Biodegradation of methyl parathion in the presence of goethite: The effect of Pseudomonas sp. Z1 adhesion

In this research, the influence of goethite on biodegradation kinetic of methyl parathion was investigated in the presence of Pseudomonas sp. Z1. Semipermeable membrane experiments were performed to demonstrate the role of adhesion of degrading bacteria to surface of goethite in biodegradation of methyl parathion. Sorption of methyl parathion and bacteria onto goethite particles were also measured to assess the distribution of methyl parathion and bacteria between water and goethite surface. The first-order degradation rate constant of methyl parathion in different concentrations of goethite was in the order of 0.1 g L⁻¹ > 0.01 g L⁻¹ > 0 g L⁻¹ > 1 g L⁻¹ > 20 g L⁻¹, suggesting the presence of low concentrations of goethite accelerated the biodegradation of methyl parathion and high concentrations of goethite inhibited this biodegradation process. According to the result of semipermeable membrane experiment, when no bacterial attachment occurred in the system, the promotive effect of 0.1 g L⁻¹ goethite for microbial degradation was disappeared and the inhibition effect of 20 g L⁻¹ goethite increased. The results clearly demonstrated that the adhesion of bacteria to goethite was beneficial to the biodegradation of methyl parathion. The information obtained is of fundamental significance for the understanding of microbial degradation of organic pollution in soil.     

Soil Colloids and Minerals Modulate Metabolic Activity of Pseudomonas putida Measured Using Microcalorimetry

Substantial interactions of microbes with soil particles present fundamental influences on microbial activities relevant to a series of biogeochemical processes. However, how soil surface-active particles modulate microbial metabolism has received scant attention. The extent to which composition of soil colloids alter the metabolism is not well addressed. This work examined the impacts of soil colloids and minerals on the metabolic activity of Pseudomonas putida using microcalorimetry and carbon utilization. The results showed that montmorillonite remarkably improved metabolic activity of P. putida, whereas kaolinite, goethite and soil colloids significantly inhibited the activity. Humus may weaken the inhibition of soil colloids on bacterial metabolism via interfacial interaction rather than nutrient supplements. Soils bearing higher amount of kaolinite and iron oxide may have greater depression on bacterial activity. The thermodynamic method provides different and complementary information to that from other techniques in characterizing microbial activities. The quantity and affinity for the adhesion of bacteria onto soil components together with the detoxification of metabolites were assigned to the modifications of bacterial activities.     

Interaction of anoxygenic phototrophic bacteria Rhodopseudomonas sp. with kaolinite

The interaction between freshwater nonsulfur purple bacteria Rhodopseudomonas sp. UZ-25p (Uzon caldera, Kamchatka, Russia) and two kaolinite samples (Zhuravlinyi Log, Chelyabinsk oblast) was investigated. Alterations in the chemical composition of the minerals and solutions, the parameters of bacterial growth, and crystal morphology and mineralogy of the kaolinite samples indicated the interactions between all components of the system (minerals, water, growth medium, and bacteria). Bacteria removed some elements from the medium, used them for growth, and promoted their transition into the mineral exchange pool. In the presence of bacteria, kaolinite cation exchange capacity increased and saturation of kaolinites with bases occured. Partial biodegradation of kaolinites, accompanied by ordering of the crystalline structure of their lamellar phase, was the main factor responsible for the increase in cation exchange capacity. For the first time anoxygenic phototrophic bacteria were found to degrade kaolinite with formation of gibbsite. The theoretical and applied significance of the experimental results is discussed.     

Adsorption of DNA by Bacteria and Their Composites with Minerals

Previous studies revealed the thermodynamic properties of DNA adsorption on pure minerals or biomasses; however, there has been little attempt to develop such studies on bacteria–mineral composites. Equilibrium adsorption experiments, attenuated total reflectance Fourier transform infrared spectroscopy, and isothermal titration calorimetry were employed to investigate the adsorption of DNA by Bacillus subtilis, Pseudomonas putida, and their composites with minerals. Similar capacity and affinity were observed for DNA adsorption on two bacterial cells. However, different patterns were found in the adsorption of DNA by bacteria–mineral composites. The Gram-positive bacterium B. subtilis enhanced the adsorption of DNA on its mineral composites compared with their individual components, while the composites of Gram-negative bacterial cells with kaolinite and goethite bound lower amounts of DNA than the predicted values. The thermodynamic parameters and the Fourier transform infrared spectra showed that van der Waals force and hydrogen bonding are responsible for the DNA adsorption on B. subtilis–minerals and P. putida–kaolinite. By contrast, the entropy increases of excluded water rearrangement and dehydration effect play key roles in the interaction between DNA and P. putida–montmorillonite/goethite composites.     

Effects of Solution Chemistry on Bacterial Adhesion with Phyllosilicates and Goethite Explained by the Extended DLVO Theory

Adhesion of Bacillus subtilis on kaolinite, montmorillonite, and goethite was investigated over a wide range of ionic strength (IS) and pH using batch experiment. The related surface properties (size, zeta potential, and hydrophobicity) under varying conditions were systematically determined and the interaction energy between the cell and minerals were calculated using the extended Derjaguin, Landau, Verwey, and Overbeek (ExDLVO) theory. Adhesion on kaolinite and montmorillonite increased with IS at low level (< 0.01 mol L^?1 MgCl₂) but declined at high IS level. An increase in IS generally depressed bacterial adhesion on goethite. Elevated pH resulted in decreasing the adhesions on all three minerals. The IS- and pH-effects on adhesion for phyllosilicate systems followed the ExDLVO predictions. For goethite systems, this theory predicted the adhesion trend with IS and that under basic pH, but failed to explain the adhesion at low pH. Such deviation from the theory possibly resulted from chemical interactions between extracellular polymeric substances on cell surface and goethite. These results imply that bacterial adhesions on phyllosilicates are primarily governed by the ExDLVO interactions, and those on iron oxides are mediated by the combination of ExDLVO and non-ExDLVO interactions.     

Transmission Electron Microscopic Observation of Mercury-Bearing Bacterial Clay Minerals in a Small-Scale Gold Mine in Tanzania

Mercury is a toxic substance that is widely distributed throughout the hydrosphere, biosphere, and lithosphere. Mine waste environments and mine waters support a wide diversity of microbial life. The microbial ecology of environments where mine waters are polluted with heavy metals is poorly understood. Here, we describe the features of bacteria in mercury-contaminated gold panning ponds in a small-scale gold mine (Geita) near Lake Victoria, Tanzania using energy filtering transmission electron microscopy (EF-TEM) and scanning transmission electron microscopy equipped with energy dispersive X-ray spectroscopy (STEM-EDX). Most bacteria in the panning pond showed thick exopolysaccharides (EPSs), and many clay minerals attached onto the surface of EPSs. The clay minerals and EPSs might act as protective layers for the bacteria against toxic materials. The clay minerals were composed of smectite, halloysite, and kaolinite associated with calcite and goethite. Scanning electron microscopy equipped with energy dispersive X-ray spectroscopy indicated that the bulk soil samples contained abundant Si, Al, K, Ca, and Fe with heavy metals such as Au, Ti, and Ag. The results indicate that Hg pollution from panning ponds is caused by not only volatilization of Hg from Au-Hg amalgams, but Hg is also released into the air as dust mixed with dry fine clays, suggesting high long-term environmental risks. Mercury-resistant bacteria associated with clay minerals may have a significant effect on the weathering processes of the ore during long-term bioremediation. The clay mineral complexes on the surface of bacterial cell walls are a stimulator for Hg-resistant bacterial growth in mud ponds contaminated with the Au-Hg materials.     

Use of bacteria-immobilized cotton fibers to absorb and degrade crude oil

Using enrichment culture technique, two isolates that brought a significant degradation and dispersion of crude oil were obtained from contaminated sediments of the Bohai Bay, China. 16S rRNA gene sequencing and phylogenetic analysis indicated that the two bacterial strains affiliated with the genera Vibrio and Acinetobacter. Subsequently, the bacterial cells were immobilized on the surface of cotton fibers. Cotton fibers were used as crude oil sorbent as well as a biocarrier for bacteria immobilization. Among the two isolates, the marine bacteria Acinetobacter sp. HC8-3S showed a strong binding to the cotton fibers, possibly enhanced through extracellular dispersant excreted by Acinetobacter sp. HC8-3S. Both planktonic and immobilized bacteria showed relatively high biodegradation (>60%) of saturated hydrocarbons fraction of crude oil, in the pH range of 5.6–8.6. The degradation activities of planktonic and immobilized bacteria were not affected significantly when the NaCl concentration reached 70 g/L. The immobilized bacterial cells exhibited an enhanced biodegradation of crude oil. The efficiency of saturated hydrocarbons degradation by the immobilized bacterial cells increased about 30% compared to the planktonic bacterial cells.     

The adaptation responses of bacterial cytoplasmic membrane fluidity in the presence of environmental stress factors — polychlorinated biphenyls and 3-chlorobenzoic acid

Only bacteria sufficiently resistant to the toxic compounds in their environment can be used for the efficient biodegradation process in order to eliminate a widespread contamination by polychlorinated biphenyls (PCBs). The presence of PCBs results in bacterial controlled rigidification of cytoplasmic membrane. The four bacterial isolates from long-term PCB-contaminated soil (Alcaligenes xylosoxidans, Pseudomonas stutzeri) and sediment (Ochrobactrum anthropi, Pseudomonas veronii) have been used to select the strain most adapted to the PCBs, i.e. with efficient changes in the membrane phospholipid fatty acids. PCBs and their toxic degradation products — the 3-chlorobenzoic acids (3-CBA as the most toxic one) — were added separately to the liquid medium with glucose in two experimental sets: at lag phase and in stationary phase of bacterial growth in order to evaluate the effects of chemicals to cytoplasmic membrane. The main parameter — the changes in fatty acids composition (in the total lipids and the main membrane phospholipid phosphatidyletanolamine) were studied. 3-CBA caused growth inhibition when added at lag phase. However, when added during the stationary growth, inhibition was not observed. Similarly, after addition of PCBs to the stationary growth culture, inhibition of growth was not observed with all tested strains (except for P. stutzeri). This fact indicates the importance of time contact of bacteria during growth phase with xenobiotics. O. anthropi and A. xylosoxidans appeared to be the most adapted to the presence of PCBs (with sufficient membrane adaptation), active under the adverse conditions, and able to survive in the contaminated environment.     

Aerobic degradation of adamantanes at highly acidic conditions

Biodegradation of alkyl-substituted adamantane derivatives (1-methyl, 1,3-dimethyl-, and 1,3,5-trimethyladamantane) by slow-growing bacteria Mycobacterium AG_S10 was studied. The process was carried out under extremely acidic conditions (pH 2.5). Bacterial strain AG_S10 was able to utilize these alicyclic hydrocarbons with a high degree of condensation and diamond-like structure, which are usually resistant to microbial transformation. Efficiency of alkyaldamantane biodegradation by the cells growing with these substrates as the sole carbon and energy sources was affected significantly by their aggregate state, which depended on molecular structure. Compared to the solid 1-methyladamantane, 1,3-dimethyladamantane, which is liquid under normal conditions, was a preferable substrate. Adamantanes in the gas condensate were generally more resistant to bacterial degradation than such markers as normal and isoprenoid alkanes. Moreover, biodegradation had no significant effect on relative distribution of the tested С₁₁–С₁₃ alkyladamantanes.     

Effects of Temperature,pH and Salt Concentrations on the Adsorption of Bacillus subtilis on Soil Clay Minerals Investigated by Microcalorimetry

Adsorption of microorganisms on minerals is a ubiquitous interfacial phenomenon in soil. Knowledge of the extent and mechanisms of bacterial adsorption on minerals is of great agronomic and environmental importance. This study examined adsorption of Bacillus subtilis on three common minerals in soils such as kaolinite, montmorillonite and goethite under various environmental conditions. Isothermal titration calorimetry (ITC) was used to investigate the effects of temperature (20, 30, and 40°C), pH (5.0, 7.0, and 9.0) and KNO₃ concentration (0.001, 0.01, and 0.1 mol L^?1) on the adsorption by direct measurement of enthalpies. The results revealed that the adsorption process in all the mineral systems were exothermic, with the enthalpy changes (ΔH_ads ) ranging from ?52 to ?137, ?33 to ?147, and ?53 to ?141 kJ kg^?1 (dry weight of adsorbed bacteria) for kaolinite, montmorillonite, and goethite, respectively. No obvious dependence of ΔH_ads on temperature was observed. The heat release for all the systems generally declined with pH and decrease of salt concentration, which can be explained by the variations of hydrophobicity and electrostatic force with pH or salt concentration. The largest decrease was found for goethite among the three minerals from pH 5.0 to 7.0, suggesting that electrostatic attraction may play a more important role in bacterial adsorption on this mineral. The ΔH_ads values for all the minerals became nearly the same at pH 9.0, indicating that the same force probably hydrophobicity governing the adsorption for the minerals in alkaline environment. It is assumed that acidic or saline soils and the associated environments favor the adsorption of B. subtilis on clay minerals. In addition, the negative enthalpies expressed as kJ kg^?1 (carbon) revealed an energy flow into the environment accompanied by the carbon adsorption on the minerals in soil.     

Bt毒素在三种矿物表面的吸附与解吸

研究了Bt库斯塔克亚种(kurstaki）毒素（65 kDa）在高岭土、针铁矿和氧化硅表面的吸附和解吸特性.结果表明：在磷酸盐缓冲体系（pH 8）中,3种矿物的等温吸附曲线均符合Langmuir方程（R²>0.9661）,它们对Bt毒素的吸附顺序为：针铁矿﹥高岭土﹥二氧化硅.矿物对Bt毒素的吸附1 h就基本达到了吸附平衡.在pH 6～8范围内,针铁矿、高岭土和二氧化硅对Bt毒素的吸附量随pH值的升高而降低.10 ℃～50 ℃范围内,针铁矿和氧化硅对Bt毒素吸附量随温度升高有所下降（8.39％和47.06％）,高岭土对Bt毒素吸附则略有升高（5.91％）.红外光谱分析显示,Bt毒素被矿物吸附后结构仅有微小变化.被矿物吸附的Bt毒素不易被去离子水解吸,水洗3次总解吸率为28.48%～42.04%.     

Biodegradation of fluoroanilines by the wild strain Labrys portucalensis

Aniline and halogenated anilines are known as widespread environmental toxic pollutants released into soil and water. In contrast to aniline, which is rapidly metabolized via catechol, halosubstituted anilines are more resistant to microbial attack. A fluorobenzene-degrading bacterium, Labrys portucalensis strain F11, was tested under different culture conditions for the degradation potential towards 2-, 3- and 4-fluoroaniline (2-, 3- and 4-FA). Strain F11 was able to use FAs as a source of carbon and nitrogen however, supplementation with a nitrogen source improved substrate consumption and its dehalogenation extent. When F11 cells were previously grown on fluorobenzene (FB), higher biodegradation rates were achieved for all isomers. Complete 2-FA biodegradation with stoichiometric fluoride release was achieved when FB-induced cells were used. On the other hand, the degradation of 3- and 4-FA was characterized by incomplete defluorination of the target compounds suggesting accumulation of fluorinated intermediates. F11 cultures simultaneously supplied with FB and the fluorinated anilines showed a concomitant degradation of both substrates, suggesting co-metabolic biodegradation. To our knowledge, this is the first time that biodegradation of 2- and 3-FA as a sole carbon and nitrogen source and co-metabolic degradation of FA isomers in the presence of a structural analogous compound is reported.     

Dual Roles of Capsular Extracellular Polymeric Substances in Photocatalytic Inactivation of Escherichia coli: Comparison of E. coli BW25113 and Isogenic Mutants

The dual roles of capsular extracellular polymeric substances (EPS) in the photocatalytic inactivation of bacteria were demonstrated in a TiO₂-UVA system, by comparing wild-type Escherichia coli strain BW25113 and isogenic mutants with upregulated and downregulated production of capsular EPS. In a partition system in which direct contact between bacterial cells and TiO₂ particles was inhibited, an increase in the amount of EPS was associated with increased bacterial resistance to photocatalytic inactivation. In contrast, when bacterial cells were in direct contact with TiO₂ particles, an increase in the amount of capsular EPS decreased cell viability during photocatalytic treatment. Taken together, these results suggest that although capsular EPS can protect bacterial cells by consuming photogenerated reactive species, it also facilitates photocatalytic inactivation of bacteria by promoting the adhesion of TiO₂ particles to the cell surface. Fluorescence microscopy and scanning electron microscopy analyses further confirmed that high capsular EPS density led to more TiO₂ particles attaching to cells and forming bacterium-TiO₂ aggregates. Calculations of interaction energy, represented by extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) potential, suggested that the presence of capsular EPS enhances the attachment of TiO₂ particles to bacterial cells via acid-base interactions. Consideration of these mechanisms is critical for understanding bacterium-nanoparticle interactions and the photocatalytic inactivation of bacteria.     

复合菌系降解纤维素过程中微生物群落结构的变化

为明确高效纤维素降解复合菌系降解过程中微生物群落结构的变化规律及关键的降解功能菌,利用该复合菌系对滤纸和稻秆进行生物处理,通过底物降解、微生物生长量、发酵液pH的变化情况,选择不同降解时期复合菌系提取的总DNA进行细菌16S rRNA基因扩增子高通量测序。通过分解特性试验确定在接种后培养第12、72、168 h分别作为降解初期、高峰期、末期。该复合菌系分别主要由1个门、2个纲、2个目、7个科、11个属组成。随着降解的进行,短芽胞杆菌属Brevibacillus、喜热菌属Caloramator的相对丰度逐渐降低;梭菌属Clostridium、芽胞杆菌属Bacillus、地芽胞杆菌属Geobacillus、柯恩氏菌属Cohnella的相对丰度逐渐升高;解脲芽胞杆菌属Ureibacillus、泰氏菌属Tissierella、刺尾鱼菌属Epulopiscium在降解高峰期时相对丰度最高;各时期类芽胞杆菌属Paenibacillus、瘤胃球菌属Ruminococcus的相对丰度无明显变化。上述11个主要菌属均属于厚壁菌门,具有嗜热、耐热、适应广泛pH、降解纤维素或半纤维素的特性。好氧型细菌是降解初期的主要优势功能菌,到中后期厌氧型细菌逐渐增多,并逐步取代好氧型细菌成为降解纤维素的主要细菌。     

Understanding the degradation of Congo red and bacterial diversity in an air–cathode microbial fuel cell being evaluated for simultaneous azo dye removal from wastewater and bioelectricity generation

We investigated the mechanism of Congo red degradation and bacterial diversity in a single-chambered microbial fuel cell (MFC) incorporating a microfiltration membrane and air–cathode. The MFC was operated continuously for more than 4 months using a mixture of Congo red and glucose as fuel. We demonstrated that the Congo red azo bonds were reduced at the anode to form aromatic amines. This is consistent with the known mechanism of anaerobic biodegradation of azo dyes. The MFC developed a less dense biofilm at the anode in the presence of Congo red compared to its absence indicating that Congo red degradation negatively affected biofilm formation. Denaturing gradient gel electrophoresis and direct 16S ribosomal DNA gene nucleotide sequencing revealed that the microbial communities differed depending on whether Congo red was present in the MFC. Geobacter-like species known to generate electricity were detected in the presence or absence of Congo red. In contrast, Azospirillum, Methylobacterium, Rhodobacter, Desulfovibrio, Trichococcus, and Bacteroides species were only detected in its presence. These species were most likely responsible for degrading Congo red.     

Impacts of Goethite Particles on UV Disinfection of Drinking Water

A unique association between bacterial cells and small goethite particles (~0.2 by 2 μm) protected Escherichia coli and Pseudomonas putida from UV inactivation. The protection increased with the particle concentration in the turbidity range of 1 to 50 nephelometric turbidity units and with the bacterium-particle attachment time prior to UV irradiation. The lower degree of bacterial inactivation at longer attachment time was mostly attributed to the particle aggregation surrounding bacteria that provided shielding from UV radiation.     

In vitro phagocytosis by Limulus blood cells.

Limulus blood cells maintained in culture are able to phagocytose particles under conditions where bacterial endotoxin is absent. In the presence of endotoxin, phagocytosis is inhibited because the cells are immobile under these conditions and because the extracellular gel found in the presence of endotoxin prevents cell-particle contact. It is suggested that Limulus blood cells respond to Gram-negative organisms by the formation of an extracellular gel matrix that entraps the bacteria and handles other types of foreign particles by phagocytosis.     

DNA Probe Method for the Detection of Specific Microorganisms in the Soil Bacterial Community

We developed a protocol which yields purified bacterial DNA from the soil bacterial community. The bacteria were first dispersed and separated from soil particles in the presence of polyvinylpolypyrrolidone, which removes humic acid contaminants by adsorption to this insoluble polymer. The soil bacteria were then collected by centrifugation and lysed by using a comprehensive protocol designed to maximize disruption of the various types of bacteria present. Total bacterial DNA was purified from the cell lysate and remaining soil contaminants by using equilibrium density gradients. The isolated DNA was essentially pure as determined by UV spectral analysis, was at least 48 kilobases long, and was not subject to degradation, which indicated that there was no contaminating nuclease activity. The isolated DNA was readily digested by exogenously added restriction endonucleases and successfully analyzed by slot blot and Southern blot hybridizations. Using single-stranded, ³²P-labeled DNA probes, we could detect and quantitate the presence of a specific microbial population in the natural soil community on the basis of the presence of a DNA sequence unique to that organism. The sensitivity of our methodology was sufficient to detect Bradyrhizobium japonicum at densities as low as 4.3 × 10⁴ cells per g (dry weight) of soil, which corresponds to about 0.2 pg of hybridizable DNA in a 1-μg DNA sample.     

The effect of inorganic particle concentration on bacteria-virus-nanoflagellate dynamics

The effect of inorganic particle concentrations on bacteria-virus-nanoflagellate dynamics in an oligotrophic coastal system was investigated using a model aluminosilicate, kaolinite, with a modal size of 2.1 μm. Virus-only, bacteria-only and bacteria-virus-nanoflagellate incubations were carried out at increasing kaolinite concentrations to elucidate the microbial response. The sorption of bacteria and viruses to kaolinite particles was negligible over a concentration range of 1-50 mg l(-1). In contrast, the abundance of heterotrophic nanoflagellates was negatively correlated with kaolinite concentrations following both 48 and 96 h incubations. Calculated nanoflagellate bacterial ingestion rates were reduced by 5-35% depending on kaolinite particle concentration. In the bacteria-virus-nanoflagellate incubations viral production increased by 56 × 10(3) to 104 × 10(3) VLPs ml(-1) h(-1) as a function of kaolinite particle concentration. Our results demonstrate for the first time that the interaction of microbial populations with inorganic particles can shift the balance between protist and virally mediated mortality of marine heterotrophic prokaryotes.