Munusamy Madhaiyan and Lianghui Ji
Temasek Life Sciences Laboratory, 1 Research Link, National University of Singapore, Singapore
Jatropha curcas is promising new non-food crop for biodiesel production because of its ability to thrive on marginal land, with strong tolerance to draught and poor soil nutrient content [1-3]. Nevertheless, high fertilizer input remains essential in order to have commercially acceptable oil productivity. This reduces the green index of Jatropha biofuel. To address this issue, we studied the taxonomical distribution of 1017 cultivable endophytic bacterial strains isolated from different parts of Jatropha with an emphasis on nitrogen-fixing bacteria. Like other reports, we found strong tissue preferences of the bacteria in Jatropha. The16S rRNA gene sequences can be assigned to five major phyla and, surprisingly, 31.2% of them potentially represent new taxa. Nitrogen fixing isolates were found diverse and present in five classes belonging to α, β, γ- Proteobacteria, Actinobacteria and Firmicutes. The phylum Proteobacteria was the most dominant amongst strains that were positive for both nifH gene and endoglucanase activity. Methylobacterium species account for 69.1% of the leaf endophytic bacterial isolates. Notably, many Methylobacterium isolates were able to fix nitrogen.
We will present genomic, physiology and plant-bacteria interaction studies on two strong nitrogen-fixing isolates: Kosakonia sp. R4-368 (previously Enterobacter R4-368 [4,5]) that mainly colonizes in roots and stems and Methylobacterium radiotolerans L2-4 that mainly colonizes leaf tissues both as endophyte and epiphyte. Root treatment of R4-368 or foliar application of L2-4 significantly improved growth parameters, such as plant height, leaf number, relative chlorophyll content and stem volume. Importantly, strain L2-4 improved seed yield by 222.2% and 96.3% in plants potted in sterilized and non-sterilized soil pots respectively. Strain R4-368 improved seed set by approximately 177% and 49.0% in sterilized and non-sterilized soil respectively. The average single seed weight was increased approximately 10% by strain R4-368. Yield improvements were mainly attributed to an increase of female-male flower ratio, which led to a corresponding increase of fruit and seed sets. Furthermore, there was an additive effect for seed yield of root and leaf treatments were both performed. We will present the effects of application of the two isolates on other crops.
Key words: Nitrogen-fixation, biofuel, plant growth promoting bacteria, Jatropha curcas
REFERENCES
[1] Fairless D (2007) Biofuel: The little shrub that could - maybe. Nature 449:652-655. doi:doi:10.1038/449652a
[2] Gaydou AM, Menet L, Ravelojaona G, Geneste P (1982) Vegetable energy sources in Madagascar: ethyl alcohol and oil seeds.
Oleagineux 37 ((3)):135–141
[3] Openshaw K (2000) A review of Jatropha curcas: an oil plant of unfulfilled promise. Biomass Bioenergy 19 (1):1-15
[4] Madhaiyan M, Peng N, Ji L (2013) Complete Genome Sequence of Enterobacter sp. Strain R4-368, an Endophytic N-Fixing
Gammaproteobacterium Isolated from Surface-Sterilized Roots of Jatropha curcas L. Genome announcements 1 (4):e00544-
00513
[5] Yan H, Ji L (2013) Improvement of plant growth and seed yield in Jatropha curcas by a novel nitrogen-fixing root associated
Enterobacter species.