Y. Teng et al., “Plant-derived exosomal microRNAs shape the gut microbiota,” Cell Host Microbe, 24:637–52, 2018.
When Huang-Ge Zhang was younger, his parents would often make him ginger tea when he was ill. Now, as a microbiologist at the University of Louisville in Kentucky, Zhang investigates the mechanisms through which ginger and other edible plants might affect health.
In previous studies, he had found that exosome-like nanoparticles (ELNs)—small extracellular vesicles that often contain RNA—derived from plants such as broccoli and ginger can help prevent alcohol-induced liver damage and artificially induced colitis in mouse models. Recently, when he sequenced ginger-derived ELNs (GELNs), he found that they contained many microRNAs. This made him wonder whether the edible plant RNA could be taken up by gut bacteria and drive expression of bacterial genes—something that human fecal microRNAs have been shown to do in mice.
GINGER FEAST: Using a mouse model of colitis, researchers studied the effects of ginger-derived exosome-like nanoparticles (GELNs) on gut flora. The team found that GELNs are preferentially taken up by Lactobacillus gut bacteria, and boost their abundance (1). The particles contain microRNAs, which stimulate a suite of bacterial genes (2). In particular, they activate a pathway that results in the expression of interleukin-22 in colon mucus (3). This is believed to promote tissue repair and antimicrobial immunity, ultimately improving colitis symptoms in the mice (4). See full infographic: WEB | PDF
To find out, Zhang and his colleagues fed purified GELNs to mice, and analyzed the makeup of their gut microbes by sequencing the 16S rRNA gene. The researchers found a substantial increase in Lactobacillaceae—a family of beneficial bacteria often used as probiotics—in GELN-treated mice compared to mice given a neutral medium. In vitro cultures also showed that GELNs promoted the growth of Lactobacillus rhamnosus and several other Lactobacillus species—but ELNs from grapefruit had the opposite effect.
To see if the GELN mechanism could translate to beneficial health effects, Zhang and his collaborators induced colitis in mice using the chemical dextran sulfate sodium, which causes ulcers and lesions in the gut lining similar to human colitis. After consuming GELN RNAs, the mice showed improvements in their colitis symptoms. By contrast, control mice that had been given particles of scrambled RNA encapsulated in GELN-derived lipid did not.
Further experiments suggested that the microRNAs contained in GELNs activate a suite of bacterial genes, including an enzyme in L. rhamnosus that activates a pathway that triggers the expression of the cytokine IL-22 in colon mucus. IL-22 has been shown in other studies to promote tissue repair at the gut lining, and is therefore thought to ameliorate colitis symptoms.
Zhang says the results are a proof of concept that plant-derived ELNs can affect microbiome composition and health, and present “a new avenue for future studies.” He is in the process of constructing a library of other ELNs derived from vegetables and fruit—“not just ginger,” he says—so that he can test how they affect the microbiome.
For University of Minnesota geneticist Ran Blekhman, who was not involved in the study, the findings illustrate “a remarkable mechanism of these interactions between the diet, the microbes, and the host.” Many studies establish correlations between dietary interventions and changes in the microbiome, whereas very few examine the molecular mechanisms involved, he notes. “In general, there should be a lot more studies like this.”
水產養殖（aquaculture）通常歸類在農業當中的漁業，是一種生產漁業產品的初級產業。然而，「初級」的概念實不足以掌握水產養殖所歷經的變化以及簡化後的複雜性：半陸半水、半漁半牧、半科學（技）半實作、既是食物的生產也是商品的交易等。正因為這種「半X半Y」的混雜性，遇上追求明確與清晰再現的科學，以及轉化現實為可計算、可測量與可掌控的現代管理和經濟技術－簡言之，如同 Bruno Latour 所言之處在混種和純化的恆久張力之間－水產養殖於是得以成形。本文所處理的課題是台灣的水產養殖相對於西方的相似與差異，並指出台灣的水產養殖領域儘管看似存在科學與實作的分離，但這兩個部門卻同樣展現了從原本鑲嵌的「社會-自然」秩序脫離並代之以「技術-經濟」秩序的企圖。最後，本文指出偏重食用或商品目的對於養殖漁業的不同意義。
CALLON的扇貝復育與漁民
只要對「行動者-網絡理論」（ANT）稍有涉獵，大概很難錯過法國社會學家 Michel Callon 的 St. Brieuc Bay「扇貝復育」研究。由於法國民眾在年節對於扇貝的消費需求大，漁民只需幾個月的工作就可以有豐厚的收入，然而或許因為過漁或氣候變化，St. Brieuc Bay 當地的扇貝數量越來越少。三位法國科學家在日本參觀了成效不錯的貝苗收集器，引進 St. Brieuc Bay，協同當地漁民進行實地操作。漁民最重要的協作是同意「禁漁」：暫停捕撈，給收集器和扇貝一點時間。初期成效不錯。科學家四處參加研討會發表收集器跨國轉移和扇貝附著的成果。然而，最終結果是：收集器遠不若在日本的成效；心急難耐的漁民片面終止了禁漁協議，科學家的科研成果變成漁業科學的一段插曲。
花蓮縣民黃先生日前在花蓮壽豐荖溪流域，發現野生大尾鱸鰻，捕獲的鱸鰻長約150公分。（民眾提供）
花蓮縣民黃先生日前在花蓮壽豐荖溪流域，發現野生大尾鱸鰻，捕獲的鱸鰻長約150公分，重達25斤。（花蓮縣水產培育所提供）
花蓮縣民黃先生日前在花蓮壽豐荖溪流域，發現野生大尾鱸鰻，捕獲的鱸鰻長約150公分，重達25斤。（花蓮縣水產培育所提供）
花蓮縣民黃先生日前在花蓮壽豐荖溪流域，發現野生大尾鱸鰻，捕獲的鱸鰻長約150公分，重達25斤。（花蓮縣水產培育所提供）
