Role of small colony variants in persistence of Pseudomonas aeruginosa infections in cystic fibrosis lungs

Jacob G Malone1,21John Innes Centre, Norwich, UK; 2School of Biological Sciences, University of East Anglia, Norwich, UKAbstract: Pseudomonas aeruginosa is an opportunistic pathogen that predominates during the later stages of cystic fibrosis (CF) lung infections. Over many years of chronic lung colonization, P. aeruginosa undergoes extensive adaptation to the lung environment, evolving both toward a persistent, low virulence state and simultaneously diversifying to produce a number of phenotypically distinct morphs. These lung-adapted P. aeruginosa strains include the small colony variants (SCVs), small, autoaggregative isolates that show enhanced biofilm formation, strong attachment to surfaces, and increased production of exopolysaccharides. Their appearance in the sputum of CF patients correlates with increased resistance to antibiotics, poor lung function, and prolonged persistence of infection, increasing their relevance as a subject for clinical investigation. The evolution of SCVs in the CF lung is associated with overproduction of the ubiquitous bacterial signaling molecule cyclic-di-GMP, with increased cyclic-di-GMP levels shown to be responsible for the SCV phenotype in a number of different CF lung isolates. Here, we review the current state of research in clinical P. aeruginosa SCVs. We will discuss the phenotypic characteristics underpinning the SCV morphotype, the clinical implications of lung colonization with SCVs, and the molecular basis and clinical evolution of the SCV phenotype in the CF lung environment.Keywords: small colony variants, cystic fibrosis, cyclic-di-GMP, Pseudomonas aeruginosa, RsmA, antibiotic

Nucleotide second messengers in bacterial decision making

Since the initial discovery of bacterial nucleotide second messengers (NSMs), we have made huge progress towards understanding these complex signalling networks. Many NSM networks contain dozens of metabolic enzymes and binding targets, whose activity is tightly controlled at every regulatory level. They function as global regulators and in specific signalling circuits, controlling multiple aspects of bacterial behaviour and development. Despite these advances there is much still to discover, with current research focussing on the molecular mechanisms of signalling circuits, the role of the environment in controlling NSM pathways and attempts to understand signalling at the whole cell/community level. Here we examine recent developments in the NSM signalling field and discuss their implications for understanding this important driver of microbial behaviour

Life in earth – the root microbiome to the rescue?

Manipulation of the soil microbiome holds great promise for contributing to more environmentally benign agriculture, with soil microbes such as Pseudomonas promoting plant growth and effectively suppressing pathogenic microorganisms. Next-generation sequencing has enabled a new generation of research into soil microbiomes, presenting the opportunity to better understand and exploit these valuable resources. Soil bacterial communities are both highly complex and variable, and contain vast interspecies and intraspecies diversity, both of which respond to environmental variation. Therefore, we propose that a combination of whole microbiome analyses with in-depth examination of key microbial taxa will likely prove the most effective approach to understanding rhizosphere microbial interactions. This review highlights recent efforts in this direction, based around the important biocontrol bacterium Pseudomonas fluorescens

Plant-associated pseudomonads

This article belongs to the Special Issue Plant-Associated PseudomonadsBacteria belonging to the genus Pseudomonas (the pseudomonads) are a group of Gammaproteobacteria that are characterized by a high metabolic versatility and adaption to different ecological niches [...] Full articl

Bacterial pathogenesis of plants: Future challenges from a microbial perspective

Plant infection is a complicated process. Upon encountering a plant, pathogenic microorganisms must first adapt to life on the epiphytic surface, and survive long enough to initiate an infection. Responsiveness to the environment is critical throughout infection, with intracellular and community-level signal transduction pathways integrating environmental signals and triggering appropriate responses in the bacterial population. Ultimately, phytopathogens must migrate from the epiphytic surface into the plant tissue using motility and chemotaxis pathways. This migration is coupled to overcoming the physical and chemical barriers to entry into the plant apoplast. Once inside the plant, bacteria use an array of secretion systems to release phytotoxins and protein effectors that fulfil diverse pathogenic functions (Fig. 1)(Phan Tran et al., 2011, Melotto & Kunkel, 2013)

Blockchain – The Gateway to Trust-Free Cryptographic Transactions

Recently, the Bitcoin-underlying blockchain technology gained prominence as a solution that offers the realization of distributed trust-free systems, where economic transactions are guaranteed by the underlying blockchain. We are still at an early stage and thus require a deeper understanding of how the blockchain potentials can be realized, and what are the opportunities and challenges in so doing. Following a design science approach, we developed a proof of concept prototype that has the poten-tial to replace a trust-based coffee shop payment solution that is based on an analogue, pre-paid punch card solution. The demonstrator provides a starting point to evaluate the strengths and weak-nesses of the blockchain technology when replacing a trust-based by a trust-free transaction system. We conclude that the secure and trust-free blockchain-based transaction has the potential to change many existing trust-based transaction systems, but that scalability issues, costs, and volatility in the transaction currency are hindrances

Analyzing the Complex Regulatory Landscape of Hfq – an Integrative, Multi-Omics Approach

The ability of bacteria to respond to environmental change is based on the ability to coordinate, redirect and fine-tune their genetic repertoire as and when required. While we can learn a great deal from reductive analysis of individual pathways and global approaches to gene regulation, a deeper understanding of these complex signaling networks requires the simultaneous consideration of several regulatory layers at the genome scale. To highlight the power of this approach we analyzed the Hfq transcriptional/translational regulatory network in the model bacterium Pseudomonas fluorescens. We first used extensive ‘omics’ analyses to assess how hfq deletion affects mRNA abundance, mRNA translation and protein abundance. The subsequent, multi-level integration of these datasets allows us to highlight the discrete contributions by Hfq to gene regulation at different levels. The integrative approach to regulatory analysis we describe here has significant potential, for both dissecting individual signaling pathways and understanding the strategies bacteria use to cope with external challenges

Differential regulation of genes for cyclic-di-GMP metabolism orchestrates adaptive changes during rhizosphere colonization by Pseudomonas fluorescens

Bacteria belonging to the Pseudomonas genus are highly successful colonizers of the plant rhizosphere. The ability of different Pseudomonas species to live either commensal lifestyles or to act as agents of plant-growth promotion or disease is reflected in a large, highly flexible accessory genome. Nevertheless, adaptation to the plant environment involves a commonality of phenotypic outputs such as changes to motility, coupled with synthesis of nutrient uptake systems, stress-response molecules and adherence factors including exopolysaccharides. Cyclic-di-GMP (cdG) is a highly important second messenger involved in the integration of environmental signals with appropriate adaptive responses and is known to play a central role in mediating effective rhizosphere colonization. In this study, we examined the transcription of multiple, reportedly plant-upregulated cdG metabolism genes during colonization of the wheat rhizosphere by the plant-growth-promoting strain P. fluorescens SBW25. While transcription of the tested genes generally increased in the rhizosphere environment, we additionally observed a tightly orchestrated response to environmental cues, with a distinct transcriptional pattern seen for each gene throughout the colonization process. Extensive phenotypical analysis of deletion and overexpression strains was then conducted and used to propose cellular functions for individual cdG signaling genes. Finally, in-depth genetic analysis of an important rhizosphere colonization regulator revealed a link between cdG control of growth, motility and stress response, and the carbon sources available in the rhizosphere

Interaction and Signalling Networks:a report from the fourth 'Young Microbiologists Symposium on Microbe Signalling, Organisation and Pathogenesis'

At the end of June, over 120 microbiologists from 18 countries gathered in Dundee, Scotland for the fourth edition of the Young Microbiologists Symposium on ‘Microbe Signalling, Organisation and Pathogenesis’. The aim of the symposium was to give early career microbiologists the opportunity to present their work in a convivial environment and to interact with senior world-renowned scientists in exciting fields of microbiology research. The meeting was supported by the Microbiology Society, the Society of Applied Microbiology and the American Society for Microbiology with further sponsorship from the European Molecular Biology Organisation and the Royal Society of Edinburgh. In this report, we highlight some themes that emerged from the many interesting talks and poster presentations, as well as some of the other activities that were on offer at this energetic meeting

Communication, co-operation and social interactions:a report from the third 'Young Microbiologists Symposium on Microbe Signaling, Organization and Pathogenesis'

The third Young Microbiologists Symposium took place on the vibrant campus of the University of Dundee, Scotland, from the 2nd to 3rd of June 2014. The symposium attracted over 150 microbiologists from 17 different countries. The significant characteristic of this meeting was that it was specifically aimed at providing a forum for junior scientists to present their work. The meeting was supported by the Society for General Microbiology and the American Society for Microbiology, with further sponsorship from the European Molecular Biology Organization, the Federation of European Microbiological Societies, and The Royal Society of Edinburgh. In this report, we highlight some themes that emerged from the many exciting talks and poster presentations given by the young and talented microbiologists in the area of microbial gene expression, regulation, biogenesis, pathogenicity, and host interaction.</p