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Schematic diagram of the assessment of actinomycete antagonism. The resident actinomycete was inoculated in the center of a Petri dish and left at room temperature for three weeks, after which a suspension of the intruder actinomycete was inoculated to the entire unoccupied Petri dish area (top). One week after the intruder strain was applied, the minimum diameter of the resident strain and the minimum zone of inhibition (zoi) imposed on the intruder strains were measured. The bottom section of the figure shows four examples of actinomyceteactinomycete reactions, with no antagonism displayed by the residing clone towards the intruding actinomycete (top left), intermediate levels of antagonism with slight to strong inhibition (top right and bottom left), and to complete inhibition of the intruder by the residing strain (bottom right). Pictures are framed with colors according to the size of the zoi: white = no inhibition, light grey = 0.01-0.29 cm, grey = 0.300.59 cm, darker grey = 0.60-0.89 cm, and darkest grey.0.90 cm. doi:10.1371/journal.pone.0000960.g001
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Conflict within mutually beneficial associations is predicted to destabilize relationships, and theoretical and empirical work exploring this has provided significant insight into the dynamics of cooperative interactions. Within mutualistic associations, the expression and regulation of conflict is likely more complex than in intraspecific cooperat...
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... experiments, biossay challenges involved co-culturing two strains of actinomycetes on YMEA with antifungals (concentra- tions as above) in 8.5 cm diameter Petri dishes. The first strain (hence forth referred to as the ''resident'' strain) was point inoculated in the center of the Petri dish and left to grow at room temperature for three weeks (Fig. 1). The second strain (hence forth referred to as the ''intruder'' strain) was inoculated to the entire unoccupied Petri dish area by applying 200 ml of autoclaved water containing a suspension of approximately 800-1200 bacterial cells per ml (Fig. 1). The plates were checked regularly until the intruder strain had sufficient time to grow ...
Context 2
... inoculated in the center of the Petri dish and left to grow at room temperature for three weeks (Fig. 1). The second strain (hence forth referred to as the ''intruder'' strain) was inoculated to the entire unoccupied Petri dish area by applying 200 ml of autoclaved water containing a suspension of approximately 800-1200 bacterial cells per ml (Fig. 1). The plates were checked regularly until the intruder strain had sufficient time to grow to fill the Petri plate or a distinct zone of inhibition (zoi) imposed by the resident strain had established and no longer changed over time. When present, typically one week after the intruder strain was applied, the minimum zone of inhibition ...
Context 3
... the Petri plate or a distinct zone of inhibition (zoi) imposed by the resident strain had established and no longer changed over time. When present, typically one week after the intruder strain was applied, the minimum zone of inhibition (zoi) imposed on the intruder strains were measured as well as the minimum diameter of the resident strain (Fig. 1). Actinomycete strains were paired in all possible combinations, 361 in the cross-phylogeny experiment and 144 in the within-Acromyrmex experiment, and three replicates were performed for each pairing. In the cross-phylogeny bioassay experiment the three replicates for each pairing were applied on three succeeding days, because the ...
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... Based on the previous report of ECO-0501's antibacterial activity, we wondered whether it might antagonize other bacterial strains that we isolated from these ants. Bacterial niche defense mediated by antibacterials is known from other ant-associated Actinobacteria (13,14,39,40). Our assays confirm that this molecule has antibacterial activity against Pseudonocardia from T. smithi, which are potential competitors for the ant cuticle niche (Table 1). ...
Symbiotic Actinobacteria help fungus-growing ants suppress fungal pathogens through the production of antifungal compounds. Trachymyrmex ants of the southwest desert of the United States inhabit a unique niche far from the tropical rainforests in which most fungus-growing ant species are found. These ants may not encounter the specialist fungal pathogen Escovopsis known to threaten colonies of other fungus-growing ants. It is unknown whether Actinobacteria associated with these ants antagonize contaminant fungi and, if so, what the chemical basis of such antagonism is. We find that Pseudonocardia and Amycolatopsis strains isolated from three desert specialist Trachymyrmex species do antagonize diverse contaminant fungi isolated from field-collected ant colonies. We did not isolate the specialist fungal pathogen Escovopsis in our sampling. We trace strong antifungal activity from Amycolatopsis isolates to the molecule ECO-0501, an antibiotic that was previously under preclinical development as an antibacterial agent. In addition to suppression of contaminant fungi, we find that this molecule has strong activity against ant-associated Actinobacteria and may also play a role in bacterial competition in this niche. By studying interspecies interactions in a previously unexplored niche, we have uncovered novel bioactivity for a structurally unique antibiotic. IMPORTANCE Animal hosts often benefit from chemical defenses provided by microbes. These molecular defenses are a potential source of novel antibiotics and offer opportunities for understanding how antibiotics are used in ecological contexts with defined interspecies interactions. Here, we recover contaminant fungi from nests of Trachymyrmex fungus-growing ants of the southwest desert of the United States and find that they are suppressed by Actinobacteria isolated from these ants. The antibiotic ECO-0501 is an antifungal agent used by some of these Amycolatopsis bacterial isolates. This antibiotic was previously investigated in preclinical studies and known only for antibacterial activity.
... Consequently, when there are more genetically differentiated lineages, and so relatedness between interacting bacterial symbionts is lower, bacterial symbionts will put more resources into killing each other. This increased bacteriocin production will reduce growth, such that the population of symbionts will be less beneficial to their hosts [21]. We suggest that hosts will be selected to transmit or house their symbionts in ways that increased relatedness, to decrease this costly conflict [22]. ...
Cooperative symbionts enable their hosts to exploit a diversity of environments. A low genetic diversity (high relatedness) between the symbionts within a host is thought to favour cooperation by reducing conflict within the host. However, hosts will not be favoured to transmit their symbionts (or commensals) in costly ways that increase relatedness, unless this also provides an immediate fitness benefit to the host. We suggest that conditionally expressed costly competitive traits, such as antimicrobial warfare with bacteriocins, could provide a relatively universal reason for why hosts would gain an immediate benefit from increasing the relatedness between symbionts. We theoretically test this hypothesis with a simple illustrative model that examines whether hosts should manipulate relatedness, and an individual-based simulation, where host control evolves in a structured population. We find that hosts can be favoured to manipulate relatedness, to reduce conflict between commensals via this immediate reduction in warfare. Furthermore, this manipulation evolves to extremes of high or low vertical transmission and only in a narrow range is partly vertical transmission stable.
... From various biological levels of conflict (e.g. predator/prey, herbivore/plant, competitors, mating partners, host/pathogen, host/(endo)symbiont, mitonuclear, and intragenomic conflicts) it has become obvious that conflict breeds coevolution (Van Valen 1973;Jaenike 1978;Hamilton 1980;Bell 1982;Rice & Holland 1997;Zeh & Zeh 2000;Arnqvist & Rowe 2002Itoh et al. 2002;Rice & Chippindale 2002;Eberhard 2004;Hongoh et al. 2005;Lessells 2006;Pal et al. 2007;Poulsen et al. 2007;Kikuchi et al. 2009;Paterson et al. 2010;Wilkins 2010;Morgan & Koskella 2011;Rice 2013). Like interspecific competition, intraspecific competition may lead to coevolutionary processes (Roughgarden 1972;Rosenzweig 1978;Gibbons 1979;Wilson & Turelli 1986;Doebeli 1996;Dieckmann & Doebeli 1999;Drossel & McKane 2000;Bolnick 2001;Wichman et al. 2005;Svanbäck & Bolnick 2007). ...
... The importance of trade-offs as dynamic rather than static relationships was emphasized (Roff et al. 2002). From various biological levels of conflict, it has become obvious that conflict causes antagonistic coevolution (Rice & Holland 1997;Zeh & Zeh 2000;Arnqvist & Rowe 2002;Rice & Chippindale 2002;Eberhard 2004;Lessells 2006;Poulsen et al. 2007;Wilkins 2010). As a result, there is selection on each interacting partner to manipulate the trait towards its own optimum and resist such manipulation by the other partner (Lessells 2006). ...
... Actinobacteria secretions may also protect fungal gardens from other fungi (Seipke et al. 2011;Sen et al. 2009) and bacteria (Ortius-Lechner et al. 2000). Other compounds secreted from these symbionts have also been shown to suppress bacterial growth (Bot et al. 2002;Carr et al. 2012;Poulsen et al. 2007), including from the inhibition of soil bacteria (Schoenian et al. 2011). These broad-spectrum secretions could therefore change the soil resistome by applying selective pressure. ...
Actinobacteria that live mutualistically with leaf-cutter ants secrete antibiotics that may induce antibiotic resistance in nearby soil bacteria. We tested for the first time whether soil bacteria near and inside Atta cephalotes nests in Costa Rica show higher levels of antibiotic resistance than bacteria collected farther away. We collected soil samples 0 m to 50 m away from ant nests and grew bacteria from them on agar with paper discs treated with antibiotics of common veterinary use. As a proxy for antibiotic resistance, we measured the distance from the edge of each disc to the closest bacterial colonies. In general, resistance to oxytetracycline increased with proximity to leaf-cutter ant nests. Antibiotic resistance to oxytetracycline was also higher in samples collected inside the nest than in samples from the nest mound; not all antibiotics demonstrated the same trend. A preliminary exploratory morphological analysis suggests bacterial communities between 0 m and 50 m from ant nests were similar in diversity and abundance, indicating the pattern of antibiotic resistance described above may not be caused by differences in community composition. We conclude that actinobacteria living mutualistically with A. cephalotes drive natural antibiotic resistance to tetracycline in proximal bacterial communities.
... [6][7][8] Pseudonocardia isolates from fungus-growing ants are often observed to antagonize other strains of ant-associated Pseudonocardia, which are likely competitors in this niche. 9 The molecular basis for this antagonism is known for Pseudonocardia from a population of the Central American ant Apterostigma dentigerum, in which a plasmid-encoded rebeccamycin antibiotic antagonizes Pseudonocardia from neighboring ant colonies. 10 In a population of the North American ant Trachymyrmex septentrionalis, Pseudonocardia antagonize competitors using the thiopeptide antibiotic GE37468. ...
... 12 Competition is expected when multiple bacterial strains co-occur in an ant population and conceptual frameworks have been developed for such bacteria-bacteria competition in the context of fungus-growing ants. 9,13,14 Chemical defenses from bacterial symbionts of fungus-growing ants, both antibacterial and antifungal, have recently been a productive source for chemical discovery. We have turned our attention to the chemical ecology of desert-dwelling fungus-growing ants as their microbial partnerships are largely unexplored and their adaptation to a unique environment may include unique defensive compounds from their microbial associates. ...
Fungus-growing ants are defended by antibiotic-producing bacterial symbionts in the genus Pseudonocardia. Nutrients provisioned by the ants support these symbionts but also invite colonization and competition from other bacteria. As an arena for chemically-mediated bacterial competition, this niche offers a window into ecological antibiotic function with well-defined competing organisms. From multiple colonies of the desert specialist ant Trachymyrmex smithi, we isolated Amycolatopsis bacteria that inhibit the growth of Pseudonocardia symbionts. Using bioassay-guided fractionation, we discovered a novel analog of the antibiotic nocamycin that is responsible for this antagonism. We identified the biosynthetic gene cluster for this antibiotic, which has a suite of oxidative enzymes consistent with this molecule's more extensive oxidative tailoring relative to similar tetramic acid antibiotics. High genetic similarity to globally distributed soil Amycolatopsis isolates suggest that this ant-derived Amycolatopsis strain may be an opportunistic soil strain whose antibiotic production allows for competition in this specialized niche. This nocamycin analog adds to the catalog of novel bioactive molecules isolated from bacterial associates of fungus-growing ants and its activity against ant symbionts represents, to our knowledge, the first documented ecological function for the widely distributed enoyl tetramic acid family of antibiotics.
... Recent studies of infectious agents have clearly demonstrated the limits of the 'one microbe-one disease' postulate, and opened the door to a novel way of considering infectious diseases than by simply considering the effects of a single pathogen. Multiple factors influence and drive the ability of a community of microorganisms to become pathogens, among others, the interaction and 'barrier effect' of resident microflora [17], the exchange of virulence and antibiotic resistance genes through horizontal gene transfer within the host or the environment [18], the presence of endosymbionts preventing pathogens transmission by vectors [19], the antagonistic and mutualistic relationships [20], the presence of grazing bacterivorous protozoa [21] and the modulation effects of bacteriophages on the microbial community [22]. ...
Microbial contamination of surface waters is of particular relevance in low-income and middle-income countries (LMICs) since they often represent the only available source of water for drinking and domestic use. In the recent years, a growing urbanization, profound demographic shifts and drastic climate events have greatly affected LMICs capacity to reach access to safe drinking water and sanitation practices, and to protect citizens’ health from risks associated to the exposure and use of contaminated water.
Detailed phylogenetic and microbiological information on the exact composition of pathogenic organisms in urban and peri-urban water is scarce, especially in rapidly changing settings of sub-Saharan Africa. In this review we aim to highlight how large-scale water pathobiome studies can support the LMICs challenge to global access to safe water and sanitation practices.
... In contrast, Meirelles et al. (2014) showed that several Pseudonocardia strains isolated from Trachymyrmex ants may have a generalized inhibitory activity against Escovopsis (38). Other previous studies have documented similar activities (41,42,(75)(76)(77). Taken together, these studies suggest that there is high variability in antimicrobial activity by Pseudonocardia (42). ...
In some plants and animals, beneficial microbes mediate host immune response against pathogens, including by serving as defensive symbionts that produce antimicrobial compounds. Defensive symbionts are known in several insects, including some leaf-cutter ants where antifungal-producing Actinobacteria help protect the fungal mutualist of the ants from specialized mycoparasites.
... This suggests that a potential mutualist must have the dual, but contrasting, capability of acting as an antagonist towards Pseudoxylaria, but, as a mutualist towards Termitomyces. However, most candidate mutualists, identified in both fungus-growing ants and fungus-growing termites, show clear fungicidal effects against the crop fungus [11,14,26] as well. For example, many strains of candidate mutualists, like Pseudonocardia and Amycolatopsis in fungusgrowing ants and Streptomyces in fungus-growing termites, act as generalized anti-fungal agents [11,14]. ...
Insects that farm monocultures of fungi are canonical examples of nutritional symbiosis as well as independent evolution of agriculture in non-human animals. But just like in human agriculture, these fungal crops face constant threat of invasion by weeds which, if unchecked, take over the crop fungus. In fungus-growing termites, the crop fungus (Termitomyces) faces such challenges from the weedy fungus Pseudoxylaria. The mechanism by which Pseudoxylaria is suppressed is not known. However, evidence suggests that some bacterial secondary symbionts can serve as defensive mutualists by preventing the growth of Pseudoxylaria. However, such secondary symbionts must possess the dual, yet contrasting, capabilities of suppressing the weedy fungus while keeping the growth of the crop fungus unaffected. This study describes the isolation, identification, and culture-dependent estimation of the roles of several such putative defensive mutualists from the colonies of the wide-spread fungus-growing termite from India, Odontotermes obesus. From the 38 bacterial cultures tested, a strain of Pseudomonas showed significantly greater suppression of the weedy fungus than the crop fungus. Moreover, a 16S rRNA pan-microbiome survey, using the Nanopore platform, revealed Pseudomonas to be a part of the core microbiota of O. obesus. A meta-analysis of microbiota composition across different species of Odontotermes also confirms the widespread prevalence of Pseudomonas within this termite. These lines of evidence indicate that Pseudomonas could be playing the role of defensive mutualist within Odontotermes.
... Through these selection mechanisms, we posit that they may facilitate the stability and persistence of certain host-symbiont associations over evolutionary periods. In support of this hypothesis, a previous study suggests that antagonism between actinomycetous bacterial symbionts from different ant isolates may facilitate strain specificity of ant-symbiont associations (Poulsen et al., 2007). For future studies, it will be important to contextualize these molecular factors for strain specificity in the ecology and evolution of host-symbiont associations. ...
Microbial symbionts are ubiquitous and can have significant impact on hosts. These impacts can vary in the sign (positive or negative) and degree depending on the identity of the interacting partners. Studies on host-symbiont associations indicate that subspecies (strain) genetic variation can influence interaction outcomes, making it necessary to go beyond species-level distinction to understand host-symbiont dynamics. In this review, we discuss examples of strain specificity found in host-symbiont associations, from binary model systems to the human microbiome. Although host and bacterial factors identified as mediators for specificity could be distinct at the molecular level, they generally fall into two broad functional categories: (1) those that contribute a required activity in support of the association and (2) those involved in antagonistic interactions with organisms outside of the association. We argue here based on current literature that factors from these two categories can work in concert to drive strain specificity and that this strain specificity must be considered to fully understand the molecular and ecological dynamics of host-symbiont associations, including the human microbiome.
