Plant-microbe communication - the stimulation of bacterial sulfatases
The roots of all crop plants are surrounded by a myriad of other organisms, including bacteria, fungi, protozoa and invertebrates. This community plays a crucial role in maintaining soil health and promoting plant growth, and many of the microbes are particularly important in processes such as fixing atmospheric nitrogen for plant nutrition, or mobilizing nutrients such as P or S, which are commonly bound in the soil and not directly available to plants. Understanding which members of the rhizosphere community are keystone organisms responsible for these particular functions will potentially allow us to stimulate these microbes specifically, helping reduce the need for fertilization and promoting a more sustainable approach to crop management. This project will examine the microbes that play a role in the mobilization of bound sulfur in the soil, and expand our knowledge of how plants communicate with these microbes in the soil-plant ecosystem.
Like all organisms, plants require sulfur for growth, in order to synthesize proteins and build stable photosynthetic complexes. They obtain this element from the soil as inorganic sulfate, but are also reliant on other forms of bound soil sulfur, including sulfate esters. However, plants cannot release sulfate esters from the soil themselves, and so they depend on interactions with bacteria that inhabit the region surrounding the roots (rhizosphere), who play a crucial role in mobilizing this sulfur for plant uptake.
Bacteria, on the other hand, have no interest in producing more sulfur than they need for themselves, and the sulfatase genes that are responsible for desulfurization of sulfate esters are normally switched off when bacteria are utilizing sulfate. We have recently obtained fascinating new data which show that plants can overcome this by stimulating the activity of bacterial sulfatases in the rhizosphere and inducing soil bacterial sulfatase gene expression. The proposed Ph.D. project will examine the biochemical basis of these phenomena, investigating the mechanisms used by plants to increase soil sulfatase levels, and characterizing how they communicate with rhizosphere bacteria. The student will:
- Screen a range of commercial crop species and cultivars to establish the diversity of plant species able to stimulate soil bacterial sulfatase,
- Identify the mechanisms used by plants to increase bacterial sulfatase activity in the soil, and characterize the biochemical nature of these signals,
- Investigate how the level of plant nutrition influences the regulation of bacterial sulfatase genes by plants.
This project would suit a student with interest in soil microbiology, and some background in biochemistry and molecular genetics. The plant work will be primarily in the glasshouse, under controlled conditions, and some experience with plant cultivation would therefore be useful, though it is not essential. Potential applicants may be interested in reading the following publications from the research group:
- Schmalenberger, A. & Kertesz, M. A. (2007). Desulfurization of aromatic sulfonates by rhizosphere bacteria - high diversity of the asfA gene. Environ. Microbiol. 9, 535-545,
- Kertesz, M. A., Fellows, E. & Schmalenberger, A. (2007). Rhizobacteria and plant sulfur supply. Adv. Appl. Microbiology 62, 235-268,
- Kertesz, M. A. & Mirleau, P. (2004). The role of soil microbes in plant sulfur nutrition. J. Exp. Bot. 55, 1939-1945.
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The opportunity ID for this research opportunity is: 1089
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