| Summary: | Bacteria can evade antibiotics by acquiring resistance genes, as well as switching to a non-growing dormant state without accompanying genetic modification. Bacteria in this quiescent state are called persisters, and this non-inheritable ability to withstand multiple antibiotics is referred to as antibiotic tolerance. Although all bacteria are considered to be able to form antibiotic-tolerant persisters, the antibiotic tolerance of extremophilic bacteria is poorly understood. Previously, we identified the psychrotolerant bacterium <i>Pseudomonas</i> sp. B14-6 from the glacier foreland of Midtre Lovénbreen in High Arctic Svalbard. Herein, we investigated the resistance and tolerance of <i>Pseudomonas</i> sp. B14-6 against aminoglycosides at various temperatures. This bacterium was resistant to streptomycin and susceptible to apramycin, gentamicin, kanamycin, and tobramycin. The two putative aminoglycoside phosphotransferase genes <i>aph</i>1 and <i>aph</i>2 were the most likely contributors to streptomycin resistance. Notably, unlike the mesophilic <i>Pseudomonas</i> <i>aeruginosa</i> PA14, this cold-adapted bacterium demonstrated reduced susceptibility to all tested aminoglycosides in a temperature-dependent manner. <i>Pseudomonas</i> sp. B14-6 at a lower temperature formed the persister cells that shows tolerance to the 100-fold minimum inhibitory concentration (MIC) of gentamicin, as well as the partially tolerant cells that withstand 25-fold MIC gentamicin. The temperature-dependent gentamicin tolerance appears to result from reduced metabolic activity. Lastly, the partially tolerant <i>Pseudomonas</i> sp. B14-6 cells could slowly proliferate under the bactericidal concentrations of aminoglycosides. Our results demonstrate that <i>Pseudomonas</i> sp. B14-6 has a characteristic ability to form cells with a range of tolerance, which appears to be inversely proportional to its growth rate.
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