Abstract
BackgroundMany 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.Methodology and Principal FindingsWe 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.SignificanceBased 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.
Highlights
Interference competition is an important strategy of bacterial strains to establish and maintain themselves within microbial communities [1]
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
P. fluorescens Pf0-1 antibiotic production and growth rate The optical density (OD) measurements indicated that Pf0-1 grew only a short period (1–2 hr) exponentially in nutrient-poor liquid media followed by linear increase (Figure 2; Figure S1)
Summary
Interference competition is an important strategy of bacterial strains to establish and maintain themselves within microbial communities [1]. Theoretical models have demonstrated that, instead of decreasing diversity by leaving only the most aggressive strains, microbial warfare could promote diversity, with dynamic coexistence of many strains differing in their antibiotic production and sensitivity profiles [1,6,7,8]. These results are obtained when it is assumed that both resistance to- and production of antibiotics come at a fitness cost, resulting in a reduced growth rate. 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
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