Modulation of Shigella virulence in response to available oxygen in vivo

Bacteria coordinate expression of virulence determinants in response to localized microenvironments in their hosts. Here we show that Shigella flexneri, which causes dysentery, encounters varying oxygen concentrations in the gastrointestinal tract, which govern activity of its type three secretion system (T3SS). The T3SS is essential for cell invasion and virulence. In anaerobic environments (for example, the gastrointestinal tract lumen), Shigella is primed for invasion and expresses extended T3SS needles while reducing Ipa (invasion plasmid antigen) effector secretion. This is mediated by FNR (fumarate and nitrate reduction), a regulator of anaerobic metabolism that represses transcription of spa32 and spa33, virulence genes that regulate secretion through the T3SS. We demonstrate there is a zone of relative oxygenation adjacent to the gastrointestinal tract mucosa, caused by diffusion from the capillary network at the tips of villi. This would reverse the anaerobic block of Ipa secretion, allowing T3SS activation at its precise site of action, enhancing invasion and virulence

Beneficial soil microbiome for sustainable agricultural production

The projected increase in world population and the need to reduce the reliance on non-renewable inputs, such as synthetic agrochemicals, are challenging the current vision of agriculture. In particular, to achieve a fair and sustainable global food security, disruptive changes in crop production are unavoidable. A promising strategy proposes to exploit the metabolic capabilities of soil microbial communities, i.e., the microbiome, to conjugate stable yield with reduced impact on the agroecosystem. In this chapter, we introduce the microbiome populating the root-soil interface from an evolutionary perspective. Next, we discuss the molecular bases of plant-microbe interactions in soil and how these interactions impact plant growth, development and health. We illustrate how plant-probiotic members of the microbiome can be isolated from soil and further characterized for their biological activities, a key pre-requisite for translational applications. In addition, we focus on paradigmatic examples of soil microbes turned into inoculants for agriculture, their fate on soil, their impact on the native microbiome and the beneficial effects exerted on crop productio