Antagonism between killer yeast strains as an experimental model for biological nucleation dynamics

Antagonistic interactions are widespread in the microbial world and affect microbial evolutionary dynamics. Natural microbial communities often display spatial structure, which affects biological interactions, but much of what we know about microbial warfare comes from laboratory studies of well-mixed communities. To overcome this limitation, we manipulated two killer strains of the budding yeast Saccharomyces cerevisiae, expressing different toxins, to independently control the rate at which they released their toxins. We developed mathematical models that predict the experimental dynamics of competition between toxin-producing strains in both well-mixed and spatially structured populations. In both situations, we experimentally verified theory's prediction that a stronger antagonist can invade a weaker one only if the initial invading population exceeds a critical frequency or size. Finally, we found that toxin-resistant cells and weaker killers arose in spatially structured competitions between toxin-producing strains, suggesting that adaptive evolution can affect the outcome of microbial antagonism in spatial settings.

A fungal member of the Arabidopsis thaliana phyllosphere antagonizes Albugo laibachii via a GH25 lysozyme

Plants are not only challenged by pathogenic organisms, but also colonized by commensal microbes. The network of interactions these microbes establish with their host and amongst each other is suggested to contribute to the immune responses of plants against pathogens. In wild Arabidopsis thaliana populations, the oomycete pathogen Albugo laibachii plays an influential role in structuring the leaf phyllosphere. We show that the epiphytic yeast Moesziomyces bullatus ex Albugo on Arabidopsis, a close relative of pathogenic smut fungi, is an antagonistic member of the A. thaliana phyllosphere, which reduces infection of A. thaliana by A. laibachii. Combination of transcriptomics, reverse genetics and protein characterization identified a GH25 hydrolase with lysozyme activity as a major effector of this microbial antagonism. Our findings broaden the understanding of microbial interactions within the phyllosphere, provide insights into the evolution of epiphytic basidiomycete yeasts and pave the way for novel biocontrol strategies.

Antagonism between killer yeast strains as an experimental model for biological nucleation dynamics

Antagonistic interactions are widespread in the microbial world and affect microbial evolutionary dynamics. Natural microbial communities often display spatial structure, which affects biological interactions, but much of what we know about microbial warfare comes from laboratory studies of well-mixed communities. To overcome this limitation, we manipulated two killer strains of the budding yeast Saccharomyces cerevisiae, expressing different toxins, to independently control the rate at which they released their toxins. We developed mathematical models that predict the experimental dynamics of competition between toxin-producing strains in both well-mixed and spatially structured populations. In both situations, we experimentally verified theory’s prediction that a stronger antagonist can invade a weaker one only if the initial invading population exceeds a critical size. Finally, we found that toxin-resistant cells and weaker killers arose in spatially structured competitions between toxin-producing strains, suggesting that adaptive evolution can affect the outcome of microbial antagonism.

A fungal member of the Arabidopsis thaliana phyllosphere antagonizes Albugo laibachii via a secreted lysozyme

Plants are not only challenged by pathogenic organisms, but also colonized by commensal microbes. The network of interactions these microbes establish with their host and amongst each other is suggested to contribute to the immune responses of plants against pathogens. In wild Arabidopsis thaliana populations, the oomycete pathogen Albugo laibachii has been shown to play an influential role in structuring the leaf phyllosphere. We show that the epiphytic yeast Moesziomyces bullatus ex Albugo on Arabidopsis, a close relative of pathogenic smut fungi, is an antagonistic member of the A. thaliana phyllosphere, which reduces infection of A. thaliana by A. laibachii. Combination of transcriptome analysis, reverse genetics and protein characterization identified a GH25 hydrolase with lysozyme activity as the major effector of this microbial antagonism. Our findings broaden the understanding of microbial interactions within the phyllosphere, provide insights into the evolution of epiphytic basidiomycete yeasts and pave the way for the development of novel biocontrol strategies.

Klebsiella pneumoniae type VI secretion system-mediated microbial competition is PhoPQ controlled and reactive oxygen species dependent

ABSTRACTKlebsiella pneumoniae is recognized as an urgent threat to human health due to the increasing isolation of multidrug resistant strains. Hypervirulent strains are a major concern due to their ability to cause life-threating infections in healthy hosts. The type VI secretion system (T6SS) is widely implicated in microbial antagonism, and it mediates interactions with host eukaryotic cells in some cases. In silico search for genes orthologous to T6SS component genes and T6SS effector genes across 700 K. pneumoniae genomes shows extensive diversity in T6SS genes across the K. pneumoniae species. Temperature, oxygen tension, pH, osmolarity, iron levels, and NaCl regulate the expression of the T6SS encoded by a hypervirulent K. pneumoniae strain. Polymyxins and human defensin 3 also increase the activity of the T6SS. A screen for regulators governing T6SS uncover the correlation between the transcription of the T6SS and the ability to kill E. coli prey. Whereas H-NS represses the T6SS, PhoPQ, PmrAB, Hfq, Fur, RpoS and RpoN positively regulate the T6SS. K. pneumoniae T6SS mediates intra and inter species bacterial competition. This antagonism is only evident when the prey possess an active T6SS. The PhoPQ two component system governs the activation of K. pneumoniae T6SS in bacterial competitions. Mechanistically, PhoQ periplasmic domain, and the acid patch within, is essential to activate K. pneumoniae T6SS. Klebsiella T6SS also mediates anti-fungal competition. We have delineated the contribution of each of the individual VgrGs in microbial competition, and identified VgrG4 as a T6SS effector. Structurally, domain DUF2345 of VgrG4 is sufficient to intoxicate bacteria and yeast. ROS generation mediates the antibacterial effects of VgrG4, and the antitoxin Sel1E protects against the toxic activity of VgrG4. Our findings provide a better understanding of the regulation of the T6SS in bacterial competitions, and place ROS as an early event in microbial competition.AUTHOR SUMMARYKlebsiella pneumoniae has been singled out as an “urgent threat to human health” due to extremely drug resistant strains. Numerous studies investigate the molecular mechanisms underlying antibiotic resistance in K. pneumoniae, while others dissect the virulence strategies of this pathogen. However, there is still limited knowledge on the fitness of Klebsiella in the environment, and particularly the competition of Klebsiella with other species. Here, we demonstrated that Klebsiella exploits the type VI secretion system (T6SS) nanoweapon to kill bacterial competitors and fungi. K. pneumoniae perceives T6SS attacks from bacterial competitors, resulting in retaliation against the aggressive cell. The perception of the attack involved the sensor PhoPQ and led to the up-regulation of the T6SS. We identified one of the toxins deployed by the T6SS to antagonize other microbes, and revealed how Klebsiella protects itself from this toxin. Our findings provide a better understanding of the T6SS role in microbial competition and uncover new aspects on how bacteria regulate T6SS-mediated microbial antagonism.

ETIOTROPIC THERAPY OF INFECTIOUS DIARRHEA

The issues of etiotropic therapy of infectious diarrhea require a differentiated approach not only depending on the etiological factor, but also on the type of diarrhea caused by the location of the pathological process. Infectious diarrhea occur in the form of three main types: secretory, osmotic, inflammatory (invasive). Secretory and osmotic type of diarrhea are found in infectious gastroenteritis. In the mechanisms of elimination of infectious gastroenteritis pathogens, the following factors play a leading role: the destructive effect on pathogens in the lumen of the small intestine of trypsin, chemotrypsin and acid duodenal content entering the small intestine; the «killer» action of interepithelial large granular lymphocytes (M-cells) on pathogens; the increase in resistance of the small intestine epithelium under the influence of M-cell cytokines; the difficulty of intercellular distribution of pathogens due to faster than in the gut, small intestine epithelial cell renewal; microbial antagonism of representatives of normal intestinal microflora. The appointment of etiotropic agents in cases of infectious gastroenteritis, at least, suppresses the manifestations of microbial antagonism on the part of representatives of the normal intestinal microflora, creating prerequisites for the delay of the pathogen in the body. The inflammatory type of diarrhoea occurs when invasion of pathogens to the mucosal lining of the colon, with subsequent development of the destructive changes and the possibility of further translocation. Obstacles to adhesion, penetration and intercellular spread of invasive pathogens in the colon mucosa is much less than in the small intestine. Pathogens of the same genera, species and serological variants (e.g. Salmonella, Campylobacter) can cause both secretory and invasive types of diarrhea. However, the appointment of antibacterial therapy will depend on the location of the pathological process. When gastroenteritis etiotropic therapy in most cases is impractical. In the presence of clinical manifestations of colitis, involving the implementation of invasive properties of the causative agent, the appointment of etiotropic treatment is justified.

ETIOTROPIC THERAPY OF INFECTIOUS DIARRHEA

The issues of etiotropic therapy of infectious diarrhea require a differentiated approach not only depending on the etiological factor, but also on the type of diarrhea caused by the location of the pathological process. Infectious diarrhea occur in the form of three main types: secretory, osmotic, inflammatory (invasive). Secretory and osmotic type of diarrhea are found in infectious gastroenteritis. In the mechanisms of elimination of infectious gastroenteritis pathogens, the following factors play a leading role: the destructive effect on pathogens in the lumen of the small intestine of trypsin, chemotrypsin and acid duodenal content entering the small intestine; the «killer» action of interepithelial large granular lymphocytes (M-cells) on pathogens; the increase in resistance of the small intestine epithelium under the influence of M-cell cytokines; the difficulty of intercellular distribution of pathogens due to faster than in the gut, small intestine epithelial cell renewal; microbial antagonism of representatives of normal intestinal microflora. The appointment of etiotropic agents in cases of infectious gastroenteritis, at least, suppresses the manifestations of microbial antagonism on the part of representatives of the normal intestinal microflora, creating prerequisites for the delay of the pathogen in the body. The inflammatory type of diarrhoea occurs when invasion of pathogens to the mucosal lining of the colon, with subsequent development of the destructive changes and the possibility of further translocation. Obstacles to adhesion, penetration and intercellular spread of invasive pathogens in the colon mucosa is much less than in the small intestine. Pathogens of the same genera, species and serological variants (e.g. Salmonella, Campylobacter) can cause both secretory and invasive types of diarrhea. However, the appointment of antibacterial therapy will depend on the location of the pathological process. When gastroenteritis etiotropic therapy in most cases is impractical. In the presence of clinical manifestations of colitis, involving the implementation of invasive properties of the causative agent, the appointment of etiotropic treatment is justified.