Folman L B, Postma J, van Veen J A
Institute of Evolutionary and Ecological Sciences, University of Leiden, P.O. Box 9516, 2300 RA Leiden, The Netherlands.
Microb Ecol. 2003 Jan;45(1):72-87. doi: 10.1007/s00248-002-2013-0. Epub 2002 Dec 10.
A collection of 821 rhizobacteria from cucumber, originating from different root locations and stages of plant development, was screened for potential biocontrol agents of Pythium aphanidermatum (Edson) Fitzp. The screening procedure exploited carbon source utilization profiles and growth rates of bacteria as indicators of a partial niche overlap with the pathogen. The bacteria were tested for growth on nine carbon sources (glucose, fucose, sucrose, maltose, asparagine, alanine, galacturonic acid, succinic acid, and linoleic acid), most of which are reported to be used by the zoospores of P. aphanidermatum in the infection process. The isolates were classified as fast- or slow-growing, depending on their growth rate in 1/10 strength TSB. By nonhierarchical cluster analysis, 20 clusters were generated of bacteria with similar profiles of carbon source utilization. Redundancy analysis showed that the type of root sample explained 47% of the variance found in the relative abundance of bacteria from the clusters. Bacteria from clusters using none or few of the carbon sources, e.g., maltose and linoleic acid, with many slow-growing isolates, showed a preference for plants in the vegetative or generative stage, or for old root regions (root base). Bacteria from clusters with fast-growing isolates, using many carbon sources, were relatively abundant in the seedling stage. A selection of 127 bacteria from the different clusters was tested for disease suppressive capabilities in bioassays on young cucumber plants in nutrient solution, inoculated with zoospores of P. aphanidermatum. Nine of these bacteria produced biosurfactants, and 27 showed antibiosis against mycelial growth in plate assays. For 31 isolates, significant positive effects on plant biomass were shown, as analyzed with a general linear regression model. For most isolates, these effects occurred only in one of two replicate assays and no reductions in the degree of root and crown rot were found. Of the isolates that used many of the tested carbon sources, only four had positive effects on plant biomass. The majority of the isolates that positively affected plant biomass used few to moderate numbers of carbon sources and did not produce antibiotics or biosurfactants. In conclusion, competition for the tested carbon sources with the zoospores did not play a decisive role in disease suppression, and no clear relation was found between ecophysiological traits and disease suppression. Only isolate 3.1T8, isolated from root tips in the generative stage of plant growth, significantly increased plant biomass and suppressed root and crown rot symptoms in five out of six bioassays. The isolate produced an antifungal substance in plate assays and showed biosurfactant production in several (cucumber-derived) media.
从黄瓜中收集了821株根际细菌，这些细菌来自不同的根系位置和植物发育阶段，对其进行筛选，以寻找瓜果腐霉（Pythium aphanidermatum (Edson) Fitzp.）的潜在生防菌。筛选过程利用细菌的碳源利用谱和生长速率作为与病原菌部分生态位重叠的指标。测试了这些细菌在九种碳源（葡萄糖、岩藻糖、蔗糖、麦芽糖、天冬酰胺、丙氨酸、半乳糖醛酸、琥珀酸和亚油酸）上的生长情况，据报道，其中大多数碳源在瓜果腐霉游动孢子的感染过程中会被利用。根据它们在1/10强度胰蛋白胨大豆肉汤（TSB）中的生长速率，将分离菌株分为快速生长型或缓慢生长型。通过非层次聚类分析，生成了20个具有相似碳源利用谱的细菌聚类。冗余分析表明，根系样本类型解释了聚类中细菌相对丰度变化的47%。使用很少或不使用碳源（如麦芽糖和亚油酸）的聚类中的细菌，有许多缓慢生长的分离株，它们更倾向于存在于营养期或生殖期的植物中，或老根区域（根基部）。具有快速生长分离株、使用多种碳源的聚类中的细菌，在幼苗期相对丰富。从不同聚类中挑选了127株细菌，在营养液中对黄瓜幼苗进行生物测定，接种瓜果腐霉的游动孢子，测试它们的病害抑制能力。其中9株细菌产生生物表面活性剂，27株在平板试验中对菌丝生长表现出抗菌活性。用一般线性回归模型分析，31株分离株对植物生物量有显著的正向影响。对于大多数分离株，这些影响仅在两个重复试验中的一个中出现，并且未发现根腐和冠腐程度降低。在使用多种测试碳源的分离株中，只有4株对植物生物量有正向影响。对植物生物量有正向影响的大多数分离株使用少量至适量的碳源，且不产生抗生素或生物表面活性剂。总之，与游动孢子竞争测试碳源在病害抑制中不起决定性作用，并且在生态生理特征与病害抑制之间未发现明确的关系。只有从植物生长生殖期的根尖分离得到的3.1T8菌株，在六次生物测定中的五次中显著增加了植物生物量并抑制了根腐和冠腐症状。该分离株在平板试验中产生了一种抗真菌物质，并且在几种（黄瓜来源的）培养基中表现出生物表面活性剂的产生。
