Biology subjects

Miebach, M.

Publications and source records attributed to Miebach, M..

4 recordsLinked to original sources

bioRxiv2025

Comparative genomics of epiphytic and endophytic bacterial culture collections from Arabidopsis thaliana in Otautahi (Christchurch), Aotearoa New Zealand

Bacterial culture collections are essential resources for exploring the diversity of microorganisms and their interactions with each other and their hosts. Here, we report on the sequencing of the first 129 bacterial isolates, representing 34 genera, from a culture collection of more than 600 bacterial strains originally isolated from leaves of a naturalised Arabidopsis thaliana population from [O]tautahi (Christchurch), Aotearoa New Zealand. Epiphytic (leaf surface), and endophytic (apoplastic) bacteria were isolated separately from the same leaves, providing complementary insights into both compartments. The recovered isolates encompass the dominant taxa typically associated with the Arabidopsis phyllosphere, including Pseudomonas, Sphingomonas, Methylobacterium, and Flavobacterium. Their full genome assemblies (BUSCO average completeness > 99%, checkM average completeness > 97% and average contamination < 1%) were analysed and compared to assess genomic features across epiphytic and endophytic lineages. While the epiphytic and endophytic strain collections did not show large genomic differences, certain functional categories differ, such as terpene biosynthesis and biofilm formation being enriched in epiphytic strains, while arginine biosynthesis and carbohydrate degradation were associated with endophytic strains. These data provide a genomic foundation for future experimental work on leaf-associated microbial ecology and plant-microbe interactions. To our knowledge, this is the first Arabidopsis leaf culture collection established from a Southern Hemisphere source.

microbiology↗

bioRxiv2023

Non-pathogenic leaf-colonising bacteria elicit pathogen-like responses in a colonisation density-dependent manner

Leaves are colonised by a complex mix of microbes, termed the leaf microbiota. Even though the leaf microbiota is increasingly recognised as an integral part of plant life and health, our understanding of its interactions with the plant host is still limited. Here, mature, axenically grown Arabidopsis thaliana plants were spray-inoculated with six diverse leaf-colonising bacteria. The transcriptomic changes in leaves were tracked over time and significant changes in ethylene marker (ARL2) expression were observed only two to four days after spray-inoculation. Whole transcriptome sequencing revealed that four days after inoculation, leaf transcriptional changes to colonisation by non-pathogenic and pathogenic bacteria differed in strength but not in the type of response. Inoculation of plants with different densities of the non-pathogenic bacterium Williamsia sp. Leaf354 showed that high bacterial titers caused disease phenotypes and led to severe transcriptional reprogramming with a strong focus on plant defence. An in silico epigenetic analysis of the data was congruent with the transcriptomic analysis. These findings suggest (1) that plant responses are not rapid after spray-inoculation, (2) that plant responses only differ in strength and (3) that plants respond to high titers of non-pathogenic bacteria with pathogen-like responses. Plain Language SummaryPlants are colonised by diverse bacteria affecting many aspects of plant life. Here we show that plants do not differentiate between different bacteria but measure their quantities to keep bacterial numbers in check.

plant biology↗

bioRxiv2022

Plant protoplast-based assay to screen for salicylic acid response-modulating bacteria

Leaves host remarkably diverse microbes, collectively referred to as the leaf microbiota. While many beneficial functions have been attributed to the plant microbiota, the individual contributions of leaf-colonising bacteria range from pathogenic to mutualistic interactions. Omics approaches demonstrated that some leaf-colonising bacteria evoke substantial changes in gene expression and metabolic profiles in the plant host, including plant immunity. While omic approaches provide a system level view on cellular functions, they are costly and laborious, thereby severely limiting the throughput of the number of bacterial strains that can be tested in planta. To enable cost-effective high-throughput screens, we have developed a plant protoplast-based assay to measure real-time target gene expression changes following bacterial inoculation. Here, protoplasts were isolated from leaves of stable transgenic plants containing a pPR1:eYFP-nls construct. Changes in yellow fluorescence were captured for up to 96 treatments using a plate reader. This allowed the monitoring of changes in the salicylic acid-dependent plant immune response over time. Protoplast isolation per se evoked mild fluorescence responses, likely linked to endogenous salicylic acid production. This is advantageous in a bacterial assay, as bidirectional changes in PR1 expression can be measured. Plate reader-generated data were validated via fluorescence microscopy and RT-qPCR. Fluorescence microscopy further demonstrated heterogeneity in the response of individual protoplasts, which is potentially linked to differences in cell-type. In summary, the protoplast assay is an affordable and easily up-scalable way of measuring changes in target gene expression to bacterial colonisation.

microbiology↗

bioRxiv2020

Litterbox - A gnotobiotic zeolite-clay system to investigate Arabidopsis-microbe interactions

Plants are colonised by millions of microorganisms representing thousands of species with varying effects on plant growth and health. The microbial communities found on plants are compositionally consistent and their overall positive effect on the plant is well known. However, the effects of individual microbiota members on plant hosts and vice versa, as well as the underlying mechanisms remain largely unknown. Here, we describe Litterbox, a highly controlled system to investigate plant-microbe interactions. Plants were grown gnotobiotically on zeolite-clay, an excellent soil replacement that retains enough moisture to avoid subsequent watering. Plants grown on zeolite phenotypically resemble plants grown under environmental conditions. Further, bacterial densities on leaves in the Litterbox system resembled those in temperate environments. A PDMS sheet was used to cover the zeolite, thereby significantly lowering the bacterial load in the zeolite and rhizosphere. This reduced the likelihood of potential systemic responses in leaves induced by microbial rhizosphere colonisation. We present results of example experiments studying the transcriptional responses of leaves to defined microbiota members and the spatial distribution of bacteria on leaves. We anticipate that this versatile and affordable plant growth system will promote microbiota research and help in elucidating plant-microbe interactions and their underlying mechanisms.

plant biology↗