Department of Microbial Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Wageningen, The Netherlands.
PLoS One. 2011;6(11):e27266. doi: 10.1371/journal.pone.0027266. Epub 2011 Nov 16.
Many soil-inhabiting bacteria are known to produce secondary metabolites that can suppress microorganisms competing for the same resources. The production of antimicrobial compounds is expected to incur fitness costs for the producing bacteria. Such costs form the basis for models on the co-existence of antibiotic-producing and non-antibiotic producing strains. However, so far studies quantifying the costs of antibiotic production by bacteria are scarce. The current study reports on possible costs, for antibiotic production by Pseudomonas fluorescens Pf0-1, a soil bacterium that is induced to produce a broad-spectrum antibiotic when it is confronted with non-related bacterial competitors or supernatants of their cultures.
We measured the possible cost of antibiotic production for Pseudomonas fluorescens Pf0-1 by monitoring changes in growth rate with and without induction of antibiotic production by supernatant of a bacterial competitor, namely Pedobacter sp.. Experiments were performed in liquid as well as on semi-solid media under nutrient-limited conditions that are expected to most clearly reveal fitness costs. Our results did not reveal any significant costs for production of antibiotics by Pseudomonas fluorescens Pf0-1. Comparison of growth rates of the antibiotic-producing wild-type cells with those of non-antibiotic producing mutants did not reveal costs of antibiotic production either.
Based on our findings we propose that the facultative production of antibiotics might not be selected to mitigate metabolic costs, but instead might be advantageous because it limits the risk of competitors evolving resistance, or even the risk of competitors feeding on the compounds produced.
许多土壤栖息细菌被认为会产生次生代谢物，可以抑制争夺相同资源的微生物。抗生素化合物的产生预计会对产生细菌的适应性造成代价。这些代价为抗生素产生菌和非抗生素产生菌共存的模型提供了基础。然而，到目前为止，量化细菌产生抗生素的代价的研究还很少。本研究报告了荧光假单胞菌 Pf0-1 产生抗生素的可能代价，该细菌在面对不相关的细菌竞争者或其培养物上清液时会被诱导产生广谱抗生素。
我们通过监测有无细菌竞争者 Pedobacter sp. 的上清液诱导抗生素产生时的生长率变化，来测量荧光假单胞菌 Pf0-1 产生抗生素的可能代价。实验在液体和半固体培养基中进行，在营养有限的条件下进行，这些条件预计最能明显揭示适应性代价。我们的结果没有显示荧光假单胞菌 Pf0-1 产生抗生素的任何显著代价。抗生素产生野生型细胞与非抗生素产生突变体的生长率比较也没有显示抗生素产生的代价。
根据我们的发现，我们提出，兼性抗生素的产生可能不是为了减轻代谢代价而被选择的，而是因为它限制了竞争者进化出抗性的风险，甚至限制了竞争者利用产生的化合物的风险，所以具有优势。
