Archive for the ‘cyanobacteria’ Category
on cyanobacteria, mostly
green stuff
So, since reading about photosynthesis and its emergence with cyanobacteria – perhaps – I’ve been fascinated and confused by the early ages of this planet and the beginnings of life. Here’s how Oliver Morton defines these bacteria in the glossary to Eating the Sun:
Cyanobacteria: the only bacteria which practice oxygenic photosynthesis. The chloroplasts in algae and plants are derived from cyanobacteria.
Is there another kind of photosynthesis? Clever me looked it up and, yes, anoxic photosynthesis is a thing. It’s a ‘light-driven metabolic process used by certain bacteria to make energy and organic compounds without producing oxygen as a byproduct’, according to AI.
Chloroplasts, to be clear to myself, are plant and algal organelles which convert sunlight into chemical energy. This photosynthesis process uses chlorophyll, a sunlight-absorbing green pigment, to turn CO2 and H2O into glucose and O2. It absorbs red and blue wavelengths and reflects green, hence the colour of all plants (I love that), and I notice it’s popular in dietary supplements – bien sûr!
So how did these cyanobacteria evolve, and how are they going these days? Apparently they evolved in the ocean – remembering how very watery our planet once was – some 3 billion years ago or more. The general view apparently is that those ocean waters were rather hot, with barely any oxygen. Anaerobic microbes existed in these waters (here be magic?) – for whom oxygen was toxic, although there were some ‘aerotolerant anaerobes’ who didn’t mind oxygen but had no use for it.
So cyanobacteria, aka blue-green algae, are thought to have evolved in freshwater (low salt) environments, in the ‘photic zone’, that’s to say the upper, sunlit layer. We only have clear evidence of their existence from 2.1 billion years ago, and disputed evidence from 2.7 billion, and maybe they go back to 3.5 billion, but their effect on the planet, via the ‘Great Oxygenation Event’ (GOE), wasn’t felt until after about 2.4 billion. This rise in oxygen is likely to have adversely affected the biosphere of the time (made up of archaea, not bacteria), which fed largely on methane.
Much of our evidence of early life forms is based on stromatolites and oncolites. Stromatolites (prime examples are found at Shark Bay, Western Australia), are ‘layered biochemical accretionary structures formed in shallow water [the photic zone] by the trapping, binding, and cementation of sedimentary grains by biofilms (microbial mats) of microorganisms, especially cyanobacteria’ (Wikipedia), and they are the oldest known fossil remains. Oncolites are small near-spherical structures forming around a spherical nucleus, like a shell fragment, and are untethered, unlike stromatolites. They’re an indication of warming waters in the photic zone, and are also found in contemporary freshwater. Oh, and they’re also formed by cyanobacterial growth.
So here’s another Wikipedia quote which I’ll then try to make my own sense of:
Oxygenic photosynthesis only evolved once (in prokaryotic cyanobacteria), and all photosynthetic eukaryotes (including all plants and algae) have acquired this ability from endosymbiosis with cyanobacteria or their endosymbiont hosts. In other words, all the oxygen that makes the atmosphere breathable for aerobic organisms originally comes from cyanobacteria or their plastid descendants
Aerobic organisms, that’s us, amongst quite a few others. So, to unpack. I sort of know the prokaryote to eukaryote story, but let me go a bit deeper, or a bit less shallow. It’s where endosymbiosis comes in – a symbiosis, I think, where it’s the end o’ me as an independent organism, but I live on as an essential element in something bigger and grander, usually. Mitochondria are often the go-to example, former bacteria harnessed by eukaryotes to break down nutrients and convert them to energy in the form of ATP.
So what is ATP and why is it the energy molecule? See what I did there? I forced myself further into the murk. Adenosine triphosphate, the energy provider of all living cells, is made up of a nitrogenous purine base called adenine – formula C5H5 N5 (those three elements are always in there somewhere), and fundamental to DNA and RNA and no doubt much else that sparks with life.
This reminds me that there are purines and pyrimidines, but getting back to energy, AI never lies (and I have to say I’m quite frightened of this AI shite, because, as we all know, it’s controlled by billionaires who don’t have the interests of people like myself in mind) tells me this:
ATP does not technically create energy; instead, it acts as a chemical battery that stores and delivers energy. It releases this energy when a water molecule breaks the weak bond holding its third phosphate group off, turning ATP into ADP (adenosine diphosphate) and releasing usable power for the cell.
So why does this bond get broken? And I note that there’s also adenosine monophosphate (AMP). And the adenosine part consists of adenine, a nitrogenous base, and ribose (sugar). And all these complicated changes and breaking-downs are part of the process called metabolism, the conversion of the energy food provides into molecules that keep us going, such as proteins, but of course many others.
I’ve never spent much more than an hour or two in a lab, so I find it hard to think through these metabolic developments. Let me return to the ubiquitous cyanobacteria. I may be repeating myself, but mea culpa – they have a vast variety of forms (all with much the same colour), and some are much given to symbiosis with various unicellular and multicellular organisms. So, with their photoautotrophic, oxygen-producing abilities they’ve been the sine qua non of complex, oxygen-based life on this planet. I think I’ll just stop here.
References
Oliver Morton, Eating the Sun: the everyday miracle of how plants power the planet, 2007
why are our river fish dying?
Canto: So here’s a question. Why are so many fish dying in our rivers? I believe it has something to do with oxygen, but that raises a whole heap of questions, like why do fish need oxygen, how does this relate to fish physiology, what’s the difference between freshwater and saltwater fish (is all fish physiology basically the same), and is climate change a factor in all this – or rather, how is it a factor?
Jacinta: Okay so that’s a good focussed question, or set of questions, a bit easier to deal with than the management of our river systems, which would involve inter(and intra)-state politics and the rights or wrongs of irrigators, farmers, industry and the like. I’ve heard all that is rather complicated.
Canto: Right, so we’re just going to focus on the internal and external environment of freshwater fish.
Jacinta: Well, maybe. News reports have claimed up to a million fish deaths in the Darling River, with critically endangered Murray cod being among the victims. Algal blooms ‘which can be caused by agricultural chemicals’ (sky news) are being cited as the proximal cause, but the ultimate cause, according to Menindee Lakes residents, is government mismanagement.
Canto: I would wonder whether there are so many fish in the river to begin with – and that million figure is grossly exaggerated according to various sources. The figure appears to be something between 100,000 and 200,000, still a staggering number, and I wonder about the deaths in proportion to the population, and if some species are dying more than others. We need some science here.
Jacinta: And my preliminary enquiries into the science show that it’s complex and unsettled. The most recent mass death occurred in the Menindee Lakes, south of Broken Hill, a series of lakes connected to the Darling. We know that there was very little flow-through at the time, the water levels were low and water temperature had risen. As a result, there was a large bloom of cyanobacteria, aka blue-green algae. But apparently according to an ABC Science report, the cyanobacteria weren’t exactly the problem, it was their death, caused by a cold front, and the sudden explosion of other bacteria feeding on the dead and dying cyanobacteria, and in the process depleting the water of oxygen, that caused the fish to drown.
Canto: So what we call drowning is really loss of oxygen, which fish have evolved to capture from water but we can’t. How do they do that?
Jacinta: Gills. Fish breathe through their mouths like us. And also like us they need oxygen to function and they breathe out carbon dioxide. Gills – and we could expend pages and pages on their origin, structure and function – are those organs found on each side of the pharynx or throat, and they’re made up of protein structures called filaments. Each filament has a tiny network of blood vessels, providing a large surface area for the exchange of gases. So fish suck in water, with its oxygen, and then pump it out through the gills, where all the essential gas exchange occurs. But if the water isn’t sufficiently oxygenated, then it’s goodnight, sweet fish.
Canto: So the proximal cause isn’t the blue-green algae, it’s the oxygen-consuming bacteria that feed on the algae.
Jacinta: But if the algae weren’t there in the first place, the bacteria that feed on them wouldn’t be there.
Canto: Yes, but that’s only because the algae were dying. What if there hadn’t been this sudden drop in water temperature? Do the algae themselves affect the oxygen levels?
Jacinta: Well, actually, very much so. Cyanobacteria were the first photosynthesising organisms – we wouldn’t be here without them, and they’re now incorporated, in the form of chloroplasts, in all the plants around us. They were the principal means of oxygenating the biosphere.
Canto: So does that mean it’s good to have blue-green algae in our waterways? I’m confused.
Jacinta: The answer is yes and no. The Murray Darling Basin Authority (MDBA), currently under fire from all and sundry, have a useful factsheet about what we’ll henceforth call cyanobacteria. They’re a natural part of the system, and there are a number of species, the two most prominent being Dolichospermum and Microcystis. Under certain optimal conditions for growth, they produce ‘blooms’, which can be toxic at high levels. Mostly though, they don’t affect irrigation, recreational use of the river, or drinking water, if properly treated. It’s the decay of these blooms that causes most problems…
Canto: I note that these fish deaths occurred in the Menindee Lakes, and may have been a result of low water levels, which in turn were due to drought. Lower water levels means a lower volume of water, so that the environmental temperature would more rapidly affect the water temperature than if the volume was greater – no doubt there’s an equation to account for that – which would more quickly affect the decay of the bloom and the growth of the oxygen-depleting bacteria feeding on the bloom. So it seems to me that the ultimate cause is drought, which creates a less stable environment for the fish, and other organisms. How’s that?
Jacinta: Well, it’s the beginning of an explanation, but it’s too simple. It isn’t just drought that’s affecting water levels, it’s the fact that water is drawn from the system. And that involves politics, which we were hoping to steer clear of – oh well. By the way, the fish that have died include Murray cod, golden perch, silver perch, and bony herring. I don’t have relative numbers though. The Menindee Lakes region, which is at the centre, not only of this fish death controversy, but of the entire Murray-Darwin Basin management controversy, appears to be at crisis point, and the locals aren’t happy. Here are some quotes from The Guardian on the issue:
Since the 1960s, the original Menindee Lakes have been significantly altered to serve as a major storage for water for the Murray-Darling Basin as well as the water supply for Broken Hill. The lakes are also a major fish breeding area for native fish, and critical to maintaining stocks of fish throughout the river system.
However, the NSW government has proposed shrinking the lakes and altering the way it manages the water storage, in order to reduce evaporation. It is currently building a $500m pipeline from the Murray to Broken Hill in order to provide the inland city with an alternative water supply.
But the plan is highly controversial because it will mean the government has less reason to keep the lakes full and will likely see the Lower Darling run dry more often.
Local graziers and the towns of Wilcannia and Pooncarie are up in arms about the state of the river, accusing the NSW government of sacrificing their 500km stretch of the Darling in order to benefit upstream cotton growers.
They say the current crisis is due to Water NSW’s decision to run the lakes dry despite forecasts of drought.
Canto: The MDBA, which is a federal body, presents their reasons for the fish deaths in two concise points:
- the lack of water flowing into the northern rivers
- the impact of 100 years of over-allocation of precious water resources throughout the entire Basin.
Drought and the removal of water from the system, precisely your point, Jacinta. The MDBA of course avoids blame, and says nothing about possible current over-allocation. It does, however, say, in the same information page, that ‘the Menindee Lakes are currently under the sole control of New South Wales and have been carefully managed since December 2017’, which appears to court some controversy.
Jacinta: And finally, something important to watch out for as we seek an ultimate answer to our question. An independent panel of six science worthies has been appointed by the Federal government to enquire into these deaths. Fields of expertise include catchment hydrology, fluvial geomorphology, freshwater ecology, plant ecotoxicology, aquatic ecosystem health and much much more. The team will provide a preliminary report to the Feds by February 20, and a final report should be completed by March 31. We’ll look out for it – presumably it will be released to the public.