AUTHOR=Nguyen Thi Thu Huong , Kikuchi Taisei , Tokunaga Tadaaki , Iyoda Sunao , Iguchi Atsushi 

TITLE=Diversity of the Tellurite Resistance Gene Operon in Escherichia coli

JOURNAL=Frontiers in Microbiology

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2021.681175

DOI=10.3389/fmicb.2021.681175

ISSN=1664-302X

ABSTRACT=<p>Tellurite is highly toxic to most bacteria owing to its strong oxidative ability. However, some bacteria demonstrate tellurite resistance. In particular, some <italic>Escherichia coli</italic> strains, including Shiga toxin-producing <italic>E. coli</italic> O157:H7, are known to be resistant to tellurite. This resistance is involved in <italic>ter</italic> operon, which is usually located on a prophage-like element of the chromosome. The characteristics of the <italic>ter</italic> operon have been investigated mainly by genome analysis of pathogenic <italic>E. coli</italic>; however, the distribution and structural characteristics of the <italic>ter</italic> operon in other <italic>E. coli</italic> are almost unknown. To clarify these points, we examined 106 <italic>E. coli</italic> strains carrying the <italic>ter</italic> operon from various animals. The draft genomes of 34 representative strains revealed that <italic>ter</italic> operons were clearly classified into four subtypes, <italic>ter</italic>-type 1–4, at the nucleotide sequence level. Complete genomic sequences revealed that operons belonging to three <italic>ter</italic>-types (1, 3, and 4) were located on the prophage-like elements on the chromosome, whereas the <italic>ter</italic>-type 2 operon was located on the IncHI2 plasmid. The positions of the tRNA<sup>Ser</sup>, tRNA<sup>Met</sup>, and tRNA<sup>Phe</sup> indicated the insertion sites of elements carrying <italic>the ter</italic> operons. Using the PCR method developed in this study, 106 strains were classified as type 1 (<italic>n</italic> = 66), 2 (<italic>n</italic> = 13), 3 (<italic>n</italic> = 8), and 4 (<italic>n</italic> = 17), and two strains carried both types 1 and 2. Furthermore, significant differences in the minimum inhibitory concentration (MIC) of tellurite were observed between strains carrying <italic>ter</italic>-type 4 and the others (<italic>p</italic> &lt; 0.05). The <italic>ter</italic>-type was also closely related to the isolation source, with types 2 and 4 associated with chickens and deer, respectively. This study provided new insights related not only to genetic characteristics of the <italic>ter</italic> operons, but also to phenotypic and ecological characteristics that may be related to the diversity of the operon.</p>