Inhibition of Cyclopropane Fatty Acid Synthesis in the Membrane of Halophilic Halomonas socia CKY01 by Kanamycin

Abstract

Antibiotics are powerful and reliable substances that can control microorganism growth. However, microbes employ several countermeasures to adapt to external stresses such as extreme salt concentrations and antibiotics. Among them, microbes can regulate the fatty acid composition of their cell membrane. Our previous study reported that Halomonas socia CKY01, a various hydrolase producing halophilic bacterium, exhibited NaCl concentration-dependent kanamycin resistance. In this study, kanamycin, which is known to interfere with protein synthesis by targeting bacterial ribosomes, was unexpectedly found to inhibit cyclopropane fatty acid (CFA) synthesis in the cell membrane of this microbe. As a result, the aim of the current study was to elucidate the mechanism underlying this unique function of kanamycin. Reverse transcription-polymerase chain reaction was used to examine cfa expression, which encodes cyclopropane-fatty acid-acyl-phospholipid synthase, and it was found that the mRNA expression of cfa was not significantly affected by kanamycin treatment. Inhibition of CFA production was also observed when oleic acid, a CFA precursor, was supplied to cells. Additionally, inhibition of CFA synthase was monitored in cfa-overexpressing Escherichia coli, and CFA production did not differ significantly, suggesting that this phenomenon is specific to H. socia CKY01. Although the exact mechanism of CFA inhibition by kanamycin remains unclear, the study findings demonstrate the impact of kanamycin on the cell membrane composition of H. socia CKY01, suggesting possible synergetic effects with membrane-targeted antibiotics.