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Knowing where you are helps getting you to where you need to be. Consider being dumped into an environment of which you had no prior knowledge. Add to this the fact that you are blind, and react to surfaces, electrical fields, gas concentrations and temperature. You also know what is up and what is down, so you are aware of gravity, which is good as you are spending your life underground. Also, most of the time you need to move in water, and your life cycle is at best a couple of days at optimum temperature, and the temperature is rarely optimal. Now, find your way to a food source and avoid obstacles and predators. What strategy would you adopt to keep yourself alive and functional? This scenario roughly summarizes the challenges facing archaea, bacteria, protozoa, nematodes and, to a lesser extent, fungi in soil systems. These organisms control to a great extent our ability to utilize the Earth as a resource: growing food, clean water, etc. These organisms reside and are active in a dark, dank, complex physical environment that exhibits extreme changes in moisture, temperature and architecture over very short spatial and temporal scales. Thus, they have evolved perhaps unrivalled abilities to adapt rapidly to constantly changing environmental conditions. Alexander et al. (2006), in a summary of energy taxis in microorganisms, highlight the fact that genome sequencing of marine and soil microbes has shown that they possess large numbers of chemoreceptors, whereas microbes in environments that experience relatively constant environmental conditions are more likely to have significantly fewer chemoreceptors. The question is: How do they sense and respond to these conditions in soil? |
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