叶际微生物研究进展

Advance in the research of phyllospheric microorganism

植物的叶际是一个复杂的生态系统,微生物的生存环境条件严苛。其可被利用的营养成分较少,温湿度波动大。此外,较强的紫外线辐射对于叶际微生物的生存也有很大影响。但是植物叶际却有着丰富的微生物多样性,其中还有许多有益细菌和真菌。它们通过和植物寄主的互作,改善着叶际微生物的栖居环境;其对植物病原体的拮抗亦可提高植物的抗病性。植物叶际的微生物还可以产生激素以促进植物生长,还有一些微生物可以利用农药等污染有机物作为营养物质,在污染物的环境生物修复方面显示巨大的潜力。此外,叶际微生物作为一种生态学指标在生态稳定与环境安全评价中开始发挥显著的作用。

The aerial portion of a plant colonized by microbes is known as a phyllosphere,which is a complex ecosystem that is hostile to microbial colonists.In Phyllosphere,there are wide temperature fluctuations;the humidity is changed repeatedly due to the presence and absence of free moisture from rain and dew.Under these conditions,the nutrient availability on the plant surface is also limited,and the dose of ultraviolet radiation is very strong.In addition,some foreign chemicals such as pesticides are sometimes located on the phyllosphere.Although all of these factors influence microbial communities,a large number of microbes,including bacteria,filamentous fungi,yeast and algae,in addition to a small quantity of wireworm and protozoa,still colonize this area.These colonizing microorganisms are known as phyllospheric microorganisms or epiphytes.Such organisms tend to colonize the lower leaf sides in the field,whereas colonization of upper leaf sides is greater on plants cultivated in the greenhouse.Some phyllospheric microorganisms are plant pathogens,but most are nonpathogenic microorganisms that are beneficial and have many important functions.Many studies have shown that phyllospheric microorganisms have close interactions with the host.For example,leaf-surface properties such as cuticular water permeability can be influenced by bacteria（for instance Pseudomonas rhizosphaerae）,leading to improved colonial conditions on the phyllosphere.In addition,some phyllospheric microorganisms can promote the growth of plants,which leads to improved root and shoot growth by means of producing auxins,cytokinins and vitamin B12.As a result,these organisms can increase the yield of some plant species.Moreover,biological control agents（BCAs）,including bacteria,filamentous fungi and yeast,are currently being widely applied to control pests and plant diseases.These organisms have a positive impact because BCAs are able to colonize or compete with pathogens for nutrients and sites of interaction on the host,as well as to exert antagonism through antibiotics or hydrolytic enzymes,interfere with pathogen signals,or stimulate the induction of systemic resistance within the plant.Some phyllospheric microorganisms can also utilize organic contaminants such as insecticides and lipophilic gaseous organic compounds,including phenol,as sources of nutrients.Organisms capable of utilizing such compounds have the potential for use in bioremediation of pollutants in the environment.Therefore,they can easily access and degrade organic pollutants from the air.Conversely some bacteria might serve as ideal microbial indicators of insecticides due to their sensitivity to specific compounds.Finally,phyllospheric microorganisms also have the potential for application in industrial biotechnology because some filamentous fungi isolated from olives have the ability to produce enzymes of industrial interest such as beta-glucosidase,CMCellulase,lipase and polygalacturonase,which are meaningful for the olive oil industry and have other industrial applications.Furthermore,phyllospheric microorganisms are beginning to play a conspicuous role as an index of ecological stability and environmental security.Using this index,some studies have revealed that photocatalytic nanomaterials have the potential to impact the environment.Here we review recent advances in the study of phyllospheric microorganisms.