Refraction and absorption of light in bacterial suspensions

Summary The apparent average refractive indices of three types of microorganism in liquid suspension have been estimated by two methods. In the first, the refractive index of the aqueous suspension is measured in an interferometer, the bacterial cell volume fraction is estimated from the dilution of an added inert solute, and the refractive index of the disperse phase is calculated with the aid of a mixture rule. In the second method, optical density spectra of suspensions in several concentrated solutions of nonpenetrating solutes are measured as a function of the refractive index,n ₁, of the solution. The value ofn ₁ when the optical density,E, has its smallest value is equated to the average cell refractive index and the constants of the parabolaE (n ₁) are related to the heterogeneity of the cell population in respect to refractive index. The preliminary results obtained by the two methods are in satisfactory agreement and are consistent with the specific refractive increments of protein and nucleic acid and their concentrations in the cell. It is pointed out that measurements of optical density spectra can also give useful information concerning the number and size of cells in a suspension and their optical dispersion constants. To obtain such information, however, a spectrophotometer specially designed to exclude forward-scattered light must be used and an acceptable theory must be available. Finally, the apparent spectral absorption of clarified cell suspensions is presented and compared with spectra obtained by other methods. It is pointed out that because of refractive heterodispersity even clarified suspensions are turbid, so that this method does not provide a completely satisfactory technique for cell spectrophotometry.

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Zusammenfassung Es wurde der scheinbare mittlere Brechungsindex von 3 Typen von Mikroorganismen in flüssiger Suspension nach zwei Methoden abgeschätzt:Bei der ersten Methode wird der Brechungsindex der bisherigen Lösung in einem Interferometer gemessen. Die Volumenkonzentration der Bakterienzellen wird aus der Verdünnung mit einer zugesetzten inerten Komponente abgeschätzt. Der Brechungsindex der dispersen Phase wird mit Hilfe der Mischungsregel berechnet.Nach der 2. Methode werden Spektren der optischen Dichte der Suspensionen in verschiedenen konzentrierten Lösungen von nicht-mischbarer 2. Komponente als Funktion des Brechungsindexn ₁ gemessen. Dieser Brechungsindexn ₁ hat seinen kleinsten Wert, wenn die optische DichteE dem mittleren Brechungsindex der Zellen gleich ist, und die Konstanten der ParabelnE (n ₁) stehen in Beziehung zur Heterogenität der Zellverteilung in Bezug auf den Brechungsindex.Die vorläufig nach den beiden Methoden erhaltenen Ergebnisse stimmen befriedigend überein und sind konsistent mit den spezifischen Refractionsinkrementen von Eiweiß- und Nukleinsäure und deren Konzentrationen in der Zelle. Es sei betont, daß Messungen der optischen Dichtespektren auch gute Information über Zahl und Größe der Zellen in einer Suspension und über deren optische Dispersionskonstanten geben können. Um diese Information zu erhalten, muß jedoch speziell ein Spektrometer gebaut werden, das gestattet, das vorwärtsgestreute Licht auszuschließen. Außerdem muß eine akzeptable Theorie vorhanden sein. Schließlich wird die scheinbare Spektralabsorption von geklärten Zellsuspensionen dargelegt und mit den Spektren, die nach anderen Methoden erhalten werden, verglichen. Es ist ausgeführt, daß wegen der Heterodispersität auch geklärte Suspensionen streuen, so daß diese Methode keine vollständig befriedigende Technik für Zellspektrometrie darstellt.

     

Reactivities of cellulases from fungi towards ribbon-type bacterial cellulose and band-shaped bacterial cellulose

We have investigated the reactivities of various cellulases onribbon-type bacterial cellulose (BC I) and band-shaped bacterial cellulose (BCII) so as to clarify the properties of different cellulases. BC I waseffectively hydrolyzed by exo-type cellulases from different fungi from twicetofour times as much as BC II, but endo-type cellulases showed little differencein reactivity on those substrates. One of the endo-type cellulases, EG II fromTrichoderma reesei, degraded BC II more rapidly thanexo-type cellulases even in the production of reducing sugars. The degree ofpolymerization (DP) of BC II was rapidly decreased by endo-type cellulases atanearly stage, while exo-type cellulases did not cause the decrease of DP atthe initial stage, though the decrease of DP was observed after an incubation of24 h. All exo-type cellulases adsorbed on BC I and BC II,whileendo-type cellulases except for EG II adsorbed slightly on both substrates. Itwas interesting to observe EG II adsorbed on BC I but not on BC II. It issuggested that the adsorption of enzyme on cellulose is important for thedegradation of BC I, but not for BC II. It is proposed that the ratio of aspecific activity of each enzyme between BC I and BC II represents thedifference in the mode of action of cellulase. Furthermore, the K _RW value, which we can calculate from thedecrease of DP/reducing sugar produced, is effective for discriminating themode of action of cellulase, especially the evaluation of randomness in thehydrolysis of cellulose by endo- and exo-type cellulases.     

Determination of heptoses in bacterial lipopolysaccharides

A method is proposed for the quantitative determination of heptoses in polysaccharide preparations of bacterial origin which eliminates the influence of all the other components present in the mixture on the results of the analysis. The method described is distinguished by high specificity, sensitivity, and reproducibility of the results, and also by simplicity of determination. It provides the possibility of determining low concentrations of heptoses in the presence of predominating amounts of other components. The standard deviation does not exceed 3.5%.     

Recent advances in bacterial cellulose

Bacterial cellulose (BC) produced by some microorganisms has been widely accepted as a multifunctional nano-biomaterial. It is composed of linear glucan molecules attached with hydrogen bonds, which appears similar to plant cellulose. However, when compared with other conventional natural or synthesized counterparts, BC performs better in areas such as biomedicine, functional devices, water treatment, nanofillers, etc. for its distinct superior chemical purity, crystallinity, biocompatibility, and ultrafine network architecture. When BC is incorporated in a material or used as a scaffold, novel features result that are related to BC’s intrinsic characteristics mentioned above. This review mainly summarizes the recent developments of the functional products fabricated with BC. Besides, the controllable cultivation conditions should also be discussed for expecting to make a breakthrough in its productivity. We highlight the literatures mainly in last 5 years, exerting ourselves to provide the state-of-the-art opinions in areas wherever are focused on for BC researching.     

Autophagy and bacterial infectious diseases

Autophagy is a housekeeping process that maintains cellular homeostasis through recycling of nutrients and degradation of damaged or aged cytoplasmic constituents. Over the past several years, accumulating evidence has suggested that autophagy can function as an intracellular innate defense pathway in response to infection with a variety of bacteria and viruses. Autophagy plays a role as a specialized immunologic effector and regulates innate immunity to exert antimicrobial defense mechanisms. Numerous bacterial pathogens have developed the ability to invade host cells or to subvert host autophagy to establish a persistent infection. In this review, we have summarized the recent advances in our understanding of the interaction between antibacterial autophagy (xenophagy) and different bacterial pathogens.     

Energetics and kinetics of primary charge separation in bacterial photosynthesis

We report the results of molecular dynamics (MD) simulations and formal modeling of the free-energy surfaces and reaction rates of primary charge separation in the reaction center of Rhodobacter sphaeroides. Two simulation protocols were used to produce MD trajectories. Standard force-field potentials were employed in the first protocol. In the second protocol, the special pair was made polarizable to reproduce a high polarizability of its photoexcited state observed by Stark spectroscopy. The charge distribution between covalent and charge-transfer states of the special pair was dynamically adjusted during the simulation run. We found from both protocols that the breadth of electrostatic fluctuations of the protein/water environment far exceeds previous estimates, resulting in about 1.6 eV reorganization energy of electron transfer in the first protocol and 2.5 eV in the second protocol. Most of these electrostatic fluctuations become dynamically frozen on the time scale of primary charge separation, resulting in much smaller solvation contributions to the activation barrier. While water dominates solvation thermodynamics on long observation times, protein emerges as the major thermal bath coupled to electron transfer on the picosecond time of the reaction. Marcus parabolas were obtained for the free-energy surfaces of electron transfer by using the first protocol, while a highly asymmetric surface was obtained in the second protocol. A nonergodic formulation of the diffusion-reaction electron-transfer kinetics has allowed us to reproduce the experimental results for both the temperature dependence of the rate and the nonexponential decay of the population of the photoexcited special pair.     

Availability of surface hydroxyl groups in valonia and bacterial cellulose

The chemical microstructural analysis (CMA) developed by Rowland and his school was applied to Valonia and bacterial cellulose and the results compared to those obtained with cellulose from cotton linters. It was found that the surface reactivity of Valonia was very small, roughly one half of that found for bacterial and cotton cellulose. Valonia and bacterial cellulose crystals were found to be of high surface perfection as their surface O(3)H was almost inaccessible. In contrast, in the cotton sample, this hydroxyl group was almost as accessible as in the fully disorganized native cellulose.     

New role of antibody in bacterial isolation

To eliminate the interference caused by Pseudomonas aeruginosa in the isolation of Salmonella, a rabbit polyclonal antibody against P. aeruginosa was prepared by inoculating four New Zealand rabbits with the pathogen. The antiserum was purified using saturated ammonium sulfate and added into Rappaport-Vassiliadis medium with soya (RVS) broth and Muller-Kauffmann tetrathionate novobiocin broth (MKTTn broth) to evaluate whether it could inhibit the growth of P. aeruginosa. Observations by scanning electron microscopy demonstrated that P. aeruginosa was attacked and destroyed by the antibody when incubated for 10 min at 37 degrees C. The activity of the antibody was also effective against 11 other strains of P. aeruginosa. Twenty-six strains of Salmonella were mixed with P. aeruginosa in RVS and MKTTn broth at 37 degrees C for 12 h, respectively, and the cultures were plated on Salmonella chromogenic medium (SCM; Oxoid, Basingstoke, UK). Only Salmonella grew on SCM; five colonies were randomly selected for identification by VITEK 2 (bioMérieux, Lyon, France). Additionally, when mixed with two strains of Enterobacter cloacae (ATCC 700323 and YG001), the prepared antibody did not affect the growth of E. cloacae. The results demonstrated that the microbicidal activity of the antibody did not affect the tested Salmonella sp. or E. cloacae strains. Therefore, the antibody generated could be used to increase the accuracy of Salmonella isolation.     

Mechanisms of charge separation in bacterial photosynthesis

The physical aspects of the primary charge separation processes in bacterial photosynthesis are discussed. The donor-acceptor model of electron transfer due to participation of protein current states is used. The kinetics of photosynthetic reaction center (PRC ) processes is investigated and the PRC energetic scheme is constructed using the nonequilibrium density matrix method. It is shown that with allowance for the effect of vibrational sublevels of states participating in transitions the theory describes well experimental data.     

Observation of oscillation in bacterial luminescence.

Oscillation in the bioluminescent intensity from a luminous bacteria suspension was observed. The time course of the luminescence intensity from a suspension containing luminous bacteria was measured. The oscillation mode changed with the liquid broth component. The optical density and dissolved oxygen (DO) concentration were measured simultaneously with the luminescence intensity, and a possibility was indicated that both diauxic growth and oxygen reaction-consumption resulted with oscillation.     

Structure and function of bacterial initiation factors

Bacteria require three initiation factors, IF1, IF2 and IF3, to start protein synthesis. In the last few years the elucidation of both structural and mechanistic aspects pertaining to these proteins has made substantial progress. In this article we outline the translation initiation process in bacteria and review these recent developments giving a summary of the main features of the structure and function of the initiation factors.     

Potentiometric detection and study of bacterial activity

The potentiometric technique leads to practical and fundamental applications, for the moment limited to the field of public health. Further possible extensions, e.g. the control of microbial contaminations in liquid foods, would bring it closer to industrial preoccupations. As an analytical application of the technique to the biotechnological processes, the feasibility of bacterial sensors, based on the potentiometric detection of lipoic acid reduction, may be considered for monitoring the concentrations of various substrates of microbial metabolism.     

Role of nonadsorbing polymers in bacterial aggregation

Bacteria exhibit properties similar to those of nonbiological colloids and can display pairwise attractions when in close proximity. This interaction is governed by the surface chemistry of the cells. We seek to understand bacterial aggregation at the cellular level using Escherichia coli (E. coli) AB1157. Aggregation studies were carried out using 0.5 to 2.5 wt% E. coli AB1157 harvested in different growth phases with varying concentrations of a nonadsorbing polymer, sodium polystyrene sulfonate (SPS). The electrophoretic mobility of E. coli AB1157 in different growth phases was determined using phase-amplitude light scattering. E. coli AB1157 was found to be negatively charged, and the cell surface properties changed in different growth phases. The electrokinetic results correlated well with the different concentrations of nonadsorbing polymer needed to induce depletion aggregation. This shows that a difference in aggregation properties is due to changes in the bacteria electrokinetic properties during their growth.     

Sedimentation of DNA supercoils and bacterial nucleoids

The sedimentation of DNA supercoils and bacterial nucleoids is discussed in terms of an asymptotic expression for the size of branched supercoils exhibiting an excluded-volume effect between superhelical segments. A Kirkwood–Riseman approximation is adopted for the sedimentation coefficient. The theory predicts the sedimentation of DNA supercoils fairly well despite their relatively small size in current simulations and experiments. We introduce a crosslinked supercoil model for bacterial nucleoids that are known to contain a variety of adsorbed proteins. Sedimentation experiments of the 1970s are discussed.     

细菌漆酶的功能与催化特性

正漆酶(laccase)(EC 1.10.3.2)是一类含铜的多酚氧化酶(copper-containing polyphenol oxidase),属于蓝色多铜氧化酶(blue multi-copper oxidase,MCO)家族,能催化多种酚类、芳胺类化合物的氧化,同时将分子氧还原成水.漆酶突出的催化特性是它的底物具有广泛性、催化反应具有复杂性,生     

Mercerization and acid hydrolysis of bacterial cellulose

Structural changes in never- dried, disintegrated bacteria l cellulose by treatment with aqueous NaOH were examined by electron microscopy, X-ray diffractometry and acid hydrolysis behaviour and compared with those of cotton cellulose. The microfibril kept its fibrillar morphology after treatment with NaOH solutions of less than 9% (w/w), but changed into irregular aggregates when treated with NaOH above 12% (w/w), corresponding to the crystal conversion to cellulose II. The crystallinity of the resulting cellulose II was very low after a brief alkali treatment, but was increased significantly by elongated treatment (up to 10 days). In contrast, cotton cellulose was converted to cellulose II of fairly high crystallinity by alkali treatment of as little as 3 min duration, and the crystallinity did not change with longer treatments. The leveling-off degree of polymerization (LODP) of bacterial cellulose was decreased from 150 to 50 by 18% (w/w) NaOH treatment, while that of cotton linter decreased from 260 to 70. These characteristic differences between cotton linter cellulose and bacterial cellulose can be ascribed to a basic difference in microfibrillar organization in these materials: the microfibrils in cotton cellulose are in close contact with neighbouring microfibrils having opposite polarity, and in bacterial cellulose are isolated from each other and require chain folding to form the antiparallel cellulose II crystal     

Mechanistic parallels in bacterial and human multidrug efflux transporters

Bacteria carry a battery of multidrug transporters, which belong to six families of transporters. Members of at least three families the ATP-Binding Cassette superfamily, the Major Facilitator Superfamily and the Multidrug Endosomal Transporter family have been shown to contribute to multidrug resistance phenotype in eukaryotic cells. This review is focused on comparison of bacterial and eukaryotic transporters that do not have a common evolutionary trait and use different sources of energy to perform the transport. Yet they demonstrate an impressive resemblance. All multidrug transporters are capable of recognizing a broad spectrum of structurally diverse compounds. The accumulated data suggest that structural and mechanistic determinants of such ability are similar among unrelated proteins. Despite the apparent similarity, many features are still unique for different classes of transporters. Intriguingly, some cells appear to simultaneously express transporters belonging to different classes. Depending on mechanistic particularities of transporters such concurrent expression can result in synergistic or non-synergistic effects.     

Structural and mechanical anisotropy in rheotactically aligned bacterial cellulose

Cellulose - In this work, we demonstrate the preparation of oriented bacterial cellulose from Komagataeibacter sucrofermentans by rheotactic growth in a simple and adaptable setup. The resulting...