El Conocimiento Didáctico del Contenido en ciencias: estado de la cuestión

This paper gives a descriptive overview of the literature related to Pedagogical Content Knowledge - PCK - in the sciences. It is expected that this review can contribute to a better understanding of PCK, pointing out what has been investigated about this concept. Specifically, we analyze: a) how PCK is defined, what are its main features and how it has been appropriated by teachers; b) the relationship between PCK, knowledge of the contents to be taught and students learning; c) how PCK was actually used in teachers' training and teachers' evaluation; and, d) the scientific areas in which PCK has been studied. It concludes that PCK is an essential tool for improving the quality of teacher training

Epistemic beliefs and prior knowledge as predictors of the construction of different types of arguments on socioscientific issues

This study investigates whether university students’ epistemic beliefs and prior knowledge about controversial socioscientific issues (SSIs) can predict the different types of arguments that students construct. Two hundred forty‐three university students were asked to construct different types of supportive arguments—social, ethical, economic, scientific, ecological—as well as counterarguments and rebuttals after they had read a scenario on a SSI. Participants’ epistemic beliefs and prior knowledge were assessed separately. Results showed that students’ epistemic beliefs and prior knowledge predicted the quantity, quality, and diversity of the different types of arguments the students constructed. In particular, students who held sophisticated epistemic beliefs about the structure of knowledge and exhibited relatively more robust prior knowledge scores, produced arguments of greater quantity, better quality, and higher diversity than students with less sophisticated epistemic beliefs and low prior knowledge scores. Educational implications are discussed

Analysis of the Rhizobium meliloti exoH/exoK/exoL fragment: ExoK shows homology to excreted endo-beta-1,3-1,4-glucanases and ExoH resembles membrane proteins

BECKER A, KLEICKMANN A, Arnold W, Pühler A. Analysis of the Rhizobium meliloti exoH/exoK/exoL fragment: ExoK shows homology to excreted endo-beta-1,3-1,4-glucanases and ExoH resembles membrane proteins. Mol Gen Genet. 1993;238(1-2):145-154.Nucleotide sequencing of a 4.15 kb DNA fragment from megaplasmid 2 of Rhizobium meliloti 2011 revealed the location of the genes exoH, exoK and exoL. The putative proteins encoded by these genes have molecular weights of 41, 30, and 44 kDa, respectively. The hydrophobicity profile of the ExoH amino acid sequence resembles that of transmembrane proteins. The predicted exoL gene product does not contain hydrophobic regions, indicating a cytoplasmic localization. The exoK gene product is characterized by a putative signal peptide and exhibits significant homology to endo-beta-1,3-1,4-glucanases of bacilli and Clostridium thermocellum. R. meliloti exoK mutants induced pink nodules and synthesized a reduced amount of exopolysaccharide (EPS). Colonies of this mutant showed a delay in the appearance of the Calcofluor white fluorescence. In addition, the formation of the characteristic halo was strongly delayed. R. meliloti exoL and exoH mutants induced pseudonodules. The exoH, but not the exoL mutant, synthesized an EPS that could be precipitated by cetyl pyridinium chloride (CPC) and also by ethanol. Plasmid integration mutagenesis revealed promoter regions preceding exoH, exoK and exoL

Identification and analysis of the Rhizobium meliloti exoAMONP genes involved in exopolysaccharide biosynthesis and mapping of promoters located on the exoHKLAMONP fragment

BECKER A, KLEICKMANN A, KELLER M, Arnold W, Pühler A. Identification and analysis of the Rhizobium meliloti exoAMONP genes involved in exopolysaccharide biosynthesis and mapping of promoters located on the exoHKLAMONP fragment. Mol Gen Genet. 1993;241(3-4):367-379

THE RHIZOBIUM-MELILOTI PMI GENE ENCODES A NEW TYPE OF PHOSPHOMANNOSE ISOMERASE

SCHMIDT M, Arnold W, NIEMANN A, KLEICKMANN A, Pühler A. THE RHIZOBIUM-MELILOTI PMI GENE ENCODES A NEW TYPE OF PHOSPHOMANNOSE ISOMERASE. GENE. 1992;122(1):35-43.Interspecific complementation of a Xanthomonas campestris pv. campestris phosphomannose isomerase (PMI) mutant was used to isolate a cosmid from a genomic library of Rhizobium meliloti 2011 carrying the pmi gene of this strain. Subcloning experiments localized the coding region to a 2.0-kb SalI-ClaI fragment. Nucleotide sequence analysis of this fragment indicated the presence of two open reading frames (ORFs), coding for 18- and 43-kDa polypeptides. The analysis of the gene function by gene disruption experiments showed that ORF2 codes for pmi. A comparison of the deduced amino acid sequence with the corresponding sequences of the Pseudomonas aeruginosa and Escherichia coli PMIs revealed no significant homology, indicating that the isolated gene encodes a new type of PMI. The construction of a pmi-deficient mutant of R. meliloti using the sacB-sacR cassette technique showed that the loss of PMI activity does not affect the symbiotic properties of this strain

Analysis of the Rhizobium meliloti genes exoU, exoV, exoW, exoT, and exoI involved in exopolysaccharide biosynthesis and nodule invasion: exoU and exoW probably encode glucosyltransferases

BECKER A, KLEICKMANN A, KUESTER H, KELLER M, Arnold W, Pühler A. Analysis of the Rhizobium meliloti genes exoU, exoV, exoW, exoT, and exoI involved in exopolysaccharide biosynthesis and nodule invasion: exoU and exoW probably encode glucosyltransferases. Mol Plant Microbe Interact. 1993;6(6):735-744.Sequence analysis of a 5.780-kb DNA fragment originating from megaplasmid 2 of Rhizobium meliloti 2011 involved in biosynthesis of exopolysaccharide I (EPS I) and invasion of alfalfa nodules revealed the presence of five exo genes designated exoU, exoV, exoW, exoT, and exoI. ExoT resembled transmembrane proteins, whereas ExoI displayed a characteristic signal peptide. Sequence comparisons with several polysaccharide-polymerizing enzymes of both prokaryotic and eukaryotic origin indicated that exoW and exoU encode glucosyltransferases. Moreover, ExoV displayed weak homologies to the ExoO, ExoA, ExoL, and ExoM proteins of R. meliloti, which are also discussed as glucosyltransferases. Using exo-lacZ transcription fusions in connection with plasmid integration mutagenesis, promoters were identified in front of exoI, exoT, exoW, exoV, and exoU. R. meliloti 2011 strains with mutations in exoT, exoW, exoV, and exoU produced no detectable EPS I and were unable to infect alfalfa nodules, whereas exoI mutants synthesized a reduced amount of EPS I and did infect alfalfa nodules