Johansen J E, Binnerup S J, Lejbølle K B, Mascher F, Sørensen J, Keel C
Laboratorie de Biologie Microbienne, Université de Lausanne, Switzerland.
J Appl Microbiol. 2002;93(6):1065-74. doi: 10.1046/j.1365-2672.2002.01778.x.
To assess the impact of the biocontrol strain Pseudomonas fluorescens CHA0 on a collection of barley rhizosphere bacteria using an agar plate inhibition assay and a plant microcosm, focusing on a CHA0-sensitive member of the Cytophaga-like bacteria (CLB).
The effect of strain CHA0 on a collection of barley rhizosphere bacteria, in particular CLB and fluorescent pseudomonads sampled during a growth season, was assessed by a growth inhibition assay. On average, 85% of the bacteria were sensitive in the May sample, while the effect was reduced to around 68% in the July and August samples. In the May sample, around 95% of the CLB and around 45% of the fluorescent pseudomonads were sensitive to strain CHA0. The proportion of CHA0-sensitive CLB and fluorescent pseudomonad isolates decreased during the plant growth season, i.e. in the July and August samples. A particularly sensitive CLB isolate, CLB23, was selected, exposed to strain CHA0 (wild type) and its genetically modified derivatives in the rhizosphere of barley grown in gnotobiotic soil microcosms. Two dry-stress periods were imposed during the experiment. Derivatives of strain CHA0 included antibiotic or exopolysaccharide (EPS) overproducing strains and a dry-stress-sensitive mutant. Despite their inhibitory activity against CLB23 in vitro, neither wild-type strain CHA0, nor any of its derivatives, had a major effect on culturable and total cell numbers of CLB23 during the 23-day microcosm experiment. Populations of all inoculants declined during the two dry-stress periods, with soil water contents below 5% and plants reaching the wilting point, but they recovered after re-wetting the soil. Survival of the dry-stress-sensitive mutant of CHA0 was most affected by the dry periods; however, this did not result in an increased population density of CLB23.
CLB comprise a large fraction of barley rhizosphere bacteria that are sensitive to the biocontrol pseudomonad CHA0 in vitro. However, in plant microcosm experiments with varying soil humidity conditions, CHA0 or its derivatives had no major impact on the survival of the highly sensitive CLB strain, CLB23, during two dry-stress periods and a re-wetting period; all co-existed well in the rhizosphere of barley plants.
Results indicate a lack of interaction between the biocontrol pseudomonad CHA0 and a sensitive CLB when the complexity increases from agar plate assays to plant microcosm experiments. This suggests the occurrence of low levels of antibiotic production and/or that the two bacterial genera occupy different niches in the rhizosphere.
利用琼脂平板抑制试验和植物微宇宙试验，评估生防菌株荧光假单胞菌CHA0对大麦根际细菌群落的影响，重点关注噬纤维菌样细菌（CLB）中对CHA0敏感的成员。
通过生长抑制试验评估了CHA0菌株对大麦根际细菌群落的影响，特别是在生长季节采集的CLB和荧光假单胞菌。平均而言，5月份样本中85%的细菌敏感，而7月和8月样本中的影响降至约68%。在5月份样本中，约95%的CLB和约45%的荧光假单胞菌对CHA0菌株敏感。在植物生长季节，即7月和8月样本中，对CHA0敏感的CLB和荧光假单胞菌分离株的比例下降。选择了一种特别敏感的CLB分离株CLB23，在无菌土壤微宇宙中生长的大麦根际中，将其暴露于CHA0菌株（野生型）及其基因修饰衍生物。实验期间施加了两个干旱胁迫期。CHA0菌株的衍生物包括抗生素或胞外多糖（EPS）高产菌株以及干旱敏感突变体。尽管它们在体外对CLB23具有抑制活性，但在为期23天的微宇宙实验中，野生型菌株CHA0及其任何衍生物对CLB23的可培养细胞数和总细胞数均无重大影响。在两个干旱胁迫期，所有接种物的数量均下降，土壤含水量低于5%，植物达到萎蔫点，但在土壤重新湿润后它们恢复了。CHA0的干旱敏感突变体的存活受干旱期影响最大；然而，这并未导致CLB23的种群密度增加。
CLB占大麦根际细菌的很大一部分，这些细菌在体外对生防假单胞菌CHA0敏感。然而，在不同土壤湿度条件下的植物微宇宙实验中，CHA0及其衍生物在两个干旱胁迫期和一次重新湿润期对高度敏感的CLB菌株CLB23的存活没有重大影响；它们在大麦植物根际中均能良好共存。
结果表明，当从琼脂平板试验到植物微宇宙实验的复杂性增加时，生防假单胞菌CHA0与敏感CLB之间缺乏相互作用。这表明抗生素产量较低，或者这两个细菌属在根际占据不同的生态位。
