Cyanobacteria: Good week, or bad week..? Part IV

This is the last of our quartet of blog posts looking at the newsworthy world of the blue-greens, and looks at those organisms from a different viewpoint…

Cyanobacteria lighting the way for fossil fuel alternatives

In an environment where light levels are reduced by atmospheric pollution blocking out the sun – such as the situation inferred in the immediate aftermath of the Chicxulub asteroid impact (Kunio Kaiho et al., 2016; Charles Bardeen et al., 2017), and which persisted for several years thereafter – the ability of photosynthetic organisms to use as wide a range of solar wavelengths as an energy source is useful, and offers a clear ecological advantage to such organisms. Sunlight-driven photosynthesis is largely powered by wavelengths of light between 400 and 700 nm (PAR – photosynthetically-active radiation), which is captured by a range of pigments such as chlorophylls and accessory pigments.

However, and in addition to Chlorophyll a (the ultimate sunlight energy-capturing pigment of oxygenic photosynthesis), some cyanobacteria contain Chlorophyll f (Suleyman Allakhverdiev et al., 2016). This pigment absorbs in the range of 700–760 nm (Dennis Nürnberg et al., 2018; Michael Kühl et al., 2020), i.e. well beyond the historically presumed ‘red limit of’ 700 nm*. The ability to harvest sunlight energy extended into the infra-red (IR) region is clearly of benefit to those cyanobacteria. It’s also of relevance to other organisms with interests in trapping energy for purposes other than photosynthesis and food production. And so it is that this bit of blue-green biology has not escaped the interests of those who are looking at alternative – and ideally renewable – sources of energy to non-renewable fossil fuels.

In that regard biological insights from work of Koji Kato et al. (2020) into the structural basis for the adaptation and function of chlorophyll f in photosystem I in the cyanobacterium Halomicronema hongdechloris is of interest to those engaged in solar panel technology. Why? Well, according to Prof. Tatsuya Tomo – one of the study’s authors, “About half of the solar energy that falls on the earth is visible light, and the other half is infrared light. Our research puts forth a mechanism that can use light on the lower energy spectrum, which has never been seen before. Our findings show how to improve the efficiency of energy transfer in photosynthesis and, by extension, also provide important insights into artificial photosynthesis.” Although solar panels don’t undergo artificial photosynthesis, they do mimic photosynthesis in capturing sunlight energy (which is subsequently converted into electricity rather than ‘chemical energy’ locked up within inter-atomic bonds in carbohydrates, as in photosynthesis). If solar panels can be engineered to absorb a greater range of solar radiation than at present – maybe using insights from red-shifted cyanophyte Chlorophyll f biology – they can provide more energy for human uses, and hopefully reduce our (over-)reliance on polluting fossil fuels.

And there we have it, rather sadly, this news item underlines the real reason why humans are interested in plants – including honorary plants such as cyanobacteria – and their biology, to see what they can do for us, and how their remarkable abilities can be exploited by and for the benefit of Mankind.

Time to decide: Reviewing this and the preceding three posts [Parts I, II, and III – Botany One URLs to add], has it been a good week or a bad week for cyanobacteria? Well, it all depends on your point of view, whether as a ‘good’ cyanophyte, a ‘bad’ ‘un, a grateful-to-have-survived-an-end-of-the-world-scenario blue-green, or a human being concerned about the state of the planet and its dwindling energy reserves… [Ed. – you didn’t expect a straight answer from Mr Cuttings, did you?]

* Whether that was a factor in helping the early colonisation of the Chicxulub impact site by those intrepid, pioneering cyanobacteria is not known (see Part III). For more on Chlorophyll f and the ‘red limit’, see this Botany One post.