Metabolite Analysis of Soils and Soil Microorganisms in Response to Water Stress.

Natural swings in water potential impose significant physiological challenges to soil microorganisms. To adapt to changes in water availability, it is known that many microorganisms alter the chemistry and concentration of their cytoplasmic contents. Yet, there have been no studies to assess whether the phenomenon measured in laboratory studies using salt induced water stress are consistent with how microorganisms cope in oligotrophic and drought prone ecosystems, such as soil. To better understand the insitu response of microorganisms to drying and re-wetting fluctuations that are reminiscent of water dynamics in soil ecosystems we have conducted laboratory experiments and analyzed the metabolites from the soil microbial pool. The ultimate goal of the research is to understand how the microbial biomass and their cytoplasm changes in response to wetting and drying. Our current objectives are to characterize intracellular and extracellular metabolites 1) in moist 2) dried and 2) salt stressed soils.  The 0.01 M K₂SO₄ extracts from these soils were analyzed for sugars and amino acids-like compounds using phenol sulphuric acid and ninhydrin methods, respectively. The extracts obtained from multiple extraction methods showed much higher concentrations of sugars (250-300 µg g^-1 of soil) than amino acids (1-7 µg N g^-1 of soil). Dried soils contained ~20% more sugar than the moist samples. The IR spectroscopy also noted the presence of sugars and proteins/amino acids in the extracts. Conversion of the extracts into TMS and TBDMS derivatives and analysis on GC-MS, detected the presence of sugars but no amino acids. Identified sugars include glucose, galactose, inositol, fructose, and sugar alcohols (e.g glucitol and xylitol). Quantitative characterization of the sugars and unidentified GC-MS peaks in the dried and continuously-moist samples may reveal metabolites that are useful for microbial adaptation to water stress in soil.