An Archaeal Photosignal-Transducing Module Mediates Phototaxis in Escherichia coli

Halophilic archaea, such as Halobacterium salinarum and Natronobacterium pharaonis, alter their swimming behavior by phototaxis responses to changes in light intensity and color using visual pigment-like sensory rhodopsins (SRs). In N. pharaonis, SRII (NpSRII) mediates photorepellent responses through its transducer protein, NpHtrII. Here we report the expression of fusions of NpSRII and NpHtrII and fusion hybrids with eubacterial cytoplasmic domains and analyze their function in vivo in haloarchaea and in eubacteria. A fusion in which the C terminus of NpSRII is connected by a short flexible linker to NpHtrII is active in phototaxis signaling for H. salinarum, showing that the fusion does not inhibit functional receptor-transducer interactions. We replaced the cytoplasmic portions of this fusion protein with the cytoplasmic domains of Tar and Tsr, chemotaxis transducers from enteric eubacteria. Purification of the fusion protein from H. salinarum and Tar fusion chimera from Escherichia coli membranes shows that the proteins are not cleaved and exhibit absorption spectra characteristic of wild-type membranes. Their photochemical reaction cycles in H. salinarum and E. coli membranes, respectively, are similar to those of native NpSRII in N. pharaonis. These fusion chimeras mediate retinal-dependent phototaxis responses by Escherichia coli, establishing that the nine-helix membrane portion of the receptor-transducer complex is a modular functional unit able to signal in heterologous membranes. This result confirms a current model for SR-Htr signal transduction in which the Htr transducers are proposed to interact physically and functionally with their cognate sensory rhodopsins via helix-helix contacts between their transmembrane segments

The ‘why’ and ‘how’ of flexible learning spaces: A complex adaptive systems analysis

© 2019, Springer Nature B.V. This article presents the perceptions and experiences of 12 school principals, 35 teachers and 85 students on the influences and processes used by eight Australian government primary and secondary schools to transform traditionally arranged classrooms into flexible learning spaces. Characterised by a variety of furniture and layout options, these spaces are designed to enable a range of learning styles and activities and facilitate student-centred pedagogy. These changes to school learning environments are discussed in light of some central constructs of complexity theory, including inertial momentum, emergence, agent interaction, information flow, feedback loops and lock-in. The findings highlight the role of consultation, participation and ownership as central elements of sustainable change processes. Further effective design and transformation of learning environments requires a reflexive school community, pedagogical shift, professional development, and ongoing support to teachers and students. The discussion emphasizes the sociomaterial interplay between the pedagogical and physical classroom environment