摘要:

Organotin compounds are ubiquitous in the environment. The general order of toxicity to microorganisms increases with the number and chain length of organic groups bonded to the tin atom. Tetraorganotins and inorganic tin have little toxicity. Because of their lipophilicity, organotins are regarded as membrane active. There is evidence that the site of action of organotins may be both at the cytoplasmic membrane and intracellular level. Consequently, it is not known whether cell surface adsorption or accumulation within the cell, or both is a prerequisite for toxicity. Biosorption studies on a fungus, cyanobacteria, and microalgae indicates that cell surface binding alone occurred in these organisms, while studies on the effects of TBT (tributyltin) on certain microbial enzymes indicated that in some bacteria TBT can interact with cytosolic enzymes. Microorganism-organotin interactions are influenced by environmental conditions. In aquatic systems, both pH and salinity can determine organotin speciation and therefore reactivity. These environmental factors may also alter selectivity for resistant microorganisms in polluted systems. Tin-resistant microorganisms have been identified, and resistance can be either plasmid or chromosomally mediated. In one TBT-resistant organism, anAltermonassp., an efflux system was suggested as the resistance mechanism. Biotransformation of organotin compounds by debutylation or methylation has been observed. These reactions may influence the toxicity, mobility, and environmental fate of organotin compounds.Key words: inorganic tin, organotins, microorganisms, organotin resistance, biosorption, biotransformation.

ISSN:0008-4166    

DOI:10.1139/w99-048

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

In July 1996, bacterial abundance and incorporation of [3H]thymidine (3H-TdR) were determined every 4 h during a mesocosm experiment initially designed to study the effects of different intensities of ultraviolet-B (UVB) radiation on the summer planktonic community of the lower St. Lawrence Estuary. Water was obtained from the quay of the Maurice Lamontagne Institute (Mont-joli, Qué.) and incubated in experimental mesocosms (1500 L total volume,n= 8) with continuous mixing provided by a pumping system. During 72 h, different UVB intensities showed no significant effects on the bacterial incorporation of3H-TdR. This indicates that in the presence of other trophic levels and with continuous mixing, bacterioplankton responses to UVB are substantially different from those reported in axenic bacterial cultures or even whole-water incubations exposed to UVB at fixed depths. In conjunction with this observation,3H-TdR incorporation exhibited a significant periodic variation within all experimental treatments. The periodicity consisted of a 16-h cycle occurring independently of the time of the day. When the3H-TdR incorporation was normalized to cell abundance, the resulting cell-specific thymidine incorporation exhibited the same periodic oscillatory pattern. On the other hand, other factors suspected of inducing such a variability showed no consistent oscillation. In addition to suggesting an endogenously controlled activity of the studied bacterial community, the results of the present study indicate that failure of taking temporal variations of bacterial activity into account may introduce an error of almost 50% in the estimation of the daily thymidine incorporation rates. This represents a considerable error, because several studies rely on this measurement to estimate bacterial carbon production and to establish carbon budgets within different oceanic provinces.Key words: bacterioplankton, [3H]thymidine, ultraviolet-B radiation, periodicity, endogenous cycles, St. Lawrence Estuary

ISSN:0008-4166    

DOI:10.1139/w99-047

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

As genomic sequence data become more prevalent, the challenges in microbial physiology shift from identifying biochemical pathways to understanding the interactions that occur between them to create a robust but responsive metabolism. One of the most powerful methods to identify such interactions is in vivo phenotypic analysis. We have utilized thiamine synthesis as a model to detect subtle metabolic interactions due to the sensitivity allowed by the small cellular requirement for this vitamin. Although purine biosynthesis produces an intermediate in thiamine synthesis, mutants blocked in the first step of de novo purine biosynthesis (PurF) are able to grow in the absence of thiamine owing to an alternative synthesis. A number of general metabolic defects have been found to prevent PurF-independent thiamine synthesis. Here we report stimulation of thiamine-independent growth caused by a mutation in one or both genes encoding the pyruvate kinase isozymes. The results presented herein represent the first phenotype described for mutants defective inpykAorpykF, and thus identify metabolic interactions that exist in vivo.Key words: thiamine synthesis, metabolic integration.

ISSN:0008-4166    

DOI:10.1139/w99-042

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The influence of environmental factors on the nitrogen fixation activity of free-living, terrestrial cyanobacteria from a high arctic area were investigated using experimental manipulations with two different types of field samples, including macroscopic sheets ofNostoc communeand soil samples with a cyanobacterial crust from aPuccinelliasalt marsh. In addition, a culturedAnabaenasp. previously isolated from the salt marsh was examined. Nitrogen fixation activity was measured using the acetylene reduction method. The nitrogen fixation mainly took place in the light, but even after 12 h incubation in darkness, low activities were maintained. Phosphorus fertilization stimulated the nitrogen fixation activity, and the highest activities were obtained with about 300 &mgr;M phosphate, both in the field samples and the culturedAnabaenasp. Ammonium (28 mM) immediately inhibited the nitrogen fixation activity of the culturedAnabaenasp, whereas 14 mM urea and 540 &mgr;M glutamate led to a weaker and slower inhibition of the nitrogen fixation activity, showing that the culturedAnabaenasp. was able to assimilate these combined nitrogen sources. Nitrate did not have any inhibitory effect on nitrogen fixation activity, either in the field samples or in the culturedAnabaenasp. Both the field samples and the culturedAnabaenasp. showed tolerance against sodium chloride concentrations corresponding to the concentration in seawater. The temperature optimum of the nitrogen fixation activity of the culturedAnabaenasp. was about 20°C.Key words: nitrogen fixation, cyanobacteria,Nostoc commune,Anabaenasp., high arctic

ISSN:0008-4166    

DOI:10.1139/w99-040

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The presence of microfilamentous-like structures of tubular appearance (MFS) in cell walls and extracellular sheath material (ES) in a number of isolates ofOphiostoma novo-ulmiBrasier grown on various substrates and following various treatments is reported. Standard fixation or high-pressure freezing methods were used, and cytochemical tests were carried out to detect fungal and host wall components and, in some cases, fungal DNA. In some cases, serial 0.2-&mgr;m-thick sections were examined at 120 kV and tilted to obtain stereoscopic images. Whether the fungal cell walls were thick and composed of an outer opaque and inner more electron-lucent layers, or thin and barely perceptible, MFS were observed to extend from the cell cytoplasm as parallel structures across the walls into the surrounding medium, including host cell components in infected elm tissues. MFS were associated (in samples from inoculated trees) with cleavage and desquamation of fungal walls. ES and MFS did not label for cellulose or chitin, but generally labelled slightly for &bgr;-(1-3)-glucan and mannose, and strongly for galactose. Only the lucent, inner fungal wall layer labelled for chitin and cellulose. DNA labelling was confined to nuclei and mitochondria in fungal cells from cultures on agar medium; in cells from cultures on millipore membranes, it was pronounced over imprecisely delimited cell regions. The possible ontogeny of MFS components and their importance are discussed.Key words: chitin, Dutch elm disease, fungal fimbriae, fungal walls, gold-complexed probes, microfilamentous structures (MFS).

ISSN:0008-4166    

DOI:10.1139/w99-045

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

GenusPectinatusis strictly anaerobic bacteria described as a new beer spoilage flora. The physiological response ofPectinatus frisingensisto increasing heat treatments has been studied. Cell death occurred at temperatures higher than 50°C and increased with time. During heat treatment at 50°C, a potassium efflux of more than 50% of the internal potassium was measured at pH 6.2 in starving bacteria, whereas a small transient potassium efflux was measured with a similar 50°C treatment in energized cell suspensions. At beer pH values (pH 4.0), potassium content ofP. frisingensiscells was not changed by a moderate heat treatment. Internal pH values of cells were only slightly (0.1 pH unit) decreased upon heat treatments. In contrast, membrane potential value was lowered by a heat treatment at pH 6.2 in deenergized cells, while only a transient decrease of delta was measured with glucose in the medium. A moderate heat treatment at 50°C had no effect on the membrane potential value at pH 4.0, even after 1 h of treatment. In addition, compared with a high level of adenylate energy charge (AEC) measured in energized cell suspensions, an AEC of 0.7 was routinely measured in starving cell suspensions. Moderate heat treatments at pH 4.0 lowered the AEC of cells to 0.6. The physiological response ofP. frisingensisto mild heat treatments demonstrated a significant ability of the cell to maintain internal homeostasis at pH conditions encountered in beer.Key words:Pectinatus, thermal death, beer spoilage, homeosta

ISSN:0008-4166    

DOI:10.1139/w99-038

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Exoenzyme S fromP. aeruginosaDG1 and recombinant exoenzyme S derived from strain 388 have distinct characteristics, which has led to a controversy about their homology and their pathophysiologic consequences. We have been investigating the ability of exoenzyme S to activate T lymphocytes, and therefore performed studies to determine whether exoenzyme S fromP. aeruginosaDG1 and recombinant exoenzyme S derived from strain 388 and expressed inPseudomonas aeruginosaPA103 or inE. coliBL21(DE3), could induce T lymphocyte activation and proliferation. Both preparations were able to activate T cells and induce lymphocyte proliferation at similar levels as measured by flow cytometry of surface-activation markers and DNA synthesis, respectively. Further, a monoclonal antibody raised against exoenzyme S from strain DG1 partially neutralized T cell activation induced by recombinant exoenzyme S and bound to it in an immunoblot suggesting that the epitope responsible for T cell activation is shared by exoenzyme S from strain DG1 and recombinant exoenzyme S. These data suggest that the two different preparations of exoenzyme S, despite biochemical differences, share the characteristic that is responsible for T lymphocyte activation.Key words: exoenzyme S,Pseudomonas aeruginosa, T lymphocyte, cystic fibrosis.

ISSN:0008-4166    

DOI:10.1139/w99-044

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Pseudomonas chloroaphis3732 RN-L11 is a genetically modified bacterial strain that contains thelacZY marker genes in its chromosome. This strain is known to be a vigorous colonizer of plant roots and rhizosphere soil, and has been used as a model to evaluate survival and persistence of field-released genetically engineered microorganisms (GEMs). However, the possibility that strain 3732 RN-L11 may also colonize internal plant tissues has not previously been investigated. Using spring wheat as a model system, we studied the ability of strain 3732 RN-L11 to colonize external and internal root tissues after seed inoculation. Strain 3732 RN-L11 was recovered from rhizosphere soil of 28-, 42-, and 56-day-old seedlings with mean population sizes of 3.3 × 105, 7.5 × 104, and 2.2 × 105CFU·g-1fresh root tissue, respectively. In addition, this strain was consistently recovered from surface-sterilized root tissues of 28- to 56-day-old seedlings with mean population sizes of 1.0 × 102to 6.2 × 103CFU·g-1fresh root tissue. Our results indicate that evaluation of plant-associated GEM populations after field release should include all possible colonization niches, including internal plant tissues.Key words: genetically engineered microorganism, rhizosphere, endop

ISSN:0008-4166    

DOI:10.1139/w99-049

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The metal-binding properties ofPseudomonas aeruginosaPAO1 biofilms were investigated using four metals (Cu, Fe, Au, and La). All but one of the metals (i.e., Cu) were bound by the biofilms in amounts that were significantly greater than those bound by planktonically grown cells of the same strain. Lanthanum precipitation appeared to be limited to the base of the biofilms and was not promoted by a shift in lipopolysaccharide production by the cells.Key words: metal binding, biofilms, Gram-negative bacteria, bioremediation.

ISSN:0008-4166    

DOI:10.1139/w99-051

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Strain Lep1, isolated from a bacterial consortium capable of aerobic degradation of 4-methylquinoline (4-MQ), was chosen for further characterization as it was the only member of the consortium able to grow on 4-MQ in pure culture. Lep1 was identified as aSphingomonassp. based on phylogenetic analysis of 16S rDNA. Furthermore, the presence of sphingolipids and 2-hydroxy fatty acids in the membrane, and a 63% G + C ratio supports the placement of Lep1 in this genus. Additional genetic, physiological, and ecological characterization of bacteria such as Lep1 will allow for the potential exploitation of degradative strains for purposes of bioremediation of contaminated soils.Key words:Sphingomonas, degradation, 4-methylquinoline.

ISSN:0008-4166    

DOI:10.1139/w99-046

出版商:NRC Research Press    

年代:1999

数据来源: NRC