scispace - formally typeset
Search or ask a question
Author

Jan J. Tech

Bio: Jan J. Tech is an academic researcher from University of California, Davis. The author has contributed to research in topics: Phyllosphere & Bacteroidetes. The author has an hindex of 6, co-authored 6 publications receiving 505 citations.

Papers
More filters
Journal ArticleDOI
TL;DR: One of the largest surveys of leaf surface microbiology offers new insights into the extent and underlying causes of variability in bacterial community composition on plant leaves as a function of time, space and environment.
Abstract: The presence, size and importance of bacterial communities on plant leaf surfaces are widely appreciated. However, information is scarce regarding their composition and how it changes along geographical and seasonal scales. We collected 106 samples of field-grown Romaine lettuce from commercial production regions in California and Arizona during the 2009-2010 crop cycle. Total bacterial populations averaged between 10(5) and 10(6) per gram of tissue, whereas counts of culturable bacteria were on average one (summer season) or two (winter season) orders of magnitude lower. Pyrosequencing of 16S rRNA gene amplicons from 88 samples revealed that Proteobacteria, Firmicutes, Bacteroidetes and Actinobacteria were the most abundantly represented phyla. At the genus level, Pseudomonas, Bacillus, Massilia, Arthrobacter and Pantoea were the most consistently found across samples, suggesting that they form the bacterial 'core' phyllosphere microbiota on lettuce. The foliar presence of Xanthomonas campestris pv. vitians, which is the causal agent of bacterial leaf spot of lettuce, correlated positively with the relative representation of bacteria from the genus Alkanindiges, but negatively with Bacillus, Erwinia and Pantoea. Summer samples showed an overrepresentation of Enterobacteriaceae sequences and culturable coliforms compared with winter samples. The distance between fields or the timing of a dust storm, but not Romaine cultivar, explained differences in bacterial community composition between several of the fields sampled. As one of the largest surveys of leaf surface microbiology, this study offers new insights into the extent and underlying causes of variability in bacterial community composition on plant leaves as a function of time, space and environment.

377 citations

Journal ArticleDOI
TL;DR: A PCR-based method is presented that allows a priori determination of the degree of chloroplast and mitochondrial contamination in DNA samples from plant environments, and proposes two primer pairs which between them offer an indirect means of faithfully estimating bacterial abundances on plants.

83 citations

Journal ArticleDOI
01 Aug 2011
TL;DR: The method of high-throughput pyrosequencing of 16S ribosomal RNA (rRNA) gene amplicons was used to analyze the diversity of bacteria associated with the leaf and berry surfaces of 'Chardonnay' grape in a vineyard close to harvest, finding a novel Proteobacterium that dominated the bacterial community on berry surface.
Abstract: We used the culture-independent method of high-throughput pyrosequencing of 16S ribosomal RNA (rRNA) gene amplicons to analyze the diversity of bacteria associated with the leaf and berry surfaces of 'Chardonnay' grape in a vineyard close to harvest. Combined, more than half of all bacterial sequences were classified as Proteobacteria. Other well-represented phyla were the Firmicutes, Bacteroidetes, and Actinobacteria. The most abundantly represented genera were Sphingomonas, Hymenobacter, Bacillus, Pseudomonas, Skermanella, Leuconostoc, Massilia, Methylobacterium, Cellvibrio, and Curtobacterium. Together, these top 10 genera accounted for almost one-third of all sequences. We observed differences in the composition of bacterial communities between leaves and berries. Members of the genera Sphingomonas, Hymenobacter and Methylobacterium were abundant on foliage, whereas Achromobacter, Flavobacterium and Cellvibrio were typical for the fruit. Moreover, certain Pseudomonas species appeared to associate exclusively with leaf surfaces, while others were found more frequently on berries. Unanticipated was the discovery of a novel Proteobacterium that dominated the bacterial community on berry surfaces. Our results form the basis for future investigations into the relationship between the structure of microbial communities on grape leaves and berries and the ecosystem (dis)services that these communities provide to grape growers at different pre- and post-harvest stages of production.

65 citations

Journal ArticleDOI
TL;DR: Functional characterization of the soil culturable bacteria from the pygmy and non-pygmy forest terraces revealed that the soilacteria from the non-Pygmy terraces were significantly more effective in solubilizing minerals and more abundant than in the pyGmy terrace.
Abstract: The ecological staircase of Mendocino (California, USA) is characterized by a succession of uplifted marine terraces that are derived from the same mineralogical parent material but have different ages, levels of fertility, and types of vegetation, from grassland in the youngest and most fertile terrace to a pygmy forest in the older terraces. Such conditions present a unique opportunity to determine how the structure, abundance, and function of bacterial communities vary with soil fertility along this natural chronosequence. Pyrosequencing analysis of 16S rRNA gene amplicons revealed that Acidobacteria, Proteobacteria, Actinobacteria, and Bacteroidetes were the most abundantly represented phyla. Bacteroidetes, Firmicutes, Verrucomicrobia were significantly enriched in the grasslands, while the less fertile forested terraces showed higher abundance of Acidobacteria Gp2 and Alphaproteobacteria. The pygmy forest soil harboured significantly more Actinobacteria and OP10 than the non-pygmy forest. Between samples from different terraces, the structure of the bacterial community clearly correlated with soil characteristics. Notably, the number of operational taxonomic units was greater in the fertile terrace, as was the density of culturable bacterial populations. Functional characterization of the soil culturable bacteria from the pygmy and non-pygmy forest terraces revealed that the soil bacteria from the non-pygmy terrace were significantly more effective in solubilizing minerals and more abundant than in the pygmy terrace. Our results provide new information on bacterial community structure as a function of soil age, land cover and fertility, which improve our understanding of soil evolution.

47 citations

Journal ArticleDOI
TL;DR: The idea that plant hosts restrict pathogen access to iron, either directly, or indirectly through their associated microbiota is discussed in the context of ‘nutritional immunity,’ to suggest a possible opportunity for iron-based management of ALS.
Abstract: In commercial production settings, few options exist to prevent or treat angular leaf spot (ALS) of strawberry, a disease of economic importance and caused by the bacterial pathogen Xanthomonas fragariae. In the process of isolating and identifying X. fragariae bacteria from symptomatic plants, we observed growth inhibition of X. fragariae by bacterial isolates from the same leaf macerates. Identified as species of Pseudomonas and Rhizobium, these isolates were confirmed to suppress growth of X. fragariae in agar overlay plates and in microtiter plate cultures, as did our reference strain Pseudomonas putida KT2440. Screening of a transposon mutant library of KT2440 revealed that disruption of the biosynthetic pathway for the siderophore pyoverdine resulted in complete loss of X. fragariae antagonism, suggesting iron competition as a mode of action. Antagonism could be replicated on plate and in culture by addition of purified pyoverdine or by addition of the chelating agents tannic acid and dipyridyl, while supplementing the medium with iron negated the inhibitory effects of pyoverdine, tannic acid and dipyridyl. When co-inoculated with tannic acid onto strawberry plants, X. fragariae's ability to cause foliar symptoms was greatly reduced, suggesting a possible opportunity for iron-based management of ALS. We discuss our findings in the context of 'nutritional immunity,' the idea that plant hosts restrict pathogen access to iron, either directly, or indirectly through their associated microbiota.

14 citations


Cited by
More filters
Journal ArticleDOI
TL;DR: The plant microbiota emerges as a fundamental trait that includes mutualism enabled through diverse biochemical mechanisms, as revealed by studies on plant growth- Promoting and plant health-promoting bacteria.
Abstract: Plants host distinct bacterial communities on and inside various plant organs, of which those associated with roots and the leaf surface are best characterized. The phylogenetic composition of these communities is defined by relatively few bacterial phyla, including Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria. A synthesis of available data suggests a two-step selection process by which the bacterial microbiota of roots is differentiated from the surrounding soil biome. Rhizodeposition appears to fuel an initial substrate-driven community shift in the rhizosphere, which converges with host genotype–dependent finetuning of microbiota profiles in the selection of root endophyte assemblages. Substrate-driven selection also underlies the establishment of phyllosphere communities but takes place solely at the immediate leaf surface. Both the leaf and root microbiota contain bacteria that provide indirect pathogen protection, but root microbiota members appear to serve additional host functions through the acquisition of nutrients from soil for plant growth. Thus, the plant microbiota emerges as a fundamental trait that includes mutualism enabled through diverse biochemical mechanisms, as revealed by studies on plant growth–promoting and plant health–promoting bacteria.

2,169 citations

Journal ArticleDOI
TL;DR: This review addresses the concept of endophytism, considering the latest insights into evolution, plant ecosystem functioning, and multipartite interactions.
Abstract: All plants are inhabited internally by diverse microbial communities comprising bacterial, archaeal, fungal, and protistic taxa. These microorganisms showing endophytic lifestyles play crucial roles in plant development, growth, fitness, and diversification. The increasing awareness of and information on endophytes provide insight into the complexity of the plant microbiome. The nature of plant-endophyte interactions ranges from mutualism to pathogenicity. This depends on a set of abiotic and biotic factors, including the genotypes of plants and microbes, environmental conditions, and the dynamic network of interactions within the plant biome. In this review, we address the concept of endophytism, considering the latest insights into evolution, plant ecosystem functioning, and multipartite interactions.

1,677 citations

Journal ArticleDOI
Julia A. Vorholt1
TL;DR: Insights into the underlying structural principles of indigenous microbial phyllosphere populations will help to develop a deeper understanding of the phyllospheric microbiota and will have applications in the promotion of plant growth and plant protection.
Abstract: Our knowledge of the microbiology of the phyllosphere, or the aerial parts of plants, has historically lagged behind our knowledge of the microbiology of the rhizosphere, or the below-ground habitat of plants, particularly with respect to fundamental questions such as which microorganisms are present and what they do there. In recent years, however, this has begun to change. Cultivation-independent studies have revealed that a few bacterial phyla predominate in the phyllosphere of different plants and that plant factors are involved in shaping these phyllosphere communities, which feature specific adaptations and exhibit multipartite relationships both with host plants and among community members. Insights into the underlying structural principles of indigenous microbial phyllosphere populations will help us to develop a deeper understanding of the phyllosphere microbiota and will have applications in the promotion of plant growth and plant protection.

1,450 citations

Journal ArticleDOI
TL;DR: The fundamental role of microbe-microbe interactions (prokaryotes and micro-eukaryotes) for microbial community structure and plant health is discussed and a conceptual framework illustrating that interactions among microbiota members are critical for the establishment and the maintenance of host-microbial homeostasis is provided.
Abstract: Since the colonization of land by ancestral plant lineages 450 million years ago, plants and their associated microbes have been interacting with each other, forming an assemblage of species that is often referred to as a “holobiont.” Selective pressure acting on holobiont components has likely shaped plant-associated microbial communities and selected for host-adapted microorganisms that impact plant fitness. However, the high microbial densities detected on plant tissues, together with the fast generation time of microbes and their more ancient origin compared to their host, suggest that microbe-microbe interactions are also important selective forces sculpting complex microbial assemblages in the phyllosphere, rhizosphere, and plant endosphere compartments. Reductionist approaches conducted under laboratory conditions have been critical to decipher the strategies used by specific microbes to cooperate and compete within or outside plant tissues. Nonetheless, our understanding of these microbial interactions in shaping more complex plant-associated microbial communities, along with their relevance for host health in a more natural context, remains sparse. Using examples obtained from reductionist and community-level approaches, we discuss the fundamental role of microbe-microbe interactions (prokaryotes and micro-eukaryotes) for microbial community structure and plant health. We provide a conceptual framework illustrating that interactions among microbiota members are critical for the establishment and the maintenance of host-microbial homeostasis.

651 citations

Journal ArticleDOI
01 May 2015-Mbio
TL;DR: It is shown that soil serves as a key source of vine-associated bacteria and that edaphic factors and vineyard-specific properties can influence the native grapevine microbiome preharvest.
Abstract: Grapevine is a well-studied, economically relevant crop, whose associated bacteria could influence its organoleptic properties. In this study, the spatial and temporal dynamics of the bacterial communities associated with grapevine organs (leaves, flowers, grapes, and roots) and soils were characterized over two growing seasons to determine the influence of vine cultivar, edaphic parameters, vine developmental stage (dormancy, flowering, preharvest), and vineyard. Belowground bacterial communities differed significantly from those aboveground, and yet the communities associated with leaves, flowers, and grapes shared a greater proportion of taxa with soil communities than with each other, suggesting that soil may serve as a bacterial reservoir. A subset of soil microorganisms, including root colonizers significantly enriched in plant growth-promoting bacteria and related functional genes, were selected by the grapevine. In addition to plant selective pressure, the structure of soil and root microbiota was significantly influenced by soil pH and C:N ratio, and changes in leaf- and grape-associated microbiota were correlated with soil carbon and showed interannual variation even at small spatial scales. Diazotrophic bacteria, e.g., Rhizobiaceae and Bradyrhizobium spp., were significantly more abundant in soil samples and root samples of specific vineyards. Vine-associated microbial assemblages were influenced by myriad factors that shape their composition and structure, but the majority of organ-associated taxa originated in the soil, and their distribution reflected the influence of highly localized biogeographic factors and vineyard management. IMPORTANCE Vine-associated bacterial communities may play specific roles in the productivity and disease resistance of their host plant. Also, the bacterial communities on grapes have the potential to influence the organoleptic properties of the wine, contributing to a regional terroir. Understanding that factors that influence these bacteria may provide insights into management practices to shape and craft individual wine properties. We show that soil serves as a key source of vine-associated bacteria and that edaphic factors and vineyard-specific properties can influence the native grapevine microbiome preharvest.

649 citations