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1.
A new apparatus for the continuous cultivation of mono and mixed bacterial plaque on solid surfaces is described. The features are: (i) easy preparation and handling; (ii) freedom from technical problems and microbial contamination; (iii) self-sufficient for periods of up to 56 d; (iv) 12 samples are taken simultaneously; (v) programmable supply inlet. Experiments were performed with Streptococcus mutans C 67–1 for mono bacterial inoculation and in combination with Veillonella alcalescens V-1 for mixed bacterial inoculations. The results showed that the controlled conditions and versatility of the apparatus make possible the study of plaque-development and lesion production on a time-dependent basis. It is concluded that the apparatus is suitable for a wide range of dental and non-dental applications. 相似文献
2.
在湖北省宜昌县百里荒草场山地黄棕壤上配合施用氮锌硒肥,研究其对混播白三叶,混播黑麦草及单播黑麦草的干重及混播白三叶的固氮作用和氮转移的影响,试验结果表明:(1)氮锌硒肥配合施用,混播黑麦草的干重均高于相应处理的单播黑麦草,混播牧草和单播黑麦草重最高的处理都是N46Zn0Se5,其干重辚25.38 g/盆和19.93g/盆。(2)施氮对混播白三叶,混播黑麦草及单播黑麦草的生长有明显的促进作用,施锌,硒对混播白三叶,混播黑麦草及单播黑麦草的生长作用不明显。(3)混播白三叶氮素的主要来源是固氮作用,占全氮产量的57.6000%-77.258%。(4)混播白三叶固定氮的转移量只占混播黑麦草的全氮产量的0.316%-12.251%,通过正交方差分析发现,适量氮肥(N30mg/kg)促进固定氮的转移,高量氮肥(N46mg/kg)抑制固定氮的转移。 相似文献
3.
The review summarizes the data on new directions in biosensor technologies based on whole bacterial cells. Biosensors for the monitoring of mono(poly)aromatic hydrocarbons and their chlorinated derivatives, which are constructed with genetically modified bacterial cells bearing a reporter gene fusion, are considered. The operating principle of these biosensors is based on the expression of reporter genes ( luc, lux, gfp, rfp) under the control of a promoter and a regulator that specifically respond to a detected compound. 相似文献
4.
A dot-blot, enzyme-linked immunosorbent method and a latex agglutination test were studied for their abilities to detect Vibrio cholerae serotype O1 in aquatic samples by testing artificially contaminated water as well as samples from natural potential sources. Water samples were preenriched with alkaline peptone and then enriched with Monsur peptone water. For the dot-blot test, enriched cultures of organisms in a small portion of the Monsur peptone water were transferred to a polyvinylidene difluoride membrane with a microfiltration apparatus. The enzyme-linked immunosorbent assay was performed by using biotin-labeled antibodies and avidin-biotin-peroxidase complex; brown dots developed in the wells that contained serotype O1 vibrios. Latex agglutination tests were performed by mixing 1 drop of the culture in Monsur with 1 drop of reagent coated with monoclonal antibody specific for antigen A. The sensitivities and specificities of the methods were compared with those of the colony-blot method, which identified individual colonies of V. cholerae O1 in mixed bacterial cultures on isolation media. Our results indicate that the dot-blot method is as sensitive as the colony-blot method and is useful for screening for V. cholerae serotype O1 even in specimens that are heavily contaminated with non-O1 vibrios. 相似文献
5.
In the apparatus described a multi-channel peristaltic pump is employed to supply precisely controlled amounts of two media (saliva substitute and nutrient broth) to bacterial plaques growing on extracted teeth and other surfaces, in 6 independent chambers under identical conditions. The same pump also removes waste products. A timer-controlled pneumatic switch programmes the delivery of medium as required. The assembly is compact and is sterilizable in a hospital autoclave as a complete unit. Surface cultures have been established following inoculation with both selected single strains and with mixed bacteria derived from saliva; in the latter instance, the bacterial deposits showed morphological resemblance to natural dental plaque. 相似文献
6.
The growth and composition of a population were studied during long-term (up to 50 days) batch cultivation of mono and mixed cultures of Pseudomonas aeruginosa S- and M-dissociants and Rhodobacter sphaeroides R- and M-dissociants without the addition of nutrients. During the cultivation of P. aeruginosa on a glucose-containing mineral medium, periodic lysis followed by polyculture growth resumption in the late stationary phase occurred on account of the M-dissociant: the change in its cell number corresponded to the change in the total cell number of the association. It was shown that the periodic occurrence of reducing sugars in the medium preceded the resumption of polyculture growth. Periodic secondary growth of the mixed culture of R. sphaeroides photosynthesizing bacteria occurred because of fast growing R-cells after the lysis of some part of the R-dissociant population. In the monoculture of the R. sphaeroides M-dissociant, R-cells were found during the whole period of cultivation, making up to 1–10% of the population irrespective of its size, which probably corresponded to the frequency of occurrence of this dissociant. In the R-dissociant monoculture, M-cells were found only after 26 days, and their number gradually decreased to half of population by the end of cultivation period. The joint growth of dissociants was characterized by the biomass increment and bacterial growth acceleration compared to monocultures, which is important for the fast development of new habitats under natural conditions. The cells of both bacterial species were lysed during long-term cultivation by exoproteinases secreted by the thin-wall cells of M-dissociants. 相似文献
7.
Algal production of dissolved organic carbon and the regeneration of nutrients from dissolved organic carbon by bacteria are important aspects of nutrient cycling in the sea, especially when inorganic nitrogen is limiting. Dissolved free amino acids are a major carbon source for bacteria and can be used by phytoplankton as a nitrogen source. We examined the interactions between the phytoplankton species Emiliania huxleyi and Thalassiosira pseudonana and a bacterial isolate from the North Sea. The organisms were cultured with eight different amino acids and a protein as the only nitrogen sources, in pure and mixed cultures. Of the two algae, only E. huxleyi was able to grow on amino acids. The bacterium MD1 used all substrates supplied, except serine. During growth of MD1 in pure culture, ammonium accumulated in the medium. Contrary to the expectation, the percentage of ammonium regenerated from the amino acids taken up showed no correlation with the substrate C/N ratio. In mixed culture, the algae grew well in those cultures in which the bacteria grew well. The bacterial yields (cell number) were also higher in mixed culture than in pure culture. In the cultures of MD1 and T. pseudonana, the increase in bacterial yield (number of cells) over that of the pure culture was comparable to the bacterial yield in mixed culture on a mineral medium. This result suggests that T. pseudonana excreted a more-or-less-constant amount of carbon. The bacterial yields in mixed cultures with E. huxleyi showed a smaller and less consistent difference than those of the pure cultures of MD1. It is possible that the ability of E. huxleyi to use amino acids influenced the bacterial yield. The results suggest that interactions between algae and bacteria influence the regeneration of nitrogen from organic carbon and that this influence differs from one species to another. 相似文献
8.
Type IV secretion (T4S) systems are versatile bacterial secretion systems mediating transport of protein and/or DNA. T4S systems are generally composed of 11 VirB proteins and 1 VirD protein (VirD4). The VirB1‐11 proteins assemble to form a secretion machinery and a pilus while the VirD4 protein is responsible for substrate recruitment. The structure of VirD4 in isolation is known; however, its structure bound to the VirB1‐11 apparatus has not been determined. Here, we purify a T4S system with VirD4 bound, define the biochemical requirements for complex formation and describe the protein–protein interaction network in which VirD4 is involved. We also solve the structure of this complex by negative stain electron microscopy, demonstrating that two copies of VirD4 dimers locate on both sides of the apparatus, in between the VirB4 ATPases. Given the central role of VirD4 in type IV secretion, our study provides mechanistic insights on a process that mediates the dangerous spread of antibiotic resistance genes among bacterial populations. 相似文献
9.
L ‐Dibenzoyl tartaric acid was mono‐esterified with benzyl alcohol, and then chlorinated with SOCl 2 to give (2 S,3 S)‐1‐(benzyloxy)‐4‐chloro‐1,4‐dioxobutane‐2,3‐diyl dibenzoate (Selector 1 ). (1 R,2 R)‐1,2‐Diphenylethylenediamine was mono‐functionalized with phenyl isocyanate and phenylene diisocyanate in sequence to give (1 R,2 R)‐1,2‐diphenyl‐2‐(3‐phenylureido)ethyl 4‐ isocyanatophenylurea (Selector 2 ). Two brush‐type chiral stationary phases (CSPs) of single selector were prepared by separately immobilizing selectors 1 and 2 on aminated silica gel. Selectors 1 and 2 were simultaneously immobilized on aminated silica gel to give a mixed selector CSP. The enantioseparation ability of these CSPs was studied. The CSP of selector 1 has strongest separation ability, while the enantioseparation ability of the mixed selector CSP is relatively lower. Chirality 2010. © 2009 Wiley‐Liss, Inc. 相似文献
10.
The mitotic apparatus that a plasmid uses to ensure its stable inheritance responds to the appearance of an additional copy of the plasmid's centromere by segregating it from the pre-existing copies: if the new copy arises by replication of the plasmid the result is partition, if it arrives on a different plasmid the result is incompatibility. Incompatibility thus serves as a probe of the partition mechanism. Coupling of distinct plasmids via their shared centromeres to form mixed pairs has been the favoured explanation for centromere-based incompatibility, because it supports a long-standing assumption that pairing of plasmid replicas is a prerequisite for their partition into daughter cells. Recent results from molecular genetic and fluorescence microscopy studies challenge this mixed pairing model. Partition incompatibility is seen to result from various processes, including titration, randomized positioning and a form of mixed pairing that is based on co-activation of the same partition event rather than direct contact between partition complexes. The perspectives thus opened onto the partition mechanism confirm the continuing utility of incompatibility as an approach to understanding bacterial mitosis. The results considered are compatible with the view that direct pairing of plasmids is not essential to plasmid partition. 相似文献
11.
Polychlorinated biphenyls (PCBs), also known by the trade name Sovol, are toxic industrial wastes. They have been subjected to chemical treatment by polyethylene glycols (PEGs) and potassium hydroxide. As a result of the interaction of the Sovol with various molecular mass PEGs (MM PEG-4 ~ 200, MM PEG-22 ~ 1000), water-soluble mixtures M1 and M2 containing mono(polyethylene glycol)oxy-derivatives (PCB-PEG-4 and PCB-PEG-22), polychlorobiphenylols, and unreacted PCB congeners (PCB 44, PCB 47, PCB 49, PCB 52, and PCB 66) were obtained. It was shown for the first time that mixtures M1 and M2 are susceptible to bacterial degradation without their fractionation. According to the gas-liquid chromatography with flame-ionization and mass-spectrometric detection, the Rhodococcus wratislaviensis KT112-7 strain degraded all of the chemical compounds occurring in the mixtures. In a 5-day experiment, it was found that the KT112-7 strain decomposes mono(polyethylene glycol)oxy-derivatives completely (by 100%) and polychlorobiphenylols and PCB congeners by 90–95% in the M1 and M2 mixtures. The culture medium did not contain transformation products, whereas free chlorine ions were accumulated (72–94% of the maximum possible amount). Thus, the use of the chemical modification and consecutive bacterial degradation provided an effective destruction of technical PCB mixtures with a high content of highly chlorinated congeners. 相似文献
12.
Accumulated evidence points to Porphyromonas gingivalis, Treponema denticola, and Tannerella forsythia as three major etiologic agents of chronic periodontitis. Epithelial cells and macrophages play a major role in the host response to periodontopathogens, and the secretion of inflammatory mediators and matrix metalloproteinases (MMPs) by these host cells is believed to contribute to periodontal tissue destruction. The aim of this study was to investigate the inflammatory response of a macrophage/epithelial cell co-culture model following mono or mixed infections with the above three periodontopathogens. An in vitro co-culture model composed of epithelial-like transformed cells (HeLa cell line) and macrophage-like cells (phorbol myristic acid-differentiated U937 monocytic cell line) was challenged with whole cells or lipopolysaccharides (LPS) of P. gingivalis, T. denticola, and T. forsythia, individually and in combination. Following stimulation, the production of interleukin-1 beta (IL-1beta), IL-6, IL-8, tumor necrosis factor alpha (TNF-alpha), regulated on activation normal T cell expressed and secreted (RANTES), prostaglandin E2 (PGE2), and MMP-9 were quantified by enzyme-linked immunoassays. We observed that mono or mixed infections of the co-culture model induced the secretion of IL-1beta, IL-6, IL-8, PGE2, and MMP-9. P. gingivalis and T. forsythia induced an increase in RANTES secretion, whereas T. denticola alone or in combination resulted in a significant decrease in RANTES levels. All LPS challenges induced an increase in chemokine, MMP-9, and PGE2 production. No synergistic effect on the production of cytokines, chemokines, PGE2, and MMP-9 was observed for any of the bacterial or LPS mixtures tested. This study supports the view that P. gingivalis, T. denticola, and T. forsythia may induce high levels of pro-inflammatory mediators and MMP-9 in periodontal lesions, thus contributing to the progression of periodontitis. 相似文献
13.
Microbial biomass which mostly generated from the microbial processes of bacteria, yeasts, and microalgae is an important resource. Recent concerns in microbial biomass production field, especially microbial lipid production for biofuel, have been focused towards the mixed culture of microalgae and yeast. To more comprehensive understanding of the mixed culture for microbial biomass, mono Chlorella pyrenoidosa, mono Yarrowia lipolytica and the mixed culture were investigated in the present work. Results showed that the mixed culture achieved significantly faster cell propagation of microalga and yeast, smaller individual cell size of yeast and higher relative chlorophyll content of microalga. The mixed culture facilitated the assimilation of carbon and nitrogen and drove the carbon flow to carbohydrate. Besides higher lipid yield (0.77 g/L), higher yields of carbohydrates (1.82 g/L), protein (1.99 g/L) and heating value (114.64 kJ/L) indicated the microbial biomass harvested from the mixed culture have more potential utilization in renewable energy, feedstuff, and chemical industry. 相似文献
14.
The type III secretion system (TTSS) of gram-negative bacteria is responsible for delivering bacterial proteins, termed effectors, from the bacterial cytosol directly into the interior of host cells. The TTSS is expressed predominantly by pathogenic bacteria and is usually used to introduce deleterious effectors into host cells. While biochemical activities of effectors vary widely, the TTSS apparatus used to deliver these effectors is conserved and shows functional complementarity for secretion and translocation. This review focuses on proteins that constitute the TTSS apparatus and on mechanisms that guide effectors to the TTSS apparatus for transport. The TTSS apparatus includes predicted integral inner membrane proteins that are conserved widely across TTSSs and in the basal body of the bacterial flagellum. It also includes proteins that are specific to the TTSS and contribute to ring-like structures in the inner membrane and includes secretin family members that form ring-like structures in the outer membrane. Most prominently situated on these coaxial, membrane-embedded rings is a needle-like or pilus-like structure that is implicated as a conduit for effector translocation into host cells. A short region of mRNA sequence or protein sequence in effectors acts as a signal sequence, directing proteins for transport through the TTSS. Additionally, a number of effectors require the action of specific TTSS chaperones for efficient and physiologically meaningful translocation into host cells. Numerous models explaining how effectors are transported into host cells have been proposed, but understanding of this process is incomplete and this topic remains an active area of inquiry. 相似文献
15.
BACKGROUND: Chloroplast division in plant cells occurs by binary fission, yielding two daughter plastids of equal size. Previously, we reported that two Arabidopsis homologues of FtsZ, a bacterial protein that forms a cytokinetic ring during cell division, are essential for plastid division in plants, and may be involved in the formation of plastid-dividing rings on both the stromal and cytosolic surfaces of the chloroplast envelope membranes. In bacteria, positioning of the FtsZ ring at the center of the cell is mediated in part by the protein MinD. Here, we identified AtMinD1, an Arabidopsis homologue of MinD, and investigated whether positioning of the plastid-division apparatus at the plastid midpoint might involve a mechanism similar to that in bacteria. RESULTS: Sequence analysis and in vitro chloroplast import experiments indicated that AtMinD1 contains a transit peptide that targets it to the chloroplast. Transgenic Arabidopsis plants with reduced AtMinD1 expression exhibited variability in chloroplast size and number and asymmetrically constricted chloroplasts, strongly suggesting that the plastid-division machinery is misplaced. Overexpression of AtMinD1 inhibited chloroplast division. These phenotypes resemble those of bacterial mutants with altered minD expression. CONCLUSIONS: Placement of the plastid-division machinery at the organelle midpoint requires a plastid-targeted form of MinD. The results are consistent with a model whereby assembly of the division apparatus is initiated inside the chloroplast by the plastidic form of FtsZ, and suggest that positioning of the cytosolic components of the apparatus is specified by the position of the plastidic components. 相似文献
16.
We describe an economical 20 litre bench-top fermenter suitable for production of recombinant antibody fragments in bacterial expression systems. The bacterial culture contained within a polycarbonate carboy is mixed (400-600 rpm) and aerated (1 vessel vol./min) by a high-shear radial flow impeller mounted on a hollow stainless steel shaft, through which pressurised air is pumped. Air is dispersed as fine bubbles into the culture medium by the turbine impeller, without the need for a porous sparger. A stainless steel baffle stabilised by a gliding counterweight increases mixing. The components can easily be disassembled for cleaning and sterilisation. Temperature (range 20-37 degrees C) and pH (range 7.0-7.5) are controlled manually. Using the apparatus, it proved possible to achieve Escherichia coli cell culture densities equivalent to an optical density at 600 nm (OD(600)) of 30-32, compared with OD(600) 4-6 in shake flasks. A yield of 40 mg/litre/day of a recombinant antibody fragment was obtained with the fermenter, which was 15-fold more than the yield of 2.5mg/litre/day achieved in shake flasks. The fermenter may be particularly suited for research purposes. 相似文献
17.
A specially built thermochemical death-rate apparatus is described which can be used to determine the resistance of microorganisms to ethylene oxide under controlled conditions. The apparatus was designed to provide instantaneous exposure of microorganisms to ethylene oxide and to eliminate variables that could result in errors when death kinetic reaction rates are calculated. The apparatus is used to obtain ethylene oxide resistance data which are useful in evaluating and developing sterilizing cycles for materials with known bacterial concentrations, as well as for calculating probability factors on which a given test condition can be expected to provide sterilization. 相似文献
18.
Bacterial type III secretion systems are thought to translocate virulence proteins directly from the bacterial cytoplasm into host cells through a continuous molecular channel. Little is known about how the apparatus itself interacts with membranes and whether insertion of this structure into the host membrane has consequences for the bacteria apart from its beneficial role in delivering virulence proteins. New evidence suggests that membrane insertion of the bacterial type III apparatus might turn on a calcium-dependent signaling pathway resulting in phagolysosomal fusion. 相似文献
19.
The type III secretion system (TTSS) of gram-negative bacteria is responsible for delivering bacterial proteins, termed effectors, from the bacterial cytosol directly into the interior of host cells. The TTSS is expressed predominantly by pathogenic bacteria and is usually used to introduce deleterious effectors into host cells. While biochemical activities of effectors vary widely, the TTSS apparatus used to deliver these effectors is conserved and shows functional complementarity for secretion and translocation. This review focuses on proteins that constitute the TTSS apparatus and on mechanisms that guide effectors to the TTSS apparatus for transport. The TTSS apparatus includes predicted integral inner membrane proteins that are conserved widely across TTSSs and in the basal body of the bacterial flagellum. It also includes proteins that are specific to the TTSS and contribute to ring-like structures in the inner membrane and includes secretin family members that form ring-like structures in the outer membrane. Most prominently situated on these coaxial, membrane-embedded rings is a needle-like or pilus-like structure that is implicated as a conduit for effector translocation into host cells. A short region of mRNA sequence or protein sequence in effectors acts as a signal sequence, directing proteins for transport through the TTSS. Additionally, a number of effectors require the action of specific TTSS chaperones for efficient and physiologically meaningful translocation into host cells. Numerous models explaining how effectors are transported into host cells have been proposed, but understanding of this process is incomplete and this topic remains an active area of inquiry. 相似文献
20.
The aim of this study was to evaluate the use of mono and mixed lactic acid bacteria (LAB) cultures to determine suitable LAB combinations for a type II sourdough system. In this context, previously isolated sourdough LAB strains with antimicrobial activity, which included Lactobacillus plantarum PFC22, Lactobacillus brevis PFC31, Pediococcus acidilactici PFC38, and Lactobacillus sanfranciscensis PFC80, were used as mono or mixed culture combinations in a fermentation system to produce type II sourdough, and subsequently in bread dough production. Compared to the monoculture fermentation of dough, the use of mixed cultures shortened the adaptation period by half. In addition, the use of mixed cultures ensured higher microbial viability, and enhanced the fruity flavor during bread dough production. It was determined that the combination of L. plantarum PFC22 + P. acidilactici PFC38 + L. sanfranciscensis PFC80 is a promising culture mixture that can be used in the production of type II sourdough systems, and that may also contribute to an increase in metabolic activity during bread production process. 相似文献
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