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At least 199 records · Page 11Linked to original sources
PubMed1974

High-affinity accumulation of chloroquine by mouse erythrocytes infected with Plasmodium berghei.

Washed erythrocytes infected with chloroquine-susceptible (CS) or with chloroquine-resistant (CR) P. berghei were used in model systems in vitro to study the accumulation of chloroquine with high affinity. The CS model could achieve distribution ratios (chloroquine in cells: chloroquine in medium) of 100 in the absence of substrate. 200-300 in the presence of 10 mM pyruvate or lactate, and over 600 in the presence of 1 mM glucose or glycerol. In comparable studies of the CR model, the distribution ratios were 100 in the absence of substrate and 300 or less in the presence of glucose or glycerol. The presence of lactate stimulated chloroquine accumulation in the CR model, whereas the presence of pyruvate did not. Lactate production from glucose and glycerol was undiminished in the CR model, and ATP concentrations were higher than in the CS model. Cold, iodoacetate, 2,4-dinitrophenol, or decreasing pH inhibited chloroquine accumulation in both models. These findings demonstrate substrate involvement in the accumulation of chloroquine with high affinity.In studies of the CS model, certain compounds competitively inhibited chloroquine accumulation, while others did not. This finding is attributable to a specific receptor that imposes structural constraints on the process of accumulation. For chloroquine analogues, the position and length of the side chain, the terminal nitrogen atom of the side chain, and the nitrogen atom in the quinoline ring are important determinants of binding to this receptor.

Acetates↗
PubMed2000

[NO emission from winter wheat fields of rice-wheat rotation ecosystem in southeast China].

Measurements of NO emission from the winter wheat field of rice-wheat rotation ecosystem in southeast China during the whole period of wheat growth show that a higher NO emission was observed in spring than in autumn, and almost no emission in winter could be detected. Temperature was the most important factor determining the seasonal variation pattern of NO emission. Although the N fertilization might enlarge NO emission by a factor of 5-7, it could not modify the seasonal variation pattern. During the period of relatively weak plant activity, the diurnal variation pattern, with the maximum emission at 9:00-14:00, was determined by temperature. When plants luxuriated, however, the competition of NH4+ by plant uptake and by microbial nitrification led to a night-peak variation pattern, in which, the maximum diurnal emission usually occurred during 18:00 and 4:00 of next day, and the minimum at 8:00-16:00.

China↗
PubMed1996

Human natural yeast killer toxin-like candidacidal antibodies.

A murine mAb (mAbKT4, IgG1) that neutralized in vitro the anti-Candida activity of a killer toxic (KT) from the yeast Pichia anomala acted as an idiotypic (Id) vaccine in eliciting anti-Id Abs with toxin-like activity (KT-IdAb) in a rat vaginitis model. In this study, we demonstrate that intravaginal or intragastric inoculations of Candida albicans bearing a receptor for the toxin was able to recall KT-IdAb production in the vagina of the animals primarily immunized with mAbKT4 and also to elicit by themselves an Ab that functionally mimicked the KT (KTAb). Anti-Id-like, KT-like Abs were also consistently found in the vaginal fluid of human vaginitis patients who were infected by Candida but who had never been exposed to the Id vaccine. These Abs were as candidacidal in vitro as those raised in rat vagina by the Id vaccination, and, likewise, their cytocidal effect was totally neutralized by previous reaction with mAbKT4. Importantly, they were also able to confer a significant anticandidal protection in the rat vaginitis model, comparable to that achievable by KT-IdAb passively transferred to naive rats from Id-vaccinated animals. Thus, candidacidal Abs representing the internal image of a yeast KT are part of the Ab repertoire that follows infection or immunization with Candida. It is speculated that the host's immune system response may exploit the KT receptor of microbial pathogens to produce microbicidal Abs, possibly mirroring competition events among microorganisms in natural habitats.

Administration, Intravaginal↗
PubMed1997

Population dynamics and competition in chemostat models with adaptive nutrient uptake.

The standard Monod model for microbial population dynamics in the chemostat is modified to take into consideration that cells can adapt to the change of nutrient concentration in the chemostat by switching between fast and slow nutrient uptake and growing modes with asymmetric thresholds for transition from one mode to another. This is a generalization of a modified Monod model which considers adaptation by transition between active growing and quiescent cells. Global analysis of the model equations is obtained using the theory of asymptotically autonomous systems. Transient oscillatory population density and hysteresis growth pattern observed experimentally, which do not occur for the standard Monod model, can be explained by such adaptive mechanism of the cells. Competition between two species that can switch between fast and slow nutrient uptake and growing modes is also considered. It is shown that generically there is no coexistence steady state, and only one steady state, corresponding to the survival of at most one species in the chemostat, is a local attractor. Numerical simulations reproduce the qualitative feature of some experimental data which show that the population density of the winning species approaches a positive steady state via transient oscillations while that of the losing species approaches the zero steady state monotonically.

Animals↗
PubMed2026

The metabolic and anatomical complexity of root microhabitats modulate their interaction with the microbiota.

Plant roots constantly communicate with their microbiota, adapting their anatomy to facilitate microbial colonisation under abiotic stresses. Microbes, in turn, can reshape root anatomy once they establish. However, the mechanisms that coordinate this interplay remain largely unknown. Working with the aquatic plant family Lemnaceae, we reveal that the inherent complexity of root anatomy determines root plasticity in response to microbial colonisation. This microbiota-driven anatomical plasticity enhances plant survival in nutrient-competitive environments. By combining synthetic root models with real roots, we also find that anatomical plasticity is associated with metabolic reprogramming during microbial establishment. Moreover, we identify a plant metabolite, N6,N6,N6-Trimethyl-L-lysine, that regulates anatomical plasticity in response to microbial colonisation. Our work generalizes the importance of microhabitat complexity for microbiome recruitment under challenging environmental conditions.

Plant Roots↗
PubMed2004

Frontal and stealth attack strategies in microbial pathogenesis.

Interactions between microbes and human hosts can range from a benign, even symbiotic collaboration to a competition that may turn fatal--resulting in death of the host, the microbe or both. Despite advances that have been made over the past decades in understanding microbial pathogens, more people worldwide still die every year from infectious disease than from any other cause. This highlights the relevance of continuing to probe the mechanisms used by microorganisms to cause disease, and emphasizes the need for new model systems to advance our understanding of host-pathogen interactions.

Bartonella↗
PubMed2002

A two-species test of the hypothesis that spatial isolation influences microbial diversity in soil.

The hypothesis that spatial isolation is a key determinant of microbial community structure in soils was evaluated by examining the competitive dynamics of two species growing on a single resource in a uniform sand matrix under varied moisture content. One species dominated the community under highly connected, saturated treatments, suggesting that these conditions allow competitive interactions to structure the community. As moisture content decreased, however, the less competitive species became established in the community. This effect was most pronounced at a matric water potential of -0.14 MPa where estimates of final population density and species fitness were equal. A second but more closely related species pair exhibited a similar response to decreasing moisture, suggesting that the effects of spatial isolation we observed are not simply a species-pair-specific phenomenon. These findings indicate that spatial isolation, created by low moisture content, plays an important role in structuring soil microbial communities.

Cupriavidus necator↗
PubMed1996

An Experimental Test of the Rhizopine Concept in Rhizobium meliloti.

In some Rhizobium-legume symbioses, compounds known as rhizopines are synthesized by bacteroids and subsequently catabolized by free-living cells of the producing strain. It has been suggested than rhizopines act as proprietary growth substrates and enhance the competitive ability of the producing strain in its interactions with the diverse microbial community found within the rhizosphere. Wild-type, rhizopine-producing Rhizobium meliloti L5-30 and mutant L5-30 strains deficient for either rhizopine synthesis or catabolism were inoculated onto lucerne host plants in competition experiments. These experiments demonstrated that no apparent advantage resulted from the ability to synthesize a rhizopine, whereas the ability to catabolize rhizopine provided a clear advantage when an organism was in competition with a strain without this ability. The results suggest that when an organism is in competition with a catabolism-deficient mutant, the ability to catabolize rhizopine results in enhanced rates of nodulation. The results of the experiments were not consistent with the hypothesis that the sole role of rhizopines is to act as proprietary growth substrates for the free-living population of the producing strain.

Journal Article↗
PubMed2025

Health-associated key gut microbiota drives the variation in community metabolic interactions in non-human primates.

Gut microbiota often undergo metabolic cross-feeding and resource competition. However, our understanding of global variations in these interactions and their implications for host health remain elusive. By analyzing a microbial genome catalog from 841 fecal metagenomes across 53 primate species worldwide, we identified key microbiota assigned to two taxa, i.e., Bacillota_A and Pseudomonadota, which well predicted the trade-off of community-level interaction types between metabolic competition and cooperation. Specifically, Bacillota_A species were inherently competitive and amino acid auxotrophic and typically found in anaerobic habitats. In contrast, members of Pseudomonadota were inherently cooperative, siderophore producers, and more abundant in aerobic conditions. Random forest models successfully distinguished unhealthy gut samples from healthy samples through the key competitive and cooperative microbiota, suggesting potential links between community metabolic interactions and host health. Together, this study enhances our mechanistic understanding of microbial interaction dynamism within complex gut ecosystems, offering new targets for understanding host health.

Animals↗
PubMed1987

Slow-binding inhibition of chymotrypsin and cathepsin G by the peptide aldehyde chymostatin.

The microbial, peptide-derived aldehyde chymostatin is a potent, competitive inhibitor of chymotrypsin and cathepsin G: Ki = 4 X 10(-10) and 1.5 X 10(-7) M, respectively. Et is "slow-binding inhibitor" of both proteases and, as such, allows determination of rate constants for its association with and dissociation from these proteases. Inhibition kinetics indicate second-order rate constants for the association of chymostatin with chymotrypsin and cathepsin G of 360,000 and 2000 M-1 S-1, respectively and a first-order rate constant for the dissociation of both protease-chymostatin complexes of approximately 0.0002 s-1. Thus, the extreme difference in potency of chymostatin as an inhibitor of chymotrypsin and cathepsin G originates entirely in Kon. Solvent deuterium isotope effects (SIE) were determined to probe the reaction step that rate limits Kon. For the reaction of chymotrypsin with chymostatin, the SIE for Kon is 1.6 +/- 0.1, while for the reaction of chymotrypsin with the peptide substrates Ala-Ala-Phe-pNA and Suc-Ala-Ala-Pro-Phe-pNA, the SIE's for Kc/Km are 2.8 +/- 0.2 and 1.9 +/- 0.1, respectively. These results suggest that Kon for the association of chymotrypsin with chymostatin is at least partially rate limited by a reaction step involving proton transfer. Combined with results for the inhibition of chymotrypsin by Bz-Phe-H [Kennedy, W.P., & Schultz, R. M. (1979) Biochemistry 18, 349-356], these data suggest a mechanism for inhibition by chymostatin involving the general-base-catalyzed formation of an enzyme-bound hemiacetal, followed by a conformational change of this intermediate that produces the final, stable complex of enzyme and inhibitor.(ABSTRACT TRUNCATED AT 250 WORDS)

Cathepsin G↗
PubMed2003

Persistence of biofilm-associated Escherichia coli and Pseudomonas aeruginosa in groundwater and treated effluent in a laboratory model system.

This study was based on the hypothesis that groundwater-derived biofilms may provide a reservoir for coliform or pathogenic bacteria as has been observed in drinking water distribution systems. Escherichia coli, labelled with green fluorescent protein, was found to colonize all layers of mixed-population biofilms developed in association with indigenous groundwater micro-organisms in a laboratory-scale reactor. Biofilm-associated E. coli was removed at a slower rate from the reactor flasks than planktonic E. coli under a continuous flow regime. During flow-through of groundwater, planktonic E. coli removal was slower in flasks containing coverslips for enhanced biofilm development compared to a control flask without coverslips. Conversely, during flow-through of treated effluent, planktonic E. coli removal was faster in flasks with coverslips compared to without. Removal of attached E. coli was also fastest in the coverslip-containing flasks with effluent flow-through. This suggests that an increase in available nutrients may reduce E. coli survival potential due to either enhanced competition for nutrients or enhanced antagonism by the indigenous microbial population. Under identical conditions, GFP-labelled Pseudomonas aeruginosa was found to persist in the biofilms for longer than E. coli, most notably when exposed to flow-through of treated effluent. However, prolonged persistence of P. aeruginosa in the effluent could not be attributed to an association with the biofilms. This study has shown that under certain conditions the presence of mixed-population biofilms may limit the survival potential of enteric bacterial pathogens introduced into groundwater.

Biofilms↗
PubMed1993

Purification and biochemical characterization of the hydantoin hydrolyzing enzyme from Agrobacterium species. A hydantoinase with no 5,6-dihydropyrimidine amidohydrolase activity.

A soluble hydantoinase (5,6-dihydropyrimidine amidohydrolase) was purified to homogeneity from a newly isolated Agrobacterium species. This hydrolase consists of about 578 aminoacyl residues and is a slightly acidic protein with an isoelectric point of 6.5. The first 22 N-terminal amino acid residues were determined by Edman degradation. Determination of the relative molecular mass of the protein by gel-filtration chromatography gave an apparent value of 250,000. The subunit M(r) was 62,000, as estimated by analytical SDS/PAGE and 66,500, as estimated by denaturing gel-filtration chromatography. The pure hydantoinase exhibits the following hydrodynamic properties: a sedimentation coefficient of 8.8 S as determined by sedimentation velocity experiments; a Stokes radius of 6.8 nm; a diffusion coefficient of 31.5 microns2.s-1 as determined by analytical gel-filtration chromatography. From these experimental data, the following physical constants could be calculated: a theoretical M(r) of 265,000, a frictional ratio, f/fo, of 1.59, a maximal axial ratio, a/b, of 3.1; a Perrin shape factor, F, of 1.37. As shown by different Km values, the preferred substrates of this hydrolase were 5-monosubstituted hydantoins bearing aromatic substituents. 5,5-Dimethylhydantoin and different thio analogs of the 5-p-hydroxyphenylhydantoin molecule are competitive inhibitors of this hydrolase. The classification of this microbial hydantoinase, which exhibits no hydrolytic activity with all the dihydropyrimidines tested, under the systematic name of 5,6-dihydropyrimidine amidohydrolase, and its putative metabolic role are further discussed.

Amidohydrolases↗
PubMed1997

Characteristics of alcohol dehydrogenases of certain aerobic bacteria representing human colonic flora.

We have recently proposed the existence of a bacteriocolonic pathway for ethanol oxidation [i.e., ethanol is oxidized by alcohol dehydrogenases (ADHs) of intestinal bacteria resulting in high intracolonic levels of reactive and toxic acetaldehyde]. The aim of this in vitro study was to characterize further ADH activity of some aerobic bacteria, representing the normal human colonic flora. These bacteria were earlier shown to possess high cytosolic ADH activities (Escherichia coli IH 133369, Klebsiella pneumoniae IH 35385, Klebsiella oxytoca IH 35339, Pseudomonas aeruginosa IH 35342, and Hafnia alvei IH 53227). ADHs of the tested bacteria strongly preferred NAD as a cofactor. Marked ADH activities were found in all bacteria, even at low ethanol concentrations (1.5 mM) that may occur in the colon due to bacterial fermentation. The Km for ethanol varied from 29.9 mM for K. pneumoniae to 0.06 mM for Hafnia alvei. The inhibition of ADH by 4-methylpyrazole was found to be of the competitive type in 4 of 5 bacteria, and Ki varied from 18.26 +/- 3.3 mM for Escherichia coli to 0.47 +/- 0.13 mM for K. pneumoniae. At pH 7.4, ADH activity was significantly lower than at pH 9.6 in four bacterial strains. ADH of K. oxytoca, however, showed almost equal activities at neutral pH and at 9.6. In conclusion, NAD-linked alcohol dehydrogenases of aerobic colonic bacteria possess low apparent Km's for ethanol. Accordingly, they may oxidize moderate amounts of ethanol ingested during social drinking with nearly maximal velocity. This may result in the marked production of intracolonic acetaldehyde. Kinetic characteristics of the bacterial enzymes may enable some of them to produce acetaldehyde even from endogenous ethanol formed by other bacteria via alcoholic fermentation. The microbial ADHs were inhibited by 4-methylpyrazole by the same competitive inhibition as hepatic ADH, however, with nearly 1000 times lower susceptibility. Individual variations in human colonic flora may thus contribute to the risk of alcohol-related gastrointestinal morbidity, such as diarrhea, colon polyps and cancer, and liver injury.

Acetaldehyde↗
PubMed2000

Quantification of phnAc and nahAc in contaminated new zealand soils by competitive PCR.

Unculturable polycyclic aromatic hydrocarbon (PAH)-degrading bacteria are a significant reservoir of the microbial potential to catabolize low-molecular-weight PAHs. The population of these bacteria is larger than the population of nah-like bacteria that are the dominant organisms in culture-based studies. We used the recently described phn genes of Burkholderia sp. strain RP007, which feature only rarely in culture-based studies, as an alternative genotype for naphthalene and phenanthrene degradation and compared this genotype with the genotypically distinct but ubiquitous nah-like class in different soils. Competitive PCR quantification of phnAc and nahAc, which encode the iron sulfur protein large (alpha) subunits of PAH dioxygenases in nah-like and phn catabolic operons, revealed that the phn genotype can have a greater ecological significance than the nah-like genotype.

Biodegradation, Environmental↗
PubMed2025

Exploring genetic adaptation and microbial dynamics in engineered anaerobic ecosystems via strain-level metagenomics.

Genetic heterogeneity exists within all microbial populations, with sympatric cells of the same species often exhibiting single-nucleotide variations that influence phenotypic traits, including metabolic efficiency. However, the evolutionary dynamics of these strain-level differences in response to environmental stress remain poorly understood. Here, we present a first-of-its-kind study tracking the adaptive evolution of an anaerobic, carbon-fixing microbiota under a controlled engineered ecosystem focused on carbon dioxide bioconversion into methane. Leveraging strain-resolved metagenomics with an ad hoc variant calling and phasing approach, we mapped mutation trajectories and observed that the two dominant Methanothermobacter species maintained distinct sweeping haplotypes over time, most likely due to niche-specific metabolic roles. By combining population genetic statistics and peptide reconstruction, mer and mcrB genes emerged as potential drivers of archaeal strain-level competition. These findings pave the way for targeted engineering of microbial communities to enhance bioconversion efficiency, with significant implications for sustainable energy and carbon management in anaerobic systems.

Metagenomics↗
PubMed2002

Antibodies against homologous microbial caseinolytic proteases P characterise primary biliary cirrhosis.

BACKGROUND/AIMS: Antibodies to caseinolytic protease P(177-194) (ClpP(177-194)) of the proteolytic subunit of the Clp complex of Escherichia coli (E. coli) are uniquely present in primary biliary cirrhosis (PBC). Molecular mimicry between the regulatory subunit ClpX and the principal T-cell epitope of pyruvate dehydrogenase complex (PDC-E2) in PBC, has been proposed to account for this. Since ClpP is highly conserved among bacteria we investigated whether the micro-organisms triggering these antibodies may be other than E. coli. METHODS/RESULTS: E. coli ClpP(177-194) is homologous with ClpP peptides of Yersinia enterocolitica (YEREN) and Haemophilus influenzae (HAEIN). Enzyme linked immunosorbent assay (ELISA) reactivity to these peptides was tested in 45 patients with PBC, 44 pathological and 32 healthy controls. Reactivity to at least one of the ClpP peptides was observed in 21 (47%) PBC patients, 5.8% pathological and 3.1% healthy controls (P<0.01 for all). Among these 21 seropositive PBC patients, 15 (71%) reacted to ECOLI ClpP(177-194), alone or in association with YEREN and/or HAEIN peptides, compared to three (14.2%) reactive with YEREN, two (9.5%) with YEREN/HAEIN and one (4.7%) with HAEIN peptide. Simultaneous reactivity to homologous sequences was due to cross-reactivity as confirmed by competition ELISAs. CONCLUSIONS: The PBC-specificity of anti-microbial ClpP reactivity is confirmed: the questions as to primary trigger(s) and relevance to PBC pathogenesis remain open.

Adenosine Triphosphatases↗
PubMed1996

Competition and coexistence of sulfate-reducing and methanogenic populations in anaerobic biofilms.

The microbial population structure and function of natural anaerobic communities maintained in laboratory fixed-bed biofilm reactors were tracked before and after a major perturbation, which involved the addition of sulfate to the influent of a reactor that had previously been fed only glucose (methanogenic), while sulfate was withheld from a reactor that had been fed both glucose and sulfate (sulfidogenic). The population structure, determined by using phylogenetically based oligonucleotide probes for methanogens and sulfate-reducing bacteria, was linked to the functional performance of the biofilm reactors. Before the perturbation, the methanogenic reactor contained up to 25% methanogens as well as 15% sulfate-reducing bacteria, even though sulfate was not present in the influent of this reactor. Methanobacteriales and Desulfovibrio spp. were the most abundant methanogens and sulfate-reducing bacteria, respectively. The presence of sulfate-reducing bacteria (primarily Desulfovibrio spp. and Desulfobacterium spp.) in the absence of sulfate may be explained by their ability to function as proton-reducing acetogens and/or fermenters. Sulfate reduction began immediately following the addition of sulfate consistent with the presence of significant levels of sulfate-reducing bacteria in the methanogenic reactor, and levels of sulfate-reducing bacteria increased to a new steady-state level of 30 to 40%; coincidentally, effluent acetate concentrations decreased. Notably, some sulfate-reducing bacteria (Desulfococcus/Desulfosarcina/Desulfobotulus group) were more competitive without sulfate. Methane production decreased immediately following the addition of sulfate; this was later followed by a decrease in the relative concentration of methanogens, which reached a new steady-state level of approximately 8%. The changeover to sulfate-free medium in the sulfidogenic reactor did not cause a rapid shift to methanogenesis. Methane production and a substantial increase in the levels of methanogens were observed only after approximately 50 days following the perturbation.

Journal Article↗
PubMed1992

Characterization and growth response of bacteria in soil following application of carbofuran.

Enhanced biodegradation of carbofuran (2, 3-dihydro-2, 2 dimethyl-7-benzofuranyl methyl carbamate) is an economically significant, but poorly understood, microbial phenomenon in soil. A series of experiments was conducted to examine short term changes in soil bacterial populations stimulated by carbofuran application at field rates. In the field experiment, commercially formulated carbofuran and butylate (S-ethyl diisobutyl carbamothioate) were applied at 5.6 kg ai ha-1 and 8.4 kg ai ha-1, respectively, on a soil (Putnam silt loam) exhibiting enhanced degradation of carbofuran. In laboratory studies, technical grade carbofuran (20 mg kg-1 soil) was applied to samples of the field soil. Bacterial populations were estimated using non-selective (tryptic soy agar) and selective media containing carbofuran or butylate. Largest population increases in pesticide-treated soil were observed between 7 and 15 days after treatment (DAT) compared to populations in non-treated soil. Significant increases (P less than 0.05) in total bacterial populations and presumed carbofuran-degraders due to carbofuran application were associated with increased populations of Pseudomonas spp. and Flavobacterium spp. Application of carbofuran appeared to provide a competitive advantage to these species over actinomycetes persisting beyond 20 DAT. Growth responses of bacteria to carbofuran in the Putnam soil were compared to those in a native prairie soil (Mexico silt loam), which exhibited a much slower rate of carbofuran degradation. Bacterial population response to carbofuran was measurable, but small and short-lived. Perpetuation of the enhanced degradation phenomenon may lie in a persistent pesticide-induced competitive advantage given to a very small segment of the microbial population. This advantage may not be detectable after 20 days using conventional plating techniques.

Bacteria↗