Studies on the relatedness of bacterial fumarate reductases

Abstract A collection of 10 Gram-negative bacteria was examined for the presence of a fumarate reductase related to that of Escherichia coli K-12. When the frd genes encoding the E. coli enzyme were used as DNA:DNA hybridization probes good signals were obtained from all members of the family Enterobacteriaceae. No significant hybridization was detected, even under non-stringent conditions, with the well characterized fumarate reducer Vibrio succinogenes or with Pseudomonas aeruginosa . These findings were confirmed and extended by immuno-diffusion studies using cell membranes and antiserum against the E. coli reductase. Precipitin lines were observed in all cases where frd homologies were detected. It was concluded that the V. succinogenes enzyme differs extensively from the E. coli fumarate reductase.     

Biodegradation of 2,4,6-trinitrotoluene (TNT): An enzymatic perspective

Enzymatic degradation of TNT by aerobic bacteria is mediated by oxygen insensitive (Type 1) or by oxygen sensitive nitroreductases (Type II nitroreductases). Transformation by Type I nitroreductases proceeds through two successive electron reductions either by hydride addition to the aromatic ring or by direct nitro group reduction following a ping pong kinetic mechanism. TNT is reduced to the level of hydroxylaminodinitrotoluenes and aminodinitrotoluenes by pure enzyme preparations without achieving mineralization. Interestingly, database gene and amino acid sequence comparisons of nitroreductases reveal a close relationship among all enzymes involved in TNT transformation. They are all flavoproteins which use NADPH/NADH as electron donor and reduce a wide range of electrophilic xenobiotics. TNT degradation by fungi is initiated by mycelia bound nitroreductases which reduce TNT to hydroxylaminodinitrotoluenes and aminodinitrotoluenes. Further degradation of these products and mineralization is achieved through the activity of oxidative enzymes especially lignin degrading enzymes (lignin and manganese peroxidases).     

Changes in the bacterial community and extracellular compounds associated with the disaggregation of Microcystis colonies

Microcystis is a well-studied type of bloom-forming genus cyanobacteria that occurs as colonies in lakes. However, whenever Microcystis colonies are transferred to the laboratory, they always disaggregate into a unicellular form. The mechanism underlying this disaggregation of Microcystis colonies remains uncharacterized. Here, we report on the changes in morphology and the changes in the composition of the associated bacterial community of Microcystis wesenbergii colonies. Denaturing gradient gel electrophoresis analysis (DGGE) showed that the diversity of the associated bacterial community decreased during the disaggregation of Microcystis colonies. Two γ-Proteobacteria and one Bacteroidetes species from the mucilage of Microcystis colonies were not detected following colony disaggregation, suggesting that these species may influence Microcystis colony morphology. Solid phase microextraction and gas chromatography–mass spectrometry (SPME GC/MS) analysis revealed that seven of the forty-one extracellular compounds detected were exclusively present in the media of the Microcystis colony extracts; these compounds may be secreted by bacteria and may be a beneficial role in Microcystis colony maintenance. The results of this study indicate that changes in the composition of the bacterial community associated with Microcystis colonies are likely responsible for the disaggregation of these colonies in the laboratory.     

Synoptic determination of living/dead and active/dormant bacterial fractions in marine sediments

The most widely used methods for the estimation of the living/dead fractions of bacterial cells involve specific stains that are able to reveal membrane integrity. Here, we have compared two different probes (propidium iodide and ethidium homodimer-2) that have different molecular weights and steric hindrance effects. We have also combined this method with the staining/destaining procedure that is currently used in the identification of potentially active cells. The procedure for marine sediments described here allows the synoptic (i.e. from the same filter) identification of: (i) the number of living bacteria; (ii) the number of active vs. dormant cells within this living fraction; (iii) the bacterial fraction with an intact nucleoid region without membrane integrity; and (iv) dead cells (devoid of the nucleoid region and without membrane integrity). Our results demonstrate that the concentration of propidium is crucial for the correct estimation of the dead bacterial fraction, ethidium homodimer-2 allows efficient and accurate estimates that are independent of the concentrations used and the sample storage. The active bacterial fraction represented c. 40% of the total bacterial abundance, the inactive/dormant fraction c. 30%, and the dead fraction was, on average, c. 30%. This method allows the processing of a large number of samples with high precision and at relatively low cost, and thus it provides additional synoptic insights into the metabolic state of bacteria in marine sediments.     

植物病原细菌毒性调控网络的研究进展

植物病原细菌通过复杂和精细的全局性调控网络来协调多个层面的毒性决定因子。在不同的植物病原细菌中,这些全局性的毒性调控网络控制着细菌的侵染策略、存活以及在面临寄主植物防卫系统的互作环境中实现成功侵染的病程。本文详细分析了植物病原细菌4个重要属(假单胞菌属、果胶杆菌属、黄单胞菌属和雷尔氏菌属)的模式病原菌主要的毒性调控系统,包括群体感应系统、双组分调控系统、转录激活调控子以及转录后、翻译后的调控机制。在此基础上,重点评价了一些模式菌株全局性毒性调控机制的异同点,总结了一些最新的研究进展,并绘制了精细的网络调控图。这些分析表明,虽然一些相同的调控系统控制着病原菌的毒性,但是在不同种以及种下的亚种或者致病变种中这些调控机制功能各异,对于病原菌全毒性的贡献也存在着明显的差异。     

Mini-review of the concentration variations found inthe alfresco atmospheric bacterial populations

Variations in the atmospheric surface layer's culturable, and to a lesser extent, total bacteria-associated atmospheric particlecharacteristics will be discussed in terms of (a)their temporal variation from 2 min resolutionthrough diurnal to annual periods, (b) the effect ofmeteorological conditions on their abundance andsize, (c) total to culturable bacterial ratio, and(d) the total number of bacteria per culturableparticle (e) bacterial survival in droplet/particles, and (f) the general particle size distribution including aerodynamic Count MedianDiameter (CMD).Meteorological and topographic conditions thatcontrol total and culturable bacteria-associatedatmospheric particle concentration will be presentedin terms of (a) precipitation, (b) wind direction,(c) time of day, (d) sky conditions (i.e., cloudy,sunny, rain, etc.), (e) season, and (f) atmosphericinversion conditions.Simulation models will be described that supporthypotheses of diurnal and annual concentrationcycles in the Earth's (and perhaps other planetaryatmospheres) atmospheric surface layer.     

Treating cancer with infection: a review on bacterial cancer therapy

There is an increasing need for new cancer therapies. The antitumour effect of bacterial infection has been well observed and practiced throughout history. Bacteria are well‐suited to serve as anticancer agents due to their intrinsic mobility, cell toxicity, immunogenicity, and preferential accumulation within the anoxic tumour environment. Furthermore, advances in biotechnology and molecular techniques have made it easier than ever to engineer bacteria as both therapeutic agents themselves and as therapeutic vectors. Here, we review bacteriolytic therapy and immunotherapy strategies, and examine the development of bacteria as vehicles for cell‐ and tissue‐targeted delivery of genetic cancer therapeutics.     

Efficacy of single versus multiple exposure by electromagnetic modalities on gram-negative and positive bacterial strains in an in-vitro model

ObjectivesThe primary purpose of the recent experiment was to scrutinize the dissimilarity between single and multiple exposures by electrotherapeutic modalities to determine the development of Gram-positive and Gram negative bacteria spectrum.Material and methodsBacterial strains employed in this study were Gram-negative bacteria such as Pseudomonas aeruginosa, Escherichia coli, and Klebsiella pneumonae and Gram-positive bacteria such as Staphylococcus aureus, Staphylococcus saprophyticus and Streptococcus pyogenes. Fluence for Low level laser therapy (LLLT) (810 nm) was 40 J/cm² for 80 s, for microwave (MWD) a dosage of 100-Watt with duration of 5 min and for magnetic field therapy (MT) duration of 30 min with 100% intensity was used.ResultsRepeated Measures of analysis of variances (RANOVA) for within-subject effects was used to detect a global significant change within the means at dissimilar time points. The experiments of within-subjects revealed a significant difference within groups, df of (3, 40), F value of 39.38 and a p value less than 0.001, representing a significant variation between the three groups between pre and post exposures. There was a significant variation between single exposure and multiple exposures in the experimental sample’s pre-post between the four groups with df (1, 40) f value of 2943.69 and p value less than 0.001. Scanning and Transmission electron microscopy images were also taken into account to determine the extent of damage caused to the bacterial cells surface topography in Gram negative and Gram positive spectrums.ConclusionThe study demonstrated that single high exposure with the LLLT appears to have the most emphatic effect followed by exposure by MWD and MT.     

Use of MALDI-TOF mass spectrometry in the battle against bacterial infectious diseases: recent achievements and future perspectives

Introduction: Advancements in microbial identification occur increasingly faster as more laboratories explore, refine and extend the use of mass spectrometry in the field of microbiology.

Areas covered: This review covers the latest knowledge found in the literature for quick identification of various classes of bacterial pathogens known to cause human infection by the use of MALDI-TOF MS technology. Except for identification of bacterial strains, more researchers try to ‘battle time’ in favor of the patient. These novel approaches to identify bacteria directly from clinical samples and even determine antibiotic resistance are extensively revised and discussed.

Expert commentary: Mass spectrometry is the future of bacterial identification and creates a new era in modern microbiology. Its incorporation in routine practice seems to be not too far, providing a valuable alternative, especially in terms of time, to conventional techniques. If the technology further advances, quick bacterial identification and probable identification of common antibiotic resistance might guide patient decision-making regarding bacterial infectious diseases in the near future.     

茶小绿叶蝉成虫唾液细菌蛋白的鉴定

[目的]通过鉴定茶小绿叶蝉Empoasca flavescens成虫水状唾液蛋白中的细菌蛋白,解析叶蝉唾液的细菌种类.[方法]利用自制的收集装置和Parafilm膜夹营养液法对叶蝉成虫唾液进行收集,经超滤浓缩和电泳分离后,使用膜辅助样品制备技术法(filter-aided sample preparation,FASP...     

Changing the specificity of a bacterial chemoreceptor

The methyl-accepting chemotaxis proteins are a family of receptors in bacteria that mediate chemotaxis to diverse signals. To explore the plasticity of these proteins, we have developed a simple method for selecting cells that swim to target attractants. The procedure is based on establishing a diffusive gradient in semi-soft agar plates and does not require that the attractant be metabolized or degraded. We have applied this method to select for variants of the Escherichia coli aspartate receptor, Tar, that have a new or improved response to different amino acids. We found that Tar can be readily mutated to respond to new chemical signals. However, the overall change in specificity depended on the target compound. A Tar variant that could detect cysteic acid still showed a strong sensitivity to aspartate, indicating that the new receptor had a broadened specificity relative to wild-type Tar. Tar variants that responded to phenylalanine or N-methyl aspartate, or that had an increased sensitivity to glutamate showed a strong decrease in their response to aspartate. In at least some of the cases, the maximal level of sensitivity that was obtained could not be attributed solely to substitutions within the binding pocket. The new tar alleles and the techniques described here provide a new approach for exploring the relationship between ligand binding and signal transduction by chemoreceptors and for engineering new receptors for applications in biotechnology.     

Manual and expert annotation of the nearly complete genome sequence of Staphylococcus sciuri strain ATCC 29059: A reference for the oxidase-positive staphylococci that supports the atypical phenotypic features of the species group

Staphylococcus sciuri is considered to be one of the most ancestral species in the natural history of the Staphylococcus genus that consists of 48 validly described species. It belongs to the basal group of oxidase-positive and novobiocin-resistant staphylococci that diverged from macrococci approximately 250 million years ago. Contrary to other groups, the S. sciuri species group has not developed host-specific colonization strategies. Genome analysis of S. sciuri ATCC 29059 provides here the first genetic basis for atypical traits that would support the switch between the free-living style and the infective state in animals and humans. From among the most remarkable features, it was noticed in this extensive study that there were a number of phosphoenolpyruvate:carbohydrate phosphotransferase systems (PTS), almost twice as many as any other staphylococci, and the co-occurrence of mevalonate and non-mevalonate pathways for isoprenoid synthesis. The sequenced strain was devoid of the main virulence factors present in Staphylococcus aureus, although it exhibited numerous heme and iron acquisition systems, as well as crt and aldH genes necessary for gold pigment synthesis. The sensing and signaling networks, exemplified by a large and typical repertoire of two-component regulatory systems and a complete panel of master regulators, such as agr, rex, mgrA, rot, sarA and sarR genes, depict the background in which S. aureus virulence genes were later acquired. An additional sigma factor, a distinct set of electron transducer elements and many gene operons similar to those found in Bacillus spp. would constitute the most visible remnant links with Bacillaceae organisms.     

Reduction in the urinary aflatoxin M1 biomarker as an early indicator of the efficacy of dietary interventions to reduce exposure to aflatoxins

Abstract

Aflatoxin B₁ is a persistent public health issue in Ghana. Assessment of AFB₁ intervention efficacy is currently dependent on long-term biomarkers. This study was designed to determine whether daily AFM₁ biomarker levels could be utilized as an early detection method for intervention efficacy. Participants were treated with a refined calcium montmorillonite clay (UPSN) or a placebo (calcium carbonate) in a crossover study. Urine samples were assessed for AFM₁ levels daily. UPSN treatment reduced AFM₁ biomarkers by 55% compared to the placebo. This is the first study to show that daily urinary AFM₁ levels can be used as a biomarker of internal aflatoxin B₁ exposure in short-term intervention trials to determine efficacy.     

Quantifying heterogeneity: flow cytometry of bacterial cultures

Flow cytometry is a technique which permits the characterisation of individual cells in populations, in terms of distributions in their properties such as DNA content, protein content, viability, enzyme activities and so on. We review the technique, and some of its recent applications to microbiological problems. It is concluded that cellular heterogeneity, in both batch and continuous axenic cultures, is far greater than is normally assumed. This has important implications for the quantitative analysis of microbial processes.     

Pathogenicity of bacterial isolates to Cyclocephala signaticollis (Coleoptera: Scarabaeidae)

We describe the isolation and identification of pathogenic bacteria obtained from haemolymph of Cyclocephala signaticollis larvae. Two pathogenic bacteria, a Bacillus thuringiensis and an Arthrobacter sp. caused 90–100% mortality to C. signaticollis in 4 days after hemocoel injection, suggesting they might be useful as biological control agents.