Detection, with a pH indicator, of bacterial mutants unable to denitrify

Mazoch, Jiří; Kučera, Igor

doi:10.1016/s0167-7012(02)00059-3

Cited by 10 publications

(4 citation statements)

References 20 publications

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“…Such microsites may be created within and around clusters of actively denitrifying cells. This has been demonstrated in biofilms (15) and utilized to differentiate between denitrifying and nondenitrifying colonies in agar (16). We are not aware of any studies of this phenomenon in soils, but alkalinization (1 to 2 pH units) of the soil close to roots during active uptake of NO 3 − has been demonstrated (17).…”

Section: Discussionmentioning

confidence: 99%

Impaired Reduction of N ₂ O to N ₂ in Acid Soils Is Due to a Posttranscriptional Interference with the Expression of nosZ

Liu

Frostegård

Bakken

2014

mBio

188

156

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Accumulating empirical evidence over the last 60 years has shown that the reduction of N2O to N2 is impaired by low soil pH, suggesting that liming of acid soils may reduce N2O emissions. This option has not gained much momentum in global change research, however, possibly due to limited understanding of why low pH interferes with N2O reductase. We hypothesized that the reason is that denitrifying organisms in soils are unable to assemble functional N2O reductase (N2OR) at low pH, as shown to be the case for the model strain Paracoccus denitrificans. We tested this by experiments with bacteria extracted from soils by density gradient centrifugation. The soils were sampled from a long-term liming experiment (soil pH 4.0, 6.1, and 8.0). The cells were incubated (stirred batches, He atmosphere) at pH levels ranging from 5.7 to 7.6, while gas kinetics (NO, N2O, and N2) and abundances of relevant denitrification genes (nirS, nirK, and nosZ) and their transcripts were monitored. Cells from the most acidic soil (pH 4.0) were unable to reduce N2O at any pH. These results warrant a closer inspection of denitrification communities of very acidic soils. Cells from the neutral soils were unable to produce functional N2OR at pH values of ≤6.1, despite significant transcription of the nosZ gene. The N2OR expressed successfully at pH 7.0, however, was functional over the entire pH range tested (5.7 to 7.6). These observations lend strong support to our hypothesis: low soil pH diminishes/prevents reduction of N2O, primarily by precluding a successful assembly of functional N2O reductase.

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Section: Discussionmentioning

confidence: 99%

Impaired Reduction of N ₂ O to N ₂ in Acid Soils Is Due to a Posttranscriptional Interference with the Expression of nosZ

Liu

Frostegård

Bakken

2014

mBio

188

156

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“…Tests for nitrate and nitrite reduction were performed using Griess reagents (27). Selection for denitrifiers was based on the results of the reduction tests and the pH indicator (19). This selection approach was validated by confirmation of the denitrifying activity of all isolates of the first batch with N 2 O measurements.…”

Section: Methodsmentioning

confidence: 99%

Cultivation of Denitrifying Bacteria: Optimization of Isolation Conditions and Diversity Study

Heylen

Vanparys

Wittebolle

et al. 2006

Appl Environ Microbiol

254

129

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An evolutionary algorithm was applied to study the complex interactions between medium parameters and their effects on the isolation of denitrifying bacteria, both in number and in diversity. Growth media with a pH of 7 and a nitrogen concentration of 3 mM, supplemented with 1 ml of vitamin solution but not with sodium chloride or riboflavin, were the most successful for the isolation of denitrifiers from activated sludge. The use of ethanol or succinate as a carbon source and a molar C/N ratio of 2.5, 20, or 25 were also favorable. After testing of 60 different medium parameter combinations and comparison with each other as well as with the standard medium Trypticase soy agar supplemented with nitrate, three growth media were highly suitable for the cultivation of denitrifying bacteria. All evaluated isolation conditions were used to study the cultivable denitrifier diversity of activated sludge from a municipal wastewater treatment plant. One hundred ninety-nine denitrifiers were isolated, the majority of which belonged to the Betaproteobacteria (50.4%) and the Alphaproteobacteria (36.8%). Representatives of Gammaproteobacteria (5.6%), Epsilonproteobacteria (2%), and Firmicutes (4%) and one isolate of the Bacteroidetes were also found. This study revealed a much more diverse denitrifying community than that previously described in cultivation-dependent research on activated sludge.For nearly 2 decades, molecular biology has provided the tools to successfully overcome the "great plate count anomaly" and allow the study of uncultured microbial diversity (3). The growing awareness that molecular methods cannot or, in very few cases, can only indirectly investigate the function of specific microorganisms in the environment has raised interest in new cultivation efforts and approaches once again (14,15,34). Simple adjustments to the classical cultivation approach, such as prolonging the incubation time and avoiding complex or nutrient-rich growth media, have successfully resulted in cultivation of previously uncultured bacteria (12,30).A physiological trait such as denitrification, the respiratory reduction of nitrate and nitrite to N 2 O and nitrogen gas, is not limited to specific microbial taxa and is therefore studied independent of culture through the relevant functional genes (6,25,32,38). To date, however, it is not clear to what extent, if at all, these functional genes contain phylogenetic information. Phillipot (22) showed that the phylogeny of nir and nor genes, coding for the key enzymes nitrite reductase and NO reductase in the denitrification pathway, does not always agree with the phylogeny of the 16S rRNA gene. New isolation and cultivation approaches are therefore imperative to provide the basis for further research on phylogenetic and functional gene diversity.The isolation of specific physiological groups of bacteria, such as denitrifiers, requires knowledge of the interactions of a large number of medium components and growth conditions. Genetic or evolutionary algorithms (EAs) are heuristic op...

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“…Macreadie et al have demonstrated in-vitro that by supplementing Candida albicans with ergesterol in aerobic culture can overcome the inhibition caused by statins [13]. Importantly, Nash et al have demonstrated that the addition of pravastatin or lovastatin does not affect fluconazole activity [21]. …”

Section: Discussionmentioning

confidence: 99%

Statins in Candidemia: clinical outcomes from a matched cohort study

Forrest

Kopack²,

Perencevich

2010

BMC Infect Dis

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BackgroundHMG CoA reductase inhibitors (statins) in patients with bacteremic sepsis have shown significant survival benefits in several studies. There is no data on the effect of statins in candidemic patients, however in-vitro models suggest that statins interfere with ergesterol formation in the wall of yeasts.MethodsThis retrospective matched- cohort study from 1/2003 to 12/2006 evaluated the effects of statins on patients with candidemia within intensive care units. Statin-users had candidemia as a cause of their systemic inflammatory response and were on statins throughout their antifungal therapy, while non-statin users were matched based on age +/- 5 years and co-morbid factors. Primary analysis was 30-day survival or discharge using bivariable comparisons. Multivariable comparisons were completed using conditional logistic regression. All variables with a p-value less than 0.10 in the bivariable comparisons were considered for inclusion in the conditional logistic model.ResultsThere were 15 statin-users and 30 non-statin users that met inclusion criteria, all with similar demographics and co-morbid conditions except the statin group had more coronary artery disease (P < 0.01) and peripheral vascular disease (P = 0.03) and lower median APCAHE II scores (14.6 vs 17, p = 0.03). There were no differences in duration of candidemia, antifungal therapy or Candida species between the groups. Statins were associated with lower mortality on bivariable (OR 0.09, 95% CI 0.11-0.75, p = 0.03) and multivariable (OR 0.22, 95% CI 0.02-2.4, p = 0.21) analyses compared to controls; although, in the latter the protective effect lacked statistical signficance.ConclusionIn our small, single-center matched-cohort study, statins may provide a survival benefit in candidemia, however further studies are warranted to validate and further explore this association.

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Detection, with a pH indicator, of bacterial mutants unable to denitrify

Cited by 10 publications

References 20 publications

Impaired Reduction of N ₂ O to N ₂ in Acid Soils Is Due to a Posttranscriptional Interference with the Expression of nosZ

Impaired Reduction of N ₂ O to N ₂ in Acid Soils Is Due to a Posttranscriptional Interference with the Expression of nosZ

Cultivation of Denitrifying Bacteria: Optimization of Isolation Conditions and Diversity Study

Statins in Candidemia: clinical outcomes from a matched cohort study

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Detection, with a pH indicator, of bacterial mutants unable to denitrify

Cited by 10 publications

References 20 publications

Impaired Reduction of N 2 O to N 2 in Acid Soils Is Due to a Posttranscriptional Interference with the Expression of nosZ

Impaired Reduction of N 2 O to N 2 in Acid Soils Is Due to a Posttranscriptional Interference with the Expression of nosZ

Cultivation of Denitrifying Bacteria: Optimization of Isolation Conditions and Diversity Study

Statins in Candidemia: clinical outcomes from a matched cohort study

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Product

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Impaired Reduction of N ₂ O to N ₂ in Acid Soils Is Due to a Posttranscriptional Interference with the Expression of nosZ

Impaired Reduction of N ₂ O to N ₂ in Acid Soils Is Due to a Posttranscriptional Interference with the Expression of nosZ