Chiral evasion and stereospecific antifolate resistance in Staphylococcus aureus

Antimicrobial resistance presents a significant health care crisis. The mutation F98Y in Staphylococcus aureus dihydrofolate reductase (SaDHFR) confers resistance to the clinically important antifolate trimethoprim (TMP). Propargyl-linked antifolates (PLAs), next generation DHFR inhibitors, are much more resilient than TMP against this F98Y variant, yet this F98Y substitution still reduces efficacy of these agents. Surprisingly, differences in the enantiomeric configuration at the stereogenic center of PLAs influence the isomeric state of the NADPH cofactor. To understand the molecular basis of F98Y-mediated resistance and how PLAs’ inhibition drives NADPH isomeric states, we used protein design algorithms in the osprey protein design software suite to analyze a comprehensive suite of structural, biophysical, biochemical, and computational data. Here, we present a model showing how F98Y SaDHFR exploits a different anomeric configuration of NADPH to evade certain PLAs’ inhibition, while other PLAs remain unaffected by this resistance mechanism.     

Status of the so-called African pygmy elephant (Loxodonta pumilio (NOACK 1906)): phylogeny of cytochrome b and mitochondrial control region sequences

Among the African elephants, it has been unanimously acknowledged that the forest elephants (cyclotis form) are peculiar, so that they have been elevated to the specific rank. The development of molecular analyses of extant Loxodonta has only focused on two forms yet: the savannah form (africana) and the forest form (cyclotis), disregarding the so-called pygmy elephants (pumilio or fransseni) the systematic status of which has been debated since their discovery. Therefore, we have sampled nine dwarfed-labelled specimens in collection and eight specimens of typical forest elephants that we compared to three savannah elephants and two Asian elephants. Because of the degraded nature of the nuclear DNA content in bone samples of old specimens, we assayed mitochondrial markers; 1961 bp of the mitochondrial genome were sequenced (over a continuous range spanning the cytochrome b gene, tRNA Thr, tRNA Pro, hypervariable region 1 and central conserved region of the control region). Pumilio and cyclotis are not sister-taxa: the phylogenetic analyses rather account for the inclusion of the so-called pygmy elephants within a monophyletic group of forest elephants sensu lato. The internal structure of this clade reveals to depend on isolation and remoteness between populations, characteristics that may have been extensively influenced by climatic variations during the Quaternary period. We conclude that the specific taxon Loxodonta pumilio (or Loxodonta fransseni) should be abandoned.     

Taxonomic studies of the genus Hypoxis in East Africa

East African material of the genus Hypoxis L. has preliminarily been divided into the heterogenous, probably apomictic H. obtusa Burch- complex (2n = 40–50, ca. 75, 76, ca. 85, >86, ca. 92, ca. 98, ca. 108, 130–135, 160–200) and 5 rather homogenous species: H. angustifolia Lam. (2n = 14, 28), H. goetzei Harms (2n = ca. 62), H. kilimanjarica Bak., H. malosana Bak. (2n = 14) and H. macrocarpa Holt & Staubo sp. nov. H. kilimanjarica is divided into ssp. kilimanjarica and ssp. prostrata Holt & Staubo ssp. nov.     

A cationic chalcogenoxanthylium photosensitizer effective in vitro in chemosensitive and multidrug-resistant cells

Pentacyclic thio- (1) and seleno- (2) analogues of tetramethylrosamine (TMR) were prepared with a julolidyl fragment replacing the 3-dimethylamino substituent in the xanthylium core. The pentacylic structure increases the lipophilicity of 1 and 2 relative to TMR-S and TMR-Se and locks the lone-pair of electrons on the julolidyl N atom into conjugation with the xanthylium core. This conformational rigidization leads to longer wavelengths of absorption, but has little impact on other photophysical properties such as quantum yields for fluorescence and singlet-oxygen generation and fluorescence lifetimes in 1 and 2 relative to TMR-S and TMR-Se. Both 1 and 2 are effective photosensitizers against chemosensitive AUXB1 cells in vitro at 1 × 10⁻⁷ M and compound 2 is an effective photosensitizer against multidrug-resistant CR1R12 cells in vitro at 1 × 10⁻⁷ M. While the uptake TMR-S into CR1R12 cells as measured by fluorescence is significantly lower than uptake into chemosensitive AUXB1 cells, there is no significant difference in the uptake of 1 into either AUXB1 or CR1R12 cells. The addition of 2 × 10⁻⁴ M verapamil to the cells prior to treatment with 1 had no significant effect on the uptake of 1 into either AUXB1 or CR1R12 cells. Treating lipid-activated, purified Pgp with 2 and light gave complete inhibition of Pgp ATPase activity.     

Deletions of muscle mitochondrial DNA in mitochondrial myopathies: sequence analysis and possible mechanisms.

Forty per cent of patients with mitochondrial myopathies, a diverse group of multisystem diseases predominantly affecting skeletal muscle and the brain, have large deletions of a proportion of muscle mitochondrial DNA (mt DNA). These appeared to be identical in 13 of 28 cases, contained within the region 8286-13595 bp. Analysis of the deletion junction in two cases showed a 13 nucleotide sequence which occurred in the normal genome as a direct repeat flanking the region deleted in the mutant mt DNAs. Mt DNA deletions may arise from recombination or slippage between short sequence repeats during replication.     

Hearing sensitivity in two black bass species using the auditory brainstem response approach

Recently, several bioacoustic studies have focused on the red eye bass (Micropterus coosae). One of these studies documented sound production, while the other played back sounds produced by prey items in order to determine their attractiveness to M. coosae. Surprisingly, the hearing ability of fishes in the genus Micropterus has received very little attention. The need for audiograms describing hearing in Micropterus is apparent. This study utilized the auditory brainstem response (ABR) approach to determine hearing sensitivity in terms of both sound pressure level (SPL) and particle acceleration in two black bass species, the red eye bass (M. coosae) and the Alabama bass (M. henshalli). Audiograms produced in this study expressed in both SPL and particle acceleration showed a positive relationship between hearing threshold and frequency. Micropterus coosae was most sensitive to frequencies that overlap with the peak frequencies of their vocalizations, and the vocalizations of a prey species, Cyprinella trichroistia. Bass hearing sensitivities at lower frequencies, measured in terms of particle acceleration, were similar to several sciaenid species.     

Production of butanol by Clostridium puniceum in batch and continuous culture

Summary The pink-pigmented, amylolytic and pectinolytic bacterium Clostridium puniceum in anaerobic batch culture at pH 5.5 and 25–30°C produced butan-1-ol as the major product of fermentation of glucose or starch. The alcohol was formed throughout the exponential phase of growth and surprisingly little acetone was simultaneously produced. Furthermore, acetic and butyric acids were only accumulated in low concentrations, and under optimal conditions were completely re-utilised before the fermentation ceased. Thus, in a minimal medium containing 4% w/v glucose as sole source of carbon and energy, after 65 h at 25°C, pH 5.5 all of the glucose had been consumed to yield (g product/100 g glucose utilised) butanol 32, acetone 3 and ethanol 2. Butanol was again the major product of glucose fermentation during phosphate-limited chemostat culture wherein, although the organism eventually lost its capacity to sporulate and to synthesize granulose, production of butanol continued for at least 100 volume changes. Under no growth condition was the organism capable of producing more than 13.3 g l^-1 of butanol. At pH 5.5, growth on pectin was slow and yielded a markedly lesser biomass concentration than when growth was on glucose or starch; acetic acid was the major fermentation product with lower concentrations of methanol, acetone, butanol and butyric acid. At pH 7, growth on all substrates produced virtually no solvents but high concentrations of both acetic and butyric acids.