The bacterial microflora of witloof chicory (Cichorium intybus L. var.foliosum Hegi) leaves

Bacteria in the leaf ecosystem with emphasis on Pseudomonas syringae-a pathogen, ice nucleus, and epiphyte

The extremely large number of leaves produced by terrestrial and aquatic plants provide habitats for colonization by a diversity of microorganisms. This review focuses on the bacterial component of leaf microbial communities, with emphasis on Pseudomonas syringae-a species that participates in leaf ecosystems as a pathogen, ice nucleus, and epiphyte. Among the diversity of bacteria that colonize leaves, none has received wider attention than P. syringae, as it gained notoriety for being the first recombinant organism (Ice(-) P. syringae) to be deliberately introduced into the environment. We focus on P. syringae to illustrate the attractiveness and somewhat unique opportunities provided by leaf ecosystems for addressing fundamental questions of microbial population dynamics and mechanisms of plant-bacterium interactions. Leaf ecosystems are dynamic and ephemeral. The physical environment surrounding phyllosphere microbes changes continuously with daily cycles in temperature, radiation, relative humidity, wind velocity, and leaf wetness. Slightly longer-term changes occur as weather systems pass. Seasonal climatic changes impose still a longer cycle. The physical and physiological characteristics of leaves change as they expand, mature, and senesce and as host phenology changes. Many of these factors influence the development of populations of P. syringae upon populations of leaves. P. syringae was first studied for its ability to cause disease on plants. However, disease causation is but one aspect of its life strategy. The bacterium can be found in association with healthy leaves, growing and surviving for many generations on the surfaces of leaves as an epiphyte. A number of genes and traits have been identified that contribute to the fitness of P. syringae in the phyllosphere. While still in their infancy, such research efforts demonstrate that the P. syringae-leaf ecosystem is a particularly attractive system with which to bridge the gap between what is known about the molecular biology of genes linked to pathogenicity and the ecology and epidemiology of associated diseases as they occur in natural settings, the field.

Prokaryotes: the unseen majority

The number of prokaryotes and the total amount of their cellular carbon on earth are estimated to be 4-6 x 10(30) cells and 350-550 Pg of C (1 Pg = 10(15) g), respectively. Thus, the total amount of prokaryotic carbon is 60-100% of the estimated total carbon in plants, and inclusion of prokaryotic carbon in global models will almost double estimates of the amount of carbon stored in living organisms. In addition, the earth's prokaryotes contain 85-130 Pg of N and 9-14 Pg of P, or about 10-fold more of these nutrients than do plants, and represent the largest pool of these nutrients in living organisms. Most of the earth's prokaryotes occur in the open ocean, in soil, and in oceanic and terrestrial subsurfaces, where the numbers of cells are 1.2 x 10(29), 2.6 x 10(29), 3.5 x 10(30), and 0. 25-2.5 x 10(30), respectively. The numbers of heterotrophic prokaryotes in the upper 200 m of the open ocean, the ocean below 200 m, and soil are consistent with average turnover times of 6-25 days, 0.8 yr, and 2.5 yr, respectively. Although subject to a great deal of uncertainty, the estimate for the average turnover time of prokaryotes in the subsurface is on the order of 1-2 x 10(3) yr. The cellular production rate for all prokaryotes on earth is estimated at 1.7 x 10(30) cells/yr and is highest in the open ocean. The large population size and rapid growth of prokaryotes provides an enormous capacity for genetic diversity.

Detection and enumeration of Erwinia carotovora subsp. atroseptica using spiral plating and immunofluorescence colony staining

Immunofluorescence colony staining (IFC) and a new technique using spiral plating combined with IFC were evaluated for the soft-rot pathogen Erwinia carotovora subsp. atroseptica in witloof chicory. Target bacteria could be detected in platings at various dilutions of plant washings. Brilliance of the stained colonies of E. carotovora subsp. atroseptica was high. Spiral plating, used for both the plating of the bacteria and for the delivery of the conjugated antiserum, had a positive effect on the reduction of the background compared with the staining of the bacteria. The combination of spiral plating and IFC proved to be a functional tool for the quantification of target and nontarget bacteria and the isolation of target bacteria as pure culture from IFC-positive colonies. The method uses less conjugated antiserum than traditional IFC and produces results with very small variation within replications. The recovery of the bacteria in both pure culture and plant washing is significantly higher than the recovery using crystal violet pectate medium.Key words: soft rot, witloof chicory, detection, Erwinia carotovora subsp. atroseptica.