I am constantly amazed at the importance of microbiology and the places that it crops up as being useful and necessary in our environments, soils and also our own digestive system. I feel it has been somewhat overlooked and greatly underestimated in its importance, and to the detriment of our own health and the health of our land and its capital value. I’d like to share with you another way in which it impacts our environments – of which you may not be aware. It relates to rain, something we know is ever important to us as farmers.
It seems that rainfall production is a little more complicated than what I learnt in year 10 geography. What I didn’t learn at school is that each raindrop needs a nucleus around which to form. These nuclei come in the form of atmospheric dust, soot, or pollen, but can also be microbial in nature – bacterial, fungal or algal. In the atmosphere, water will either condense around these nuclei (to form clouds – cloud condensation nuclei), or freeze around them, to form rain (ice nucleators).1 This is how many raindrops begin – as ice crystals, which melt as they fall to form rain or they remain frozen to fall as snow.2
The advantage of the microbial ice nucleators over dust or soot is that they allow the freezing and formation of ice crystals, at much warmer temperatures than what dust or soot allow. So, fungal, bacterial and algal microorganisms are considered superior ice nucleators – or ‘raindrop formers’, and it is the bacterial microbes that are most studied in this regard. It is only a small percentage of bacteria that have the appropriate structure to be ice nucleators. Pseudomonas Syringae is one such strain identified, that is present in many different climatic environments.
Ice nucleating bacteria in the atmosphere are part of a cycle, as proposed by Professor David Sands of Montana University. The bacteria live in little groups on the surface of plants – trees, grasses and shrubs. The bacteria make it into the atmosphere with the wind, where they go through the rain forming process described above and fall back to earth as the nuclei of raindrops, where they can land on plants, multiply and repeat this cycle again.3 This cycle ‘might incite feedback processes that are beneficial to their proliferation’,5 which is another positive of bacterial ice nuclei over dust or soot.
Can we influence rain?
So, having had my attention brought to this process by a truly holistic thinking friend of mine, it made me think, ‘Can microbial rich farming environments actually help to bring rain’? And this is exactly what a group of scientists across the globe are investigating.
Can specific crops or plant species be grown with the intention of seeding clouds with the bacteria that are supported on their leaves?
The short answer is that there is much work to be done in this area, but ‘land use practices appear to influence the flux of biological ice nuclei to the atmosphere’.4 It has been suggested that ‘a reduced amount of bacteria on crops could affect the climate and overgrazing in a dry year could actually decrease rainfall, which could then make the next year even dryer’.3
‘Different crop cultivars and plant species in general are very different in terms of the abundance of microbial ice nucleators that they harbor.’5 Even one wheat plant to the next can host a difference of up to 1000 times the number of bacteria. Why the difference within the same variety and species? Plant growth occurs mainly through the expansion of old cells, rather than the growth of new cells. When old cells expand they ‘leak’ plant sugars, which is what the bacteria feed on. Different plants may ‘leak’ different amounts of sugars, which may explain the differences in bacterial hosting. It raises the question as to what could be inadvertently selected for or against in crop breeding programmes that are not being monitored for in the breeding process, which could affect natural plant immunity, among other things.
How can we use this knowledge of ice nucleating microbes?
As you might assume, this knowledge is a way off creating rain for us next week! There are some suggestions however, as to how this information might be useful in the future.
One suggestion is the possibility of inoculating crop planting seed with non-disease forming bacteria that are prolific ice nucleators. While this most likely wouldn’t benefit that farmer with rain – it may benefit others 50km downwind and may generally increase the amount of ice nuclei in the environment.
As a side – it is also suggested that plant leaves have protecting microbial coatings on their leaves – protecting them from disease attack. These bacteria may produce a natural fungicide that protects the plant from fungal diseases – such as stripe rust. Identifying bacteria that have such functions – that are also effective ice nuclei may encourage farmers to inoculate their crop for the benefit of their own crops and for the greater good of the influences on rainfall.
Then there is the question of whether the biology of the soil may impact the amount of rain-producing microbial ice nuclei as an addition to the bacteria of plant leaves. Gabor Vali from the University of Wyoming says that ‘organic rich soils are enriched with ice nucleators’4, so it’s possible that there are links.
As I indicated, there is much needing to be done to prove the likely success of some of the proposed applications for the knowledge in this area. There are large gaps in understanding, however I write about this to demonstrate the importance of a holistic view to farming, health and life. When we interfere with nature, we may be having much wider spread impacts than we could have ever imagined.
Professor David Sands who I spoke to in understanding ice nucleation said that last century was the century of physics and chemistry, and this will be the biological century and I tend to agree.
References
Cloud photograph thanks to Glenn Morris of Fig Trees Organic Farms – Inverell, NSW, who introduced me to the idea of microbiology’s influence on rainfall.
- Cloud nucleation. www.weforest.org/clouds 28th Feb 2015
- The Bacteria that make it rain. (2006) http://inspiringscience.net/2012/09/24the-bacteria-that-make-it-rain/ Inspiring Science. 26th Feb 2015
- Pettinger, A. (2008) MSU Professor’s research on bacteria’s role in precipitation cycle published by “Science”. http://www.montana.edu/news/5659/msu-professor-s-research-on-bacteria-s-role-in-precipitation-cycle-published-by-science
- Christner, Brent. Cloudy with a chance of microbes. Terrestrial microbes swept into clouds can catalyze the freezing of water and may influence precipitation on a global scale. Microbe Magazine. http://www.microbemagazine.org/index.php?option=com_content&view=article&id=4400:cloudy-with-a-chance-of-microbes&catid=928:07-2011-features&Itemid=1195
- Morris, CE; Sands, DC. 2012, From Grains to Rain: the link between landscape, airborne microorganisms and climate processes, e-book, accessed 28th Feb 2015, http://bioice.wordpress.com/.