NDLI: Assessing the Role of Pseudomonas aeruginosa Surface-Active Gene Expression in Hexadecane Biodegradation in Sand

Content Provider	PubMed Central
Author	Holden, P. A. Lamontagne, M. G. Bruce, A. K. Miller, W. G. Lindow, S. E.
Copyright Year	2002
Abstract	Low pollutant substrate bioavailability limits hydrocarbon biodegradation in soils. Bacterially produced surface-active compounds, such as rhamnolipid biosurfactant and the PA bioemulsifying protein produced by Pseudomonas aeruginosa, can improve bioavailability and biodegradation in liquid culture, but their production and roles in soils are unknown. In this study, we asked if the genes for surface-active compounds are expressed in unsaturated porous media contaminated with hexadecane. Furthermore, if expression does occur, is biodegradation enhanced? To detect expression of genes for surface-active compounds, we fused the gfp reporter gene either to the promoter region of pra, which encodes for the emulsifying PA protein, or to the promoter of the transcriptional activator rhlR. We assessed green fluorescent protein (GFP) production conferred by these gene fusions in P. aeruginosa PG201. GFP was produced in sand culture, indicating that the rhlR and pra genes are both transcribed in unsaturated porous media. Confocal laser scanning microscopy of liquid drops revealed that gfp expression was localized at the hexadecane-water interface. Wild-type PG201 and its mutants that are deficient in either PA protein, rhamnolipid synthesis, or both were studied to determine if the genetic potential to make surface-active compounds confers an advantage to P. aeruginosa biodegrading hexadecane in sand. Hexadecane depletion rates and carbon utilization efficiency in sand culture were the same for wild-type and mutant strains, i.e., whether PG201 was proficient or deficient in surfactant or emulsifier production. Environmental scanning electron microscopy revealed that colonization of sand grains was sparse, with cells in small monolayer clusters instead of multilayered biofilms. Our findings suggest that P. aeruginosa likely produces surface-active compounds in sand culture. However, the ability to produce surface-active compounds did not enhance biodegradation in sand culture because well-distributed cells and well-distributed hexadecane favored direct contact to hexadecane for most cells. In contrast, surface-active compounds enable bacteria in liquid culture to adhere to the hexadecane-water interface when they otherwise would not, and thus production of surface-active compounds is an advantage for hexadecane biodegradation in well-dispersed liquid systems.
Related Links	http://dx.doi.org/10.1128/aem.68.5.2509-2518.2002
Ending Page	2518
Page Count	10
Starting Page	2509
File Format	PDF
ISSN	00992240
e-ISSN	10985336
Journal	Applied and Environmental Microbiology
Issue Number	5
Volume Number	68
Language	English
Publisher	American Society for Microbiology
Publisher Date	2002-05-01
Access Restriction	Open
Rights Holder	American Society for Microbiology
Subject Keyword	Biotechnology Food Science Ecology Applied Microbiology and Biotechnology Research in Higher Education
Content Type	Text
Resource Type	Article
Subject	Ecology Food Science Applied Microbiology and Biotechnology Biotechnology

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