I wanted to follow up the piece last week about the oil spill and potential benefits to bacterial populations there to another bacterium that may have a larger role in the normal functioning of our environment then previously suggested. Still, I promise to include a disease this week though.
Researchers have been looking at ice nucleation particles and have been finding bacteria such as Pseudomonas syringae wherever they look. The standard model of snow and rain formation is that soot, dust, fine pollen and other small inert particles can act as ‘nuclei’ for water condensation. Following the condensation it can act as a catalyst for more condensation. Higher up in the atmosphere, where it’s a little colder these nucleation points can allow the formation of ice crystals and eventually snowflakes.
After finding P. syringae in clouds streams and irrigation ditches from Montana to France, the Yukon and ice of Antarctica it seemed like something was afoot. Some researchers including Dr. Sands from Montana State University was able to show that if the samples were digested with lysozyme (an enzyme that breaks down bacterial cell walls) greatly reduced or completely eliminated ice nucleation.
Further work showed that 69 to 100% nucleation points larger than 0.2 micrometer that were active at temperatures warmer than -7°C were biological. The proportion of bacteria in each sample varied but still made up a significant portion of each samples nucleation points.
This is all very fascinating but it always comes back to one question. Why do we care?
Well, here’s the disease bit. P. syringae is a major plant pathogen. Its related to other Pseudomonas species such as P. aeruginosa a pretty full-on human pathogen that can cause pneumonia, septic shock, infections of the urinary or gastrointestinal tract, and skin and soft tissue infections. Its particularly nasty for burns patients, but that’s another post.
P. syringae infects plants primarily by finding pores on the undersides of leaves called stomata. They can force these pores open (they naturally close in the presence of bacteria) and proceed to inject a range of ‘effectors’ that shut down plant defenses and alter plant cell activity.
As with all pathogens they are often limited by their ability to effectively spread and this is where we come back to the atmospheric water nucleation. Bacteria, more so than other nucleation centres, seem to be able to promote nucleation of water at higher temperatures allowing rain to form more readily.
It’s now been postulated (I love using that word) that the bacteria might form part of an unstudied weather determination pattern by promoting rainfall. The promotion of rainfall is thought to be a deliberate ‘ploy’ of the bacteria’s to facilitate wide spreading. As the bacteria gains access to the plant via the leaves it’s not inconceivable that the bacteria could be swept up into the atmosphere and rained down onto new plants using the leaves as a platform to both launch and landing.
This is why I like bacteria. For all the disease and horrible stuff they do they recycle our elements for passage back up the food chain, provide the tools to attack pathogenic bacteria, provide us with all sorts of other medical compounds and now bring the rain as well. They are Awesome with a capital ‘a’, even your mum thinks so.
ELAZARI-VOLCANI, B. (1943). Bacteria in the Bottom Sediments of the Dead Sea Nature, 152 (3853), 274-275 DOI: 10.1038/152274c0
Zhang, L., Wang, M., Prosser, J., Zheng, Y., & He, J. (2009). Altitude ammonia-oxidizing bacteria and archaea in soils of Mount Everest FEMS Microbiology Ecology, 70 (2), 208-217 DOI: 10.1111/j.1574-6941.2009.00775.x
Morris, C., Sands, D., Vinatzer, B., Glaux, C., Guilbaud, C., Buffière, A., Yan, S., Dominguez, H., & Thompson, B. (2008). The life history of the plant pathogen Pseudomonas syringae is linked to the water cycle The ISME Journal, 2 (3), 321-334 DOI: 10.1038/ismej.2007.113
Christner, B., Morris, C., Foreman, C., Cai, R., & Sands, D. (2008). Ubiquity of Biological Ice Nucleators in Snowfall Science, 319 (5867), 1214-1214 DOI: 10.1126/science.1149757
Christner, B., Cai, R., Morris, C., McCarter, K., Foreman, C., Skidmore, M., Montross, S., & Sands, D. (2008). Geographic, seasonal, and precipitation chemistry influence on the abundance and activity of biological ice nucleators in rain and snow Proceedings of the National Academy of Sciences, 105 (48), 18854-18859 DOI: 10.1073/pnas.0809816105