Temperature-induced Loss of Linear Catabolic Megaplasmid (pDK2) in Rhodococcus sp. Strain DK17

Abstract

The actinomycete Rhodococcus sp. strain DK17 is able to grow on various alkylbenzenes including benzene, toluene, ethylbenzene, and o-xylene (BTEX). DK17 possesses three linear megaplasmids (380-kb pDK1, 330-kb pDK2, and 750-kb pDK3). The versatile metabolic capacity of DK17 is encoded on the catabolic linear pDK2, which has been previously shown to be partially deleted or even lost when DK17 cells exposed to UV light. However, complete loss of pDK2 at a higher rate of 2.5% was observed to spontaneously occur from several DK17 cells which were heat-treated at 37℃ for 48.8 min (the doubling time of DK17 at optimal 30℃). Due to the absence of the functional catabolic pDK2, all the mutants were unable to grow on ethylbenzene selected as a representative of alkylbenzene substrates, but retained the ability to degrade phthalate. The loss of pDK2 might be attributed to an innate instability of linear megaplasmids, especially in replication during cell division, at a higher ambient temperature above the host's optimal range. It should be further investigated to conclude whether this is a common phenomenon among linear megaplasmids or not.