Mitochondria mediate septin cage assembly to promote autophagy of Shigella

Septins, cytoskeletal proteins with well-characterised roles in cytokinesis, form cage-like structures around cytosolic Shigella flexneri and promote their targeting to autophagosomes. However, the processes underlying septin cage assembly, and whether they influence S. flexneri proliferation, remain to be established. Using single-cell analysis, we show that the septin cages inhibit S. flexneri proliferation. To study mechanisms of septin cage assembly, we used proteomics and found mitochondrial proteins associate with septins in S. flexneri-infected cells. Strikingly, mitochondria associated with S. flexneri promote septin assembly into cages that entrap bacteria for autophagy. We demonstrate that the cytosolic GTPase dynamin-related protein 1 (Drp1) interacts with septins to enhance mitochondrial fission. To avoid autophagy, actin-polymerising Shigella fragment mitochondria to escape from septin caging. Our results demonstrate a role for mitochondria in anti-Shigella autophagy and uncover a fundamental link between septin assembly and mitochondria

Assessment of ecological status in UK lakes using benthic diatoms

The European Union’s Water Framework Directive (WFD) requires that all water bodies in Europe achieve good ecological status (GES) by 2015. We developed an ecological classification tool for UK lakes based on benthic diatoms, a key component of the biological-quality element macrophytes and phytobenthos. A database of 1079 epilithic and epiphytic diatom samples and matching environmental data was assembled from 228 UK lakes. The data set was divided into 3 lake types: low, medium, and high alkalinity. A lake trophic diatom index (LTDI) was developed based on modification of the trophic diatom index (TDI) for rivers, and ecological quality ratios (EQRs) were generated for each lake type. The high/good status boundary was defined as the 25th percentile of EQRs of all reference sites (identified based on independent sedimentary-diatom-assemblage data or catchment point-source and landuse data), whereas the good/moderate boundary was set at the point at which nutrient-sensitive and nutrient-tolerant taxa were present in equal relative abundance. The moderate/poor and poor/bad boundaries were defined by equal division of the remaining EQR gradient. Samples from reference sites were used to predict the expected LTDI value for each sample, and these values were compared with the classifications derived from the LTDI. For lakes identified as reference sites, 68% were classified as having high status and 32% as having good. The model predicted 81% of nonreference lakes to have good or worse status. The model was applied to 17 English lakes (10 low- and 7 medium-alkalinity) for which classification based on other WFD tools was available. The classifications based on LTDI gave the same status (within 1 class) as other biological elements for 11 of the 17 lakes (65%). Thus, the LTDI gives a reliable assessment of the condition of the littoral biofilm and is a key component of a WFD-compliant tool kit for classifying UK standing waters

Shigella sonnei infection of zebrafish reveals that O-antigen mediates neutrophil tolerance and dysentery incidence.

Funder: Lister Institute of Preventive Medicine; funder-id: http://dx.doi.org/10.13039/501100001255Shigella flexneri is historically regarded as the primary agent of bacillary dysentery, yet the closely-related Shigella sonnei is replacing S. flexneri, especially in developing countries. The underlying reasons for this dramatic shift are mostly unknown. Using a zebrafish (Danio rerio) model of Shigella infection, we discover that S. sonnei is more virulent than S. flexneri in vivo. Whole animal dual-RNAseq and testing of bacterial mutants suggest that S. sonnei virulence depends on its O-antigen oligosaccharide (which is unique among Shigella species). We show in vivo using zebrafish and ex vivo using human neutrophils that S. sonnei O-antigen can mediate neutrophil tolerance. Consistent with this, we demonstrate that O-antigen enables S. sonnei to resist phagolysosome acidification and promotes neutrophil cell death. Chemical inhibition or promotion of phagolysosome maturation respectively decreases and increases neutrophil control of S. sonnei and zebrafish survival. Strikingly, larvae primed with a sublethal dose of S. sonnei are protected against a secondary lethal dose of S. sonnei in an O-antigen-dependent manner, indicating that exposure to O-antigen can train the innate immune system against S. sonnei. Collectively, these findings reveal O-antigen as an important therapeutic target against bacillary dysentery, and may explain the rapidly increasing S. sonnei burden in developing countries

The insulin polymorphism -23Hph increases the risk for type 1 diabetes mellitus in the Romanian population

The insulin -23Hph and IGF2 Apa polymorphisms were genotyped in Romanian patients with T1DM (n = 204), T2DM (n = 215) or obesity (n = 200) and normoponderal healthy subjects (n = 750). The genotypes of both polymorphisms were distributed in concordance with Hardy-Weinberg equilibrium in all groups. The -23Hph AA genotype increased the risk for T1DM (OR: 3.22, 95%CI: 2.09-4.98, p < 0,0001), especially in patients without macroalbuminuria (OR: 4.32, 95%CI: 2.54-7.45, p < 0,0001). No other significant association between the alleles or genotypes of insulin -23Hph and IGF2 Apa and diabetes or obesity was identified

Charged and Hydrophobic Surfaces on the A Chain of Shiga-Like Toxin 1 Recognize the C-Terminal Domain of Ribosomal Stalk Proteins

Shiga-like toxins are ribosome-inactivating proteins (RIP) produced by pathogenic E. coli strains that are responsible for hemorrhagic colitis and hemolytic uremic syndrome. The catalytic A1 chain of Shiga-like toxin 1 (SLT-1), a representative RIP, first docks onto a conserved peptide SD[D/E]DMGFGLFD located at the C-terminus of all three eukaryotic ribosomal stalk proteins and halts protein synthesis through the depurination of an adenine base in the sarcin-ricin loop of 28S rRNA. Here, we report that the A1 chain of SLT-1 rapidly binds to and dissociates from the C-terminal peptide with a monomeric dissociation constant of 13 µM. An alanine scan performed on the conserved peptide revealed that the SLT-1 A1 chain interacts with the anionic tripeptide DDD and the hydrophobic tetrapeptide motif FGLF within its sequence. Based on these 2 peptide motifs, SLT-1 A1 variants were generated that displayed decreased affinities for the stalk protein C-terminus and also correlated with reduced ribosome-inactivating activities in relation to the wild-type A1 chain. The toxin-peptide interaction and subsequent toxicity were shown to be mediated by cationic and hydrophobic docking surfaces on the SLT-1 catalytic domain. These docking surfaces are located on the opposite face of the catalytic cleft and suggest that the docking of the A1 chain to SDDDMGFGLFD may reorient its catalytic domain to face its RNA substrate. More importantly, both the delineated A1 chain ribosomal docking surfaces and the ribosomal peptide itself represent a target and a scaffold, respectively, for the design of generic inhibitors to block the action of RIPs

Diel surface temperature range scales with lake size

Ecological and biogeochemical processes in lakes are strongly dependent upon water temperature. Long-term surface warming of many lakes is unequivocal, but little is known about the comparative magnitude of temperature variation at diel timescales, due to a lack of appropriately resolved data. Here we quantify the pattern and magnitude of diel temperature variability of surface waters using high-frequency data from 100 lakes. We show that the near-surface diel temperature range can be substantial in summer relative to long-term change and, for lakes smaller than 3 km2, increases sharply and predictably with decreasing lake area. Most small lakes included in this study experience average summer diel ranges in their near-surface temperatures of between 4 and 7°C. Large diel temperature fluctuations in the majority of lakes undoubtedly influence their structure, function and role in biogeochemical cycles, but the full implications remain largely unexplored

Mitochondria promote septin assembly into cages that entrap Shigella for autophagy

Septins are cytoskeletal proteins implicated in cytokinesis and host-pathogen interactions. During macroautophagy/autophagy of Shigella flexneri, septins assemble into cage-like structures to entrap actin-polymerizing bacteria and restrict their dissemination. How septins assemble to entrap bacteria is not fully known. We discovered that mitochondria support septin cage assembly to promote autophagy of Shigella. Consistent with roles for the cytoskeleton in mitochondrial dynamics, we showed that DNM1L/DRP1 (dynamin 1 like) can interact with septins to enhance mitochondrial fission. Remarkably, Shigella fragment mitochondria and escape from septin cage entrapment in order to avoid autophagy. These results uncover a close relationship between mitochondria and septin assembly, and identify a new role for mitochondria in bacterial autophagy