Bacterial and Fungal Diversity of Quaternary Cave Sediment Deposits

The bacterial and fungal assemblages of clastic sediments collected from two caves located in north-western Romania were investigated by assessing ITS and 16S rRNA gene diversity. Bacterial members belonging to Chloroflexi, Nitrospirae, Proteobacteria, Firmicutes, Acidobacteria, Gemmatimonadetes, and fungal members of Ascomycota were identified. Except for Bacillus sp., all bacteria were related to uncultured or unknown species and the majority (86%) of the bacterial sequences from one of the caves had no close GenBank relatives. The bacterial sequences obtained clustered with species found in extreme environments. Half of the bacterial operational taxonomic units were clustered with clones isolated from deep subsurface sediments of a radioactively contaminated site in the USA. The present study represents the first attempt to identify microorganisms in Quaternary cave sediments.

Supplemental materials are available for this article. Go to the publisher's online edition of Geomicrobiology Journal to view the supplemental file.     

Effects of Photosynthesis on Bacterial Phosphatase Production in Biofilms

The fraction of bacteria displaying phosphatase activity within natural photosynthetic biofilms was examined in relation to phosphorus limitation and algal photosynthesis. An artificial substrate that forms a fluorescent precipitate was used in conjunction with the nucleic acid stain DAPI to enumerate extracellular phosphatase expression by biofilm bacteria exposed to different photosynthetic activities and phosphorus supplies. The proportion of bacteria displaying phosphatase activity changed in response to the presence or absence of algal photosynthesis. In general, phosphate-deprived biofilms had positive linear trends in bacterial phosphatase activity (p <0.001), with greater proportions of bacteria displaying phosphatase under photosynthetic inhibition compared to active photosynthesis. Under sufficient phosphate supplies, biofilms had negative linear trends (p <0.05) or were lower in the proportion of bacteria displaying phosphatase activity in the presence of algal photosynthesis, whereas bacterial phosphatase activity was generally maintained when photosynthesis was inhibited. it is suggested that the amount of extracellular organic carbon released within the biofilm matrix during photosynthesis indirectly affected bacterial phosphatase synthesis.     

Effects of a Quaternary Ammonium Compound on Escherichia coli

Increasing amounts of tetradecyldimethylbenzyl ammonium chloride (TAC) were lethal to an increasing proportion of an actively growing culture of Escherichia coli. The loss of nucleic acid material by actively growing E. coli did not appear to play a major role in the lethal effect. It was found that lag-phase cells were more sensitive than logarithmic-phase cells to the lethal effect of TAC. The effect of TAC on the lysozyme sensitivity of the test organism was compared with that obtained using disodium dihydrogen ethylenediaminetetraacetate (EDTA). Although TAC was found to render the test organism susceptible to lysozyme, the degree of lysis never reached that attained with EDTA.     

A Comparison of Effects of Broad-Spectrum Antibiotics and Biosurfactants on Established Bacterial Biofilms

Current antibiofilm solutions based on planktonic bacterial physiology have limited efficacy in clinical and occasionally environmental settings. This has prompted a search for suitable alternatives to conventional therapies. This study compares the inhibitory properties of two biological surfactants (rhamnolipids and a plant-derived surfactant) against a selection of broad-spectrum antibiotics (ampicillin, chloramphenicol and kanamycin). Testing was carried out on a range of bacterial physiologies from planktonic and mixed bacterial biofilms. Rhamnolipids (Rhs) have been extensively characterised for their role in the development of biofilms and inhibition of planktonic bacteria. However, there are limited direct comparisons with antimicrobial substances on established biofilms comprising single or mixed bacterial strains. Baseline measurements of inhibitory activity using planktonic bacterial assays established that broad-spectrum antibiotics were 500 times more effective at inhibiting bacterial growth than either Rhs or plant surfactants. Conversely, Rhs and plant biosurfactants reduced biofilm biomass of established single bacterial biofilms by 74–88 and 74–98 %, respectively. Only kanamycin showed activity against biofilms of Bacillus subtilis and Staphylococcus aureus. Broad-spectrum antibiotics were also ineffective against a complex biofilm of marine bacteria; however, Rhs and plant biosurfactants reduced biofilm biomass by 69 and 42 %, respectively. These data suggest that Rhs and plant-derived surfactants may have an important role in the inhibition of complex biofilms.     

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.     

Effects of Plasticizers and Plastic Coatings on Fungal Attack of Cotton Yarn

S ummary : The presence of PVC plasticizers inhibits fungal attack on cotton yarn to various extents. Some plasticizers apparently prevent attack of yarn by inhibiting fungal growth whilst others are utilized in preference to cellulose. The fungal penetration of plastic coated cotton yarn was enhanced by incorporating susceptible plasticizers. Attempts to relate attack on coated yarn by fungi to tolerance of more anaerobic conditions were only partly successful.     

Influence of Biosurfactants from Probiotic Bacteria on Formation of Biofilms on Voice Prostheses

Biofilms were grown on preconditioned voice prostheses with biosurfactants obtained from probiotic bacteria Lactococcus lactis 53 and Streptococcus thermophilus A in an artificial throat model. Both biosurfactants greatly reduced microbial numbers on prostheses and also induced a decrease in the airflow resistance that occurs on voice prostheses after biofilm formation. This study presents a promising strategy for prolonging the lifespan of voice prostheses.     

Role of Force-Sensitive Amyloid-Like Interactions in Fungal Catch Bonding and Biofilms

The Candida albicans Als adhesin Als5p has an amyloid-forming sequence that is required for aggregation and formation of model biofilms on polystyrene. Because amyloid formation can be triggered by force, we investigated whether laminar flow could activate amyloid formation and increase binding to surfaces. Shearing Saccharomyces cerevisiae cells expressing Als5p or C. albicans at 0.8 dyne/cm² increased the quantity and strength of cell-to-surface and cell-to-cell binding compared to that at 0.02 dyne/cm². Thioflavin T fluorescence showed that the laminar flow also induced adhesin aggregation into surface amyloid nanodomains in Als5p-expressing cells. Inhibitory concentrations of the amyloid dyes thioflavin S and Congo red or a sequence-specific anti-amyloid peptide decreased binding and biofilm formation under flow. Shear-induced binding also led to formation of robust biofilms. There was less shear-activated increase in adhesion, thioflavin fluorescence, and biofilm formation in cells expressing the amyloid-impaired V326N-substituted Als5p. Similarly, S. cerevisiae cells expressing Flo1p or Flo11p flocculins also showed shear-dependent binding, amyloid formation, biofilm formation, and inhibition by anti-amyloid compounds. Together, these results show that laminar flow activated amyloid formation and led to enhanced adhesion of yeast cells to surfaces and to biofilm formation.     

Structural and Functional Dynamics of Sulfate-Reducing Populations in Bacterial Biofilms

We describe the combined application of microsensors and molecular techniques to investigate the development of sulfate reduction and of sulfate-reducing bacterial populations in an aerobic bacterial biofilm. Microsensor measurements for oxygen showed that anaerobic zones developed in the biofilm within 1 week and that oxygen was depleted in the top 200 to 400 μm during all stages of biofilm development. Sulfate reduction was first detected after 6 weeks of growth, although favorable conditions for growth of sulfate-reducing bacteria (SRB) were present from the first week. In situ hybridization with a 16S rRNA probe for SRB revealed that sulfate reducers were present in high numbers (approximately 10⁸ SRB/ml) in all stages of development, both in the oxic and anoxic zones of the biofilm. Denaturing gradient gel electrophoresis (DGGE) showed that the genetic diversity of the microbial community increased during the development of the biofilm. Hybridization analysis of the DGGE profiles with taxon-specific oligonucleotide probes showed that Desulfobulbus and Desulfovibrio were the main sulfate-reducing bacteria in all biofilm samples as well as in the bulk activated sludge. However, different Desulfobulbus and Desulfovibrio species were found in the 6th and 8th weeks of incubation, respectively, coinciding with the development of sulfate reduction. Our data indicate that not all SRB detected by molecular analysis were sulfidogenically active in the biofilm.     

Bacterial Community Structure of Biofilms on Artificial Surfaces in an Estuary

This study examined bacterial community structure of biofilms on stainless steel and polycarbonate in seawater from the Delaware Bay. Free-living bacteria in the surrounding seawater were compared to the attached bacteria during the first few weeks of biofilm growth. Surfaces exposed to seawater were analyzed by using 16S rDNA libraries, fluorescence in situ hybridization (FISH), and denaturing gradient gel electrophoresis (DGGE). Community structure of the free-living bacterial community was different from that of the attached bacteria according to FISH and DGGE. In particular, alpha-proteobacteria dominated the attached communities. Libraries of 16S rRNA genes revealed that representatives of the Rhodobacterales clade were the most abundant members of biofilm communities. Changes in community structure during biofilm growth were also examined by DGGE analysis. We hypothesized that bacterial communities on dissimilar surfaces would initially differ and become more similar over time. In contrast, the compositions of stainless steel and polycarbonate biofilms were initially the same, but differed after about 1 week of biofilm growth. These data suggest that the relationship between surface properties and biofilm community structure changes as biofilms grow on surfaces such as stainless steel and polycarbonate in estuarine water.     

Effect of Pristine Multi-Walled Carbon Nanotubes on Formation and Degradation of Bacterial Biofilms

Microbiology - The effect of pristine multi-walled carbon nanotubes (MWCNT) on the biofilms of gram-negative bacteria, typical members of the activated sludge community, and gram-positive...     

Dynamics of Bacterial and Fungal Communities on Decaying Salt Marsh Grass

Both bacteria and fungi play critical roles in decomposition processes in many natural environments, yet only rarely have they been studied as an integrated microbial community. Here we describe the bacterial and fungal assemblages associated with two decomposition stages of Spartina alterniflora detritus in a productive southeastern U.S. salt marsh. 16S rRNA genes and 18S-to-28S internal transcribed spacer (ITS) regions were used to target the bacterial and ascomycete fungal communities, respectively, based on DNA sequence analysis of isolates and environmental clones and by using community fingerprinting based on terminal restriction fragment length polymorphism (T-RFLP) analysis. Seven major bacterial taxa (six affiliated with the α-Proteobacteria and one with the Cytophagales) and four major fungal taxa were identified over five sample dates spanning 13 months. Fungal terminal restriction fragments (T-RFs) were informative at the species level; however, bacterial T-RFs frequently comprised a number of related genera. Amplicon abundances indicated that the salt marsh saprophyte communities have little-to-moderate variability spatially or with decomposition stage, but considerable variability temporally. However, the temporal variability could not be readily explained by either successional shifts or simple relationships with environmental factors. Significant correlations in abundance (both positive and negative) were found among dominant fungal and bacterial taxa that possibly indicate ecological interactions between decomposer organisms. Most associations involved one of four microbial taxa: two groups of bacteria affiliated with the α-Proteobacteria and two ascomycete fungi (Phaeosphaeria spartinicola and environmental isolate “4clt”).     

Effects of Itraconazole and Micafungin on Aspergillus fumigatus Biofilms

Aspergillus fumigatus (A. fumigatus) is the most common airborne opportunistic fungal pathogen. Biofilm formation is one of the main pathogenic mechanisms of A. fumigatus. During the past decades, A. fumigatus azole resistance has become prevalent due to the medical and agricultural use of antifungal drugs and fungicides. Until now, the role of fungal biofilms in azole resistance of A. fumigatus remains unclear. In the present study, we compared biofilm drug susceptibility and biofilm formation under itraconazole of azole-resistant strains, sensitive strains, and standard strains, separately. The biofilm viability and matrix thickness at the early and the late stage were measured by XTT assay and Calcofluor white. Our results showed that the sessile minimum inhibitory concentration of itraconazole, which describing the inhibition of drugs on fungi sessile with biofilm, was much higher than the traditional minimal inhibitory concentration of itraconazole. Additionally, low concentrations of itraconazole inhibited biofilm formation of A. fumigatus strains. Notably, biofilm formation by azole-resistant strains could not be inhibited by high concentrations of itraconazole but could be effectively restrained by low concentrations of micafungin, revealing the efficacy of a cell-wall inhibitor to disrupt A. fumigatus biofilm formation. However, late-stage biofilms of both azole-resistant strains and standard strains were hard to disrupt using itraconazole. We found that itraconazole was effective to prevent A. fumigatus biofilm formation at the early stage. For the treatment of A. fumigatus biofilm, our findings suggest that an early-stage preventive strategy is preferred and micafungin is effective to control the azole-resistant strain infection.

     

羧甲基化壳聚糖季铵盐与牛血清白蛋白的相互作用研究

应用荧光光谱研究了羧甲基化壳聚糖季铵盐(CMCQA)与牛血清白蛋白(BSA)的相互作用.研究表明:CMCQA对BSA内源性荧光猝灭机制属于CMCQA和BSA形成复合物所引起的静态猝灭.在室温下,二者的结合常数为2.45×104 L/mol,结合位点数为1.04.二者主要靠静电引力相互作用.     

Stratification of Activity and Bacterial Community Structure in Biofilms Grown on Membranes Transferring Oxygen

Previous studies have shown that membrane-aerated biofilm (MAB) reactors can simultaneously remove carbonaceous and nitrogenous pollutants from wastewater in a single reactor. Oxygen is provided to MABs through gas-permeable membranes such that the region nearest the membrane is rich in oxygen but low in organic carbon, whereas the outer region of the biofilm is void of oxygen but rich in organic carbon. In this study, MABs were grown under similar conditions but at two different fluid velocities (2 and 14 cm s⁻¹) across the biofilm. MABs were analyzed for changes in biomass density, respiratory activity, and bacterial community structure as functions of biofilm depth. Biomass density was generally highest near the membrane and declined with distance from the membrane. Respiratory activity exhibited a hump-shaped profile, with the highest activity occurring in the middle of the biofilm. Community analysis by PCR cloning and PCR-denaturing gradient gel electrophoresis of 16S rRNA genes demonstrated substantial stratification of the community structure across the biofilm. Population profiles were also generated by competitive quantitative PCR of gene fragments specific for ammonia-oxidizing bacteria (AOB) (amoA) and denitrifying bacteria (nirK and nirS). At a flow velocity of 14 cm s⁻¹, AOB were found only near the membrane, whereas denitrifying bacteria proliferated in the anoxic outer regions of the biofilm. In contrast, at a flow velocity of 2 cm s⁻¹, AOB were either not detected or detected at a concentration near the detection limit. This study suggests that, under the appropriate conditions, both AOB and denitrifying bacteria can coexist within an MAB.     

The Effect of Shear on the Desorption of Liposomes Adsorbed to Bacterial Biofilms

Abstract

With the aid of a flow cell assembly the desorption of cationic liposomes prepared from mixtures of dipalmitoylphoshatidylcholine (DDPC), cholesterol, and either dimethyldioctadecylammonium bromide (DDAB) or 3,β[N-(N¹,N-dimethylethylenediamine)-carbamoyl]cholesterol (DC-chol) from immoblized biofilms of Staphylococcus aureus has been studied as a function of shear stress by confocal microscopy. A shear stress theory has been adapted from fluid mechanics of laminar flow between parallel plates and used to determine the critical shear stress for liposome desorption. The critical shear stress for both DDAB and DC-chol liposomes has been determined as a function of cationic lipid content and hence surface charge as reflected in their zeta potentials. The critical shear stress has been used to obtain the potential energy of liposome–biofilm interaction which together with the electrostatic interaction energy has enabled estimates of the London-Hamaker constants to be made. The values of the London-Hamaker constants at small liposome-bacterial cell separation were found to be independent of liposome composition.     

The Fungal and Bacterial Flora of Stored White Cabbage

1. The predominant organisms isolated from the outer wrapper leaves of freshly harvested white cabbages were: bacteria, yeasts, Alternaria spp., Aureobasidium pullulans, Botrytis cinerea, Cladosporium spp. and Penicillium spp.
2. Few qualitative or quantitative changes were seen in the leaf surface flora during storage at 2°C for up to 33 weeks.
3. Numbers of bacteria, particularly fluorescent and pectolytic pseudomonads, were considerably higher on cabbages drenched with fungicide or water than on corresponding undrenched cabbages.     

生牛奶中分离大肠杆菌对季铵盐类消毒剂耐药性研究

目的为调查牛奶中大肠杆菌Escherichia coli的污染状况和对常见季铵盐类消毒剂的耐药情况,为大型养殖场季铵盐类消毒剂的合理使用提供指导。方法对从74份生牛奶样品中分离的45株大肠杆菌采用琼脂稀释法测定4种季铵盐类消毒剂[十六烷基三甲基溴化铵(CTAB)、苯扎氯铵(BC)、双十烷基二甲基氯化铵(DDAC)、氯代十六烷基吡啶(CPC)]的最小抑菌浓度(MIC),采用PCR法检测10种消毒剂耐药基因,并分析其MIC值与耐药基因之间的相关性。结果大肠杆菌对4种消毒剂表现出不同程度的抗性,所检测的4种消毒剂对大肠杆菌的MIC值均大于标准菌株,且比例为BC=DDACCTABCPC。大肠杆菌季铵盐类消毒剂的耐药基因检出率为ydgF(84.44%)ydgE(80.00%)sugE(c)(66.67%)emrE(40.00%)mdfA(37.78%)qacEΔ1(33.33%)qacE(17.78%)qacF(13.33%)qacG(11.11%)sugE(p)(4.44%)。分析大肠杆菌消毒剂基因检出情况与MIC值之间的关系发现,qacF基因的检出率与128 mg·L~(-1)的CPC之间差异有统计学意义。结论由此可见,牛奶中存在大肠杆菌污染严重的现象对季铵盐类消毒剂耐药情况不容乐观,需进一步规范季铵盐类消毒剂的使用。     

The Occurrence and Persistence of Mixed Biofilms in Automobile Air Conditioning Systems

Twelve automobile air conditioner systems from six manufacturers and three countries, selected mostly because of complaints of unpleasant odors in the passenger compartment, were examined for microbial growth by direct microscopy and enrichment culture. Mixed populations of fungi and bacteria (with occasional protozoa) were observed in biofilms in at least some of the components from all used units. The aluminum heat exchanger fins from ten evaporators demonstrated bacterial biofilms that yielded Methylobacterium mesophilicum. Penicillium viridicatum colonized components from four units. These bacteria and fungi were recoverable repeatedly from these units during ‘dry’ storage of up to 27 months. This report associates a bacterial-fungal community with disagreeable air quality in some automobiles. Received: 24 March 1999 / Accepted: 13 April 1999