Archive for the ‘nitrogen’ Category
more on photosynthesis: stuff about rubisco, or not
don’t ask
So in my wild wanderings on this topic I’ve been informed by a close friend that rubisco is key, and research is ongoing. So, starting off with my key text, Oliver Morton’s Eating the Sun, and a video on rubisco that’s been drawn to my attention, I’ll keep making attempts to educate myself.
So, nitrogen is essential to all living organisms, and our atmosphere is mostly nitrogen – just over 78%. It’s essential to proteins and DNA, but apparently it isn’t something we can directly access. There’s an enzyme complex called nitrogenase, which some bacteria and archaea can produce, which is able to convert inert nitrogen gas into ammonia (NH3). However, nitrogenase falls apart in the presence of oxygen, so atmospheric nitrogen can’t be used by virtually all living organisms. Only anoxic organisms – generally very basic microbes (spoiler alert – nitroplasts) – can make use of it. So, it has generally been a rule of biology that no complex organisms can utilise nitrogen, but a new bacterium was discovered quite recently, or rather its DNA. That’s to say, samples of seawater were examined for the presence of nitrogen-fixing bacteria. What was initially found, in the 1990s, in a search for a key nitrogen-fixing gene, was genetic material, without the organism it belonged to. The searcher, or researcher, felt that he had a good idea what the missing organism would look like. A hunt was on to find this organism, which left its ‘fingerprints’ everywhere, but it took years to find it, all they could find was DNA with a missing owner (I’m relying heavily on a video referenced below for all this). What they did find was quite strange – its DNA didn’t seem to contain the genes for photosynthesis. And this DNA turned up all over the place, ‘complete’ with missing genes – a lot of them, some 80% of its entire genome – which seemed to make its very survival questionable. But then it was worked out that the DNA was inside a species of algae which was hosting it. This algae, Braarudosphaera Bigelowii (Bigelowii for short), was being investigated in Japan by a female scientist, partly because of the symmetrical beauty of its shape at a particular developmental stage. She eventually managed to culture the algae (the video tells the story beautifully and movingly), and found something odd amongst the expected parts, almost like a separated container.
The Japanese researcher came across work from the team who had discovered the DNA with the missing host. It was generally a shock to both sides, but they were able to work together and discover what was effectively a symbiotic process, though the video on this suggests that the process goes beyond symbiosis, and is more like ‘two organisms fusing into one’, as with mitochondria and chloroplasts and their hosts. Bigelowii had become an organelle, dividing and growing at the same rate as its host. It was an important discovery, not only to add to the small family of organelles (it has been called a nitroplast), but to find an organism that effectively fed on nitrogen. Could this be used to produce nitrogen – which is currently produced in expensive and inefficient ways – out of the air?
So, this stuff about nitroplasts is quite recent, so it doesn’t get into Morton’s book to complexify it even further. And it’s the most complex book I’ve read – and I’ve read an awful lot of the bloody things. I can but give an example: this, about chloroplasts:
As they have spread out with and through their wormhole world, its chloroplast inhabitants have changed according to the requirements of the time-tunnels that they find themselves in; evolution applies in there just as it does out here. In some tunnels the chloroplasts are squadrons of small green capsules that still have the look of bacteria. In others they have evolved into swirling spirals pressed tight against the outer membrane like rifling in the barrel of a gun. Some are red five-pointed stars, one to a cell. But they are all descended from the same original ancestor.
There are many dead ends in the network – hundreds of thousands in every leaf that falls – billions of times as many in every fossil species bereft of descendants today. But the threads as yet unbroken are all but uncountable, and multiply still. All around us, moment by moment, the skein of wormholes pushes itself further into the future.
Oliver Morton, Eating the Sun, pp 209-10
Rifling in the barrel of a gun? I’ve managed to avoid going near such an item in the 70 years of my life. And I might know something about the look of love (or not), but the look of bacteria is well beyond me. Never owned a microscope, sadly. As for the rest, lovely writing but I can’t quite get a picture…. But, I will soldier on…
References
Oliver Morton, Eating the Sun, 2007