Permeability of the outer membrane of bacteria.

The outer membrane of Gram-negative bacteria is an attractive system for the study of the structure-function relationships in biological membranes. This membrane has, inter alia, the task of regulating the inflow of nutrients and outflow of waste products. Investigations with the aid of mutants showed that there are at least two general pathways for the diffusion of small molecules across the outer membrane: one for hydrophobic and one for hydrophilic compounds. In the case of the “hydrophobic pathway” the hydrophobic compound dissolves in the interior of the membrane and then crosses the membrane in accordance with the partition coefficient. In wild-type forms of enteric bacteria this pathway cannot be used—presumably owing to the absence of regions with phospholipid bilayers. Small hydrophilic molecules, on the other hand, penetrate the membrane through water-filled pores.     

Bacterial cell wall material properties determine E. coli resistance to sonolysis

The applications of bacterial sonolysis in industrial settings are plagued by the lack of the knowledge of the exact mechanism of action of sonication on bacterial cells, variable effectiveness of cavitation on bacteria, and inconsistent data of its efficiency. In this study we have systematically changed material properties of E. coli cells to probe the effect of different cell wall layers on bacterial resistance to ultrasonic irradiation (20 kHz, output power 6,73 W, horn type, 3 mm probe tip diameter, 1 ml sample volume). We have determined the rates of sonolysis decay for bacteria with compromised major capsular polymers, disrupted outer membrane, compromised peptidoglycan layer, spheroplasts, giant spheroplasts, and in bacteria with different cell physiology. The non-growing bacteria were 5-fold more resistant to sonolysis than growing bacteria. The most important bacterial cell wall structure that determined the outcome during sonication was peptidoglycan. If peptidoglycan was remodelled, weakened, or absent the cavitation was very efficient. Cells with removed peptidoglycan had sonolysis resistance equal to lipid vesicles and were extremely sensitive to sonolysis. The results suggest that bacterial physiological state as well as cell wall architecture are major determinants that influence the outcome of bacterial sonolysis.     

Enantioselective analysis of ofloxacin enantiomers by partial-filling capillary electrophoresis with bacteria as chiral selectors

The enantiomeric separation of ofloxacin enantiomers (OFLX) was achieved by using capillary electrophoresis partial-filled with Escherichia coli, Pseudomonas aeruginosa (Gram-negative), and Staphylococcus aureus (Gram-positive) as chiral selectors. Experimental parameters, including the concentration of background electrolyte, applied voltage, length of the filled bacteria plug, and pH of the buffer, were intensively investigated. Baseline separation of OFLX could be achieved within 7 min by using E. coli and P. aeruginosa as chiral selectors under the following conditions: electrophoretic buffer composed of 10 mM phosphate buffer at pH 7.4, applied voltage at 15 kV, and the bacteria (6.0 × 10(8) cells/mL) were injected into the capillary by gravity with injection height of 17.5 cm for 180 s (E. coli), 300 s (P. aeruginosa), and 300 s (S. aureus), respectively. E. coli and P. aeruginosa had better chiral selectivity for OFLX than S. aureus, which was in good agreement with OFLX having better antimicrobial activity on Gram-negative rather than Gram-positive bacteria. A novel method was developed for the enantioselective separation of enantiomers using bacteria as chiral selectors, which provides a new approach for antimicrobials enantioselective analysis, chiral pharmacodynamics, and chiral pharmacokinetics studies.     

石油污染地下水中铁氧化菌的筛选及其除铁效果

采用某油田污染场地石油降解菌——W2、W6、W9、W10,进行铁氧化菌的筛选。其中W9和W10对TFe去除率达90%。两株菌在24h内把Fe²⁺氧化成Fe²⁺,5d完成对TFe的去除;W9为革兰氏阴性杆菌,W10为革兰氏阳性芽孢杆菌。     

Ligational behavior of a bidentate coumarin derivative towards CoII,NiII, and CuII: synthesis,characterization, electrochemistry,and antimicrobial studies

A series of new Co(II), Ni(II), and Cu(II) complexes of Schiff base derived from coumarin have been prepared and characterized by analytical and spectral methods. The Schiff base is synthesized by the condensation of 2,6-diaminopyridine and 3-acetylcoumarin in 1 : 1 stoichiometric ratio. All complexes have 1 : 1 metal : ligand ratio except the nickel complex, where it was found to be 1 : 2. UV-Vis spectra and magnetic moment studies confirm the existence of tetrahedral and octahedral geometries around cobalt(II) and nickel(II) metal ions, respectively, but copper(II) chloride/nitrate/sulfate complexes have square-planar geometry and copper(II) acetate complex is distorted octahedral. ESR spectra of copper complexes at room temperature and liquid nitrogen temperature were tetragonal. All the complexes were found to be more active against bacteria except Ni(II) complex; only CuLSO₄ and CuL(CH₃COO)₂ have shown the enhanced activity against fungi.     

Selective fluorescence labeling and sensitive determination of Staphylococcus aureus by microchip electrophoresis with a multiple-concentration approach

In this paper we explored the use of fluorescently labelled vancomycin to specifically bind and detect Staphylococcus aureus based on an on-line multiple-concentration on microchip electrophoresis.     

The turning of magnetotactic bacteria

A magnetotactic bacterium aligns itself along the magnetic field. When the field is reversed the bacterium makes a U-turn in the surrounding water. The turning is described by a Fokker-Planck equation for the angle , which is singular at the endpoints =0 and =. The time needed for turning can be found exactly as a first-passage time. The probability distribution itself can be found in terms of an approximation for low temperature. To cover the regions near the endpoints singular perturbation theory is needed.     

Extrachromosomal DNA in bacteria

In addition to chromosomal DNA carrying the genetic information of the cell, many bacterial cells contain smaller circular DNA factors known as plasmids or episomes. These genetic elements endow the cell with additional biochemical capabilities. The fertility factors (F and F′), the antibiotic resistance factors (R), the colicinogenic factors (Col), the hemolytic factors (Hly), and other extrachromosomal DNA systems are described. These small DNA molecules can be isolated, and are therefore particularly suitable for the investigation of DNA replication and the stable establishment of genetic material in the bacterial cell.     

Bacterial transport in porous media: New aspects of the mathematical model

Transport of bacteria is an important aspect from scientific, industrial and environmental point of view. In this work, a one-dimensional mathematical model based on linear equilibrium adsorption of bacteria has been developed to predict bacterial transport through porous media. This model is more realistic than existing models because of its coupling both physicochemical and biological phenomena. Two important biological phenomena, the growth and decay of bacterial cells and chemotactic/chemotaxis of bacteria along with physicochemical properties have been adequately incorporated which are quite new aspects in our model. In agreement with experimental study by [D.K. Powelson, R.J. Simpson, C.P. Gerba, J. Environ. Qual. 19 (1990) 396], model simulations indicated that enhancement of breakthrough occurs due to increase in flow velocity, cell concentration, substrate concentration, respectively. It has also been found that chemo tactic has a significant effect on bacterial transport, especially under conditions of considerable substrate gradient and at low pore velocity. The importance of threshold concentration of captured cells (σ₀) on bacterial transport has also been identified which is also a new aspect in our model.