AUTHOR=Shindoh Suzune , Kadoya Aya , Kanechi Reo , Watanabe Kozo , Suzuki Satoru 

TITLE=Marine bacteria harbor the sulfonamide resistance gene sul4 without mobile genetic elements

JOURNAL=Frontiers in Microbiology

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2023.1230548

DOI=10.3389/fmicb.2023.1230548

ISSN=1664-302X

ABSTRACT=<p>Marine bacteria are possible reservoirs of antibiotic-resistance genes (ARGs) originating not only from clinical and terrestrial hot spots but also from the marine environment. We report here for the first time a higher rate of the sulfonamide-resistance gene <italic>sul4</italic> in marine bacterial isolates compared with other <italic>sul</italic> genes. Among four sulfonamide-resistance genes (<italic>sul1</italic>, <italic>sul2</italic>, <italic>sul3</italic>, and <italic>sul4</italic>), <italic>sul4</italic> was most abundant (45%) in 74 sulfonamide-resistant marine isolates by PCR screening. The order of abundance was <italic>sul4</italic> (33 isolates) <italic>&gt;sul2</italic> (6 isolates) <italic>&gt;sul3</italic> (5 isolates) <italic>&gt;sul1</italic> (1 isolate). Whole-genome sequencing of 23 isolates of <italic>sul4</italic>-expressing α- and γ-proteobacteria and bacilli revealed that <italic>sul4</italic> was not accompanied by known mobile genetic elements. This suggests that <italic>sul4</italic> in these marine isolates is clonally transferred and not horizontally transferable. Folate metabolism genes formed a cluster with <italic>sul4</italic>, suggesting that the cluster area plays a role in folate metabolism, at which <italic>sul4</italic> functions as a dihydropteroate synthase. Thus, <italic>sul4</italic> might be expressed in marine species and function in folate synthesis, but it is not a transferable ARG.</p>