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- Beal, Jacob, et al.
(författare)
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Robust estimation of bacterial cell count from optical density
- 2020
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Ingår i: Communications Biology. - : Springer Science and Business Media LLC. - 2399-3642. ; 3:1
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Tidskriftsartikel (refereegranskat)abstract
- Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data.
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| 2. |
- Li, Ka Lok, et al.
(författare)
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A Probabilistic Tremor Location Method
- 2020
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Ingår i: Geophysical Research Letters. - : AMER GEOPHYSICAL UNION. - 0094-8276 .- 1944-8007. ; 47:4
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Tidskriftsartikel (refereegranskat)abstract
- A method to locate tremor with an unclear onset is introduced. The method maps envelopes of cross-correlated records from pairs of seismographs to signal likelihoods using Bayes' theorem. The likelihood time series are then back projected to obtain likelihoods of source location in space. Assuming that information derived from different station pairs is independent, the joint likelihood for all station pairs is the product of all individual station pair likelihoods. Its peak and spread give the most probable source location and its uncertainty. Robustness of the method has been evaluated with synthetic tests. The method recovers true location within 0.5 km with realistic noise characteristics in synthetic data. Uncertainty estimates are consistent with location deviations for sources inside the seismic network. When applied to real data from Katla and Eyjafjallajokull volcanoes in southern Iceland, their likely tremor source is also recovered within 1 km. Plain Language Summary Locating seismic sources is an important task in seismology. An accurate location of a volcanic event, for example, helps to understand processes within the volcano and sometimes to predict an eruption. Unlike earthquakes that usually manifest themselves as impulses in seismograms, many Earth processes, for example, continuous volcanic tremor, produce complex seismic signals without a clear onset. The timing of such processes cannot be measured. Therefore, traditional earthquake location methods fail. This article introduces a method to locate such processes. It maps the likelihood that a source occurs at any given location based on correlations of tremor recordings that are sensitive to the difference in propagation times of waves from the source to the two correlated recorders. The peak of this map is where the source location is most likely and its width provides information about its uncertainty. This is a major advance since most methods only yield an estimate of the location, not its uncertainty. The method has been tested with synthetic data that simulate realistic observational geometry and noise processes at volcanoes and is able to recover the true source location to within half a kilometer. Applications to real data at Katla and Eyjafjallajokull volcanoes in southern Iceland indicate similar accuracy.
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