The glideosome of apicomplexan parasites is an actin- and myosin-based machine located at the pellicle, between the plasma membrane (PM) and inner membrane complex (IMC), that powers parasite motility, migration, and host cell invasion and egress. It is composed of myosin A, its light chain MLC1, and two gliding-associated proteins, GAP50 and GAP45. We identify GAP40, a polytopic protein of the IMC, as an additional glideosome component and show that GAP45 is anchored to the PM and IMC via its N- and C-terminal extremities, respectively. While the C-terminal region of GAP45 recruits MLC1-MyoA to the IMC, the N-terminal acylation and coiled-coil domain preserve pellicle integrity during invasion. GAP45 is essential for gliding, invasion, and egress. The orthologous Plasmodium falciparum GAP45 can fulfill this dual function, as shown by transgenera complementation, whereas the coccidian GAP45 homolog (designated here as) GAP70 specifically recruits the glideosome to the apical cap of the parasite.

The overall composition of the mammalian intestinal microbiota varies between individuals: within each individual there are differences along the length of the intestinal tract related to host nutrition, intestinal motility and secretions. Mucus is a highly regenerative protective lubricant glycoprotein sheet secreted by host intestinal goblet cells; the inner mucus layer is nearly sterile. Here we show that the outer mucus of the large intestine forms a unique microbial niche with distinct communities, including bacteria without specialized mucolytic capability. Bacterial species present in the mucus show differential proliferation and resource utilization compared with the same species in the intestinal lumen, with high recovery of bioavailable iron and consumption of epithelial-derived carbon sources according to their genome-encoded metabolic repertoire. Functional competition for existence in this intimate layer is likely to be a major determinant of microbiota composition and microbial molecular exchange with the host.

While the apicomplexan parasites Plasmodium falciparum and Toxoplasma gondii are thought to primarily depend on glycolysis for ATP synthesis, recent studies have shown that they can fully catabolize glucose in a canonical TCA cycle. However, these parasites lack a mitochondrial isoform of pyruvate dehydrogenase and the identity of the enzyme that catalyses the conversion of pyruvate to acetyl-CoA remains enigmatic. Here we demonstrate that the mitochondrial branched chain ketoacid dehydrogenase (BCKDH) complex is the missing link, functionally replacing mitochondrial PDH in both T. gondii and P. berghei. Deletion of the E1a subunit of T. gondii and P. berghei BCKDH significantly impacted on intracellular growth and virulence of both parasites. Interestingly, disruption of the P. berghei E1a restricted parasite development to reticulocytes only and completely prevented maturation of oocysts during mosquito transmission. Overall this study highlights the importance of the molecular adaptation of BCKDH in this important class of pathogens.

IgA is the dominant immunoglobulin isotype produced in mammals, largely secreted across the intestinal mucosal surface. Although induction of IgA has been a hallmark feature of microbiota colonization following colonization in germ-free animals, until recently appreciation of the function of IgA in host-microbial mutualism has depended mainly on indirect evidence of alterations in microbiota composition or penetration of microbes in the absence of somatic mutations in IgA (or compensatory IgM). Highly parallel sequencing techniques that enable high-resolution analysis of either microbial consortia or IgA sequence diversity are now giving us new perspectives on selective targeting of microbial taxa and the trajectory of IgA diversification according to induction mechanisms, between different individuals and over time. The prospects are to link the range of diversified IgA clonotypes to specific antigenic functions in modulating the microbiota composition, position and metabolism to ensure host mutualism.

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Microbiota colonization causes profound B cell stimulation and immunoglobulin induction, yet mammals colonized with many taxa have highly complex individualized immunoglobulin repertoires 1,2 . To deconstruct how the microbiota shapes the B cell pool and its functional responsiveness we have used a simplified model of defined transient microbial exposures by different taxa in germ-free mice 3 . B cell immunoglobulin repertoire development was followed by deep sequencing and in single cells. Intestinal mucosal exposure generated oligoclonal responses which differed from germ-free controls or from the diverse repertoire generated after intravenous systemic exposure. The IgA repertoire, predominantly to cellsurface antigens, did not expand following dose escalation, whereas increased systemic exposure broadened the IgG repertoire to both microbial cytoplasmic and cell-surface antigens. These microbial exposures induced characteristic immunoglobulin heavy chain B cell repertoires mainly at memory and plasma cell stages. Whereas sequential systemic exposure to different taxa diversified the IgG repertoire and facilitated alternate specific responses, sequential mucosal exposure produced limited overlapping repertoires and attrition of initial IgA binding specificities. This shows a contrast between a flexible response to systemic exposure with the need to avoid fatal sepsis, and a restricted response to mucosal exposure reflecting the generic nature of mucosal microbial mutualism. TEXTMammalian immunoglobulins (Ig) are composed of heavy (H) and light (L) chains, each assembled from one of many V H/L , (D H ) and J H/L gene segments during B cell development. The resulting genetic and structural immunoglobulin repertoire diversity and antigen recognition possibilities are further increased by additional nucleotide insertion during recombination, later somatic mutation, or class switch recombination from IgM and/or IgD to IgG, IgE or IgA. Selection and clonal expansion of particular B cells with an appropriate immunoglobulin specificity endows the system to respond to a huge variety of antigens.Comparisons of colonized and germ-free animals show that B cell numbers and immunoglobulin levels (especially IgG and IgA) are considerably amplified by colonization with a microbiota, some of which penetrate mucous membranes to prime systemic secondary lymphoid structures even in healthy hosts. 4,5 B cell repertoires have so far been shown to be largely unique to each individual animal 1,2 , although whether this is caused by differences in microbiota composition or the sequence of colonization in each animal is unknown.Using localized time-limited exposures of defined doses of single benign microbial taxa in germ-free animals 3 , we have addressed how the B cell repertoire is shaped by microbiota exposure at mucous membranes or in systemic lymphoid tissues, and how interactions between different exposure sites or subsequent exposures to different taxa affects the outcome. Distinct B cell Ig repertoires to intestinal microbes de...

Shigella flexneri proliferate in infected human epithelial cells at exceptionally high rates. This vigorous growth has important consequences for rapid progression to life-threatening bloody diarrhea, but the underlying metabolic mechanisms remain poorly understood. Here, we used metabolomics, proteomics, and genetic experiments to determine host and Shigella metabolism during infection in a cell culture model. The data suggest that infected host cells maintain largely normal fluxes through glycolytic pathways, but the entire output of these pathways is captured by Shigella, most likely in the form of pyruvate. This striking strategy provides Shigella with an abundant favorable energy source, while preserving host cell ATP generation, energy charge maintenance, and survival, despite ongoing vigorous exploitation. Shigella uses a simple three-step pathway to metabolize pyruvate at high rates with acetate as an excreted waste product. The crucial role of this pathway for Shigella intracellular growth suggests targets for antimicrobial chemotherapy of this devastating disease.infectious diseases | host-pathogen interactions

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