Microbial Profiles of Rhizosphere and Bulk Soil Microbial Communities of Biofuel Crops Switchgrass (Panicum virgatum L.) and Jatropha (Jatropha curcas L.)
The production of biofuels from the low-input energy crops, switchgrass (Panicum virgatum L.) and jatropha (Jatropha curcas L.), is a sustainable approach that can provide more usable energy and environmental benefits than food-based biofuels. Plant rhizosphere affects the microbial community structure due to variations in root exudation rates and residue chemistry. The objective of this investigation was to determine the profiles of microbial communities associated with rhizosphere and bulk soils of switchgrass or jatropha using phospholipid fatty acid (PLFA) analysis and length heterogeneity PCR (LH-PCR). Switchgrass soil contained a significantly ( ) higher abundance of Gram-positive (i14:0, i15:0, a15:0), Gram-negative (16:1ω5c, 16:1ω7c, 18:1ω5c), and saturated (14:0, 15:0) PLFAs compared to jatropha soil, whereas jatropha had a higher abundance of fungal (18:2ω6, 9c), 18:1ω9c, 20:1ω9c, and 18:0 PLFAs compared to switchgrass soil. Irrespective of plant type, rhizosphere soil contained a significantly ( ) higher abundance of saturated PLFAs (16:0, 18:0, 20:0), actinomycetes (10Me17:0), and fungal (18:2ω6, 9c) PLFAs compared to bulk soil; whereas bulk soil had higher abundance of saturated (14:0), Gram-negative (16:1ω9c, 16:1ω5c, 16:1ω7c), and 18:1ω9c PLFAs compared to rhizosphere soil. Multivariate principle component analysis of PLFAs and LH-PCR percent relative peak areas successfully differentiated the microbial communities of rhizosphere and bulk soils of switchgrass and jatropha. 1. Introduction The increasing consumption of energy, limited availability of fossil fuels, and environmental pollution from exhaust emissions have created a great demand for biofuels that can be produced from renewable biomass. This has also resulted in a renewed interest in agricultural production of high yielding biofuel crops and energy conversion technologies necessary to achieve this goal. Currently, switchgrass (Panicum virgatum L.) and jatropha (Jatropha curcas L.) are the two main energy crops employed for bioethanol and biodiesel production, respectively [1]. Both switchgrass and jatropha are low maintenance, high yielding crops that can be grown on marginal lands with low agricultural inputs. Hence, both of these crops can be used as sustainable energy sources for producing renewable transportation fuels [1]. The rhizosphere is the volume of soil adjacent to the plant roots that plays a significant role in plant health and soil fertility. Actively growing roots secrete a diverse array of organic root exudates that stimulate the growth of microbial populations
References
[1]
B. D. Solomon, “Biofuels and sustainability,” Annals of the New York Academy of Sciences, vol. 1185, pp. 119–134, 2010.
[2]
P. Hinsinger, A. G. Bengough, D. Vetterlein, and I. M. Young, “Rhizosphere: biophysics, biogeochemistry and ecological relevance,” Plant and Soil, vol. 321, no. 1-2, pp. 117–152, 2009.
[3]
J. S？rensen, “The rhizosphere as a habitat for soil microorganisms,” in Modern Soil Microbiology, J. D. Van Elsas, J. T. Trevors, and E. M. H. Wellington, Eds., pp. 21–45, Marcel Dekker, New York, NY, USA, 1997.
[4]
C. T. Green and K. M. Scow, “Analysis of phospholipid fatty acids (PLFA) to characterize microbial communities in aquifers,” Hydrogeology Journal, vol. 8, no. 1, pp. 126–141, 2000.
[5]
N. J. Ritchie, M. E. Schutter, R. P. Dick, and D. D. Myrold, “Use of length heterogeneity PCR and fatty acid methyl ester profiles to characterize microbial communities in soil,” Applied and Environmental Microbiology, vol. 66, no. 4, pp. 1668–1675, 2000.
[6]
R. D. Bardgett, P. J. Hobbs, and A. Frosteg？rd, “Changes in soil fungal:bacterial biomass ratios following reductions in the intensity of management of an upland grassland,” Biology and Fertility of Soils, vol. 22, no. 3, pp. 261–264, 1996.
[7]
A. Frosteg？rd, E. B？？th, and A. Tunlio, “Shifts in the structure of soil microbial communities in limed forests as revealed by phospholipid fatty acid analysis,” Soil Biology and Biochemistry, vol. 25, no. 6, pp. 723–730, 1993.
[8]
L. Zelles, “Fatty acid patterns of phospholipids and lipopolysaccharides in the characterisation of microbial communities in soil: A review,” Biology and Fertility of Soils, vol. 29, no. 2, pp. 111–129, 1999.
[9]
J. Moore-Kucera and R. P. Dick, “PLFA profiling of microbial community structure and seasonal shifts in soils of a Douglas-fir chronosequence,” Microbial Ecology, vol. 55, no. 3, pp. 500–511, 2008.
[10]
R. E. Hicks, R. I. Amann, and D. A. Stahl, “Dual staining of natural bacterioplankton with 4',6-diamidino-2- phenylindole and fluorescent oligonucleotide probes targeting kingdom-level 16S rRNA sequences,” Applied and Environmental Microbiology, vol. 58, no. 7, pp. 2158–2163, 1992.
[11]
R. I. Amann, L. Krumholz, and D. A. Stahl, “Fluorescent-oligonucleotide probing of whole cells for determinative, phylogenetic, and environmental studies in microbiology,” Journal of Bacteriology, vol. 172, no. 2, pp. 762–770, 1990.
[12]
B. McCune and M. J. Mefford, PC-ORD. Multivariate Analysis of Ecological Data. Version 5, MjM Software, Gleneden Beach, Ore, USA, 2006.
[13]
N. Nunan, B. Singh, E. Reid et al., “Sheep-urine-induced changes in soil microbial community structure,” FEMS Microbiology Ecology, vol. 56, no. 2, pp. 310–320, 2006.
[14]
A. M. Treonis, N. J. Ostle, A. W. Stott, R. Primrose, S. J. Grayston, and P. Ineson, “Identification of groups of metabolically-active rhizosphere microorganisms by stable isotope probing of PLFAs,” Soil Biology and Biochemistry, vol. 36, no. 3, pp. 533–537, 2004.
[15]
D. C. White and R. H. Findlay, “Biochemical markers for measurement of predation effects on the biomass, community structure, nutritional status, and metabolic activity of microbial biofilms,” Hydrobiologia, vol. 159, no. 1, pp. 119–132, 1988.
[16]
K. H. S？derberg and E. B？？th, “Bacterial activity along a young barley root measured by the thymidine and leucine incorporation techniques,” Soil Biology and Biochemistry, vol. 30, no. 10-11, pp. 1259–1268, 1998.
[17]
V. V. S. R. Gupta and J. J. Germida, “Distribution of microbial biomass and its activity in different soil aggregate size classes as affected by cultivation,” Soil Biology and Biochemistry, vol. 20, no. 6, pp. 777–786, 1988.
[18]
G. P. Zogg, D. R. Zak, D. B. Ringelberg, N. W. MacDonald, K. S. Pregitzer, and D. C. White, “Compositional and functional shifts in microbial communities due to soil warming,” Soil Science Society of America Journal, vol. 61, no. 2, pp. 475–481, 1997.
