By Stephan Kamrad
I have previously written about Just Mayo, a vegan mayonnaise that contains “pea proteins” instead of egg yolk. Another start-up company founded by Patrick Brown, Professor of Biochemistry at Stanford University, makes not only the condiment but the entire burger vegan. Their Impossible Cheeseburger is made entirely from plants and imitates beef in taste, texture and appearance almost perfectly (according to tasters).
Medicago italica root nodules
Just imagine a perfectly grilled burger: Juicy and just a tiny bit bloody in the middle. The molecule responsible for the characteristic red colour and distinct, slightly metallic taste is a complex molecule called haem. Haem contains a co-ordinated iron ion and is part of haemoglobin, the protein that transports oxygen in our red blood cells.
The Impossible Cheeseburger gets its haem not from the blood of kettle but from a plant of the legume family (which includes beans, peas and peanuts). These naturally produce leghaemoglobin which is functionally and structurally akin to mammalian haemoglobin. It is red in colour, also contains the haem co-factor and apparently makes a fake burger just as bloody as real beef.
Legumes live in symbiosis with Rhizobia bacteria that populate specially formed nodules in the roots. Those bacteria convert atmospheric nitrogen (N2) to ammonium (NH4+) which the plant is then able to use for growth and development. In exchange, the bacteria are supplied with sugars. Nitrogenase, the bacterial enzyme that fixes N2, is sensitive to oxygen and it is thus important that oxygen levels in the nodule are as low as possible while still being high enough for the bacteria to live. And this is where leghaemoglobing comes in: It is present at high levels in root nodules and buffers oxygen at a constant but low level. All that the scientists at ‘Impossible Food’ had to do was to harvest root nodules and extract the haem (which was probably a lot harder than it sounds).
Whatever your reason to eat vegan is (and there are plenty), there is an emerging industry that will allow you to do so without changing your actual eating habits or losing flavour. While this is potentially a great thing for the customer and the planet, it is important to realise that this product –while being vegan- is in no way natural. It was born in the lab, created not only by chefs but also by biochemists — who miraculously turn vegetables into meat. The “Recipe” and exact ingredients remain (just like in the case of Just Mayo) the company’s secret which makes it increasingly difficult for us as consumers to know what exactly we are eating.
The Impossible Cheeseburger will not be available in stores for another few months. If you can’t wait that long, check out this vegan burger recipe based on carrot, kidney beans and cumin.
By Nathan Smith
Deep in the dark depths of fungal taxonomy there lies a phyla known as the Glomeromycota. Members of this phyla are all obligate symbiotes, unable to support themselves independently and requiring a photosynthetic partner to provide organic carbon to them in return for gifts of phosphorous and nitrogen. For all bar one, this photosynthetic partner is a terrestrial plant; the symbiosis being better known as Arbuscular Mycorrhization and which upwards of 80% of angiosperms (flowering plants) are capable of engaging in.
The exception to this Golden Rule of the Phyla? A species known as Geosiphon pyriformis which instead forms a relationship with the cyanobacteria, specifically the species Nostoc punctiforme.
Geosiphon:Nostoc symbiosis; Geosiphon spores inset
(credit Schuessler Lab)
The Geosiphon:Nostoc symbiosis appears to be unique in nature as the only example of an endosymbiosis between a fungus and a bacteria. Adding to its mystery, it has so far been reported to have been found only 6 times in the wild in a small region of eastern Germany and Austria.
In contrast to Arbuscular Mycorrhization, where the fungal partner invades the cells of the plant to create an exchange interface, the cyanobacteria are taken in by the fungi, surrounding them with a unicellular structure known as a ‘bladder’ that can grow up to 2mm in length.
The exchange of nutrients is also different than in Arbuscular Mycorrhization. With the exception of nitrogen and carbon, all of the cyanobacteria’s nutritional needs must be met by the fungus. In return, the fungus receives organic carbon and nitrogen.
It is possible that Geosiphon:Nostoc symbiosis represents an important step in fungi being able to form symbiotic relationships with plants; it’s also possible that the Geosiphon:Nostoc developed out of the wider spread Arbuscular Mycorrhiza symbioses.
Either way it’s an interesting story of one fungus breaking the mould.
by Nathan Smith
If you were presented with a plant and a fungus and asked to pick the parasite, chances are you’d pick the fungus. Whilst this is often the case, there are significant and widespread cases of the relationship being the other way around. Enter Orchids.
Common Spotted Orchid
Orchids are family of plants distinct in physical appearance and are renowned for their sweet scent and aesthetic beauty, despite the fact they more closely related to rice than they are to roses. Their seeds contain rather small reserves of nutrients and they are unable to photosynthesise immediately after germination, instead going through an achlorophyllic stage; in fact some orchids are not capable of photosynthesis during their lifespan. Usually small reserves and an initial inability to photosynthesise would be considered a bad strategy for a plant, but Orchids are still thriving and there is a good reason why.
Throughout their non-photosynthesising stage, and indeed throughout their entire existence, they are the dominant partners in what can best be described as an uneven symbiotic relationship with a fungal partner. In fact, a fungal partner is required by the orchid for them to germinate ‘in the wild’. Orchids can be germinated in sterile conditions; however this requires exposure to the ‘fungal sugar’ trehalose. So what is the trade between the orchid and the fungus? The fungus supplies the plant with organic carbon, a source of nitrogen, phosphorous, and other minerals and nutrients, and in return, gets… well, not much really. This uneven relationship continues once the plant gains the ability to photosynthesise and there is little evidence that the fungus gains a significant amount of reduced carbon from its photosynthetic symbiont. The fact that the fungus enters into a symbiosis with the plant in the first place, and continues this relationship throughout the plant’s life, suggests the fungus gains something from the relationship or that the plant emits a strong attractant, however there is little to no evidence for this and so these hypothesises remain little more than speculation.
What about the orchids that never photosynthesise? These plants, for instance the Bird’s-nest Orchid, have a habit of forming symbioses with fungi that also associate with tree roots. This allows them to use the fungus like a straw and indirectly parasitise what they need from the unsuspecting trees. Clever stuff.
Orchids are beautiful and interesting plants and deserve to be admired, but it doesn’t mean it’s the good guy. Next time spare a thought for the poor little fungus.
Photography by Leanne Massie