Genomic Expansion of Magnetotactic Bacteria Reveals an Early Common Origin of Magnetotaxis with Lineage-specific Evolution

The origin and evolution of magnetoreception, which in diverse prokaryotes and protozoa is known as magnetotaxis and enables these microorganisms to detect Earth’s magnetic field for orientation and navigation, is not well understood in evolutionary biology. The only known prokaryotes capable of sensing the geomagnetic field are magnetotactic bacteria (MTB), motile microorganisms that biomineralize intracellular, membrane-bounded magnetic single-domain crystals of either magnetite (Fe3O4) or greigite (Fe3S4) called magnetosomes. Magnetosomes are responsible for magnetotaxis in MTB. Here we report the first large-scale metagenomic survey of MTB from both northern and southern hemispheres combined with 28 genomes from uncultivated MTB. These genomes expand greatly the coverage of MTB in the Proteobacteria, Nitrospirae, and Omnitrophica phyla, and provide the first genomic evidence of MTB belonging to the Zetaproteobacteria and “Candidatus Lambdaproteobacteria” classes. The gene content and organization of magnetosome gene clusters, which are physically grouped genes that encode proteins for magnetosome biosynthesis and organization, are more conserved within phylogenetically similar groups than between different taxonomic lineages. Moreover, the phylogenies of core magnetosome proteins form monophyletic clades. Together, these results suggest a common ancient origin of iron-based (Fe3O4 and Fe3S4) magnetotaxis in the domain Bacteria that underwent lineage-specific evolution, shedding new light on the origin and evolution of biomineralization and magnetotaxis, and expanding significantly the phylogenomic representation of MTB

Chromosomal instability in enterohaemorrhagic Escherichia coli O157:H7: impact on adherence, tellurite resistance and colony phenotype

Tellurite (Tel) resistant enterohaemorrhagic Escherichia coli (EHEC) O157:H7 is a global pathogen. In strain EDL933 Tel resistance (TelR) is encoded by duplicate ter cluster in O islands (OI) 43 and 48, which also harbour iha, encoding the adhesin and siderophore receptor Iha. We identified five EHEC O157:H7 strains that differentiate into large (L) colonies and small (S) colonies with high and low Tel minimal inhibitory concentrations (MICs) respectively. S colonies (Tel-MICs ≤ 4 µg ml−1) sustained large internal deletions within the TelR OIs via homologous recombination between IS elements and lost ter and iha. Moreover, complete excision of the islands occurred by site-specific recombination between flanking direct repeats. Complete excision of OI 43 and OI 48 occurred in 1.81 × 10−3 and 1.97 × 10−4 cells in culture, respectively; internal deletion of OI 48 was more frequent (9.7 × 10−1 cells). Under iron limitation that promotes iha transcription, iha-negative derivatives adhered less well to human intestinal epithelial cells and grew slower than did their iha-positive counterparts. Experiments utilizing iha deletion and complementation mutants identified Iha as the major factor responsible for these phenotypic differences. Spontaneous deletions affecting TelR OIs contribute to EHEC O157 genome plasticity and might impair virulence and/or fitness

The genetic organisation of prokaryotic two-component system signalling pathways

<p>Abstract</p> <p>Background</p> <p>Two-component systems (TCSs) are modular and diverse signalling pathways, involving a stimulus-responsive transfer of phosphoryl groups from transmitter to partner receiver domains. TCS gene and domain organisation are both potentially informative regarding biological function, interaction partnerships and molecular mechanisms. However, there is currently little understanding of the relationships between domain architecture, gene organisation and TCS pathway structure.</p> <p>Results</p> <p>Here we classify the gene and domain organisation of TCS gene loci from 1405 prokaryotic replicons (>40,000 TCS proteins). We find that 200 bp is the most appropriate distance cut-off for defining whether two TCS genes are functionally linked. More than 90% of all TCS gene loci encode just one or two transmitter and/or receiver domains, however numerous other geometries exist, often with large numbers of encoded TCS domains. Such information provides insights into the distribution of TCS domains between genes, and within genes. As expected, the organisation of TCS genes and domains is affected by phylogeny, and plasmid-encoded TCS exhibit differences in organisation from their chromosomally-encoded counterparts.</p> <p>Conclusions</p> <p>We provide here an overview of the genomic and genetic organisation of TCS domains, as a resource for further research. We also propose novel metrics that build upon TCS gene/domain organisation data and allow comparisons between genomic complements of TCSs. In particular, '<it>percentage orphaned TCS genes</it>' (or 'Dissemination') and '<it>percentage of complex loci</it>' (or 'Sophistication') appear to be useful discriminators, and to reflect mechanistic aspects of TCS organisation not captured by existing metrics.</p

Insight into the Assembly Properties and Functional Organisation of the Magnetotactic Bacterial Actin-like Homolog, MamK

Magnetotactic bacteria (MTB) synthesize magnetosomes, which are intracellular vesicles comprising a magnetic particle. A series of magnetosomes arrange themselves in chains to form a magnetic dipole that enables the cell to orient itself along the Earth’s magnetic field. MamK, an actin-like homolog of MreB has been identified as a central component in this organisation. Gene deletion, fluorescence microscopy and in vitro studies have yielded mechanistic differences in the filament assembly of MamK with other bacterial cytoskeletal proteins within the cell. With little or no information on the structural and behavioural characteristics of MamK outside the cell, the mamK gene from Magnetospirillium gryphiswaldense was cloned and expressed to better understand the differences in the cytoskeletal properties with its bacterial homologues MreB and acitin. Despite the low sequence identity shared between MamK and MreB (22%) and actin (18%), the behaviour of MamK monitored by light scattering broadly mirrored that of its bacterial cousin MreB primarily in terms of its pH, salt, divalent metal-ion and temperature dependency. The broad size variability of MamK filaments revealed by light scattering studies was supported by transmission electron microscopy (TEM) imaging. Filament morphology however, indicated that MamK conformed to linearly orientated filaments that appeared to be distinctly dissimilar compared to MreB suggesting functional differences between these homologues. The presence of a nucleotide binding domain common to actin-like proteins was demonstrated by its ability to function both as an ATPase and GTPase. Circular dichroism and structural homology modelling showed that MamK adopts a protein fold that is consistent with the ‘classical’ actin family architecture but with notable structural differences within the smaller domains, the active site region and the overall surface electrostatic potential

Untersuchungen zur molekularen Organisation und Regulation der mam-Gene in Magnetospirillum gryphiswaldense MSR-1

The biomineralization of the magnetosomes in magnetotactic bacteria (MTB) is governed by coordinated cellular and physico-chemical processes, which are controlled by the magnetosome membrane proteins (MMP), but poorly understood on the biochemical and molecular level. In this work the genomic and transcriptional organization of the mam and mms genes encoding these MMPs in Magnetospirillum gryphiswaldense were investigated. A close genetic linkage of the mam genes could be determined. The colocalization of all magnetosome genes, the high abundance of insertion sequence elements, and its high genetic instability lead to the discovery of a magnetosome island (MAI) of approximately 130 kb. Spontaneous non-magnetic mutants exhibiting deletions or rearrangements within the MAI occurred frequently under conditions of prolonged storage and oxygen stress. One of these non-magnetic mutants, designated strain MSR-1B, harbours a deletion of 40 kb comprising all magnetosome genes. Long polycistronic transcripts could be confirmed by RT-PCR for three major gene operons harbouring magnetosome genes. The transcriptional start points were determined 22 bp, 52 bp, and 58 bp upstream of the mamAB, mamDC and mms operons, respectively. The promoter regions showed homology to the consensus sequence of the vegetative sigma factor sigma 70. The magnetosome genes were expressed both under magnetic and non-magnetic growth conditions, but showed a down-regulation under iron-limited and aerobic conditions as revealed by microarray and real-time RT-PCR. The mamK gene product, which has homology with actin-like MreB proteins showed a linear intracellular localization as revealed by a GFP-MamK fusion, and a cytoplasmic localization was confirmed by 2D gel electrophoresis and Western blots. Therefore a putative role in the formation of the magnetosome chain was suggested

Investigation of the molecular organization and regulation of the mam genes in Magnetospirillum gryphiswaldense MSR-1

The biomineralization of the magnetosomes in magnetotactic bacteria (MTB) is governed by coordinated cellular and physico-chemical processes, which are controlled by the magnetosome membrane proteins (MMP), but poorly understood on the biochemical and molecular level. In this work the genomic and transcriptional organization of the mam and mms genes encoding these MMPs in Magnetospirillum gryphiswaldense were investigated. A close genetic linkage of the mam genes could be determined. The colocalization of all magnetosome genes, the high abundance of insertion sequence elements, and its high genetic instability lead to the discovery of a magnetosome island (MAI) of approximately 130 kb. Spontaneous non-magnetic mutants exhibiting deletions or rearrangements within the MAI occurred frequently under conditions of prolonged storage and oxygen stress. One of these non-magnetic mutants, designated strain MSR-1B, harbours a deletion of 40 kb comprising all magnetosome genes. Long polycistronic transcripts could be confirmed by RT-PCR for three major gene operons harbouring magnetosome genes. The transcriptional start points were determined 22 bp, 52 bp, and 58 bp upstream of the mamAB, mamDC and mms operons, respectively. The promoter regions showed homology to the consensus sequence of the vegetative sigma factor sigma 70. The magnetosome genes were expressed both under magnetic and non-magnetic growth conditions, but showed a down-regulation under iron-limited and aerobic conditions as revealed by microarray and real-time RT-PCR. The mamK gene product, which has homology with actin-like MreB proteins showed a linear intracellular localization as revealed by a GFP-MamK fusion, and a cytoplasmic localization was confirmed by 2D gel electrophoresis and Western blots. Therefore a putative role in the formation of the magnetosome chain was suggested

Stimulated emission depletion microscopy for imaging of engineered and biological nanostructures

The investigation of interactions between engineered nanostructures and biological systems is a key component in the assessment of potential environmental and health implications due to the increasing application of nanotechnology. Combining the high specificity of bioconjugate fluorescence labeling techniques with the sub-diffraction resolution of Stimulated Emission Depletion (STED) microscopy and state-of-the-art nonlinear image restoration allows the imaging of these interactions on the length scales demanded by the interaction partners. In this article, we give an overview of the experimental approach and discuss its implications on the biological interpretation of the resulting fluorescence micrographs

Should I Stay or Should I Go (to the Office)?—Effects of Working from Home, Autonomy, and Core Self–Evaluations on Leader Health and Work–Life Balance

Leaders represent a high-demand group in organizations. The effects of leaders’ personal and workplace resources on their health and work–life balance have often slipped under the radar, as most studies are directed outwardly and focus on follower outcomes. With this study, we closed a gap in the research and investigated the positive effects of remote work, autonomy, and leaders’ core-self evaluations (CSE) on two important leader outcomes: health and work–life balance. We hypothesized that the relationship between remote work and the outcomes would be moderated by leaders’ CSE and their autonomy—in such a way that leaders with lower resources benefit more from remote work and achieve better health and work–life balance the more days they spend working from home. A sample of 367 leaders reported their frequency of working from home, their autonomy, and CSE. Their health and work–life balance were assessed five months later. Results showed a moderating effect of CSE on both outcomes, indicating that leaders with low CSE benefit more in terms of health and work–life balance. There was no moderating effect of autonomy. Leaders with high resources (autonomy and CSE) had overall higher levels of health and work–life balance regardless of work location. Practitioners in organizations should consider working from home as a resource for leaders, particularly if personal resources are lower