Regulation of dissimilatory sulfur oxidation in the purple sulfur bacterium Allochromatium vinosum

In the purple sulfur bacterium Allochromatium vinosum, thiosulfate oxidation is strictly dependent on the presence of three periplasmic Sox proteins encoded by the soxBXAK and soxYZ genes. It is also well documented that proteins encoded in the dissimilatory sulfite reductase (dsr) operon, dsrABEFHCMKLJOPNRS, are essential for the oxidation of sulfur that is stored intracellularly as an obligatory intermediate during the oxidation of thiosulfate and sulfide. Until recently, detailed knowledge about the regulation of the sox genes was not available. We started to fill this gap and show that these genes are expressed on a low constitutive level in A. vinosum in the absence of reduced sulfur compounds. Thiosulfate and possibly sulfide lead to an induction of sox gene transcription. Additional translational regulation was not apparent. Regulation of soxXAK is probably performed by a two-component system consisting of a multi-sensor histidine kinase and a regulator with proposed di-guanylate cyclase activity. Previous work already provided some information about regulation of the dsr genes encoding the second important sulfur-oxidizing enzyme system in the purple sulfur bacterium. The expression of most dsr genes was found to be at a low basal level in the absence of reduced sulfur compounds and enhanced in the presence of sulfide. In the present work, we focused on the role of DsrS, a protein encoded by the last gene of the dsr locus in A. vinosum. Transcriptional and translational gene fusion experiments suggest a participation of DsrS in the post-transcriptional control of the dsr operon. Characterization of an A. vinosum ΔdsrS mutant showed that the monomeric cytoplasmic 41.1-kDa protein DsrS is important though not essential for the oxidation of sulfur stored in the intracellular sulfur globules

A Comparison of the Danish and the Virginia Secondary teacher Education System: Their values and Emphasis on Mathematics Content Knowledge

In this paper I will first examine an example of secondary mathematics teacher education in the USA, namely Virginia, then compare it with the secondary teacher education in Denmark. The purpose is both to investigate how much mathematics the students get in the respective systems and secondly to see what this type of teacher education communicates about the values emphasized in the various countries’ education systems. I spent more time on explaining the Danish education system than that of the USA and the single states since it is assumed that the reader is familiar with these systems. One cannot necessarily deduce from number of courses how much mathematics the student actually “gets” since this depends on particular passing requirements as well as requirements of entry, the specific content of the courses both in terms of levels of difficulty and topics, etc. However, a comparison of course load indicates how much study of “mathematics” is perceived enough, or minimum, to teach secondary mathematics from the national or state political perspective (who might see a direct link between course load and knowledge)

A Comparison of the Danish and the Virginia Secondary teacher Education System: Their values and Emphasis on Mathematics Content Knowledge

In this paper I will first examine an example of secondary mathematics teacher education in the USA, namely Virginia, then compare it with the secondary teacher education in Denmark. The purpose is both to investigate how much mathematics the students get in the respective systems and secondly to see what this type of teacher education communicates about the values emphasized in the various countries’ education systems. I spent more time on explaining the Danish education system than that of the USA and the single states since it is assumed that the reader is familiar with these systems. One cannot necessarily deduce from number of courses how much mathematics the student actually “gets” since this depends on particular passing requirements as well as requirements of entry, the specific content of the courses both in terms of levels of difficulty and topics, etc. However, a comparison of course load indicates how much study of “mathematics” is perceived enough, or minimum, to teach secondary mathematics from the national or state political perspective (who might see a direct link between course load and knowledge)