溴代阻燃剂微生物降解的研究进展

溴代阻燃剂以其优异的阻燃性能而在工业生产和日常生活中大量使用。这些外源性的化学物质因其蓄积性、持久性、生物毒性而对人类健康和生态环境造成威胁。微生物特有的降解代谢能力为溴代阻燃剂污染治理带来了希望。但是,目前有关溴代阻燃剂的微生物降解研究仍然很少。综述了国内外在溴代阻燃剂微生物降解方面的最新研究动态,包括厌氧、好氧和基团化等生物降解方式。在此基础上,提出目前溴代阻燃剂微生物降解研究中存在的主要问题和重点研究方向,并对其在溴代阻燃剂污染治理方面的应用潜力进行展望。     

The multifaceted capacity of Dps proteins to combat bacterial stress conditions: Detoxification of iron and hydrogen peroxide and DNA binding

Background

The widely expressed Dps proteins, so named after the DNA-binding properties of the first characterized member of the family in Escherichia coli, are considered major players in the bacterial response to stress.

Scope of review

The review describes the distinctive features of the “ferritin-like” ferroxidation reaction, which uses hydrogen peroxide as physiological iron oxidant and therefore permits the concomitant removal of the two reactants that give rise to hydroxyl radicals via Fenton chemistry. It also illustrates the structural elements identified to date that render the interaction of some Dps proteins with DNA possible and outlines briefly the significance of Dps–DNA complex formation and of the Dps interaction with other DNA-binding proteins in relation to the organization of the nucleoid and microbial survival.

General significance

Understanding in molecular terms the distinctive role of Dps proteins in bacterial resistance to general and specific stress conditions.

Major conclusions

The state of the art is that the response to oxidative and peroxide-mediated stress is mediated directly by Dps proteins via their ferritin-like activity. In contrast, the response to other stress conditions derives from the concerted interplay of diverse interactions that Dps proteins may establish with DNA and with other DNA-binding proteins.     

A Survey of Phytotoxic Microbial and Plant Metabolites as Potential Natural Products for Pest Management

Phytotoxic microbial metabolites produced by certain phytopathogenic fungi and bacteria, and a group of phytotoxic plant metabolites including Amaryllidacea alkaloids and some derivatives of these compounds were evaluated for algicide, bactericide, insecticide, fungicide, and herbicide activities in order to discover natural compounds for potential use in the management and control of several important agricultural and household structural pests. Among the various compounds evaluated: i) ophiobolin A was found to be the most promising for potential use as a selective algicide; ii) ungeremine was discovered to be bactericidal against certain species of fish pathogenic bacteria; iii) cycasin caused significant mortality in termites; iv) cavoxin, ophiobolin A, and sphaeropsidin A were most active towards species of plant pathogenic fungi; and v) lycorine and some of its analogues (1‐O‐acetyllycorine and lycorine chlorohydrate) were highly phytotoxic in the herbicide bioassay. Our results further demonstrated that plants and microbes can provide a diverse and natural source of compounds with potential use as pesticides.     

Development of a Real-Time PCR assay for quantitative assessment of uncultured freshwater zoosporic fungi

Recently, molecular environmental surveys of the eukaryotic microbial community in lakes have revealed a high diversity of sequences belonging to uncultured zoosporic fungi. Although they are known as saprobes and algal parasites in freshwater systems, zoosporic fungi have been neglected in microbial food web studies. Recently, it has been suggested that zoosporic fungi, via the consumption of their zoospores by zooplankters, could transfer energy from large inedible algae and particulate organic material to higher trophic levels. However, because of their small size and their lack of distinctive morphological features, traditional microscopy does not allow the detection of fungal zoospores in the field. Hence, quantitative data on fungal zoospores in natural environments is missing. We have developed a quantitative PCR (qPCR) assay for the quantification of fungal zoospores in lakes. Specific primers were designed and qPCR conditions were optimized using a range of target and non-target plasmids obtained from previous freshwater environmental 18S rDNA surveys. When optimal DNA extraction protocol and qPCR conditions were applied, the qPCR assay developed in this study demonstrated high specificity and sensitivity, with as low as 100 18S rDNA copies per reaction detected. Although the present work focuses on the design and optimization of a new qPCR assay, its application to natural samples indicated that qPCR offers a promising tool for quantitative assessment of fungal zoospores in natural environments. We conclude that this will contribute to a better understanding of the ecological significance of zoosporic fungi in microbial food webs of pelagic ecosystems.     

Identification and profiling of volatile metabolites of the biocontrol fungus Trichoderma atroviride by HS-SPME-GC-MS

In the present study we describe a method, which is based on solid phase microextraction (SPME) coupled to gas chromatography-mass spectrometry (GC-MS) and which can be used for the profiling of microbial volatile organic compounds (MVOCs) in the headspace (HS) of cultures of filamentous fungi. The method comprises the following successive steps: 1. growth of the fungus on a solid culture medium directly in headspace vials, 2. measurement of volatiles by HS-SPME-GC-MS, 3. deconvolution of mass spectra, 4. identification of volatiles by comparison of measured, deconvoluted mass spectra and linear temperature programmed retention indices (LTPRI) on two stationary GC phases with database entries and LTPRI published in the literature, and 5. profiling of the identified MVOCs.The developed method was successfully applied to cultures of the biocontrol fungus Trichoderma atroviride. An in-house library consisting of mass spectra and LTPRI values of fungal VOCs was established and used to study the profiles of MVOCs of this fungus. In total, 25 different MVOCs were identified by applying strict criteria (spectral match factor at least 90% and a maximum relative deviation of LTPRI of ± 2% from literature values). The MVOCs were assigned to the compound classes of alcohols, ketones, alkanes, furanes, pyrones (mainly the bioactive 6-pentyl-alpha-pyrone), mono- and sesquiterpenes, 13 of which have never been reported to be produced by Trichoderma spp. before. Eleven of these volatiles have been additionally confirmed using authentic standards. Finally, time course experiments and cultivation of T. atroviride in the presence of the mycotoxin fusaric acid demonstrated the potential of the method to study the dynamics of MVOC profiles as well as the effect of different environmental/biological conditions on the expression of MVOCs of filamentous fungi.     

Alpha-glucosidase and tyrosinase inhibitors from fungal hydroxylation of tibolone and hydroxytibolones

Sixteen new and one known metabolites 4-20 were obtained by incubation of tibolone (1) and hydroxytibolones (2 and 3) with various fungi. Their structures were elucidated by means of a homo and heteronuclear 2D NMR and by HREI-MS techniques. The relative stereochemistry was deduced by 2D NOESY experiment. Metabolites of tibolone (1) exhibited significant inhibitory activities against α-glucosidase and tyrosinase enzymes. Hydroxylations at C-6, C-10, C-11, C-15 positions and α,β-unsaturation at C-1/C-2, C-4/C-5 showed potent inhibitory activities against these enzymes.     

The influence of moisture on the suppression of Pseudomonas syringae by Aureobasidium pullulans on an artificial leaf surface

Abstract Isolates of Aureobasidium pullulans which produce antibacterial metabolites were compared with non-antibiotic-producing isolates of Tremella foliacea and Trichosporon beigelii for their ability to inhibit growth of Pseudomonas syringae pv phaseolicola . The bacteria and fungi were co-inoculated on an artificial leaf surface under conditions of low and high water availability. Under conditions of excess moisture, antibiotic production gave no advantage to the Aureobasidium isolates, and all the yeasts were equally antagonistic. Under drier conditions the Aureobasidium isolates reduced the population of P. syringae by 96–99%, a result which was significantly different from that which occurred when the bacteria were co-inoculated with the other yeasts under these conditions. An antibacterial compound, similar to that produced in liquid culture by Aureobasidium , was detected in washings from the artificial leaf surface following growth of this species.     

Bacterial Uptake by the Marine Sponge <Emphasis Type="Italic">Aplysina aerophoba</Emphasis>

Sponges (Porifera) are filter feeders that take up microorganisms from seawater and digest them by phagocytosis. At the same time, many sponges are known to harbor massive consortia of symbiotic microorganisms, which are phylogenetically distinct from those in seawater, within the mesohyl matrix. In the present study, feeding experiments were performed to investigate whether phylogenetically different bacterial isolates, hereafter termed “food bacteria,” microbial seawater consortia, and sponge symbiont consortia are taken up and processed differently by the host sponge. Aplysina aerophoba retained high numbers of bacterial isolates and microbial seawater consortia with rates of up to 2.76 × 10⁶ bacteria (g sponge wet weight)^–1 h^–1, whereas the retention of sponge symbionts was lower by nearly two orders of magnitude [5.37 × 10⁴ bacteria (g sponge wet weight)⁻¹ h^–1]. In order to visualize the processing of a food bacterium within sponge tissues, the green fluorescent protein-labeled Vibrio strain MMW1, which had originally been isolated from A. aerophoba, was constructed. Incubation of this strain with A. aerophoba and subsequent visualization in tissue cryosections showed its presence in the choanocytes and/or endopinacocytes lining the canals but, unlike latex beads, not in deeper regions of the mesohyl, which suggests digestion of the bacteria upon contact with the host. Denaturing gradient gel electrophoresis (DGGE) was performed on the incubation seawater to monitor the changes in phylogenetic composition after incubation of the sponge with either seawater or sponge symbiont consortia. However, the DGGE experiment provided no evidence for selective processing of individual lineages by the host sponge. In conclusion, this study extends early studies by Wilkinson et al. (Proc R Soc London B 220:519–528, 1984) that sponges, here A. aerophoba, are able to differentiate between food bacteria and their own bacterial symbionts.