Better to light a candle than curse the darkness: illuminating spatial localization and temporal dynamics of rapid microbial growth in the rhizosphere
- 1Department of Ecology and Evolutionary Biology, University of Connecticut, Storrs, CT, USA
- 2Department of Molecular and Cell Biology, University of Connecticut, Storrs, CT, USA
- 3Marine Biological Laboratory, The Ecosystems Center, Woods Hole, MA, USA
The rhizosphere is a hotbed of microbial activity in ecosystems, fueled by carbon compounds from plant roots. Basic questions about the location and dynamics of plant-spurred microbial growth in the rhizosphere are difficult to answer with standard, destructive soil assays mixing a multitude of microbe-scale microenvironments in a single, often sieved, sample. Soil microbial biosensors designed with the luxCDABE reporter genes fused to a promoter of interest enable continuous imaging of the microbial perception of (and response to) environmental conditions in soil. We used the common soil bacterium Pseudomonas putida KT2440 as host to plasmid pZKH2 containing a fusion between the strong constitutive promoter nptII and luxCDABE (coding for light-emitting proteins) from Vibrio fischeri. Experiments in liquid media demonstrated that high light production by KT2440/pZKH2 was associated with rapid microbial growth supported by high carbon availability. We applied the biosensors in microcosms filled with non-sterile soil in which corn (Zea mays L.), black poplar (Populus nigra L.), or tomato (Solanum lycopersicum L.) was growing. We detected minimal light production from microbiosensors in the bulk soil, but biosensors reported continuously from around roots for as long as six days. For corn, peaks of luminescence were detected 1–4 and 20–35 mm along the root axis behind growing root tips, with the location of maximum light production moving farther back from the tip as root growth rate increased. For poplar, luminescence around mature roots increased and decreased on a coordinated diel rhythm, but was not bright near root tips. For tomato, luminescence was dynamic, but did not exhibit a diel rhythm, appearing in acropetal waves along roots. KT2440/pZKH2 revealed that root tips are not always the only, or even the dominant, hotspots for rhizosphere microbial growth, and carbon availability is highly variable in space and time around roots.
Keywords: rhizosphere, microbiosensor, lux, roots, Pseudomonas, Zea mays, Solanum lycopersicum, Populus nigra
Citation: Herron PM, Gage DJ, Arango Pinedo C, Haider ZK and Cardon ZG (2013) Better to light a candle than curse the darkness: illuminating spatial localization and temporal dynamics of rapid microbial growth in the rhizosphere. Front. Plant Sci. 4:323. doi: 10.3389/fpls.2013.00323
Received: 31 May 2013; Paper pending published: 25 June 2013;
Accepted: 31 July 2013; Published online: 02 September 2013.
Edited by: Boris Rewald
, University of Natural Resources and Life Sciences, Austria
Copyright © 2013 Herron, Gage, Arango Pinedo, Haider and Cardon. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: Zoe G. Cardon, Marine Biological Laboratory, The Ecosystems Center, 7 MBL Street, Woods Hole, MA 02543, USA e-mail: firstname.lastname@example.org
†Present address: Patrick M. Herron, Mystic River Watershed Association, Arlington, MA, USA;
Catalina Arango Pinedo, Biology Department, Saint Joseph's University, Philadelphia, PA, USA;
Zane K. Haider, Department of Orthodontics and Dentofacial Orthopedics, Temple University, Philadelphia, PA, USA