Round James, Roccor Raphael, Li Shu-Nan, Eltis Lindsay D
Department of Microbiology and Immunology, Life Sciences Institute, The University of British Columbia, Vancouver, Canada.
Department of Microbiology and Immunology, Life Sciences Institute, The University of British Columbia, Vancouver, Canada
Appl Environ Microbiol. 2017 Sep 29;83(20). doi: 10.1128/AEM.00902-17. Print 2017 Oct 15.
Many rhodococci are oleaginous and, as such, have considerable potential for the sustainable production of lipid-based commodity chemicals. Herein, we demonstrated that RHA1, a soil bacterium that catabolizes a wide range of organic compounds, produced wax esters (WEs) up to 0.0002% of its cellular dry weight during exponential growth on glucose. These WEs were fully saturated and contained primarily 31 to 34 carbon atoms. Moreover, they were present at higher levels during exponential growth than under lipid-accumulating conditions. Bioinformatics analyses revealed that RHA1 contains a gene encoding a putative fatty acyl coenzyme A (acyl-CoA) reductase (FcrA). The purified enzyme catalyzed the NADPH-dependent transformation of stearoyl-CoA to stearyl alcohol with a specific activity of 45 ± 3 nmol/mg · min and dodecanal to dodecanol with a specific activity of 5,300 ± 300 nmol/mg · min. Deletion of did not affect WE accumulation when grown in either carbon- or nitrogen-limited medium. However, the Δ mutant accumulated less than 20% of the amount of WEs as the wild-type strain under conditions of nitric oxide stress. A strain of RHA1 overproducing FcrA accumulated WEs to ∼13% cellular dry weight under lipid-accumulating conditions, and their acyl moieties had longer average chain lengths than those in wild-type cells (C versus C). The results provide insight into the biosynthesis of WEs in rhodococci and facilitate the development of this genus for the production of high-value neutral lipids. Among the best-studied oleaginous bacteria, rhodococci have considerable potential for the sustainable production of lipid-based commodity chemicals, such as wax esters. However, many aspects of lipid synthesis in these bacteria are poorly understood. The current study identifies a key enzyme in wax ester synthesis in rhodococci and exploits it to significantly improve the yield of wax esters in bacteria. In so doing, this work contributes to the development of novel bioprocesses for an important class of oleochemicals that may ultimately allow us to phase out their unsustainable production from sources such as petroleum and palm oil.
许多红球菌属细菌是产油的，因此在可持续生产基于脂质的商品化学品方面具有相当大的潜力。在此，我们证明了RHA1，一种能分解多种有机化合物的土壤细菌，在以葡萄糖为碳源指数生长期间，产生的蜡酯（WEs）含量高达其细胞干重的0.0002%。这些蜡酯完全饱和，主要含有31至34个碳原子。此外，它们在指数生长期间的含量高于脂质积累条件下的含量。生物信息学分析表明，RHA1含有一个编码假定的脂肪酰基辅酶A（酰基辅酶A）还原酶（FcrA）的基因。纯化后的酶催化硬脂酰辅酶A依赖NADPH转化为硬脂醇，比活性为45±3 nmol/mg·min，催化十二醛转化为十二醇，比活性为5300±300 nmol/mg·min。在碳限制或氮限制培养基中生长时，缺失该基因不影响蜡酯积累。然而，在一氧化氮胁迫条件下，Δ突变体积累的蜡酯量不到野生型菌株的20%。一株过量表达FcrA的RHA1菌株在脂质积累条件下积累的蜡酯量达到细胞干重的约13%，其酰基部分的平均链长比野生型细胞中的更长（C对C）。这些结果为深入了解红球菌属细菌中蜡酯的生物合成提供了线索，并有助于开发该属用于生产高价值中性脂质。在研究得最好的产油细菌中，红球菌属在可持续生产基于脂质的商品化学品（如蜡酯）方面具有相当大的潜力。然而，这些细菌中脂质合成的许多方面仍知之甚少。当前的研究鉴定出红球菌属细菌蜡酯合成中的一种关键酶，并利用它显著提高了细菌中蜡酯的产量。通过这样做，这项工作有助于开发一类重要的油脂化学品的新型生物工艺，这最终可能使我们逐步淘汰从石油和棕榈油等来源进行的不可持续生产。
