities as they are transported through a conduit whilst exposed to biofilm communities. The first (discrete) model simulates absolute numbers of individual cells, whereas the other (continuous) model simulates the relative abundance of taxa in the bulk fluid. The discrete model is founded on a birth-death process whereby the community changes one individual at a time and the numbers of cells in the system can vary. The continuous model is a stochastic differential equation derived from the discrete model and can also accommodate changes in the carrying capacity of the bulk fluid. These models provide a novel Lagrangian framework to investigate and predict the dynamics of migrating microbial communities. In this paper we compare the two models, discuss their merits, possible applications and present simulation results in the context of drinking water distribution systems. Our results provide novel insight into the effects of stochastic dynamics on the composition of non-stationary microbial communities that are exposed to biofilms and provides a new avenue for modelling microbial dynamics in systems where fluids are being transported.