Food systems microbiome-related educational needs.

Within the European-funded Coordination and Support Action MicrobiomeSupport (https://www.microbiomesupport.eu/), the Workshop 'Education in Food Systems Microbiome Related Sciences: Needs for Universities, Industry and Public Health Systems' brought together over 70 researchers, public health and industry partners from all over the world to work on elaborating microbiome-related educational needs in food systems. This publication provides a summary of discussions held during and after the workshop and the resulting recommendations.

Metadata harmonization-Standards are the key for a better usage of omics data for integrative microbiome analysis.

BACKGROUND: Tremendous amounts of data generated from microbiome research studies during the last decades require not only standards for sampling and preparation of omics data but also clear concepts of how the metadata is prepared to ensure re-use for integrative and interdisciplinary microbiome analysis. RESULTS: In this Commentary, we present our views on the key issues related to the current system for metadata submission in omics research, and propose the development of a global metadata system. Such a system should be easy to use, clearly structured in a hierarchical way, and should be compatible with all existing microbiome data repositories, following common standards for minimal required information and common ontology. Although minimum metadata requirements are essential for microbiome datasets, the immense technological progress requires a flexible system, which will have to be constantly improved and re-thought. While FAIR principles (Findable, Accessible, Interoperable, and Reusable) are already considered, international legal issues on genetic resource and sequence sharing provided by the Convention on Biological Diversity need more awareness and engagement of the scientific community. CONCLUSIONS: The suggested approach for metadata entries would strongly improve retrieving and re-using data as demonstrated in several representative use cases. These integrative analyses, in turn, would further advance the potential of microbiome research for novel scientific discoveries and the development of microbiome-derived products.

Studying Seed Microbiomes.

Recent studies indicate that seed microbiomes affect germination and plant performance. However, the interplay between seed microbiota and plant health is still poorly understood. To get a complete picture of the system, a comprehensive analysis is required, comprising culture-dependent and culture-independent techniques. In this chapter, we provide a combination of methods that are established and optimized for the analysis of the seed microbiome. These include methods to: (1) activate and cultivate dormant seed microbiota, (2) analyze microbiota in germinated seeds (with and without substrate), (3) quantify microbial DNA via real-time PCR, (4) deplete host DNA for amplicon and metagenome analysis, and (5) visualize seed endophytes in microtomed sections using fluorescent in situ hybridization (FISH) and confocal laser scanning microscopy (CLSM). A deep understanding of the seed microbiome and its functions can help in developing new seed treatments and breeding strategies for sustainable agriculture.

Towards a unified data infrastructure to support European and global microbiome research: a call to action.

High-quality microbiome research relies on the integrity, management and quality of supporting data. Currently biobanks and culture collections have different formats and approaches to data management. This necessitates a standard data format to underpin research, particularly in line with the FAIR data standards of findability, accessibility, interoperability and reusability. We address the importance of a unified, coordinated approach that ensures compatibility of data between that needed by biobanks and culture collections, but also to ensure linkage between bioinformatic databases and the wider research community.

Correction to: Microbiome definition re-visited: old concepts and new challenges.

An amendment to this paper has been published and can be accessed via the original article.

Verticillium Wilt in Oilseed Rape-the Microbiome is Crucial for Disease Outbreaks as Well as for Efficient Suppression.

Microbiome management is a promising way to suppress verticillium wilt, a severe disease in Brassica caused by Verticillium longisporum. In order to improve current biocontrol strategies, we compared bacterial Verticillium antagonists in different assays using a hierarchical selection and evaluation scheme, and we integrated outcomes of our previous studies. The result was strongly dependent on the assessment method chosen (in vitro, in vivo, in situ), on the growth conditions of the plants and their genotype. The most promising biocontrol candidate identified was a Brassica endophyte Serratia plymuthica F20. Positive results were confirmed in field trials and by microscopically visualizing the three-way interaction. Applying antagonists in seed treatment contributes to an exceptionally low ecological footprint, supporting efficient economic and ecological solutions to controlling verticillium wilt. Indigenous microbiome, especially soil and seed microbiome, has been identified as key to understanding disease outbreaks and suppression. We suggest that verticillium wilt is a microbiome-driven disease caused by a reduction in microbial diversity within seeds and in the soil surrounding them. We strongly recommend integrating microbiome data in the development of new biocontrol and breeding strategies and combining both strategies with the aim of designing healthy microbiomes, thus making plants more resilient toward soil-borne pathogens.

Microbiome definition re-visited: old concepts and new challenges.

The field of microbiome research has evolved rapidly over the past few decades and has become a topic of great scientific and public interest. As a result of this rapid growth in interest covering different fields, we are lacking a clear commonly agreed definition of the term "microbiome." Moreover, a consensus on best practices in microbiome research is missing. Recently, a panel of international experts discussed the current gaps in the frame of the European-funded MicrobiomeSupport project. The meeting brought together about 40 leaders from diverse microbiome areas, while more than a hundred experts from all over the world took part in an online survey accompanying the workshop. This article excerpts the outcomes of the workshop and the corresponding online survey embedded in a short historical introduction and future outlook. We propose a definition of microbiome based on the compact, clear, and comprehensive description of the term provided by Whipps et al. in 1988, amended with a set of novel recommendations considering the latest technological developments and research findings. We clearly separate the terms microbiome and microbiota and provide a comprehensive discussion considering the composition of microbiota, the heterogeneity and dynamics of microbiomes in time and space, the stability and resilience of microbial networks, the definition of core microbiomes, and functionally relevant keystone species as well as co-evolutionary principles of microbe-host and inter-species interactions within the microbiome. These broad definitions together with the suggested unifying concepts will help to improve standardization of microbiome studies in the future, and could be the starting point for an integrated assessment of data resulting in a more rapid transfer of knowledge from basic science into practice. Furthermore, microbiome standards are important for solving new challenges associated with anthropogenic-driven changes in the field of planetary health, for which the understanding of microbiomes might play a key role. Video Abstract.

Harnessing the microbiomes of Brassica vegetables for health issues.

Plant health is strongly connected with plants´ microbiome. In case of raw-eaten plants, the microbiome can also affect human health. To study potential impacts on health issues of both hosts, the microbiome composition of seven different Brassica vegetables, originating from different food processing pathways, was analyzed by a combined approach of amplicon sequencing, metagenomic mining and cultivation. All Brassica vegetables harbored a highly diverse microbiota as identified by 16S rRNA gene amplicon sequencing. The composition of the microbiota was found to be rather driven by the plant genotype than by the processing pathway. We characterized isolates with potential cancer-preventing properties by tracing myrosinase activity as well as isolates with biological control activity towards plant pathogens. We identified a novel strain with myrosinase activity and we found bacterial myrosinase genes to be enriched in rhizosphere and phyllosphere metagenomes of Brassica napus and Eruca sativa in comparison to the surrounding soil. Strains which were able to suppress plant pathogens were isolated from naturally processed vegetables and represent a substantial part (4.1%) of all vegetable microbiomes. Our results shed first light on the microbiome of edible plants and open the door to harnessing the Brassica microbiome for plant disease resistance and human health.

The structure of the Brassica napus seed microbiome is cultivar-dependent and affects the interactions of symbionts and pathogens.

BACKGROUND: Although the plant microbiome is crucial for plant health, little is known about the significance of the seed microbiome. Here, we studied indigenous bacterial communities associated with the seeds in different cultivars of oilseed rape and their interactions with symbiotic and pathogenic microorganisms. RESULTS: We found a high bacterial diversity expressed by tight bacterial co-occurrence networks within the rape seed microbiome, as identified by llumina MiSeq amplicon sequencing. In total, 8362 operational taxonomic units (OTUs) of 40 bacterial phyla with a predominance of Proteobacteria (56%) were found. The three cultivars that were analyzed shared only one third of the OTUs. The shared core of OTUs consisted mainly of Alphaproteobacteria (33%). Each cultivar was characterized by having its own unique bacterial structure, diversity, and proportion of unique microorganisms (25%). The cultivar with the lowest bacterial abundance, diversity, and the highest predicted bacterial metabolic activity rate contained the highest abundance of potential pathogens within the seed. This data corresponded with the observation that seedlings belonging to this cultivar responded more strongly to the seed treatments with bacterial inoculants than other cultivars. Cultivars containing higher indigenous diversity were characterized as having a higher colonization resistance against beneficial and pathogenic microorganisms. Our results were confirmed by microscopic images of the seed microbiota. CONCLUSIONS: The structure of the seed microbiome is an important factor in the development of colonization resistance against pathogens. It also has a strong influence on the response of seedlings to biological seed treatments. These novel insights into seed microbiome structure will enable the development of next generation strategies combining both biocontrol and breeding approaches to address world agricultural challenges.

Aerial Warfare: A Volatile Dialogue between the Plant Pathogen Verticillium longisporum and Its Antagonist Paenibacillus polymyxa.

Verticillium wilt caused by Verticillium spp. results in severe yield losses in a broad range of crops. Verticillium outbreaks are challenging to control, and exacerbated by increases in soil temperatures and drought associated with global warming. Employing natural antagonists as biocontrol agents offers a promising approach to addressing this challenge. Paenibacillus polymyxa Sb3-1 was proven to reduce the growth of Verticillium longisporum during in vitro experiments and was shown to promote the growth of oilseed rape seedlings infested with V. longisporum. Our novel approach combined in vitro and in planta methods with the study of the mode of interaction between Sb3-1 and V. longisporum EVL43 via their volatile organic compounds (VOCs). Volatile and soluble substances, produced by both microorganisms as a reaction to one another's VOCs, were detected by using both gas and liquid chromatography-mass spectrometry. P. polymyxa Sb3-1 continually produced antimicrobial and plant growth promoting VOCs, such as 2-nonanone and 3-hydroxy-2-butanone. Several other antimicrobial volatile substances, such as isoamyl acetate and durenol, were downregulated. The general metabolic activity of Sb3-1, including protein and DNA biotransformations, was upregulated upon contact with EVL43 VOCs. V. longisporum increased its production of antimicrobial substances, such as 1-butanol, and downregulated its metabolic activities upon exposure to Sb3-1 VOCs. Additionally, several stress response substances such as arabitol and protein breakdown products (e.g., L-Isoleucyl-L-glutamic acid), were increased in the co-incubated samples. The results obtained depict an ongoing dialog between these microorganisms resulting in growth inhibition, the slowing down of metabolism, and the cell death of V. longisporum due to contact with the P. polymyxa Sb3-1 VOCs. Moreover, the results indicate that VOCs make a substantial contribution to the interaction between pathogens and their natural antagonists and have the potential to control pathogens in a novel, environmentally friendly manner.

Plant microbial diversity is suggested as the key to future biocontrol and health trends.

The microbiome of plants plays a crucial role in both plant and ecosystem health. Rapid advances in multi-omics tools are dramatically increasing access to the plant microbiome and consequently to the identification of its links with diseases and to the control of those diseases. Recent insights reveal a close, often symbiotic relationship between microorganisms and plants. Microorganisms can stimulate germination and plant growth, prevent diseases, and promote stress resistance and general fitness. Plants and their associated microorganisms form a holobiont and have to be considered as co-evolved species assemblages consisting of bacterial, archaeal and diverse eukaryotic species. The beneficial interplay of the host and its microbiome is responsible for maintaining the health of the holobiont, while diseases are often correlated with microbial dysbioses. Microbial diversity was identified as a key factor in preventing diseases and can be implemented as a biomarker in plant protection strategies. Targeted and predictive biocontrol approaches are possible by developing microbiome-based solutions. Moreover, combined breeding and biocontrol strategies maintaining diversity and ecosystem health are required. The analysis of plant microbiome data has brought about a paradigm shift in our understanding of its role in health and disease and has substantial consequences for biocontrol and health issues.

The plant microbiome explored: implications for experimental botany.

The importance of microbial root inhabitants for plant growth and health was recognized as early as 100 years ago. Recent insights reveal a close symbiotic relationship between plants and their associated microorganisms, and high structural and functional diversity within plant microbiomes. Plants provide microbial communities with specific habitats, which can be broadly categorized as the rhizosphere, phyllosphere, and endosphere. Plant-associated microbes interact with their host in essential functional contexts. They can stimulate germination and growth, help plants fend off disease, promote stress resistance, and influence plant fitness. Therefore, plants have to be considered as metaorganisms within which the associated microbes usually outnumber the cells belonging to the plant host. The structure of the plant microbiome is determined by biotic and abiotic factors but follows ecological rules. Metaorganisms are co-evolved species assemblages. The metabolism and morphology of plants and their microbiota are intensively connected with each other, and the interplay of both maintains the functioning and fitness of the holobiont. Our study of the current literature shows that analysis of plant microbiome data has brought about a paradigm shift in our understanding of the diverse structure and functioning of the plant microbiome with respect to the following: (i) the high interplay of bacteria, archaea, fungi, and protists; (ii) the high specificity even at cultivar level; (iii) the vertical transmission of core microbiomes; (iv) the extraordinary function of endophytes; and (v) several unexpected functions and metabolic interactions. The plant microbiome should be recognized as an additional factor in experimental botany and breeding strategies.

Complete Genome Sequence of Paenibacillus polymyxa Strain Sb3-1, a Soilborne Bacterium with Antagonistic Activity toward Plant Pathogens.

The genome of Paenibacillus polymyxa Sb3-1, a strain that shows antagonistic activities against pathogenic fungi and bacteria, consists of one 5.6-Mb circular chromosome and two plasmids of 223 kb and 8 kb. The genome reveals several genes that potentially contribute to its antagonistic and plant growth promotion activity.

Afp14 is involved in regulating the length of Anti-feeding prophage (Afp).

The anti-feeding prophage (Afp), a phage-tail-like particle that causes cessation of feeding in the New Zealand grass grub, Costelytra zealandica, is encoded by 18 open reading frames (afp1-18). C-terminal truncations of afp14 resulted in shortened Afp particles, suggesting that Afp14 is involved in Afp length determination. We constructed an Afp assembly system (afp1-18), wherein Afp14 was truncated after the N-terminal 88 residues. This construct, when expressed in trans in Escherichia coli expressing a N-terminal 98-amino acid Afp14 construct, yielded fully assembled Afp but no assembled Afp was detected in the case of a N-terminal 96-amino acid Afp14 construct. These results suggested that the 98 N-terminal, amino acid residues of Afp14 is crucial for the initiation of Afp assembly via baseplate formation. Trans-based expression of wild-type afp14 resulted in Afp particles of varying lengths, all of which were shorter than the wild-type Afp particle. On the other hand, similar expression of Afp14 harboring a C-terminal extension (KLLEH(6)) resulted in elongated Afp particles. This information, combined with bioinformatics data, allowed us to propose a model delineating the mechanism and role of Afp14 in the maturation of the Afp particle.

Three-dimensional structure of the toxin-delivery particle antifeeding prophage of Serratia entomophila.

The Serratia entomophila antifeeding prophage (Afp) is a bullet-shaped toxin-delivery apparatus similar to the R-pyocins of Pseudomonas aeruginosa. Morphologically it resembles the sheathed tail of bacteriophages such as T4, including a baseplate at one end. It also shares features with the type VI secretion systems. Cryo-electron micrographs of tilted Afp specimens (up to 60 degrees) were analyzed to determine the correct cyclic symmetry to overcome the limitation imposed by exclusively side views in nominally untilted specimens. An asymmetric reconstruction shows clear 6-fold cyclic symmetry contrary to a previous conclusion of 4-fold symmetry based on analysis of only the preferred side views (Sen, A., Rybakova, D., Hurst, M. R., and Mitra, A. K. (2010) J. Bacteriol. 192, 4522-4525). Electron tomography of negatively stained Afp revealed right-handed helical striations in many of the particles, establishing the correct hand. Higher quality micrographs of untilted specimens were processed to produce a reconstruction at 2.0-nm resolution with imposed 6-fold symmetry. The helical parameters of the sheath were determined to be 8.14 nm for the subunit rise along and 40.5° for the rotation angle around the helix. The sheath is similar to that of the T4 phage tail but with a different arrangement of the subdomain of the polymerizing sheath protein(s). The central tube is similar to the diameter and axial width of the Hcp1 hexamer of P. aeruginosa type VI secretion system. The tube extends through the baseplate into a needle resembling the "puncture device" of the T4 tail. The tube contains density that may be the toxin and/or a length-determining protein.

Role of antifeeding prophage (Afp) protein Afp16 in terminating the length of the Afp tailocin and stabilizing its sheath.

The Serratia entomophila antifeeding prophage Afp, forms a phage-tail-like particle that acts on the New Zealand grass grub, Costelytra zealandica with a 3-day LD50 of approximately 500 Afp particles per larva. Genes (afp1-18) encoding components of Afp were expressed and their products purified allowing morphological assessment of the products by transmission electron microscopy (TEM). Expression of afp1-15 resulted in the formation of a non-sheathed structure termed the tube-baseplate complex or TBC, composed of an irregular-length tube attached to a baseplate with associated tail fibres. Expression of afp1-16 produced mature, normal-length Afp particles, whereas coexpression of afp16 with afp1-15 in trans resulted in the formation of aberrant Afp particles of variable lengths. A C-terminally truncated Afp16 mutant resulted in a phenotype intermediate between mature Afp and TBC. The addition of purified Afp16 to Afp unravelled by acidic treatment resulted in the formation of shorter tubes when specimen pH was adjusted to 7 than those formed in the absence of Afp16. Analysis of TEM images of purified Afp16 revealed a hexameric ring-like structure similar to that formed by gp3 of phage T4 and gpU of phage λ. Our results suggest that Afp16 terminates tube elongation and is involved in sheath formation.

Structural study of the Serratia entomophila antifeeding prophage: three-dimensional structure of the helical sheath.

The sheath of the Serratia entomophila antifeeding prophage, which is pathogenic to the New Zealand grass grub Costelytra zealandica, is a 3-fold helix formed by a 4-fold symmetric repeating motif disposed around a helical inner tube. This structure, determined by electron microscopy and image processing, is distinct from that of the other known morphologically similar bacteriophage sheaths.