Ref ID : 7184
V.V.S.R. Gupta and J.J. Germida; Influence of Bacterial-Amoebal Interactions on Sulfur Transformations in Soil. Soil Biol.Biochem. 21(7):921-930, 1989
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Protozoa enhance the mineralization of nutrients immobilized in the microbial biomass (MB) by consuming bacteria and excreting excess nutrients. The influence of bacterial-amoebal interactions on the mineralization of biomass sulfur was investigated in microcosms. Two sterilized Dark Brown Chernozemic soils were amended with bacteria (Arthrobacter globiformis or Enterobacter aerogenes) or bacteria and amoebae (soil isolate) and held at ~25 degrees C. Respiratory activities were greater in grazed compared to ungrazed microcosms. In ungrazed microcosms, bacterial populations reached a stationary phase (>10E9 g soil-1) between days 7 and 10 and remained at this level. A significant negative correlation (R=-0.66, P < /_0.01) was observed between microbial biomass sulfur (MB-S) and extractable SO4(=) in soil. Amoebal grazing significantly reduced bacterial populations (and thus MB-S) and predatory activity peaked between days 10 and 17. A significant positive correlation (R=0.54, P < /_0.01) between respiration and MB-S on day 7 shifted to a negative correlation (R=-0.86, P < /_0.01) by the time of maximum predatory activity (day 17). A significant increase (P < /_0.01) in extractable SO4(=) concentrations between days 10 and 17 coincided with a significant decline (P < /_0.01) in arylsulfatase activity. Amoebal activity was greater in coarse-textured soil. Our results demonstrate the importance of MB-S as a sink and source for SO4(=)-S in soil, and that microbial interactions such as amoebal grazing enhance the biological and biochemical mineralization of MB-S.