Microbial Biosynthesis and Energy Metabolism in Soils: New Insights from Position-Specific Metabolic Modeling and Next Generation Sequencing.

It has long been postulated that metabolism of microbes in soil is inefficient (low C use efficiency, CUE). A low CUE indicates that cells use the limited available substrate for cell maintenance mostly, with little to spare for cell growth. Early work on soil microbes indicated that the amount of substrate available for microbes was lower than what was needed to maintain cell integrity. Therefore it was concluded that cell division in soil is rare and maintenance energy demand is high.

Over the last decades, new tools have been developed that allow us to monitor microbial metabolism and population dynamics in intact soil communities directly. These tools often find results that seem contradictory to the above mentioned paradigm. For example, work with position specific ¹³C labeled metabolic tracers indicates that microbes function with high biochemical efficiency. Moreover labeling of DNA with ¹⁸O-water reveals growth and death dynamics of whole communities and individual taxa, and their response to substrate additions. I will discuss some of the results and interpretations and what we can do in the future.

There is no doubt that microbes in soil experience stress, whether it is high and low temperatures, or when small resources deplete locally. However, our knowledge of how microbes respond to stress in intact communities is still underdeveloped. I will discuss new efforts to understand microbial stress responses in soil microbes and relate it to overall soil C and nutrient cycling.