Biology subjects

Worsley, S. F.

Publications and source records attributed to Worsley, S. F..

6 recordsLinked to original sources

bioRxiv2021

Characterisation of the symbionts in the Mediterranean fruitfly gut

Symbioses between bacteria and their insect hosts can range from very loose associations through to obligate interdependence. While fundamental evolutionary insights have been gained from the in-depth study of obligate mutualisms, there is increasing interest in the evolutionary potential of flexible symbiotic associations between hosts and their gut microbiomes. Understanding relationships between microbes and hosts also offers the potential for exploitation for insect control. Here, we investigate the gut microbiome of a global agricultural pest, the Mediterranean fruitfly (Ceratitis capitata). We used 16S rRNA profiling to compare the gut microbiomes of laboratory and wild strains raised on different diets and from flies collected from various natural plant hosts. The results showed that medfly guts harbour a fairly simple microbiome, primarily determined by the larval diet in both wild and laboratory flies. However, regardless of the laboratory diet or natural plant host on which flies were raised, Klebsiella spp dominated the medfly microbiomes and resisted removal by antibiotic treatment. We sequenced the genome of the dominant putative Klebsiella spp (designated Medkleb) isolated from the gut of the Toliman wild type fruitfly strain. Genome-wide ANI analysis placed Medkleb within the K. oxytoca / michiganensis group. Molecular, sequence and phenotypic analyses supported its identity as K. oxytoca. Medkleb has a genome size (5 825 435 bp) which is 1.6 standard deviations smaller than the mean genome size of free-living Klebsiella spp, and lacks some genes involved in environmental sensing. Moreover, the Medkleb genome contains at least two recently acquired unique genomic islands as well as genes that encode pectinolytic enzymes capable of degrading plant cell walls. This may be advantageous given that the medfly diet includes unripe fruits containing high proportions of pectin. These results suggest that the medfly harbours a commensal gut bacterium that may have developed a mutualistic association with its host and provide nutritional benefits.

evolutionary biology↗

bioRxiv2021

Soil, senescence and exudate utilisation: Characterisation of the Paragon var. spring bread wheat root microbiome

Conventional methods of agricultural pest control and crop fertilisation are contributing to a crisis of biodiversity loss, biogeochemical cycle dysregulation, and ecosystem collapse. Thus, we must find ecologically responsible means to control disease and promote crop yields. The root-associated microbiome may contribute to this goal as microbes can aid plants with disease suppression, abiotic stress relief, and nutrient bioavailability. We applied 16S rRNA gene & fungal 18S rRNA gene (ITS2 region) amplicon sequencing to profile the diversity of the bacterial, archaeal & fungal communities associated with the roots of UK elite spring bread wheat variety Triticum aestivum var. Paragon in different soils and developmental stages. This revealed that community composition shifted significantly for all three groups across compartments. This shift was most pronounced for bacteria and fungi, while we observed weaker selection on the ammonia oxidising archaea-dominated archaeal community. Across multiple soil types we found that soil inoculum was a significant driver of endosphere community composition, however several bacterial families were identified as core enriched taxa in all soil conditions. The most abundant of these were Streptomycetaceae and Burkholderiaceae. Moreover, as the plants senesce, both families were reduced in abundance, indicating that input from the living plant was required to maintain their abundance in the endosphere. To understand which microbes are using wheat root exudates in the rhizosphere, root exudates were labelled in a 13CO2 DNA stable isotope probing experiment. This shows that bacterial taxa within the Burkholderiaceae family among other core enriched taxa, such as Pseudomonadaceae, were able to use root exudates but Streptomycetaceae were not. Overall, this work provides a better understanding of the wheat microbiome, including the endosphere community. Understanding crop microbiome formation will contribute to ecologically responsible methods for yield improvement and biocontrol in the future.

microbiology↗

bioRxiv2020

Competition-based screening secures the evolutionary stability of a defensive microbiome

Cuticular microbiomes of Acromyrmex leaf-cutting ants are exceptional because they are freely colonizable, and yet the prevalence of Pseudonocardia, a native vertically transmitted symbiont that controls Escovopsis fungus-garden disease, is never compromised. Game theory suggests that competition-based screening can allow the selective recruitment of antibiotic-producing bacteria from the environment, by fomenting and biasing competition for abundant host resources. Mutual symbiont aggression benefits the host and also maintains native symbiont viability. Here we use RNA-stable isotope probing (RNA-SIP) to confirm predictions that Acromyrmex cuticles can maintain a range of microbial symbionts. We then used dual-RNA-sequencing and bioassays to show that vertically transmitted Pseudonocardia strains produce antibacterials that differentially reduce the growth rates of other microbes, ultimately eliminating non-antibiotic-producing strains that might parasitize the symbiosis while still allowing antibiotic-producing Streptomyces strains to survive. Open cuticular microbiomes can thus maintain a specific co-evolved mutualism by restricting access for other bacterial strains.

evolutionary biology↗

bioRxiv2020

Investigating the role of root exudates in recruiting Streptomyces bacteria to the Arabidopsis thaliana root microbiome

Streptomyces species are saprophytic soil bacteria that produce a diverse array of specialised metabolites, including half of all known antibiotics. They are also rhizobacteria and plant endophytes that can promote plant growth and protect against disease. Several studies have shown that streptomycetes are enriched in the rhizosphere and endosphere of the model plant Arabidopsis thaliana. Here, we set out to test the hypothesis that they are attracted to plant roots by root exudates, and specifically by the plant phytohormone salicylate, which they might use as a nutrient source. We confirmed a previously published report that salicylate over-producing cpr5 plants are colonised more readily by streptomycetes but found that salicylate-deficient sid2-2 and pad4 plants had the same levels of root colonisation by Streptomyces bacteria as the wild-type plants. We then tested eight genome sequenced Streptomyces endophyte strains in vitro and found that none were attracted to or could grow on salicylate as a sole carbon source. We next used 13CO2 DNA stable isotope probing to test whether Streptomyces species can feed off a wider range of plant metabolites but found that Streptomyces bacteria were outcompeted by faster growing proteobacteria and did not incorporate photosynthetically fixed carbon into their DNA. We conclude that, given their saprotrophic nature and under conditions of high competition, streptomycetes most likely feed on more complex organic material shed by growing plant roots. Understanding the factors that impact the competitiveness of strains in the plant root microbiome could have consequences for the effective application of biocontrol strains. ImportanceStreptomyces bacteria are ubiquitous in soil but their role as rhizobacteria is less well studied. Our recent work demonstrated that streptomycetes isolated from A. thaliana roots can promote growth and protect against disease across plant species and that plant growth hormones can modulate the production of bioactive specialised metabolites by these strains. Here we used 13CO2 DNA stable isotope probing to identify which bacteria feed on plant metabolites in the A. thaliana rhizosphere and, for the first time, in the endosphere. We found that Streptomyces species are outcompeted for these metabolites by faster growing proteobacteria and instead likely subsist on more complex organic material such as cellulose derived from plant cell material that is shed from the roots. This work thus reveals the "winners and losers" in the battle between soil bacteria for plant metabolites and could inform the development of methods to apply streptomycetes as plant growth-promoting agents.

microbiology↗

bioRxiv2019

Investigating the role of exudates in recruiting Streptomyces bacteria to the Arabidopsis thaliana root microbiome

Streptomyces bacteria are ubiquitous in soils and are well-known for producing secondary metabolites, including antimicrobials. Increasingly, they are being isolated from plant roots and several studies have shown they are specifically recruited to the rhizosphere and the endosphere of the model plant Arabidopsis thaliana. Here we test the hypothesis that Streptomyces bacteria have a beneficial effect on A. thaliana growth and could potentially be used as plant probiotics. To do this, we selectively isolated streptomycetes from surface washed A. thaliana roots and generated high quality genome sequences for five strains which we named L2, M2, M3, N1 and N2. Re-infection of A. thaliana plants with L2, M2 and M3 significantly increased plant biomass individually and in combination whereas N1 and N2 had a negative effect on plant growth, likely due to their production of polyene natural products which can bind to phytosterols and reduce plant growth. N2 exhibits broad spectrum antimicrobial activity and makes filipin-like polyenes, including 14-hydroxyisochainin which inhibits the Take-all fungus, Gaeumannomyces graminis var. tritici. N2 antifungal activity as a whole was upregulated ~2-fold in response to indole-3-acetic acid (IAA) suggesting a possible role during competition in the rhizosphere. Furthermore, coating wheat seeds with N2 spores protected wheat seedlings against Take-all disease. We conclude that at least some soil dwelling streptomycetes confer growth promoting benefits on A. thaliana while others might be exploited to protect crops against disease. ImportanceIt is vital that we reduce our reliance on agrochemicals and there is increasing interest in using bacterial strains to promote plant growth and protect against disease. Our study follows up reports that Arabidopsis thaliana specifically recruits Streptomyces bacteria to its roots. In particular, we test the hypothesis that these bacteria can offer benefits to their A. thaliana hosts and that strains isolated from these plants might be used as probiotics. We isolated Streptomyces strains from surface washed A. thaliana roots and genome sequenced five phylogenetically distinct strains. Genome mining and bioassays indicated that all five strains have plant growth promoting properties, including production of IAA, siderophores and ACC deaminase activity. Three strains significantly increased A. thaliana growth in vitro and when applied in combination in soil. Another produces potent filipin-like antifungal metabolites and we used it as a seed coating to protect germinating wheat seeds against the fungal pathogen Gaeumannomyces graminis var. tritici (wheat Take-all fungus). We conclude that introducing an optimal combination of Streptomyces strains into the root microbiome can provide significant benefits to plants.

microbiology↗

bioRxiv2018

Efficient assembly and long-term stability of defensive microbiomes via private resources and community bistability

Understanding the mechanisms promoting the assembly and maintenance of host-beneficial microbiomes is an open problem. An increasing amount of evidence supports the idea that animal and plant hosts can use private resources and the ecological phenomenon known as community bistability to favour some microbial strains over others. We briefly review empirical evidence showing that hosts can: (i) protect the growth of beneficial strains in an isolated habitat, (ii) use antibiotic compounds to suppress non-beneficial, competitor strains, and (iii) provide resources (for a limited time) that only beneficial strains are able to translate into an increased rate of growth, reproduction, or antibiotic production. We then demonstrate in a spatially explicit, individual-based model that these three mechanisms act similarly by selectively promoting the initial proliferation of preferred strains, that is, by acting as a private resource. By explicitly modelling localized microbial interactions and diffusion dynamics, we further show that an intermediate level of antibiotic diffusion is the most efficient mechanism in promoting preferred strains and that that there is a wide range of conditions under which hosts can promote the assembly of a self-sustaining defensive microbiome. This, in turn, supports the idea that hosts readily evolve to promote host-beneficial defensive microbiomes.

microbiology↗