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Genome sequences of four bacterial strains isolated from the phyllosphere of Mangifera indica trees in the polluted tropical city of Medellín, Colombia.

Complete and draft genome sequences of four phyllosphere-associated bacterial strains (Microbacterium radiodurans, Brachybacterium rhamnosum, Sphingomonas citri, and Curtobacterium sp.) isolated from Mangifera indica leaves in polluted Medellín, Colombia, are presented. These resources enable future studies on plant-microbe interactions and phyllosphere microbial mediation of atmospheric pollutants under urban stress.

Mangifera indica

Phyllosphere microflora of some Egyptian plants.

The fungal and bacterial flora of the leaf surfaces of five plants growing in Egypt were studied. The fungal flora showed seasonal fluctuations with at least one peak. Twenty three genera with fifty three species were found, Aspergillus and Penicillium being most common. Other fungi showed variable percentages of the total count. Nitrogen-fixing bacteria were not isolated from the phyllosphere of the five plant species. Micrococci were most predominant among the epiphytic bacteria. Spore-forming bacteria and actinomycetes were less frequent on the leaf surfaces of the associalte plants.

Actinomyces

Studies on the phyllosphere microflora of tapioca (Manihot utilissima Pohl).

Studies on the phyllosphere microflora of tapioca (Manihot utilissima Pohl.) revealed that incidence of bacteria, fungi, and actinomycetes is indipendent of the variety, but dependent on the age. The bacteria and fungi increased with increasing age of the leaf and were more on mature leaves, whereas no such difference was noticed in the occurrence of actinomycetes. The large majority of the isolates, that were Gram-negative bacteria, was also amino acid-requiring. The chromogenic types occurred in greater abundance. The phyllosphere mycoflora consisted mainly of species of Asperigullus, Penicillium, Mucor, Curvularia, Alternaria, Helminthosporium, Fusarium, Hormicium, and Pullularia, at first three being predominant. There was no correlation between HCN content of leaves and microorganisms in the phyllosphere, Regarding the interrelationship between different groups of microorganisms in the phyllosphere, a positive correlation between fungi and actinomycetes and bacteria and actinomycetes in two (M. 4 and H. 105/44) varieties and a negative correlation for fungi and actinomycetes in one (H. 12/49) were obtained. The effect of leaf exudate and leaf, root, and tuber extracts on the germination of the conidia of three saprobic fungi, viz., Curvalaria sp., Alternaria sp., and Helminthosporium sp. was tested. While the leaf exudate and tuber extracts slightly stimulated the germination of the conidia of the fungi, the leaf extract exerted a selective inhibitory effect on the germination of the conidia of Curvalaria sp., but not on the conidia of Helminthosporium sp. and Alternaria sp.

Alternaria

Diversity of leaf- and root microbiomes among genotypes and market classes of desert-grown lettuce (Lactuca sativa L.).

Plant microbiomes are increasingly acknowledged both as extensions of plant characteristics and as biological factors that influence plant traits important for nutrition and resilience. In the context of global change, manipulation of microbiomes has the potential to complement genetic approaches to enhance crop health and productivity under rising heat and drought stress. Understanding the factors that influence microbial communities and their variation across plant genotypes is essential for developing such capabilities. We employed metabarcoding via the Illumina sequencing platform to investigate microbial communities that occur within healthy leaves and roots of 12 lettuce genotypes (Lactuca sativa L.) grown in a desert agriculture environment. We detected diverse foliar- and root-endophytic fungi and bacteria in field-grown lettuce at the Maricopa Agricultural Center (Arizona, USA). The composition of microbial community structure varied with foliar chemistry and root traits. Notably, levels of zinc and other beneficial nutrients in the leaves were strongly linked with specific endophytes. These results document the lettuce microbiome in desert farming and provide insights into endophytes in lettuce leaves, which are noteworthy because they remain after washing and are regularly ingested.

Lactuca

Nitrogen fixation in the muskeg ecosystem of the James Bay Lowlands, Northern Ontario.

The acetylene-reduction assay was used for in situ and laboratory assessment of biological nitrogen fixation in the acidic, waterlogged, muskeg ecosystem of the southern James Bay area, in the region of Moosonee, Ontario. In situ assays and subsequent laboratory experimentation revealed that nitrogenase activity was predominately a function of the activities of heterocystic blue-green bacteria associated with surface water, with the phyllosphere of mosses, and with at least one lichen, a species of Peltigera. No such in situ activity was detected in the subsurface organic material, even when such material was amended with glucose. However, under laboratory conditions at 20 degrees C, nitrogenase activity was evident in the subsurface layers after an extended lag and was shown to be higher under anaerobic than under aerobic conditions, to have an optimum temperature range extending about a mean of 20 degrees C, and to be stimulated by glucose. This potential for subsurface nitrogen fixation proved to be related to the presence of microorganisms existing in anaerobic microsites within the organic layers and no microorganisms capable of fixation could be detected under aerobic incubation.

Acetylene

Phyllosphere microbiomes in grassland plants harbor a vast reservoir of novel antimicrobial peptides and biosynthetic diversity.

INTRODUCTION: The phyllosphere microorganisms colonizing plant surface harbor capacities to synthesize diverse specialized metabolites that mediate communication and interactions with environment and host. However, most known metabolites are derived from a few culturable microorganisms, and the genomic diversity and biosynthetic potential of the vast majority of bacteria associated with plants remain largely unexplored. OBJECTIVES: Here, we aim to explore the genome architecture, biosynthetic ability, and host specific adaptability of grassland ecosystems, uncovering new perspectives on grassland phyllosphere microbial resources. METHODS: We employed ultra-deep metagenomic sequencing, functional analysis, host-associated characterization, and bioactivity assays to explore the phyllosphere microbiome across 221 grassland plant samples representing 45 families. This approach revealed host preference in biosynthetic gene clusters (BGCs) and validated the antimicrobial efficacy of phyllosphere-derived antimicrobial peptides (AMPs). RESULTS: Grassland plant phyllosphere microbiomes encode diverse BGCs. We identified 885,396 potential AMPs from over 68 million non-redundant gene sequences. Then, we reconstructed hundreds of near-complete genomes from phyllosphere metagenomes, and 32.61 % of reconstructed genomes were identified as unclassified genomes, primarily within Pseudomonadota, Actinomycetota, Bacillota and Bacteroidota phyla. Of the near-complete genomes, 91.97 % of the BGCs and 99.76 % of the identified AMPs were previously uncharacterized. Host phylogenetic analysis revealed functional divergence. Poaceae-associated Pseudomonas genomes contain an average of 28 BGCs, significantly higher than those in Asteraceae-associated genomes (mean = 14.76, P = 0.033). Similarly, Poaceae-associated Pantoea genomes carried an average of 9 BGCs, exhibiting significant enrichment compared to genomes from Asteraceae (mean = 7.13, P = 6.1e-05), Lamiaceae (mean = 7, P = 0.015), Ranunculaceae (mean = 8.22, P = 0.0053), and Rosaceae (mean = 7.75, P = 0.00069). ParaFit analyses further confirmed that host phylogeny significantly structures microbial functional repertoires, with intra-family hosts sharing more KEGG pathways than inter-family hosts. These results suggest that host evolutionary relationships are associated with metabolic specialization in phyllosphere microbiomes. All 13 AMPs synthesized via solid-phase peptide synthesis demonstrated antimicrobial activity, inhibiting the growth of at least one tested bacterial strain. CONCLUSION: This study demonstrates the promise of grassland plant phyllosphere microbiome as a rich source for novel antimicrobial agents.

Antimicrobial Peptides

Lanthanide-dependent isolation of phyllosphere methylotrophs selects for a phylogenetically conserved but metabolically diverse community.

Lanthanides have emerged as important metal cofactors for biological processes. Lanthanide-associated metabolisms are well-studied in leaf symbiont methylotrophic bacteria, which utilize reduced one-carbon compounds such as methanol for growth. Yet, the importance of lanthanides in plant-microbe interactions and on microbial physiology and colonization in plants remains poorly understood. To investigate this, 344 pink-pigmented facultative methylotrophs were isolated from soybean leaves by selecting for bacteria capable of methanol oxidation with lanthanide cofactors, but none were obligately lanthanide-dependent. Phylogenetic analyses revealed that all strains were nearly identical to each other and are part of the extorquens clade of Methylobacterium, despite variability in genome and plasmid sizes. Strain-specific identification was enabled by the higher resolution provided with rpoB compared to 16S rRNA as marker genes. Despite the low strain-level diversity, the metabolic capabilities of the collection diverged greatly. Strains encoding identical lanthanide-dependent alcohol dehydrogenases displayed significantly different growth rates and/or final ODs from each other on alcohols in the presence and absence of lanthanides. Several strains also lacked well-characterized lanthanide-associated genes thought to be important for phyllosphere colonization. Additionally, 3% of our isolates were capable of growth on sugars and 23% were capable of growth on aromatic acids, substantially expanding the range of substrates utilized by Methylobacterium extorquens in the phyllosphere. Our findings suggest that the expansion of metabolic capabilities, as well as differential usage of lanthanides and their influence on metabolism, among closely related strains point to evolution of niche partitioning strategies to promote colonization of the phyllosphere.

Journal Article