I have a blog post that I have been trying to write for weeks about the soil and rhizosphere. Until I can get a handle on it, here is a little image I did today to illustrate how cells initiate colonization of plant root surface. An example bacterial species would be Azospirillum brasilense, a personal favorite.
As humans, we are contributing to global warming every time we breathe. Luckily, this contribution doesn’t amount to a hill of beans. The amount of carbon dioxide we excrete while breathing is easily converted to other molecules by other organisms on Earth. We, as humans, number roughly 7 billion. That is a lot of carbon dioxide. However, we are outnumbered by plants and trees by several orders of magnitude that consume this carbon dioxide and convert it back to the oxygen we so desperately need and make carbohydrates in the process.
Now, think about this: 7 billion humans converted to microbes living in the soil would amount to a pinch of soil. As you should know, there is much more than a pinch of soil on the planet, and that does not take into account the waters of Earth. So, doesn’t it make sense that what these microbes take in and “breathe” out has a much much greater impact on the composition of our atmosphere? Luckily, microbes, in the general sense, don’t breathe carbon dioxide under most conditions and some microbes like algae consume carbon dioxide like plants and give us oxygen in return.
The figure above shows how simplistic plants and animals are compared to prokaryotes in regards to what we all “breathe”. This is not an exhaustive list of molecules microbes use; it’s just one small group of bacteria from the genus Geobacter. This complexity helps put things in perspective.
My Tiny Highlight (MyTH) has been on hiedas for a while. However, I’m glad to introduce this week’s organism, Pseudomonas fluorescens. This will be the second highlight featuring a Pseudomonad (Week 5). For short hand, I will write the name Pfu. This is an interesting organism due to its effects on plants and other soil organisms. Pfu is a major constituent of the rhizosphere of plants. The rhizosphere is an active zone surrounding plant roots where soil microbes interact with the roots and each other usually in a symbiotic relationship. This is certainly the case for Pfu due to the benefits this microbe bestows upon host plants. First, Pfu produces many secondary metabolites that are probiotic for plants and can control bacterial and fungal plant pathogens. A major class of secondary metabolites produced are derivatives of phenol that display antifungal properties including 2,4-Diacetylphloroglucinol, phloroglucinol, and phloroglucinol carboxylic acid. Secondly, Pfu also produces a type of antibiotics from phenazine that can be beneficial to both plant and microbe. Third, Pfu produces siderophores than can scavenge essential iron from the environment with very high affinity giving Pfu an advantage against other soil inhabitants that are less efficient at acquiring elemental iron. Siderophores are produced within the cell and excreted into the surrounding environment. Pfu contains outer membrane receptors that can transport iron-containing siderophores back into the cell. One specific siderophore, pyoverdin, has green fluorescent properties which give P. fluorescens its name.
In a later post, I will detail more about the rhizosphere and soil in general.