Use of transcriptomic data for extending a model of the AppA/PpsR system in Rhodobacter sphaeroides

Modelling of indirect cell-cell interaction networks mediated by IFNγ/IL-4 cytokine involved in atopic dermatitis

Atopic dermatitis (AD) is an immune-driven inflammatory skin disease that is known to have a significantly high life-time prevalence in the human population. T-helper (Th) immune cells play a key role in the pathogenesis of AD which is marked by defects in the skin barrier function along with a significant increase in the population of either Th1 or Th2 sub-types of Th cells. The progression of AD from the acute to chronic phase is still poorly understood, and here we explore the mechanism of this transition through the study of a mathematical model for indirect cell-cell interactions among Th and skin cells via the secreted cytokines IFNγ and IL-4, both known to have therapeutic potential. An increase in the level of cytokine IFN γ can catalyse the transition of AD from an acute to a chronic stage, while an increase in the level of cytokine IL-4 has the reverse effect. In our model, the transition of AD from the acute to chronic stage and vice versa can be abrupt (switch-like) with hysteresis: this bistable behaviour can potentially be used to keep AD in the acute phase since therapy based on suppression of IFNγ can retard the transition to the chronic phase.

The transition of Rhodobacter sphaeroides into a microbial cell factory

Microbial cell factories are the workhorses of industrial biotechnology and improving their performances can significantly optimize industrial bioprocesses. Microbial strain engineering is often employed for increasing the competitiveness of bio‐based product synthesis over more classical petroleum‐based synthesis. Recently, efforts for strain optimization have been standardized within the iterative concept of “design‐build‐test‐learn” (DBTL). This approach has been successfully employed for the improvement of traditional cell factories like Escherichia coli and Saccharomyces cerevisiae. Within the past decade, several new‐to‐industry microorganisms have been investigated as novel cell factories, including the versatile α‐proteobacterium Rhodobacter sphaeroides. Despite its history as a laboratory strain for fundamental studies, there is a growing interest in this bacterium for its ability to synthesize relevant compounds for the bioeconomy, such as isoprenoids, poly‐β‐hydroxybutyrate, and hydrogen. In this study, we reflect on the reasons for establishing R. sphaeroides as a cell factory from the perspective of the DBTL concept. Moreover, we discuss current and future opportunities for extending the use of this microorganism for the bio‐based economy. We believe that applying the DBTL pipeline for R. sphaeroides will further strengthen its relevance as a microbial cell factory. Moreover, the proposed use of strain engineering via the DBTL approach may be extended to other microorganisms that have not been critically investigated yet for industrial applications.

Through the eyes of a pathogen: light perception and signal transduction in Acinetobacter baumannii

Sunlight is a ubiquitous environmental stimulus for the great majority of living organisms on Earth; therefore it is logical to expect the development of "seeing mechanisms" which lead them to successfully adapt to particular ecological niches. Although these mechanisms were recognized in photosynthetic organisms, it was not until recent years that the scientific community found out about light perception in chemotrophic ones. In this review we summarize the current knowledge about the mechanism of light sensing through the blue light receptor BlsA in Acinetobacter baumannii. We highlight its function as a global regulator that pleiotropically modulates a large number of physiological processes, many of which are linked to the ability of this opportunist pathogen to persist in adverse intrahospital environments. Moreover, we describe with some specific examples the molecular basis of how this photoregulator senses blue light and translates this physical signal by modulating gene expression of target regulons. Finally, we discuss the possible course of these investigations needed to dissect this complex regulatory network, which ultimately will help us better understand the A. baumannii physiology.

Quorum and Light Signals Modulate Acetoin/Butanediol Catabolism in Acinetobacter spp

Acinetobacter spp. are found in all environments on Earth due to their extraordinary capacity to survive in the presence of physical and chemical stressors. In this study, we analyzed global gene expression in airborne Acinetobacter sp. strain 5-2Ac02 isolated from hospital environment in response to quorum network modulators and found that they induced the expression of genes of the acetoin/butanediol catabolism, volatile compounds shown to mediate interkingdom interactions. Interestingly, the acoN gene, annotated as a putative transcriptional regulator, was truncated in the downstream regulatory region of the induced acetoin/butanediol cluster in Acinetobacter sp. strain 5-2Ac02, and its functioning as a negative regulator of this cluster integrating quorum signals was confirmed in Acinetobacter baumannii ATCC 17978. Moreover, we show that the acetoin catabolism is also induced by light and provide insights into the light transduction mechanism by showing that the photoreceptor BlsA interacts with and antagonizes the functioning of AcoN in A. baumannii, integrating also a temperature signal. The data support a model in which BlsA interacts with and likely sequesters AcoN at this condition, relieving acetoin catabolic genes from repression, and leading to better growth under blue light. This photoregulation depends on temperature, occurring at 23°C but not at 30°C. BlsA is thus a dual regulator, modulating different transcriptional regulators in the dark but also under blue light, representing thus a novel concept. The overall data show that quorum modulators as well as light regulate the acetoin catabolic cluster, providing a better understanding of environmental as well as clinical bacteria.