Why growing with Microbes gives us organic growers a evolutionary advantage over synthetics, until now, largely lost to the indoor grower
Bacterial Quorum Sensing as a Control Point in Rhizosphere Nitrogen Transformations
K. M. DeAngelis, M. K. Firestone, S. E. Lindow;
University of California, Berkeley, CA.
Rhizosphere bacteria play an important role in the soil N cycle and plant N nutrition through the release of extracellular enzymes. Temperate terrestrial plants are generally N-limited because most soil N is organic: chitin, proteins, lignoproteins and nucleotides. These compounds require digestion by microbial exoenzymes, likely the rate-limiting step in N mineralization. Proteobacteria in particular dominate rhizosphere bacterial communities, suggesting their importance in soil community enzyme activity. There is also evidence of specific interactions between soil bacteria and plants via quorum sensing (QS): root exudates of many plant species can disrupt bacterial QS and impact QS-controlled behaviors, like exoenzyme production. We hypothesize that (1) bacterial QS is an important control point in rhizosphere N mineralization, and that (2) density-dependent responses by specific populations are primarily responsible for much of the conversion of organic N to inorganic, mineralized N. We have examined bacterial communities in microcosms grown with Avena barbata, and our results so far are (a) Gross rates of N mineralization using 15N pool dilution were affected by addition of acyl-homoserine lactone (AHL) signals to bulk soil. (b) Chitinase and protease specific activity was significantly higher in the rhizosphere compared to bulk soil. (c) A whole-cell biosensor that responds sensitively to a broad range of AHL signals detected more QS signal in the rhizosphere compared to bulk soil. (d) Isolation of chitin- and protein- degrading bacteria from Avena rhizosphere soil reveals that 65% of isolates (347 of 533) did not survive pasteurization, 39% of those had either exo-protease or exo-chitinase activity (136 of 347), and 20 of the exoenzyme active isolates (111) produced AHL detected by the biosensor. While QS appears to play a role in rhizosphere N cycling and plant N nutrition, though the interactions are more complex than originally hypothesized. The biosensor reflects the increased cell numbers and activity observed in the rhizosphere. Our data indicate that signaling plays a major role in the soil N cycle.
Those of you wishing to read more reach out we have the full paper :)
Eco
