Moye Zachary D, Valiuskyte Kornelija, Dewhirst Floyd E, Nichols Frank C, Davey Mary E
Department of Oral Biology, College of Dentistry, University of Florida, Gainesville FL, USA.
Department of Microbiology, Forsyth Institute, CambridgeMA, USA; Department of Oral Medicine, Infection and Immunity, Harvard School of Dental Medicine, BostonMA, USA.
Front Microbiol. 2016 Nov 29;7:1919. doi: 10.3389/fmicb.2016.01919. eCollection 2016.
Bacteria alter the biophysical properties of their membrane lipids in response to environmental cues, such as shifts in pH or temperature. In essence, lipid composition determines membrane structure, which in turn influences many basic functions, such as transport, secretion, and signaling. Like other members of the phylum Bacteroidetes, the oral anaerobe possesses the ability to synthesize a variety of novel membrane lipids, including species of dihydroceramides that are distinct, yet similar in structure to sphingolipids produced by the human host. The role of dihydroceramides in the physiology and pathogenic potential of the human microbiota is only beginning to be explored; yet there is increasing data indicating that these lipids play a role in human diseases, such as periodontitis and multiple sclerosis. Here, we report on the identification of a gene (PG1780) in the chromosome of strain W83 encoding a putative serine palmitoyltransferase, the enzyme that catalyzes the first step in sphingolipid biosynthesis. While we were able to detect dihydroceramides in whole lipid extracts of cells as well as crude preparations of outer membrane vesicles, sphingolipids were absent in the PG1780 mutant strain. Moreover, we show that the synthesis of sphingolipids plays an essential role in the long-term survival of the organism as well as its resistance to oxidative stress. Further, a PG1780 mutant displayed much lower activity of cell-associated arginine and lysine gingipains, yet slightly higher activity in the corresponding culture supernates, which we hypothesize is due to altered membrane properties and anchoring of these proteases to the cell surface. In addition, we determined that sphingolipid production is critical to the presentation of surface polysaccharides, with the mutant strain displaying less K-antigen capsule and more anionic polysaccharide (APS). Overall, we have discovered that, in addition to their role in pathogenicity, the synthesis of sphingolipids is critical to the cellular homeostasis and persistence of this important dental pathogen.
细菌会根据环境线索（如pH值或温度的变化）改变其膜脂的生物物理特性。本质上，脂质组成决定膜结构，而膜结构又反过来影响许多基本功能，如运输、分泌和信号传导。与拟杆菌门的其他成员一样，这种口腔厌氧菌具有合成多种新型膜脂的能力，包括二氢神经酰胺种类，它们与人类宿主产生的鞘脂结构不同但相似。二氢神经酰胺在人类微生物群的生理学和致病潜力中的作用才刚刚开始被探索；然而，越来越多的数据表明这些脂质在人类疾病中发挥作用，如牙周炎和多发性硬化症。在此，我们报告了在菌株W83的染色体中鉴定出一个基因（PG1780），该基因编码一种假定的丝氨酸棕榈酰转移酶，该酶催化鞘脂生物合成的第一步。虽然我们能够在细胞的全脂质提取物以及外膜囊泡的粗制品中检测到二氢神经酰胺，但在PG1780突变株中却没有鞘脂。此外，我们表明鞘脂的合成在该生物体的长期存活及其对氧化应激的抗性中起着至关重要的作用。此外，PG1780突变体显示细胞相关的精氨酸和赖氨酸牙龈蛋白酶活性低得多，但在相应的培养上清液中活性略高，我们推测这是由于膜特性改变以及这些蛋白酶在细胞表面的锚定改变所致。此外，我们确定鞘脂的产生对于表面多糖的呈现至关重要，突变株显示出较少的K抗原荚膜和较多的阴离子多糖（APS）。总体而言，我们发现，除了在致病性方面的作用外，鞘脂的合成对于这种重要的牙科病原体的细胞内稳态和持久性至关重要。
