Open AccessBacterial quorum sensing and nitrogen cycling in rhizosphere soil
Author(s) -
DeAngelis Kristen M.,
Lindow Steven E.,
Firestone Mary K.
Publication year - 2008
Publication title -
fems microbiology ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.377
H-Index - 155
eISSN - 1574-6941
pISSN - 0168-6496
DOI - 10.1111/j.1574-6941.2008.00550.x
Subject(s) - rhizosphere , biology , bulk soil , mineralization (soil science) , chitinase , nitrogen cycle , soil microbiology , botany , biochemistry , bacteria , nitrogen , enzyme , soil water , chemistry , ecology , genetics , organic chemistry
Plant photosynthate fuels carbon‐limited microbial growth and activity, resulting in increased rhizosphere nitrogen (N) mineralization. Most soil organic nitrogen is macromolecular (chitin, protein, nucleotides); enzymatic depolymerization is likely rate limiting for plant nitrogen accumulation. Analyzing Avena (wild oat) planted in microcosms containing sieved field soil, we observed increased rhizosphere chitinase and protease‐specific activities, bacterial cell densities, and dissolved organic nitrogen (DON) compared with bulk soil. Low‐molecular‐weight (MW) DON (<3000 Da) was undetectable in bulk soil but comprised 15% of rhizosphere DON. Extracellular enzyme production in many bacteria requires quorum sensing (QS), cell‐density‐dependent group behavior. Because proteobacteria are considered major rhizosphere colonizers, we assayed the proteobacterial QS signals N ‐acyl‐homoserine lactones (AHLs), which were significantly increased in the rhizosphere. To investigate the linkage between soil signaling and nitrogen cycling, we characterized 533 bacterial isolates from Avena rhizosphere: 24% had chitinase or protease activity and AHL production; disruption of QS in seven of eight isolates disrupted enzyme activity. Many Alphaproteobacteria were newly found with QS‐controlled extracellular enzyme activity. Enhanced specific activities of nitrogen‐cycling enzymes accompanied by bacterial density‐dependent behaviors in rhizosphere soil gives rise to the hypothesis that QS could be a control point in the complex process of rhizosphere nitrogen mineralization.