Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts, USA
Department of Plant and Microbial Biology, University of California-Berkeley, Berkeley, California, USA.
Appl Environ Microbiol. 2020 Jan 21;86(3). doi: 10.1128/AEM.01697-19.
The wild chili pepper produces the spicy defense compounds known as capsaicinoids, including capsaicin and dihydrocapsaicin, which are antagonistic to the growth of fungal pathogens. Compared to other microbes, fungi isolated from infected seeds of possess much higher levels of tolerance of these spicy compounds, having their growth slowed but not entirely inhibited. Previous research has shown capsaicinoids inhibit microbes by disrupting ATP production by binding NADH dehydrogenase in the electron transport chain (ETC) and, thus, throttling oxidative phosphorylation (OXPHOS). Capsaicinoids may also disrupt cell membranes. Here, we investigate capsaicinoid tolerance in fungal seed pathogens isolated from We selected 16 fungal isolates from four ascomycete genera (, , , and ). Using relative growth rate as a readout for tolerance, fungi were challenged with ETC inhibitors to infer whether fungi possess alternative respiratory enzymes and whether effects on the ETC fully explained inhibition by capsaicinoids. In all isolates, we found evidence for at least one alternative NADH dehydrogenase. In many isolates, we also found evidence for an alternative oxidase. These data suggest that wild-plant pathogens may be a rich source of alternative respiratory enzymes. We further demonstrate that these fungal isolates are capable of the breakdown of capsaicinoids. Finally, we determine that the OXPHOS theory may describe a weak primary mechanism by which dihydrocapsaicin, but not capsaicin, slows fungal growth. Our findings suggest that capsaicinoids likely disrupt membranes, in addition to energy poisoning, with implications for microbiology and human health. Plants make chemical compounds to protect themselves. For example, chili peppers produce the spicy compound capsaicin to inhibit pathogen damage and animal feeding. In humans, capsaicin binds to a membrane channel protein, creating the sensation of heat, while in microbes, capsaicin limits energy production by binding respiratory enzymes. However, some data suggest that capsaicin also disrupts membranes. Here, we studied fungal pathogens (, , , and ) isolated from a wild chili pepper, By measuring growth rates in the presence of antibiotics with known respiratory targets, we inferred that wild-plant pathogens might be rich in alternative respiratory enzymes. A zone of clearance around the colonies, as well as liquid chromatography-mass spectrometry data, further indicated that these fungi can break down capsaicin. Finally, the total inhibitory effect of capsaicin was not fully explained by its effect on respiratory enzymes. Our findings lend credence to studies proposing that capsaicin may disrupt cell membranes, with implications for microbiology, as well as human health.
野辣椒产生的辣味防御化合物，如辣椒素类物质，包括辣椒素和二氢辣椒素，它们对真菌病原体的生长具有拮抗作用。与其他微生物相比，从感染种子中分离出的真菌对这些辣味化合物的耐受性要高得多，它们的生长速度减慢，但并没有完全受到抑制。先前的研究表明，辣椒素类物质通过与电子传递链（ETC）中的 NADH 脱氢酶结合来抑制微生物的 ATP 产生，从而抑制氧化磷酸化（OXPHOS）。辣椒素类物质也可能破坏细胞膜。在这里，我们研究了从 中分离出的真菌种子病原体对辣椒素类物质的耐受性。我们从四个子囊菌属（,,, 和 ）中选择了 16 种真菌分离株。使用相对生长率作为耐受性的读数，用 ETC 抑制剂来挑战真菌，以推断真菌是否具有替代的呼吸酶，以及对 ETC 的影响是否完全解释了辣椒素类物质的抑制作用。在所有分离株中，我们都发现了至少一种替代 NADH 脱氢酶的证据。在许多分离株中，我们还发现了替代氧化酶的证据。这些数据表明，野生植物病原体可能是替代呼吸酶的丰富来源。我们进一步证明，这些真菌分离株能够分解辣椒素类物质。最后，我们确定 OXPHOS 理论可能描述了二氢辣椒素（但不是辣椒素）减缓真菌生长的一种较弱的主要机制。我们的研究结果表明，辣椒素类物质可能除了能量中毒外，还会破坏细胞膜，这对微生物学和人类健康都有影响。植物会产生化学化合物来保护自己。例如，辣椒产生辣味化合物辣椒素来抑制病原体的损伤和动物的摄食。在人类中，辣椒素与膜通道蛋白结合，产生热感，而在微生物中，辣椒素通过与呼吸酶结合来限制能量产生。然而，一些数据表明，辣椒素也会破坏细胞膜。在这里，我们研究了从一种野生辣椒中分离出的真菌病原体（,,, 和 ）。通过测量存在已知呼吸靶标的抗生素时的生长速率，我们推断野生植物病原体可能富含替代呼吸酶。菌落周围的清除带以及液相色谱-质谱数据进一步表明，这些真菌可以分解辣椒素。最后，辣椒素的总抑制作用不能完全用其对呼吸酶的作用来解释。我们的研究结果支持了一些研究提出的观点，即辣椒素可能会破坏细胞膜，这对微生物学以及人类健康都有影响。
