Pollution: Transgenic pigs to the rescue
Genetically engineered pigs that digest their food better could help to reduce phosphorus and nitrogen pollution.
- Friedrich-Loeffler-Institut, Germany
In the United States alone, two nutrients, nitrogen and phosphorus, pollute the water in more than 100,000 miles of streams and rivers and almost 2.5 million acres of lakes, reservoirs and ponds (EPA, 2018). Swine manure is one of the main factors responsible for this large-scale contamination. A by-product of the pig farming industry, this bodily waste is rich in both nitrogen and phosphorus, and is widely used as fertilizer. Now, in eLife, Zhenfang Wu and colleagues at the South China Agricultural University and other institutes in China, Canada, and the United States – including Xianwei Zhang and Zicong Li as joint first authors – report that genetically engineered pigs which release less of these nutrients could be a solution to the problem (Zhang et al., 2018).
Nitrogen and phosphorus naturally occur in aquatic ecosystems, where they support the growth of algae and aquatic plants. But when large quantities of these nutrients enter the environment – especially streams, rivers, bays and coastal waters – they can boost the growth of green and blue algae. These algal blooms drain the oxygen from the water, ultimately asphyxiating aquatic life. Some algal blooms also produce toxins and support bacterial growth that can be harmful to people and animals in contact with the contaminated water.
Nitrogen and phosphorus pollution can also affect human health. Nitrate and nitrite, which derive from nitrogen, often seep into groundwater in rural areas and can be damaging to children and pregnant women if they end up in drinking water (Cockburn et al., 2013; Richard et al., 2014). Nitrates prevent the blood from efficiently carrying oxygen to the organs, and this can cause deadly methemoglobinemia, or ‘blue baby’ disease, in infants.
Reducing the levels of nitrogen and phosphorus in swine manure is one way to control this pollution. Pigs excrete large amounts of these chemicals, partly because they cannot digest phytates (which are used by plants to store phosphorus) or non-starch polysaccharides, two types of molecules that are present in their feedstuff. This means that up to 70% of the phosphorus given to a grown pig will be excreted as bodily waste (Dourmad et al., 1999). It is also estimated that a single boar can produce almost 18kg of nitrogen each year (DEFRA, 2017). Moreover, the fact that pigs cannot digest phytates or non-starch polysaccharides prevents them from accessing many of the nutrients in their feed, which limits their energy intake.
Almost two decades ago, researchers used genetic techniques to engineer a transgenic ‘Enviropig’ that could process phytates (Golovan et al., 2001). Now Zhang et al. have created transgenic pigs that express enzymes which allow them to digest both phytates and non-starch polysaccharides. Zhang et al. took five genes from bacteria and fungi and introduced them into the genomes of pigs to create animals that expressed four bacterial enzymes (two types of β-glucanase, xylanase, phytase) in their salivary glands. In the mouth of the animals, the enzymes could break phytates and non-starch polysaccharides into molecules that the pigs could then digest. The modified animals produced bodily waste that contained up to 24% less nitrogen and 44% less phosphorus compared with other pigs on the same diet. The results were slightly lower than those previously reported for transgenic pigs that can just break down phytates, possibly because of differences in the expression levels of the transgenes and changes in diet (Golovan et al., 2001; Forsberg et al., 2013; Meidinger et al., 2013).
Besides excreting fewer polluting nutrients, the transgenic pigs also grew better and fattened up more quickly. In fact, on average, they put on 24% more weight every day than their non-modified counterparts. As a result, they could be slaughtered nearly a month earlier. This is an advantage that ‘Enviropig’ did not have.
By growing fast, requiring less food and producing fewer damaging chemicals, the pigs developed by Zhang et al. might create a win-win situation for both farmers and environment.
References
-
Nitrite in feed: from animal health to human healthToxicology and Applied Pharmacology 270:209–217.https://doi.org/10.1016/j.taap.2010.11.008
-
Nitrogen and phosphorus consumption, utilisation and losses in pig production: FranceLivestock Production Science 58:199–211.https://doi.org/10.1016/S0301-6226(99)00009-3
-
Pigs expressing salivary phytase produce low-phosphorus manureNature Biotechnology 19:741–745.https://doi.org/10.1038/90788
-
Reexamining the risks of drinking-water nitrates on public healthThe Ochsner journal 14:392–398.
Article and author information
Author details
Publication history
Copyright
© 2018, Petersen
This article is distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use and redistribution provided that the original author and source are credited.
Metrics
-
- 2,577
- views
-
- 140
- downloads
-
- 2
- citations
Views, downloads and citations are aggregated across all versions of this paper published by eLife.
Download links
A two-part list of links to download the article, or parts of the article, in various formats.
Downloads (link to download the article as PDF)
Open citations (links to open the citations from this article in various online reference manager services)
Cite this article (links to download the citations from this article in formats compatible with various reference manager tools)
Pollution: Transgenic pigs to the rescue
eLife 7:e37641.
https://doi.org/10.7554/eLife.37641
Further reading
-
- Biochemistry and Chemical Biology
Glycans play an important role in modulating the interactions between natural killer cells and antibodies to fight pathogens and harmful cells.
-
- Biochemistry and Chemical Biology
- Cell Biology
The Sonic hedgehog (Shh) signaling pathway controls embryonic development and tissue homeostasis after birth. This requires regulated solubilization of dual-lipidated, firmly plasma membrane-associated Shh precursors from producing cells. Although it is firmly established that the resistance-nodulation-division transporter Dispatched (Disp) drives this process, it is less clear how lipidated Shh solubilization from the plasma membrane is achieved. We have previously shown that Disp promotes proteolytic solubilization of Shh from its lipidated terminal peptide anchors. This process, termed shedding, converts tightly membrane-associated hydrophobic Shh precursors into delipidated soluble proteins. We show here that Disp-mediated Shh shedding is modulated by a serum factor that we identify as high-density lipoprotein (HDL). In addition to serving as a soluble sink for free membrane cholesterol, HDLs also accept the cholesterol-modified Shh peptide from Disp. The cholesteroylated Shh peptide is necessary and sufficient for Disp-mediated transfer because artificially cholesteroylated mCherry associates with HDL in a Disp-dependent manner, whereas an N-palmitoylated Shh variant lacking C-cholesterol does not. Disp-mediated Shh transfer to HDL is completed by proteolytic processing of the palmitoylated N-terminal membrane anchor. In contrast to dual-processed soluble Shh with moderate bioactivity, HDL-associated N-processed Shh is highly bioactive. We propose that the purpose of generating different soluble forms of Shh from the dual-lipidated precursor is to tune cellular responses in a tissue-type and time-specific manner.
