Phytopathology. 1999 May;89(5):353-9. doi: 10.1094/PHYTO.1999.89.5.353.
ABSTRACT Bacteria associated with plant leaves, or phyllobacteria, probably employ a range of colonization strategies. Steps in these colonization strategies include modification of the leaf habitat, aggregation, ingression, and egression. Considerable evidence indicates that bacteria can modify their environment to enhance their colonization of plants, such as by increasing local nutrient concentrations or by producing a layer of extracellular polysaccharides. This local habitat modification may occur on the surface of leaves, as well as in the leaf interior, and may be enhanced by the formation of bacterial aggregates. The conspicuous presence of bacterial aggregates on leaves and the finding that the behavior of bacteria on plants varies in a density-dependent manner indicate the potential importance of cooperative interactions among phyllobacteria. Such cooperative interactions may occur among both homogeneous and heterogeneous populations, thus influencing the development of microbial communities. While the sites commonly colonized by most phyllobacteria have not been unambiguously identified, there is strong circumstantial evidence that a sizable proportion of cells, particularly of phytopathogenic strains, are localized within "protected sites" on plants. The likelihood that these protected sites are located in the interior of leaves indicates that phytopathogenic bacteria have access to more resources and greater protection from stresses associated with the leaf surface than bacteria that are restricted to the leaf surface. The internal and external leaf-associated populations probably form a continuum due to the processes of ingression and egression. For a specific pathogen, however, the extent of egression that occurs prior to disease induction is likely to influence the success of disease predictions based on external population size, i.e., the number of bacteria in leaf washings. In this review, we illustrate the complexity of the ecology of leaf-associated bacteria and propose a model of leaf colonization that emphasizes the common elements in bacterial colonization strategies, as well as allows for distinct behavior of different phyllobacterial species.
摘要 与植物叶片相关的细菌（即叶杆菌）可能采用了一系列定殖策略。这些定殖策略包括对叶片生境的修饰、聚集、内侵和外逸。大量证据表明，细菌可以修饰其环境以增强对植物的定殖能力，例如增加局部养分浓度或产生一层细胞外多糖。这种局部生境修饰可能发生在叶片表面以及叶片内部，并且可能通过细菌聚集的形成而得到增强。细菌聚集物在叶片上的明显存在以及在植物上细菌行为随密度变化而变化的发现表明叶杆菌之间可能存在合作相互作用。这种合作相互作用可能发生在同质性和异质性种群之间，从而影响微生物群落的发展。虽然大多数叶杆菌常见的定殖部位尚未明确确定，但有强有力的间接证据表明，相当一部分细胞，特别是植物病原菌菌株，位于植物“保护部位”内。这些保护部位很可能位于叶片内部的可能性表明，植物病原菌比限于叶片表面的细菌具有更多的资源和更大的保护，免受与叶片表面相关的压力。由于内侵和外逸过程，内部和外部叶相关种群可能形成一个连续体。然而，对于特定的病原体，在诱导疾病之前发生的外逸程度可能会影响基于外部种群大小（即叶片冲洗液中的细菌数量）进行疾病预测的成功。在本综述中，我们说明了叶相关细菌生态学的复杂性，并提出了一个强调细菌定殖策略共同要素的叶片定殖模型，同时允许不同叶杆菌物种具有不同的行为。
