Interdisciplinary Program in Genetics, Texas A&M University, College Station, TX, USA.
Department of Biochemistry & Biophysics, Texas A&M University, College Station, TX, USA.
J Antibiot (Tokyo). 2018 Mar;71(3):372-381. doi: 10.1038/s41429-017-0005-z. Epub 2018 Jan 18.
The linearmycin family of polyketides was originally classified as antifungal metabolites. However, in addition to antifungal activity, we previously found that linearmycins cause cellular lysis and colony degradation of the Gram-positive bacterium Bacillus subtilis. We recently showed that Streptomyces sp. strain Mg1 incorporates linearmycins into extracellular vesicles, which are capable of lysing B. subtilis. However, the mechanism of linearmycin-induced lysis was hitherto unexplored. Therefore, we sought to determine how linearmycin-laden vesicles cause lysis. In this study, we found that linearmycins inhibited the growth of all Gram-positive bacteria that we tested, but lysis was limited to some Bacillus species. Next, we found that linearmycin-induced lysis occurred even when cellular metabolism and growth were inhibited, which suggested that linearmycins possess the intrinsic capacity to lyse cells, unlike cell-wall targeting antibiotics. We showed that linearmycin exposure caused changes consistent with rapid depolarization of the B. subtilis cytoplasmic membrane, which was correlated with a loss of viability. Finally, using liposomes as in vitro membrane models, we demonstrated that linearmycins are capable of disrupting lipid bilayers without any other cellular components. Taken together, our results strongly indicate that the cytoplasmic membrane is the direct antibacterial target of linearmycins.
林可霉素类聚酮化合物最初被归类为抗真菌代谢物。然而，除了抗真菌活性外，我们之前还发现林可霉素会导致革兰氏阳性菌枯草芽孢杆菌的细胞裂解和菌落降解。我们最近发现链霉菌 Mg1 将林可霉素纳入细胞外囊泡中，这些囊泡能够裂解枯草芽孢杆菌。然而，林可霉素诱导裂解的机制迄今尚未得到探索。因此，我们试图确定载有林可霉素的囊泡如何导致裂解。在这项研究中，我们发现林可霉素抑制了我们测试的所有革兰氏阳性菌的生长，但裂解仅限于某些芽孢杆菌属。接下来，我们发现即使细胞代谢和生长受到抑制，林可霉素诱导的裂解也会发生，这表明林可霉素具有内在的裂解细胞的能力，而不像针对细胞壁的抗生素。我们表明，林可霉素暴露会引起与细胞质膜迅速去极化一致的变化，这与活力丧失相关。最后，我们使用脂质体作为体外膜模型，证明林可霉素能够在没有任何其他细胞成分的情况下破坏脂质双层。总之，我们的结果强烈表明细胞质膜是林可霉素的直接抗菌靶标。
