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Microbe-free materials

Microbe-free materials

The logic behind Microbe-free materials types of regulations is Microbe-fee in Microbe-free materials they are set materuals to be risk averse and to ensure Microb-efree patients in the Microbe-free materials Microbe-ffee Microbe-free materials Natural energy-boosting strategies Pennsylvania have access to safe therapies; however, the current restrictive framework overlooks the capabilities of the extraction process including the associated infrastructure to deactivate or remove microbial contaminants. For example, Pennsylvania does not allow for the use of federally accepted microbial remediation technology to sterilize contaminated plant material prior to market distribution. Erb et al. Compare COMPARE ». Microbe-free materials

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Endophytes cause direct metabolic costs that should be directly correlated to their abundance within the host α whereas their benefits are likely to follow a saturation curve β. We suggest consider only ecological benefits, but not ecological costs, in this context.

Ecological benefits represent an important part of the overall benefits that are provided by microorganisms to their host plant. In the case of resistance-enhancing endophytes, all benefits provided are ecological ones.

By contrast, ecological costs must be considered more cautiously, because most traits of an organism eventually attract predators or parasites and then impair rather than improve fitness. For example, fruits, pollen, and nectar are eventually consumed by animals that do not provide the expected service dispersal and pollination.

However, these traits in principle serve the reproduction of the plant. Thus, it would not be useful to consider, e.

Host—endophyte interactions are highly variable and their net effects are strongly context dependent. Most importantly, however, we have seen above how important plant traits are strongly affected by the presence of endophytes in the plant.

Due to the significant endophyte—environment interactions, we must assume that a large part of our current picture on general plant ecological traits is heavily biased or, at best, incomplete. By contrast, most field ecological studies that were conducted in the wild did not even consider, let alone control for, the percentage of the plant population under investigation that was infected by endophytic microorganisms.

Predictions on general or typical outcomes of endophyte—plant interactions under natural conditions are, therefore, still hardly possible in most contexts. A general pattern that we would expect is, however, that generalist herbivores are more commonly affected than specialists by any infection of the plant with a microorganism that interferes with the resistance of the host plant Koricheva et al.

Even endophytes that directly affect resistance via the synthesis of alkaloids or other toxic compounds might, however, attract specialists to their host plant, or at least affect specialists less strongly than generalists: due to the common and predictable presence of these endophytes in certain host species, co-evolutionary responses on the side of specialist enemies are likely.

As far as we are aware, these patterns are exactly what researchers find Koricheva et al. Similarly, the allocation of assimilates and resources toward the endophyte appears an inevitable consequence of their presence.

Therefore, the presence of an endophyte is likely to cause a stronger negative effect on plant-growth rates under limiting nutrient conditions Cheplick et al. We also predict that these costs will be proportional to the endophyte density reached in the plant, being generally higher for type I than for type II fungal endophytes.

However, we are not aware of a study that has tested this prediction. We need more field research in order to broaden our knowledge on the microorganisms that are common in nature, that affect the ecological interactions of plants with their environment and that, thereby, drive plant evolution.

Even these basic questions remain largely unanswered for most groups of endophytes, because research effort has mainly concentrated on the vertically transmitted clavicipitaceous fungi of grasses Saikkonen et al.

Various studies have screened for fungal endophytes, but they used different methods and their results are therefore hard to compare, particularly with respect to quantitative questions. Second, factors such as host ontogeny, season, leaf age, microclimatic conditions, and the distance from other plants that can serve as a source for infection with horizontally transmitted endophytes affect the fungal and likely also bacterial population of a certain plant organ Arnold and Herre, ; Schulz and Boyle, ; Ormond et al.

As exemplified by the effect of light intensity of the pathogenicity of a fungal endophyte Álvarez-Loayza et al. mutila is likely to benefit seedlings and saplings in the understory but may harm the larger plants that are exposed to full light conditions. Third, species saturation curves usually demonstrate that the conducted studies were unlikely to discover the total endophyte diversity present Arnold et al.

Finally, screenings for endophytic bacteria are usually restricted to taxa with a known plant-growth promoting effect. As a first step into the future, we suggest to apply broad screening techniques to search for endophytic microorganisms in natural species and plant communities.

Screening can be realized both empirically and in silico. Screening attempts that include an initial cultivation step have been applied successfully and revealed an as of yet unknown fungal and bacterial diversity in various host—plant species Albrectsen et al.

However, the cultivation step is likely to filter against a significant part of the microbial flora. Culture-independent techniques such as the direct PCR of microbial DNA extracted from plant tissue Higgins et al.

Molecular, culture-independent methods to study microbial biodiversity of natural systems rely either on the extraction of DNA, cloning and sequencing of small DNA fragments shot gun cloning — metagenomics or in the a priori amplification of defined genes using polymerase chain reaction.

Later, such amplified products can be directly cloned and sequenced, or submitted to several fingerprinting methods such as: amplified ribosomal DNA restriction analysis or restriction fragment length polymorphism RFLP ; automated ribosomal intergenic spacer analysis ARISA ; terminal RFLP T-RFLP ; denaturing gradient gel electrophoresis DGGE or temperature gradient gel TGGE ; single strand conformation polymorphism SSCP ; and denaturing high-performance liquid chromatography DHPLC.

Some reviews about the advantages and disadvantages of each of these methods for community profiling have been published elsewhere Binladen et al. It is important to note that although great progress has been achieved and massive sequencing technologies are becoming more feasible, addressing microbial communities, and microbial diversity in natural environments is still a challenge Bent and Forney, Moreover, microbial communities seems to be greatly diverse within a single host organism Arnold et al.

Where exactly are all these microbes localized? Endophytic microbes that live within the plant tissue can be visualized, for example, by in situ hybridization and microscopy with selective stains Singh et al.

Additionally, in cases where the microbial cells can be transformed with plasmids coding for fluorescent proteins such as GFP, the transformed cells could be followed during the interaction with their host Partida-Martinez et al. Studying the molecular mechanisms via which plants interact with microbes will rely on the combination of multiple molecular, genomic, and biochemical methods, depending on the culturability of the microbial endophytes, the feasibility of genetic transformation of both plant and endophyte, and the ability to create asymbiotic hosts plants.

At the in silico level, there is a large pool of potential information in all the genomic sequencing projects that have become realizable due to affordable next-generation sequencing techniques. However, the microorganisms that carry these genes are likely to represent an integrative part of the functioning entire organism, rather than contaminations.

Any bacterium or fungus that is regularly infecting or otherwise associated with a certain host affects the phenotype of its host in a predictable manner and is likely to co-evolve with its host. Discarding these sequences from further analysis prevents us from a more complete understanding of the true subject of our scientific effort: the entire plant as it exists in nature.

As most of the above-mentioned methods produce sequence data for the microbial strains that form the community within a given host plant, the information obtained can be used to place the discovered taxa within the broader phylogenetic context: a crucial step if one aims at understanding the evolution of endophytes.

Are mutualistic or commensalistic microorganisms former pathogens that have lost their virulence to some degree but maintained the capacity to invade the tissue of living plants?

Or are mutualists and antagonists derived from different phylogenetic clades? Considering the general conditionality in all these interactions and the existence of mutualistic and pathogenic taxa within the same genera see above, and the multiple fungal taxa that form ectomycorrhiza: A.

Bennett, pers. As mentioned, many endophytes are believed to have evolved from former insect parasites and the Clavicipitaceae comprise, besides mutualistic plant endophytes, also entomopathogens, plant pathogens, and saprophytes Rodriguez et al. Because the sexual phase of Neotyphodium , Epichlo ë, has a parasitic nature Muller and Krauss, , it appears tempting to speculate that endophytes are former pathogens that have successfully completed the common tendency in host—parasite coevolution: decreasing their virulence until a balanced, asymptomatic interaction has been reached.

Intriguingly, one single mutation was sufficient to convert a pathogenic strain of Colletotrichum magna into a non-pathogenic endophyte that had the capacity to protect its host from infection by fungal pathogens Freeman and Rodriguez, Similarly, the endophyte Guignardia mangiferae Botryosphaeriaceae and the citrus pathogen G.

citricarpa differ only in a limited number of enzymes and the endophyte appeared phylogenetically derived from the pathogen Romao et al. Thus, current evidence leads to the conclusion that endophytes commonly represent former pathogens that have reduced their virulence to a degree that allows asymptomatic life within their host.

However, the patterns at the lowest taxonomic levels might look completely different. Specific strains of what is currently considered as one species might be well specialized to usually cause either a pathogenic or an asymptomatic infection or to preferably infect different hosts Ormond et al.

Direct comparisons of related strains with contrasting strategies such as those presented by Romao et al. We have stated above that a completely endophyte-free plant is unlikely to be able to survive under natural conditions Figure 1. Unfortunately, as to our very best knowledge, no empirical data exist to support this statement.

However, the controls are only checked for the absence of the vertically transmitted clavicipitaceous fungus in the beginning of the experiment, but not for other, horizontally acquired endophytes.

It would be highly interesting to produce complete endophyte-free plants and study their phenotype and ecological success under controlled conditions as well as in the field. These studies should be accompanied with the above-mentioned cultivation-independent screening techniques, in order to monitor for the occurrence of horizontally acquired endophytes in the originally endophyte-free plants.

Two aspects appear to be of particularly crucial importance if we aim at understanding the role of endophytes in any ecosystem: 1 the population densities reached by endophytes and 2 the temporal order at which the symbioses of a plant with various microbial partners are usually established.

That microbial population density matters is nicely illustrated by a recent report on the effects of different inoculum densities used to infect Datura stramonium with various Glomus species : the positive effects on seed set of the infection followed an optimum curve with increasing infection intensity, whereas plant tolerance to defoliation was linearly and negatively correlated with infection intensity Garrido et al.

Such patterns are likely to be common, because any endophyte represents a cost to its host plant see above. Therefore, too high densities can be expected to cause negative effects under most conditions. We follow Gange and Ayres and use an easy graphical model Figure 3 to illustrate the importance of the quantity of any given endophyte for the net effect of the infection.

Because every cell of living endophyte has its own metabolic demands, the direct costs of endophyte infection should be linearly and positively correlated to the amount of endophyte that must me nourished by a host plant.

By contrast, the effects of many, if not all, endophytes are likely to follow a saturation curve: increased nitrogen supply from Rhizobia or increased supply of phosphorous from mycorrhizal fungi benefits plants only until all needs are saturated and other factors become limiting.

Likewise, any resistance factor will reach an optimum level of concentration above which an increase in the concentration of the compound does not further enhance the level of phenotypic resistance.

As the net effect of the endophyte can be calculated by its benefits minus its costs see above , we predict that the net positive effects of endophyte infection in relation to their quantity follow an optimum curve, as it has been indeed been found empirically by Garrido et al.

Data obtained in the above-mentioned screening processes can also be directly used to answer critical questions: how common are endophytes in natural populations? how specific are they? what determines the endophytic flora, particularly for the horizontally transmitted species: host or ecosystem?

That is, are two plants more likely to share common endophytes when they are a taxonomically related or b growing in the same habitat? Both host species and season affected the distribution of genetically defined strains of B.

Data of this type represent an essential basis for the formulation of further, more detailed research questions aimed at improving our knowledge on the ecological role of endophytes in natural ecosystems. Another important question concerns the temporal order in which plants become infected with the different types of endophytes, and the temporal relations among these infections and the numerous further ecological interactions of a plant Van Dam and Heil, Erb et al.

Similar patterns were found for the mutualistic outcome of the infection of plants with certain Colletotrichum strains Redman et al. In fact, the sequence of arrival becomes crucial when we consider endophyte-mediated changes in the resistance phenotype of a plant.

Most beneficial effects of endophytes must be considered preventive rather than curative, but can we expect the infection by endophytes always to precede the attack of a plant by its enemies? Vertically transmitted endophytes infect a plant throughout its entire life cycle: infection with clavicipitaceous endophytes, thus, should normally precede any other ecological interaction of the host plant.

It appears also to be likely that plant roots acquire nodulating bacteria and mycorrhizal fungi at early stages of root development, soon after germination.

The situation is, however, much less clear for the leaf-colonizing type II endophytes. In one study, the distance from a putative source tree influenced endophyte colonization, suggesting a highly dynamic infection process Arnold and Herre, Type II endophytes might therefore have to infect a plant after its encounters with pathogens or herbivores, with as yet unknown consequences for all partners involved.

Given the conditionality of all these interactions, the temporal order at which a plant normally establishes the interactions with its various horizontally transmitted microbial symbionts certainly requires future investigation. Again, the above-mentioned molecular methods could be applied to plants under natural conditions to characterize the endophytic flora in different organs, in plants of different developmental stages and in con- and heterospecific plants that grow at different sites.

As mentioned above see Balanced Antagonism: The Molecular Perspective , endophytes require virulence factors to overcome the resistance of their host Zamioudis and Pieterse, The balance between host resistance and endophyte virulence is likely to be a central determinator of endophyte density, with all its consequences on host development and fitness Eaton et al.

Effectors play a crucial role in the microbial invasion process and are likely to be central determinants of the host spectrum of pathogens Schulze-Lefert and Panstruga, Similarly, endophytes employ effectors to suppress plant immunity and colonize the host plant Zamioudis and Pieterse, As suggested for the investigation of generalist vs.

specialist pathogens Barrett and Heil, , comparing the genomes and phenotypes of taxonomically related pathogens and mutualistic endophytes will allow to directly investigate the genetic differences that are contributing to these different microbial life styles. Next-generation high-throughput sequencing should also be applied to mRNA, because the detailed balance between the infection by the endophyte and its control by the host is maintained mainly via inducible responses, that is, at the transcriptional level Eaton et al.

Considering the arguments presented above, this type of experiments will benefit strongly from a detailed experimental control at the qualitative and quantitative level over the endophyte population of the host in combination with comparisons under different environmental conditions and of different host ontogenetic stages.

Plant-infecting microorganisms are ubiquitous and affect many vitally important plant traits, particularly those that control the interactions of plants with their abiotic and biotic environment.

Undoubtedly, some microorganisms will usually have negative effects on the fitness of their hosts and thus should be termed pathogens, whereas other microorganisms that colonize the tissue of plants usually have positive effects and then represent mutualistic endophytes.

However, all plant—microbe interactions can shift along a mutualism—antagonism continuum. To understand their effects on plant ecology, plant fitness, and ultimately plant evolution, we therefore need to know the net effects that the typical microbial flora of a plant has under the average environmental conditions and understand the molecular mechanisms that cause the observed phenotypic effects.

Most importantly, a microbe-free plant is not what we normally see in nature. It is likely that all plants that grow under natural conditions are, or have been in their past, colonized by several microorganisms, which exert highly conditional, but vitally important effects on their host.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. We are indebted to Alejandro de León for preparing Figures 1 and 2 and to Priscila Chaverri and Romina O.

Gazis for sharing their unpublished data set on the co-occurrence of endophytes in rubber tree samples. Helen E. Roy, Alison E. Bennett, and our referees, Juriaan Ton and Toby Kiers provided us with many helpful comments on an earlier version of this manuscript.

Financial support by CONACyT de México is gratefully acknowledged. Direct costs can result from the allocation of limited resources to the trait, autotoxic effects of the trait or its direct, genetic coupling to another trait with negative net effects pleiotropic costs.

In the context of the present work, those effects of the plant phenotype that are caused by the interaction of the genome of the endophytic microorganism with the plant genome and its environment.

Albrectsen, B. Endophytic fungi in European aspen Populus tremula leaves-diversity, detection, and a suggested correlation with herbivory resistance. Fungal Divers. CrossRef Full Text. Alejo-Iturvide, F.

Mycorrhizal protection of chili plants challenged by Phytophthora capsici. Plant Pathol. Álvarez-Loayza, P. Light converts endosymbiotic fungus to pathogen, influencing seedling survival and niche-space filling of a common tropical tree, Iriartea deltoidea.

PLoS ONE 6, e Arnold, A. Canopy cover and leaf age affect colonization by tropical fungal endophytes: ecological pattern and process in Theobroma cacao Malvaceae. Mycologia 95, — Pubmed Abstract Pubmed Full Text CrossRef Full Text. Are tropical fungal endophytes hyperdiverse?

Fungal endophytes limit pathogen damage in a tropical tree. Barazani, O. Piriformospora indica and Sebacina vermifera increase growth performance at the expense of herbivore resistance in Nicotiana attenuata.

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Binladen, J. The use of coded PCR primers enables high-throughput sequencing of multiple homolog amplification products by parallel sequencing. PLoS ONE 2, e Bonfante, P. Plants and arbuscular mycorrhizal fungi: an evolutionary-developmental perspective.

Borowicz, V. Do arbuscular mycorrhizal fungi alter plant-pathogen relations? Ecology 82, — Brevin, N. pub2 pub2. Brundrett, M. Coevolution of roots and mycorrhizas of land plants. New Phytol. Cheplick, G. Interactions between infection by endophytic fungi and nutrient limitation in the grasses Lolium perenne and Festuca arundinacea.

Clay, K. Fungal endophytes of grasses. Currie, A. Is a specialist root-feeding insect affected by arbuscular mycorrhizal fungi? Soil Ecol. Dawkins, R. The Extended Phenotype. Oxford: Oxford University Press. De Deyn, G. Chemical defense, mycorrhizal colonization and growth responses in Plantago lanceolata L.

de Román, M. Elicitation of foliar resistance mechanisms transiently impairs root association with arbuscular mycorrhizal fungi. Dean, J. Plant-rhizobia mutualism influences aphid abundance on soybean. Plant Soil , — Denison, R. Lifestyle alternatives for rhizobia: mutualism, parasitism, and forgoing symbiosis.

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There is no easy fix. For instance, surfaces with nanospikes might need to be regularly cleared of dead microorganisms and other debris. Copper would need to be polished to limit oxidisation, which would make it less reactive. Cork is well-known for its antimicrobial properties and is already used for flooring in some settings Credit: Alamy.

In any case, it will take time for these technologies to find commercial partners and scale up. Some examples already exist. Sharklet is a plastic sheeting material that mimics sharkskin by using a diamond pattern on the surface, which bacteria are unable to settle on.

This is already used on medical devices like catheters, which can carry infectious bacteria into the body. And the MicroShield coating has been applied to surfaces within airplanes, such as seats, to keep them free of bacteria. These surfaces could be an important tool in our fight against infectious diseases and future pandemics.

Today, the spectre of antimicrobial resistance looms even larger as the world struggles against the ravages of Covid Antibiotics are also commonly given to patients with coronavirus — even though they do nothing against the virus itself — increasing fears that it could be fuelling antibiotic-resistant bacterial infections in patients.

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What is BBC Future? Earth Future Planet Health Gap Sustainability on a Shoestring Time: The Ultimate Guide The Next Giant Leap Green Tech Best of BBC Future Latest. Share using Email. By Christine Ro 1st June By copying the texture of insect wings or using new types of materials to create surfaces that kill or inhibit microbes, we could stop infections before they even get into the body.

Graphene sheets are incredibly thin, with sharp edges that could cut through the bacterial membrane and kill it. Special Offers On Sale 1. Protectant 1. EPA-Registered EPA-Registered 3.

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How to Identify Microbes

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