Carbon turnover in cell compartments and microbial groups in soil

. Microorganisms regulate the carbon (C) cycle in soil, controlling the utilization and recycling of organic substances. To reveal the contribution of particular microbial groups to C utilization and C turnover within the microbial cells, fate of 13C-labeled glucose was studied under field conditions. The 13C was traced in cytosolic substances, amino sugars and phospholipid fatty acids (PLFA) at intervals of 3, 10 and 50 days after glucose addition. 13C enrichment into PLFA (~1.5 % of PLFA C at day 3) was one order of magnitude greater than into the cytosol, showing the importance of cell membranes for initial C utilization. 13C enrichment of amino sugars in living microorganisms at day 3 accounted for 0.57 %, resulting that the turnover of cell wall components is two times slower than that of cell membranes. Turnover time of C in the cytosol (150 days) was three times longer than in PLFAs (47 days). Consequently, despite the lability of cytosol pool and expected fast turnover rates, intensive recycling of cytosol components, within the living cells, leads to a longer turnover time. Amino sugars originate mainly from microbial residues, thus longer experimental periods are required for estimation of their turnover times. Both PLFA and amino sugar profiles indicated that glucose C was preferentially used by bacteria. The 13C incorporated into bacterial cell membrane components decreased with time, but it remained constant or even increased for filamentous microorganisms. Hence, over a short period, bacteria contribute more to the utilization of low molecular weight organic substances, whereas filamentous microorganisms are responsible for further C transformations. Thus, tracing 13C in cellular compounds with contrasting turnover rates elucidated the role of microbial groups and their cellular compartments in C utilization and recycling in soil. This information is especially important for assessing C fluxes in soil and the contribution of C from microbial residues to soil organic matter.