Absence Of Microorganisms Research Articles

A comparison of mesophilic composting and unamended land treatment for the bioremediation of aged tar residues in soil

AbstractA field study was conducted to compare the effectiveness of land treatment and mesophilic composting in removing aged polycyclic aromatic hydrocarbons (PAH) from soil. The soil composting treatment, which had 20 percent (w/w) fresh organic matter incorporated into the soil, reached mesophilic temperatures of 45 to 50°C at week 3–4 and was effective in reducing PAH from 2240 mg/kg to 120 mg/kg after 224 days of treatment. Conventional land treatment with and without added cow manure (5 percent w/w) was less effective in removing the PAH from the soil than was the mesophilic soil composting treatment. In a parallel laboratory trial, PAH concentrations were reduced below 500 mg/kg (the target cleanup concentration for the site) when the contaminated soil was amended with 20 to 30 percent (w/w) fresh organic matter after 186 days of treatment. PAH degradation was lower in the laboratory trial compared with the field trial and no self‐heating of soil was demonstrated in the laboratory. Based on the relatively high total heterotrophic and naphthalene‐degrading microbial populations in the nonsterile treatments, it was apparent that the absence of microorganisms was unlikely to have limited the biodegradation of PAH in the current study. Fresh organic matter amendments of green tree waste and cow manure, regular mixing of the compost, and maintenance of moisture by regular watering were critical factors in achieving the target PAH concentrations.

Factors affecting the biodegradation of phenanthrene initially dissolved in different nonaqueous‐phase liquids

AbstractA study was conducted of the importance of measured partitioning rate, the nonaqueous‐phase liquid (NAPL)–water interfacial area, and the toxicity of NAPLs to the biodegradation of constituents of NAPLs. Bacterial mineralization of phenanthrene was slower if the compound was initially dissolved in phthalate esters than in aliphatic hydrocarbons with several NAPL–water interfacial areas. The differences were not the result of toxicity of the test NAPLs. The rates of partitioning of phenanthrene from NAPLs to water were faster with larger interfacial areas, but a consistent influence of interfacial area on the rate of mineralization was not evident. The measured rates of partitioning from NAPLs to water under sterile conditions varied among the NAPLs, the mass transfer rates being slower with phthalate esters than with alkanes. The rates of mineralization of phenanthrene initially in NAPLs were correlated with measured partitioning rates, but the rates of biodegradation were sometimes faster than the partitioning rates measured under sterile conditions. Although the rates of biodegradation of a constituent of nontoxic NAPLs are generally related to rates of mass transfer determined under sterile conditions, we suggest that the partitioning rate determined in the absence of microorganisms is not an adequate predictor of the maximum rate of biodegradation of such constituents.

Enhancement of gas-liquid mass transfer rate of apolar pollutants in the biological waste gas treatment by a dispersed organic solvent

Dispersed water-immiscible solvents are known to enhance oxygen transfer rates in oxygen-limited aerobic fermentations. Here, this technique is applied to improve the mass transfer rate of poorly water-soluble gaseous pollutants during the biological treatment of waste gases. In a stirred-tank reactor, the enhancement of mass transfer rates was studied as a function of the pollutant solubility in water. The solvent used was FC40 (up to 10% v/v) and the model gaseous pollutants were toluene and oxygen (moderately and poorly water-soluble, respectively).The overall volumetric mass transfer coefficient from the gas to the bulk liquid (klagl) was measured under nonsteady-state conditions in the absence of micro-organisms. It was found to be essentially constant for the solvent volume fractions tested and for both toluene and oxygen. Using the values of klagl and the partition coefficient gas/liquid (mgl), the enhancement of the mass transfer rate by solvent addition could be predicted theoretically. A good agreement between the theoretical evaluation and the experimental results from experiments in the presence of biological consumption was observed. An enhancement of the mass transfer rate by a factor of 1.1 was found for toluene using a dispersion containing 10% (v/v) FC40 while the oxygen transfer rate increased by a factor of two at the same solvent volume fraction. It was further demonstrated theoretically for other gaseous compounds that the addition of solvent has a more pronounced effect on the enhancement of the transfer rate in the case of poorly water-soluble compounds compared to moderately water-soluble ones.

Quantification of the presence and activity of specific microorganisms in nature.

Traditional techniques for assessment of microbial numbers and activity generally lack the specificity required for risk assessment following environmental release of genetically engineered microbial inocula. Immunological and molecular-based techniques, such as DNA probing and genetic tagging, were initially used to determine the presence or absence of microorganisms in environmental samples. Increasingly they are being developed for quantification of populations of specific organisms, either indigenous or introduced, in the environment. In addition, they are being used to quantify the activity of particular organisms or groups of organisms, greatly extending the range of techniques available to the microbial ecologist. This article reviews the use of traditional techniques for the quantification of microbial population size and activity and the application of molecular techniques, including DNA probing, genetic marking, use of fluorescent probes, and quantitative PCR, in combination with advanced cell detection techniques such as confocal laser scanning microscopy and flow cytometry.

COPE elimination reaction observed in the biodegradation of quaternary ammonium surfactants

The biodegradation of dialkyldimethylammonium compounds in aqueous solutions indicates that part of the degradation pathway includes the Cope elimination reaction, which does not occur under mild conditions in the absence of microorganisms.

Enhancement of the gas-to-water ethene transfer coefficient by a dispersed water-immiscible solvent: effect of the cells

For a mass-transfer-limited system, it was demonstrated that the volumetric ethene transfer coefficient (k l a) from gas to water could be enhanced by dispersing adequate amounts of a water-immiscible organic liquid, namely the perfluorocarbon FC40, in the aqueous phase. When 26% (v/v) FC40 was dispersed in a culture of Mycobacterium parafortuitum an enhancement of k l a, calculated on a total liquid volume basis, of 1.8 times was found. Steady-state experiments in the absence of microorganisms, however, showed a 1.2-fold enhancement of k l a at 18.5% (v/v) FC40. At all FC40 volume fractions tested, enhancement factors with cells were higher than enhancements without cells; apparently the microorganisms or their excretion products affected the interfacial areas or characteristic phase dimensions.

Physical factors negatively affecting evaluation of long-term biodegradation experiments of polychlorinated biphenyls

Behaviour of PCB added in the form of a technical mixture (Delor 106) and [ 14C]PCB 77 into different aqueous model cultivation media in long-term experiments was studied. The work was focused on monitoring PCB recovery from liquid media in the absence of micro-organisms. GC-ECD and radioanalysis were utilised for determination of PCB in the examined systems. Strong relations between duration of experiments, composition of media, degree of chlorination of biphenyls, and recovery of PCB were found. The lowest yields of PCB were observed for the extracts from model solutions based on N-limited cultivation media without veratryl alcohol and Tween 80. The addition of these components, mainly of Tween 80, caused a significant increase of PCB recoveries.

Biobeneficiation of bauxite using Bacillus polymyxa: calcium and iron removal

Calcium and iron removal from a bauxite ore by Bacillus polymyxa has been demonstrated. Within a period of 7 days, the above organism could remove all the calcium and about 45% of iron from the ore in the presence of 2% sucrose in a Bromfield medium. The highest removal of calcium and iron corresponded with the maximum in extracellular polysaccharide production by the organism. Scanning electron microscopy of the biobeneficiated bauxite surfaces indicated tenacious attachment of the bacteria onto the ore particle. Some calcium and iron removal was observed even in the presence of bacterial metabolites such as polysaccharides, organic acids and slime. However, the calcium removal in the absence of microorganism (by metabolites alone) was found to be 50% of that obtained in its presence. These observations clearly indicate that both a direct mechanism through bacterial attachment to the ore and an indirect mechanism through leaching with metabolites are involved in the biobeneficiation process.

Bioregeneration of powdered activated carbon (PAC) loaded with aromatic compounds

Bioregeneration of powdered activated carbon (PAC) loaded with aromatic compounds was quantitatively determined using carbon dioxide production as a measure of substrate consumption. Two types of powdered activated carbon (one chemically activated, wood-based carbon, CA1, and one thermally activated, peat-based carbon, SA4) and two aromatic compounds ( o-cresol and 3-chlorobenzoic acid) in single solute batch systems were used. Interaction of EDTA, present as chelating agent in all experiments with o-cresol as substrate, and SA4 resulted in abiotic CO 2 production (in absence of microorganisms). The extent of bioregeneration varied considerably, from 15 to 85% of total PAC loading, depending on type of PAC used and compound involved and, in one case, on the time of contact between PAC and the compound. The results revealed that the data corresponded with a mechanism of bioregeneration where desorption precedes biodegradation. Microorganisms reduced the dissolved compound concentration, forcing desorption and subsequent biodegradation, but were unable to influence the desorbability of the PAC-sorbed compounds. The practical applicability of the results is discussed.

Roles of bacterial attachment and spontaneous partitioning in the biodegradation of naphthalene initially present in nonaqueous-phase liquids.

The mineralization by an Arthrobacter sp. of naphthalene initially dissolved in di(2-ethylhexyl)phthalate exhibited a slow phase followed by a rapid phase. Triton X-100, which inhibited cell attachment, prevented the onset of the second phase. Triton X-100 increased the extent of mineralization of naphthalene initially present in 2,2,4,4,6,8,8-heptamethylnonane. Cells attached to the interface mineralized the aromatic hydrocarbon at a rate four times higher than the rate of partitioning in the absence of microorganisms, but this microbial activity was markedly reduced by Triton X-100. We suggest that utilization of naphthalene originally present in nonaqueous-phase liquids may involve a partitioning-limited initial stage carried out by bacteria freely suspended in the aqueous phase and a subsequent, more rapid stage effected by bacteria present directly at the nonaqueous-liquid-water interface.

Reactivity of aquatic iron(III) oxyhydroxides—implications for redox cycling of iron in natural waters

The reactivity of iron(III) oxyhydroxides as reflected by their tendency to dissolve is of great importance in the redox cycling of iron and the bioavailability of iron to phytoplankton in natural waters. In this study, various iron(III) oxyhydroxides were produced by oxygenation of iron(II) in the presence of solutes, such as phosphate, sulfate, bicarbonate, valeric acid, TRIS, humic and fulvic acids, and in the presence of minerals, such as bentonite and δ-Al 2O 3 under conditions encountered in aquatic systems. The reactivity of the different iron(III) oxyhydroxides was subsequently assessed by means of a reductive dissolution using ascorbate and non-reductive dissolution using HQS (8-hydroxyquinoline-5-sulfonic acid) or oxalate. The experimental results show that the iron(III) oxyhydroxides with a low degree of polymerization exhibit higher reactivity than those with a high degree of polymerization or with high crystallinity. The quantity of active surface sites and the coordination arrangement of the functional groups at the surface of the iron(III) oxyhydroxides, especially the extent of the endstanding -OH groups per iron(III) ion determine the reactivity of iron(III) oxyhydroxides toward dissolution. Surfaces, such as clay and aluminum oxides, not only accelerate the oxygenation reaction of iron(II), but also induce the formation of iron(III) oxyhydroxides which are more active toward the dissolution reactions. Polymerization of iron(III) oxyhydroxides on the surfaces occurs predominantly in two dimensions rather than in three dimensions. In a laboratory experiment, the iron(III) oxyhydroxide formed in the presence of TRIS can be reduced by fulvic acid in a closed system under the following conditions: Fe(OH) 3(s) 0.01 g/l, fulvic acid 5 mg/l, pH 7.5, 20°C. The kinetics of the reaction depend on the reactivity of iron(III) oxyhydroxide and reducing power of fulvic acid. Although reductants other than fulvic acid may be of importance in antural waters, this result provides the laboratory evidence that the >Fe III-OH/Fe(II) is able to act as an electron transfer mediator for the oxidation of natural organic substances, such as fulvic acid, by molecular oxygen either in the absence of microorganisms or as a supplement to microbial activity.

Kinetics of redox cycling of iron coupled with fulvic acid

The kinetics of conversion of iron(III) (hydr)oxides to ferrous iron mediated by fulvic acid have been investigated in order to improve the understanding of the redox cycling of iron at the oxic-anoxic boundary in natural waters. Under the conditions similar to natural waters, fulvic acid is able to reduce the iron(III) (hydr)oxide. The kinetics of the reaction depend on the reactivity of iron(III) (hydr)oxides and the reducing power of the fulvic acid. The rate of reaction is 60 nm/h obtained under following conditions: total concentration of Fe(III) 1.0 × 10−4 M, pH 7.5, fulvic acid 5 mg/L. The rate is considered as a net result of reduction and oxidation in the > FeIII-OH/Fe(II) “wheel” coupled with fulvic acid. In a real natural water system, reductants other than fulvic acid may be of importance. The results obtained in the laboratory, however, provide evidence that the Fe(OH)3(s)/Fe(II) redox couple is able to act as an electron-transfer mediator for the oxidation of natural organic substances, such as fulvic acid by molecular oxygen either in the absence of microorganisms or as a supplement to microbial activity.

Kinetics of quinoline biodegradation, sorption and desorption in a clay-coated model soil containing a quinoline-degrading bacterium

Kinetics of quinoline biodegradation, sorption and desorption in a clay-coated model soil containing a quinoline-degrading bacterium. Studies were initiated to compare the kinetics of quinoline sorption/desorption and biodegradation in order to predict the relative importance of abiotic and biotic processes in the transport of quinoline in columns containing a model soil. Initial biodegradation studies were conducted in a 1-cm-long column containing a quinoline-degrading bacterium (10 9 colony-forming units g −1 porous medium) attached to 100- to 150-μm-diameter glass beads that did not sorb quinoline. At a 155-nmol mL −1 quinoline influent concentration, the maximum consumption rate was 104.7 nmol quinoline min −1 cm −3 pore volume. In contrast, the maximum consumption rate of the first metabolite ( 2-hydroxyquinoline) was 24.8 nmol mL −1 cm −3 pore volume. In a second experiment, bacteria were mixed with a model soil, consisting of montmorillonite bound to alumina particles (75- to 180-μm diameter). In a 1-cm-long column of the model soil, the quinoline consumption rate at a 155-nmol mL −1 quinoline influent concentration was similar to that obtained in the glass-bead column, showing that the clay does not substantially affect quinoline biodegradation at equilibrium conditions. In a third series of experiments, sorption to the model soil was examined in the absence of microorganisms. The observed desorption rate coefficient for quinoline averaged 1.1·10 −3 s −1, which was one to three orders of magnitude smaller than was observed for 45Ca. The slow ion exchange of quinoline on the clay surface is controlled by a site-specific quinoline/montmorillonite interaction and not a larger-scale physical step (i.e. interparticle diffusion). Equilibrium first-order forward (sorption) and reverse (desorption) mass fluxes were 1160 nmol cm −1 cm −3 pore volume with a 155-nmol mL −1 quinoline influent concentration. The initial quinoline mass flux to the clay was estimated as 31,800 nmol cm −1 cm −3 pore volume. Thus, under the experimental conditions, the net rate of decrease of solution-phase quinoline is greater through abiotic processes than through biodegradation. Coefficients obtained from the individual sorption and biodegradation experiments were used in a sorption/biodegradation transport model to quantify any sorption/biodegradation interactions. Breakthrough of quinoline occured more rapidly in the sorption/biodegradation experiments, indicating substantially less sorption compared to sorption experiments. Quinoline sorption was reduced a small amount due to competitive sorption between quinoline and 2-hydroxyquinoline (biodegradation intermediate), but this effect was too small to account for the substantial decrease in quinoline sorption. Experimental and calculated estimates of biomass coverage on the particles also accounted for some decrease in quinoline sorption, but not the large decrease observed. Therefore other, undefined, processes may contribute to the observed sorption/biodegradation interaction.

Salivary film formation on defined solid surfaces in the absence and presence of microorganisms

A salivary derived proteinaceous film will condition any surface exposed in the oral cavity prior to cell attachment. Studies have shown a strong correlation between the initial surface properties of a material and its cell retaining capacity, indicating that a mechanism may exist by which surface characteristics of a solid are transmitted through the adsorbed film. The aim of this study was to monitor the film organization of salivary secretions at defined liquid‐solid interfaces, and to evaluate the effect of the critical surface tension and the presence of microorganisms on the packing of the films. Fresh secretions from human parotid (HPS) and submandibular‐sublingual glands (HSMSL) were allowed to form thin films on surfaces of low and medium critical surface tensions under controlled flow conditions, in the presence and absence of microorganisms. Two strains of Streptococcus salivarius and Streptococcus sanguis were used as test microorganisms. The resulting films were monitored in situ by nondestru...

Effect of longitudinal mixing on microbial growth in a multi‐stage column bioreactor

AbstractThe performance of a multi‐stage column bioreactor for nonlimited microbial growth was studied. The back‐flow model was employed to describe the flow pattern of the microbial suspension. Analytical solutions for calculating the microbial cell concentrations under steady‐state and unsteady‐state operations, with and without cells in feed, were obtained and the cell growth behavior was examined. Only when microbial cells were present in the feed and the reaction number was less than a critical number was a stable steady state achieved: the microbial cell concentration was then significantly affected by the extent of longitudinal mixing. In the absence of microorganisms in the feed, the steady state was not stable with either washout or nonlimited growth resulting.

Side Effects of Antibiotics on Immune Response Parameters and their Possible Implications in Antimicrobial Chemotherapy

Antibiotics may influence immune response by quite different ways. By screening the multitude of publications on this subject, the aim of this overview was to arrive at a basic generalizing statement on the relationship between chemical structure or mode of action of antibiotics and the effect on immune response and to get an indication on whether certain in vitro and/or ex vivo parameters could represent comparable effects under clinical conditions. - The influence of antibiotics on immune response may arise by direct effects on immunocompetent cells, i.e. in the absence of microorganisms, or indirectly by changes in structure or metabolic products of germs induced by subminimal inhibitory concentrations (subMIC's). In the former case, stimulatory and inhibitory effects have been observed on phagocytosis and intracellular killing activity, on antibody production including IgE, on different parameters of cellular immunity (e.g. foodpad swelling reaction, MIF-production, mitogen/antigen induced lymphocyte proliferation and delayed type hypersensitivity skin reaction), on mediator production as interleukins or prostaglandins and the expression of corresponding receptors on immunocompetent cells as well as on the course of experimental infections with primary resistant microorganisms. - Indirect effects are related to the influence of subMIC's of antibiotics on the morphology and structure of microorganisms, on their antigenicity/immunogenicity or on their serosensitivity and enzyme and toxin production. - This overview shows that - according to the actual knowledge - antibiotics may exhibit immunological side effects which, however, can not strictly be attributed to certain chemical structures or to a certain mode of action. - It has to be considered that a literary study comparing the results of different authors is rendered difficult by the often nonhomogeneity of experimental procedures and the fact that little is known yet about immunological side effects of antibiotics in man, i.e. under clinical conditions.

Rates of dissolution and biodegradation of water-insoluble organic compounds.

We conducted a study of the relationship between the dissolution rates of organic compounds that are sparingly soluble in water and the biodegradation of these compounds by mixed cultures of bacteria. The rates of dissolution of naphthalene and 4-chlorobiphenyl were directly related to their surface areas. The bacteria caused a decline in the concentration of the soluble substrate. The rate of bacterial growth fell abruptly when 4-chlorobiphenyl or naphthalene was no longer detectable in solution. The population continued to increase in media with different surface areas of insoluble 4-chlorobiphenyl, but the final counts were higher in media in which the surface areas of the substrate were larger. The rates of dissolution of palmitic acid, octadecane, di(2-ethylhexyl) phthalate, and 1-naphthyl N-methylcarbamate were determined in the absence of microorganisms. A mixed culture of microorganisms mineralized palmitic acid, di(2-ethylhexyl) phthalate, and Sevin (1-naphthyl N-methylcarbamate) at a logarithmic rate, but octadecane mineralization was linear. The rates of mineralization at the end of the active phase of the biodegradation were lower than the rate of dissolution of palmitic acid but higher than the rate of dissolution of octadecane in the uninoculated medium. We suggest that spontaneous dissolution rates are only one of the factors that govern the rates of biodegradation.

Bacteria beneath composite restorations—a culturing and histobacteriological study

The occurrence, viability and identification of the microbial flora under composite fillings using an anaerobic technique were studied. Class V cavities were prepared on clinically healthy buccal surfaces of 7 contralateral pairs of premolars in children 11--15 years of age. After preparation, rubber dam was applied and one cavity in each pair of teeth was washed with water blasted dry with air and filled with Adaptic. The other cavity was washed with a cavity cleaner (Tubulicid) and a cavity liner (Tubulitec) was applicated prior to filling with Adaptic. The teeth were extracted after 4--6 weeks. Under anerobic conditions the tooth crown was split. From one half samples were taken from the pulpal wall under the filling and cultured on blood agar and in broth medium. The other half was examined with histobacteriological technique. No growth occurred in cultures from lined cavities but in 6 of the 7 unlined cavities. Full agreement was observed between the findings from the culturing and histobacteriological examinations concerning presence or absence of microorganisms at the pulpal wall in all 14 teeth. The flora was mixed. Gram-positive bacteria, mainly Streptococcus and Actinomyces, dominated over gram-negative bacteria including Veillonella, Fusobacterium, Campylobacter and Selenomonas. The composition of the flora was more similar to that observed in dental plaque than that found in carious dentin or in saliva in other studies.

Absence of Microorganisms in Crustacean Digestive Tracts

Two marine and one terrestrial wood-boring isopod species and one wood-inhabiting amphipod species maintain a digestive tract free of microorganisms. Digestive tracts examined in toto with the scanning electron microscope were devoid of microorganisms. In contrast, the outer exoskeleton surfaces of these crustaceans support a dense bacterialflora. Observations of the hindgut of termites revealed a diverse gut microflora as expected.

Microbial growth in the rhizosphere

Barley plants were grown for up to 16 days in solution culture either under axenic conditions or in the presence of a mixed population of microorganisms. The quantities of soluble carbohydrate released by the roots grown in the absence of microorganisms and the numbers of bacteria which developed in the inoculated solutions were determined. Except for the first 4 days after germination, a greater biomass was produced than could be accounted for by the utilization of the carbohydrates released by the roots grown in the absence of microorganisms; this supports the view that the microorganisms stimulate the loss of soluble organic materials. These results are considered in relation to microbial activity in the soil and in particular to the significance of N 2 fixation by free-living rhizosphere bacteria in the nitrogen economy of plants.