Inhibition of acid production in Streptococcus mutans R9: Inhibition constants and reversibility

Abstract The pac gene encoding the penicillin G acylase (PGA) of Bacillus megaterium ATCC 14945 has been cloned in Escherichia coli HB101 ( proA, leuB ) using a selective minimal medium containing phenylacetyl-L-leucine instead of L-leucine. The nucleotide sequence of this gene has been determined and contains an open reading frame of 2406 nucleotides. The deduced amino acid sequence shows significant similarity with other β-lactam acylases. Although the PGA of B. megaterium is extracellular, the enzyme produced in E. coli appears to have a cytoplasmic localization.     

Quantifying marine snow as a food choice for zooplankton using stable silicon isotope tracers

Aggregates of biogenic origin >0.5 mm, known as marine snow,represent a concentrated potential source of food for zooplankton.Little is known, however, about whether aggregates are commonlygrazed by zooplankton in the field. While previous laboratorystudies have shown that the euphausiid Euphausia pacifica, andthe copepod, Calanus pacificus, common crustacean zooplankters,consume marine snow if it is the only food source available,it is not known if euphausiids will select marine snow in thepresence of edible dispersed cells, as readily occurs in nature.To examine this question, we offered E. pacifica the diatom,Nitzschia angularis in aggregated and dispersed form as preysimultaneously. Aggregates and dispersed food contained identicalcell types so that differing prey quality, taste or motilitywould not be a factor. A new method was developed to track foodsources by labeling the frustules of aggregated cells with differentnaturally occurring, but rare, stable isotopes of silicon, ³⁰Siand ²⁹Si. Food selection was then estimated by measuring theisotopic composition of silica within fecal pellets producedby animals feeding on mixtures of the two labeled foods. Resultsindicate that E. pacifica consumed both aggregates and dispersedcells, even when more cells were made available in dispersedform than in aggregated form. This suggests that aggregatesmay indeed be a food source in the field, even when dispersedcells are relatively abundant. The method of labeling diatomcells with stable isotopes of silica may prove useful for futuregrazing experiments to distinguish identical cell types.     

How to Report Record Open‐Circuit Voltages in Lead‐Halide Perovskite Solar Cells

Open‐circuit voltages of lead‐halide perovskite solar cells are improving rapidly and are approaching the thermodynamic limit. Since many different perovskite compositions with different bandgap energies are actively being investigated, it is not straightforward to compare the open‐circuit voltages between these devices as long as a consistent method of referencing is missing. For the purpose of comparing open‐circuit voltages and identifying outstanding values, it is imperative to use a unique, generally accepted way of calculating the thermodynamic limit, which is currently not the case. Here a meta‐analysis of methods to determine the bandgap and a radiative limit for open‐circuit voltage is presented. The differences between the methods are analyzed and an easily applicable approach based on the solar cell quantum efficiency as a general reference is proposed.     

A Roman well in Waldgirmes (Hesse,Germany): palynological analyses supported by plant macro-remains and micromorphological studies

Vegetation History and Archaeobotany - Waldgirmes in Hesse (Germany) is one of the oldest Roman towns east of the Rhine River. It was founded in 3 bc and abandoned after ad 9, probably in ad 16,...     

Ecological and geological processes impacting speciation modes drive the formation of wide-range disjunctions within tribe Putorieae (Rubiaceae)

Wide-range geographically discontinuous distributions have long intrigued scientists. We explore the role of ecology, geology, and dispersal in the formation of these large-scale disjunctions, using the angiosperm tribe Putorieae (Rubiaceae) as a case study. From DNA sequences of nuclear ITS and six plastid markers, we inferred a phylogeny with 65% of all known Putorieae species. Divergence times, ancestral ranges, and diversification rate shifts were then estimated using Bayesian inference. We further explored species climatic tolerances and performed ancestral niche reconstruction to discriminate among alternative speciation modes, including geographical and ecological vicariance, and ecogeographical, ecological, and dispersal-mediated speciation. As a result, we identified seven major clades in Putorieae, some of which exhibit striking geographical disjunctions, matching the Rand Flora pattern, with sister species in the Canary Islands andeastern and southern Africa. Initial diversification within the tribe occurred in the early Miocene, coincident with a period of climate warming; however, most clades diverged within the last 10 Myr. Aridification and high extinction rates, coupled with ecological vicariance, explain the oldest disjunctions. Adaptation to new environmental conditions, after allopatry, is observed in several clades. Dispersal, either long-distance or via corridors made available by mountain uplift, is behind the most recent disjunctions. Some of these events were followed by ecological speciation and rapid diversification, with species becoming adapted to xeric or increasingly colder continental climates. We show that an integrative approach may help discriminate among speciation modes invoked to explain disjunctions at macroevolutionary time scales, even when extinction has erased the signature of past events.