The Effect of Leaf Water Variables on Ice Nucleating Pseudomonas syringae in Beans

Pinto bean seedlings 'UI 114' (Phaseolus vulgaris L.) were subjected to temperatures between – 2° and – 5°C for periods ranging from 0.5 to 12 hr. The plants that were not sprayed with a suspension of the nucleating Pseudomonas syringae bacteria and those that were water-stressed to near wilting were most resistant to ice nucleation. Plants with dry leaf surfaces were much more apt to supercool than those with distilled water droplets on their leaves, whether inoculated with the bacteria or not. Spraying the freeze-dried bacteria suspended in distilled water on the leaves increased wettability and dew formation on the leaf surfaces. Tests with an oxytetracycline preparation, which also increased wetting, suggested that a hydrophobic leaf surface helps delay ice formation. Use of wetting agents in leaf sprays may be counterproductive so far as supercooling stability is concerned. It is obvious that leaf water relations interact with bacterial ice nucleation

Comparative genomics of plant-asssociated Pseudomonas spp.: Insights into diversity and inheritance of traits involved in multitrophic interactions

We provide here a comparative genome analysis of ten strains within the Pseudomonas fluorescens group including seven new genomic sequences. These strains exhibit a diverse spectrum of traits involved in biological control and other multitrophic interactions with plants, microbes, and insects. Multilocus sequence analysis placed the strains in three sub-clades, which was reinforced by high levels of synteny, size of core genomes, and relatedness of orthologous genes between strains within a sub-clade. The heterogeneity of the P. fluorescens group was reflected in the large size of its pan-genome, which makes up approximately 54% of the pan-genome of the genus as a whole, and a core genome representing only 45–52% of the genome of any individual strain. We discovered genes for traits that were not known previously in the strains, including genes for the biosynthesis of the siderophores achromobactin and pseudomonine and the antibiotic 2-hexyl-5-propyl-alkylresorcinol; novel bacteriocins; type II, III, and VI secretion systems; and insect toxins. Certain gene clusters, such as those for two type III secretion systems, are present only in specific sub-clades, suggesting vertical inheritance. Almost all of the genes associated with multitrophic interactions map to genomic regions present in only a subset of the strains or unique to a specific strain. To explore the evolutionary origin of these genes, we mapped their distributions relative to the locations of mobile genetic elements and repetitive extragenic palindromic (REP) elements in each genome. The mobile genetic elements and many strain-specific genes fall into regions devoid of REP elements (i.e., REP deserts) and regions displaying atypical tri-nucleotide composition, possibly indicating relatively recent acquisition of these loci. Collectively, the results of this study highlight the enormous heterogeneity of the P. fluorescens group and the importance of the variable genome in tailoring individual strains to their specific lifestyles and functional repertoir

Bioreporters in microbial ecology

Bioreporters are effective research tools for gaining an understanding of a microbe's perception of the world. Fitted with a fusion of an environmentally responsive promoter to a suitable reporter gene, a bacterial or fungal bioreporter is able to communicate its metabolic or transcriptional behavior in a habitat, and furnish us with information on the chemical, physical or biological properties of its immediate surroundings. This review details recent developments in the use of such bioreporters in microbial ecology. Emphasis is placed on reporter genes that allow detection in individual microbial cells, as they provide a high-resolution description of the habitat under investigation. In an outlook on the future of bioreporter technology, this review stresses the need to interpret the activity of a bioreporter within the context of its biology. [KEYWORDS: bioreporter; biosensor; whole cell; single cell; reporter gene; reporter protein; green fluorescent protein; beta-galactosidase; ice nucleation protein]

Bioreporters in microbial ecology

Bioreporters are effective research tools for gaining an understanding of a microbe's perception of the world. Fitted with a fusion of an environmentally responsive promoter to a suitable reporter gene, a bacterial or fungal bioreporter is able to communicate its metabolic or transcriptional behavior in a habitat, and furnish us with information on the chemical, physical or biological properties of its immediate surroundings. This review details recent developments in the use of such bioreporters in microbial ecology. Emphasis is placed on reporter genes that allow detection in individual microbial cells, as they provide a high-resolution description of the habitat under investigation. In an outlook on the future of bioreporter technology, this review stresses the need to interpret the activity of a bioreporter within the context of its biology. [KEYWORDS: bioreporter; biosensor; whole cell; single cell; reporter gene; reporter protein; green fluorescent protein; beta-galactosidase; ice nucleation protein

Phyllosphere microbiology

Aerial plant surfaces harbor large numbers of microbes, some of which are deleterious to plants whereas others are benign or beneficial. Commercial formulations of bacteria antagonistic to plant pathogenic microbes and ice nucleation active bacteria have been utilized as an environmentally safe method to manage plant disease and to prevent frost damage. Molecular genetic tools, microscopic examination and whole-cell bacterial biosensors have provided extensive information on these microbes, their complex associations and their habitat. The aerial habitat influenced by plants, termed the phyllosphere, is particularly amenable to studies of microbial ecology and the information gained should lead to more effective means of plant protection. [KEYWORDS: SYRINGAE PV. SYRINGAE, SUGAR-BEET PHYTOSPHERE, CONJUGAL GENE-TRANSFER, BACTERIAL LEAF STREAK, UV-B RADIATION, PSEUDOMONAS-SYRINGAE, BIOLOGICAL-CONTROL, FIRE BLIGHT, PANTOEA-AGGLOMERANS, POPULATION-SIZE]

The Effect of Leaf Water Variables on Ice Nucleating Pseudomonas syringae in Beans

Pinto bean seedlings 'UI 114' (Phaseolus vulgaris L.) were subjected to temperatures between – 2° and – 5°C for periods ranging from 0.5 to 12 hr. The plants that were not sprayed with a suspension of the nucleating Pseudomonas syringae bacteria and those that were water-stressed to near wilting were most resistant to ice nucleation. Plants with dry leaf surfaces were much more apt to supercool than those with distilled water droplets on their leaves, whether inoculated with the bacteria or not. Spraying the freeze-dried bacteria suspended in distilled water on the leaves increased wettability and dew formation on the leaf surfaces. Tests with an oxytetracycline preparation, which also increased wetting, suggested that a hydrophobic leaf surface helps delay ice formation. Use of wetting agents in leaf sprays may be counterproductive so far as supercooling stability is concerned. It is obvious that leaf water relations interact with bacterial ice nucleation

Stochastic modeling of <em>Pseudomonas syringae</em> growth in the phyllosphere.

Pseudomonas syringae is a gram-negative bacterium which lives on leaf surfaces. Its growth has been described using epifluorescence microscopy and image analysis; it was found to be growing in aggregates of a wide range of sizes. We develop a stochastic model to describe aggregate distribution and determine the mechanisms generating experimental observations. We found that a logistic birth-death model with migration (time-homogeneous Markov process) provides the best description of the observed data. We discuss how to analyze the joint distribution of the numbers of aggregates of different sizes at a given time and explore how to account for new aggregates being created, that is, the joint distribution of the family size statistics conditional on the total number of aggregates. We compute the first two moments. Through simulations we examine how the model&#39;s parameters affect the aggregate size distribution and successfully explain the quantitative experimental data available. Aggregation formation is thought to be the first step towards pathogenic behavior of this bacterium; understanding aggregate size distribution would prove useful to understand the switch from epiphytic to pathogenic behavior