New forms of: Carbon, water and photosynthesis

Somewhat disappointingly, this ‘three for the price of one’ item is not about plants – neither exclusively nor even specifically. However, since it deals with matters that are fundamental to all life on Earth (including those green things!), it is certainly admissible in a plant-based blog item. After all, what can be more basic and essential to plant biology than carbon – the basis of organic molecules that constitute the building blocks of construction of the plant body, water – one of the simplest of molecules but which provides the internal structural support for plant bodies, and photosynthesis – the process that provides the energy that powers the living planet? Indeed, so important are these matters to plants that you might expect we’ve discovered all there is to find out about them. Wrong! So, what’s new?

Well, we are probably all familiar with the notion that a carbon atom can form up to four chemical bonds with other atoms. That tetravalency gives carbon a tremendous ability to form a myriad of molecules with many other atoms and is at the heart of so-called organic chemistry (the chemistry of carbon-containing compounds). From an early age we’ve probably all accepted that upper limit for carbon bonding. However, Moritz Malischewski and Konrad Seppelt have increased that multiple carbonic bonding potential by 50%. Admittedly, the hexamethylbenzene – C₆(CH₃)₆²⁺– they’ve created is an unstable arrangement existing only at low temperatures, in extremely acidic liquids, and which would break down immediately at normal temperatures and humidities. So, the biological textbooks need not be rewritten for this announcement just yet. But, its discovery serves to underline how remarkable carbon is. And, who knows, maybe such hexavalent carbon compounds do remain to be discovered within biological entities? Maybe those textbooks will need to be revised in future.

In similar treasured-time-tested-truth-trouncing mode, Laura Maestro et al. have announced the discovery of a second liquid state of water.* As we’ve been led to believe there are three principal physical states of matter – gas, liquid, and solid, or steam, water, and ice in the specific case of water, H₂O. But, while investigating various physical properties of liquid water the team discovered a cross-over point between 40 and 60 °C (or 50 ± 10°C) for such factors as thermal conductivity, refractive index, surface tension, and http://whatis.techtarget.com/definition/dielectric-constant“>dielectric constant. For which their explanation is the existence of two different states within liquid water. Amongst the potential biological consequences of this (remember, water is a fantastically important molecule in biology) is the existence of different hydration shells around macromolecules such as proteins above, and below a crossover temperature of 60 °C. However, since most organisms live at temperatures well below 60 or even 50 °C, the second liquid state of water may have limited biological relevance. But, it may be an important factor in the biology of those extremophile organisms, specifically thermophiles, that live in high temperature environments such as sub-sea hydrothermal vents or land-based geothermal springs.

Finally, mention of a new type of photosynthesis – a process that in its more usual form uses both water and an oxide of carbon as substrates, and which thereby unites both of the preceding discoveries in this news item. This so-styled ‘cooperative photosynthesis’ ** involves Prosthecochloris aestaurii (a green sulphur bacterium that uses sulphide and elemental sulphur – instead of water – as electron donors in the process of anoxygenic (i.e. non-oxygen-producing)) photosynthesis and Geobacter sulfurreducens (a non-photosynthesising, heterotrophic bacterium). Investigating these two microbes, Phuc Ha et al. found that electrons produced by G. sulfurreducens during its metabolism could be transferred to, and used by, P. aestaurii, in place of the latter’s more usual electron sources in photosynthesis. The result of this microbial co-operation is a new type of ananaerobic photosynthesis. The ability of Geobacter to transfer electrons has already been exploited to generate electricity, which has applications in microbial fuel cells. The potential for the two microbes to work in co-operation in this way in nature is seen as an opportunity that could be exploited for biotechnological applications, such as waste treatment and bioenergy production.

So, there you have it, a trio of new discoveries relating to some of the most basic of biological molecules or processes. What next..?

* This is in addition to a new state of water found when it occupies nanochannels within the semi-precious mineral beryl… Coincidentally, water in this ‘semi-precious’ state is a 6-sided molecule: 6-sided water, 6 carbon bonds, is Nature trying to tell us something about the number 6?

** Or, and rather more technically – if much less user-friendly(!) – syntrophic anaerobic photosynthesis.