Role of Leaf Surface Sugars in Colonization of Plants by Bacterial Epiphytes

Abstract

The relationship between nutrients leached onto the leaf surface and the colonization of plants by bacteria was studied by measuring both the abundance of simple sugars and the growth of Pseudomonas fluorescens on individual bean leaves. Data obtained in this study indicate that the population size of epiphytic bacteria on plants under environmentally favorable conditions is limited by the abundance of carbon sources on the leaf surface. Sugars were depleted during the course of bacterial colonization of the leaf surface. However, about 20% of readily utilizable sugar, such as glucose, present initially remained on fully colonized leaves. The amounts of sugars on a population of apparently identical individual bean leaves before and after microbial colonization exhibited a similar right-hand-skewed distribution and varied by about 25-fold from leaf to leaf. Total bacterial population sizes on inoculated leaves under conditions favorable for bacterial growth also varied by about 29-fold and exhibited a right-hand-skewed distribution. The amounts of sugars on leaves of different plant species were directly correlated with the maximum bacterial population sizes that could be attained on those species. The capacity of bacteria to deplete leaf surface sugars varied greatly among plant species. Plants capable of supporting high bacterial population sizes were proportionally more depleted of leaf surface nutrients than plants with low epiphytic populations. Even in species with a high epiphytic bacterial population, a substantial amount of sugar remained after bacterial colonization. It is hypothesized that residual sugars on colonized leaves may not be physically accessible to the bacteria due to limitations in wettability and/or diffusion of nutrients across the leaf surface.

Appetite of an epiphyte: Quantitative monitoring of bacterial sugar consumption in the phyllosphere

“…Photoassimilates like sucrose, fructose, and glucose, which are found in abundances of 0.2-2.0 g per leaf on uninhabited bean leaf surfaces, were readily consumed and converted into biomass by the bacterium Pseudomonas fluorescens A506 (24). Bacterial and fungal colonization of the phyllosphere does not occur evenly across the leaf (25,26), suggesting that resources are not evenly available or exploitable.…”

“…We targeted sugars as the model nutrient, as they generally are recognized as the most abundant carbon source available in the phyllosphere (24). Our strategy involved the use of reporter gene technology in which the well-characterized bacterial epiphyte Erwinia herbicola 299R (Eh299R) (30) harbored a sugarresponsive element that was fused to a gene for green fluorescent protein (GFP).…”

Properties of dissolved and total organic matter in throughfall, stemflow and forest floor leachate of central European forests

“…Alteration in the composition of OM in throughfall, stemflow (SF) and FF solutions are assumed to be driven by various abiotic and biotic processes. In this context, precipitation patterns (Mercier and Lindow, 2000) and canopy architecture (Levia and Frost, 2006;Levia et al, 2012) basically alter the release of OM with throughfall. Atmospheric deposition (e.g.…”

Loline alkaloid production by fungal endophytes of Fescue species select for particular epiphytic bacterial microflora

“…Such large and diverse microbial communities develop despite the fact that it is considered a relatively harsh habitat with highly variable environmental conditions typified by rapidly fluctuating conditions of water availability and incidence of ultraviolet (UV) irradiation. While all leaf colonists must endure such stresses, a key factor limiting bacterial population size on leaves is nutrient availability (Mercier and Lindow, 2000;Lindow and Brandl, 2003). While exogenous carbon sources such as pollen that are occasionally deposited on leaf surfaces can supply needed nutrients for microbial growth, they are not thought to be the dominant nutrient sources on plants (Tukey, 1970).…”