Jousset Alexandre, Lara Enrique, Wall Luis G, Valverde Claudio
Programa Prioritario sobre Interacciones Biológicas, Departamento de Ciencia y Tecnología, Universidad Nacional de Quilmes, Roque Sáenz Peña 352, Bernal B1876BXD, Provincia de Buenos Aires, Argentina.
Appl Environ Microbiol. 2006 Nov;72(11):7083-90. doi: 10.1128/AEM.00557-06.
In soil ecosystems, bacteria must cope with predation activity, which is attributed mainly to protists. The development of antipredation strategies may help bacteria maintain higher populations and persist longer in the soil. We analyzed the interaction between the root-colonizing and biocontrol strain Pseudomonas fluorescens CHA0 and three different protist isolates (an amoeba, a flagellate, and a ciliate). CHA0 produces a set of antibiotics, HCN, and an exoprotease. We observed that protists cannot grow on CHA0 but can multiply on isogenic regulatory mutants that do not produce the extracellular metabolites. The in vitro responses to CHA0 cells and its exoproducts included growth inhibition, encystation, paralysis, and cell lysis. By analyzing the responses of protists to bacterial supernatants obtained from different isogenic mutants whose production of one or more exometabolites was affected and also to culture extracts with antibiotic enrichment, we observed different contributions of the phenolic antifungal compound 2,4-diacetylphloroglucinol (DAPG) and the extracellular protease AprA to CHA0 toxicity for protists and to the encystation-reactivation cycle. The grazing pressure artificially produced by a mixture of the three protists in a microcosm system resulted in reduced colonization of cucumber roots by a regulatory isogenic CHA0 mutant unable to produce toxins. These results suggest that exometabolite production in biocontrol strain CHA0 may contribute to avoidance of protist grazing and help sustain higher populations in the rhizosphere, which may be a desirable and advantageous trait for competition with other bacteria for available resources.
在土壤生态系统中，细菌必须应对主要由原生生物引起的捕食活动。抗捕食策略的发展可能有助于细菌维持较高的种群数量并在土壤中持续更长时间。我们分析了定殖于根部的生防菌株荧光假单胞菌CHA0与三种不同的原生生物分离株（一种变形虫、一种鞭毛虫和一种纤毛虫）之间的相互作用。CHA0会产生一组抗生素、HCN和一种胞外蛋白酶。我们观察到原生生物无法在CHA0上生长，但可以在不产生细胞外代谢产物的同基因调控突变体上繁殖。原生生物对CHA0细胞及其胞外产物的体外反应包括生长抑制、包囊化形成、麻痹和细胞裂解。通过分析原生生物对从不同同基因突变体获得的细菌上清液的反应，这些突变体的一种或多种胞外代谢产物的产生受到影响，以及对富含抗生素的培养提取物的反应，我们观察到酚类抗真菌化合物2,4-二乙酰基间苯三酚（DAPG）和胞外蛋白酶AprA对CHA0对原生生物的毒性以及包囊化-再激活循环有不同的贡献。在微观系统中，由这三种原生生物的混合物人为产生的捕食压力导致无法产生毒素的同基因调控CHA突变体对黄瓜根的定殖减少。这些结果表明，生防菌株CHA0中胞外代谢产物的产生可能有助于避免原生生物的捕食，并有助于在根际维持较高的种群数量，这对于与其他细菌竞争可用资源而言可能是一个理想且有利的特性。
