Abstract
Soil microbial activity controls the decomposition of organic material and ultimately the recycling of key nutrients up into higher trophic levels. The availability of water and energy (carbon) in soils are critical determinants of this activity. Yet soils are biologically and structurally complex systems that present significant technical hurdles to studying these processes. We have applied novel methodologies in three experiments to understand soil microbial activity at the intersections of water availability, root activity, and carbon availability. In the first experiment, we injected isotopically-labeled acetic acid vapor into soils to test whether water availability influenced microbial growth efficiency (MGE). MGE is the efficiency with which microbes build biomass from assimilated carbon and fundamentally binds together the immobilization and availability of carbon and nitrogen in soil. Interestingly, microbial growth efficiencies in our test cores, determined using 13C-acetic acid gaseous injections, did not vary in soil ranging from 9.7% to 20.7% soil moisture; they hovered around 47%. To study how roots were influencing processes, we applied microbial biosensors to study patterns of water and carbon availability in the rhizosphere. Microbial biosensors were tested extensively in liquid cultures that demonstrated their ability to produce reliable reports in nonsterile soils. The biosensor, Pantoea agglomerans BRT98 hosted a reporter system consisting of a proU-GFP construct that responded to variation in water potential (a function of both osmotic and matric potentials) in nonsterile soil. The proU-GFP microbiosensor reported more negative soil water potentials as a function of axial distance from tips of Zea mays L. roots, reflecting the gradient in water potential hypothesized to develop during transpiration. The second biosensor used the common soil bacterium Pseudomonas putida KT2440 as host to a plasmid we developed to report on energy availability in the rhizosphere. Plasmid pZKH2 contains a fusion between the strong constitutive promoter nptII and the genes that enocode for a light-emitting reaction, luxCDABE, from Vibrio fischeri. Biosensor KT2440/pZKH2 was able to continuously report on carbon availability around plant roots for as long as six days. ^
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Claims 6
Claim · model-written summary
Microbial growth efficiencies did not vary across 9.7% to 20.7% soil moisture and remained around 47%.
- Outcome
- microbial growth efficienciese0
- Direction
- did not varye0
- Value
- 47%e0
- Qualifier
- 9.7% to 20.7% soil moisturee0
Not reportedTaxon
Verbatim
e0“Interestingly, microbial growth efficiencies in our test cores, determined using 13C-acetic acid gaseous injections, did not vary in soil ranging from 9.7% to 20.7% soil moisture; they hovered around 47%.”
Claim · model-written summary
Liquid-culture testing demonstrated reliable biosensor reporting in nonsterile soils.
Not reportedTaxonComparator
Verbatim
e0“Microbial biosensors were tested extensively in liquid cultures that demonstrated their ability to produce reliable reports in nonsterile soils.”
Claim · model-written summary
The Pantoea agglomerans BRT98 proU-GFP reporter responded to water-potential variation in nonsterile soil.
- Taxon
- Pantoea agglomerans BRT98
Pantoea agglomeranse0 - Gene
- proU-GFPe0
- Outcome
- responded to variation in water potentiale0
- Setting
- nonsterile soile0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The biosensor, Pantoea agglomerans BRT98 hosted a reporter system consisting of a proU-GFP construct that responded to variation in water potential (a function of both osmotic and matric potentials) in nonsterile soil.”
Claim · model-written summary
The proU-GFP sensor reported increasingly negative soil water potentials with axial distance from maize root tips.
- Organ / stage
- rootse0
- Outcome
- soil water potentialse0
- Direction
- more negativee0
- Qualifier
- axial distance from tipse0
Zea maysOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The proU-GFP microbiosensor reported more negative soil water potentials as a function of axial distance from tips of Zea mays L. roots, reflecting the gradient in water potential hypothesized to develop during transpiration.”
Claim · model-written summary
The developed pZKH2 plasmid fuses nptII with Vibrio fischeri luxCDABE genes.
- Taxon
- Vibrio fischeri
Aliivibrio fischerie0 - Gene
- luxCDABEe0
- Outcome
- fusione0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Plasmid pZKH2 contains a fusion between the strong constitutive promoter nptII and the genes that enocode for a light-emitting reaction, luxCDABE, from Vibrio fischeri.”
Claim · model-written summary
KT2440/pZKH2 continuously reported carbon availability around plant roots for up to six days.
- Taxon
- Pseudomonas putida KT2440
Pseudomonas putida KT2440e1 - Organ / stage
- plant rootse0
- Outcome
- carbon availabilitye0
- Value
- six dayse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Biosensor KT2440/pZKH2 was able to continuously report on carbon availability around plant roots for as long as six days.”
e1“The second biosensor used the common soil bacterium Pseudomonas putida KT2440 as host to a plasmid we developed to report on energy availability in the rhizosphere.”