4 research outputs found
A Multilaboratory Comparison of Calibration Accuracy and the Performance of External References in Analytical Ultracentrifugation
Analytical ultracentrifugation (AUC) is a first principles based method to determine absolute sedimentation coefficients and buoyant molar masses of macromolecules and their complexes, reporting on their size and shape in free solution. The purpose of this multi-laboratory study was to establish the precision and accuracy of basic data dimensions in AUC and validate previously proposed calibration techniques. Three kits of AUC cell assemblies containing radial and temperature calibration tools and a bovine serum albumin (BSA) reference sample were shared among 67 laboratories, generating 129 comprehensive data sets. These allowed for an assessment of many parameters of instrument performance, including accuracy of the reported scan time after the start of centrifugation, the accuracy of the temperature calibration, and the accuracy of the radial magnification. The range of sedimentation coefficients obtained for BSA monomer in different instruments and using different optical systems was from 3.655 S to 4.949 S, with a mean and standard deviation of (4.304 ± 0.188) S (4.4%). After the combined application of correction factors derived from the external calibration references for elapsed time, scan velocity, temperature, and radial magnification, the range of s-values was reduced 7-fold with a mean of 4.325 S and a 6-fold reduced standard deviation of ± 0.030 S (0.7%). In addition, the large data set provided an opportunity to determine the instrument-to-instrument variation of the absolute radial positions reported in the scan files, the precision of photometric or refractometric signal magnitudes, and the precision of the calculated apparent molar mass of BSA monomer and the fraction of BSA dimers. These results highlight the necessity and effectiveness of independent calibration of basic AUC data dimensions for reliable quantitative studies
The plight of a plover: Viability of an important snowy plover population with flexible brood care in Mexico
The Family Acholeplasmataceae (Including Phytoplasmas)The Prokaryotes
The family Acholeplasmataceae was originally established to
accommodate the genus Acholeplasma, comprising the mollicutes that
could be cultivated without the supplement of cholesterol and that
use UGA as a stop codon instead of coding for tryptophan. It was
later shown that the phytoplasmas, a large group of uncultivable,
wall-less, non-helical mollicutes that are associated with plants and
insects, shared taxonomically relevant properties with members of the
genus Acholeplasma. Being not cultivable in vitro in axenic culture, the
phytoplasmas could not be classified using the standards used for other
mollicutes and are named using the category of Candidatus, as “Ca.
Phytoplasma.”
Although phytoplasmas are associated with habitats and ecology
different from acholeplasmas, the two genera Acholeplasma and
“Candidatus Phytoplasma” are phylogenetically related and form a
distinct clade within the Mollicutes. The persisting inability to grow
the phytoplasmas in vitro hinders the identification of their distinctive
phenotypic traits, important criteria for mollicute classification. Until
supplemental phenotypic traits become available, the genus “Candidatus
Phytoplasma” is designated, on the basis of phylogeny, as a tentative
member in the family Acholeplasmataceae. Phylogenetic analysis based
on gene sequences, in particular, ribosomal sequences, has provided
the major supporting evidence for the composition and taxonomic
subdivision of this group of organisms with diverse habitats and ecology
and has become the mainstream for the Acholeplasmataceae systematics.
However, without the ability to determine phenotypic properties, the
circumscription of related species among the non culturable members of
the family remains a major issue.
The genus Acholeplasma comprises 14 species predominantly associated
with animals and isolated from mammalian fluids but regarded as not
normally pathogenic. Conversely, the genus “Ca. Phytoplasma” includes
plant pathogens of major economic relevance worldwide. To date, 36
“Ca. Phytoplasma species” have been described