Plant Growth-Promoting Chitinolytic Paenibacillus elgii Responds Positively to Tobacco Root Exudates Subha Narayan Das • Swarnalee Dutta • Anil Kondreddy • Neeraja Chilukoti • Sarma V. S. R. N. Pullabhotla • Srinivas Vadlamudi • Appa Rao Podile Received: 5 August 2009 / Accepted: 26 March 2010 / Published online: 19 May 2010 Ó Springer Science+Business Media, LLC 2010 Abstract Bacterial strains from chitin/chitosan-rich soils, from two industries, were screened for their chitinolytic, antifungal, and mineral phosphate solubilization abilities. The isolate SMA-1-SDCH02, positive for all three prop- erties, was selected and identified as Paenibacillus elgii based on morphological and biochemical characters and supported by 16S rRNA gene sequence analysis. P. elgii enhanced the growth of groundnut in terms of shoot height, root length, total chlorophyll, and fresh and dry weight when applied alone or in combination with chitosan. The plant growth-promoting activity of P. elgii was seen in tobacco in a specially designed gnotobiotic setup indicating its capability to promote growth of at least groundnut and tobacco. Metabolite changes in the bacteria, studied using attenuated total reflectance-infrared (ATR-IR) spectros- copy, revealed split bands of amide I at the 1659- and 1636-cm -1 regions when grown in minimal media amended with tobacco root exudates. The difference in ATR-IR bands in the presence of tobacco root exudates indicated production of compounds with differences in functional groups. Keywords Amide I band Á Attenuated total reflectance-infrared spectroscopy Á Chitin/chitosan-rich soils Á Gnotobiotic setup Á Metabolite changes Á Paenibacillus elgii Á PGPR Introduction Biological means for plant growth promotion and disease control are preferred over synthetic chemicals as they are ecofriendly and cost effective. Plant growth-promoting rhizobacteria (PGPR) exert beneficial effects on plant growth and development that are exploited for improving plant growth and yield besides controlling diseases (Kloepper and others 1980). PGPR and their interactions with plants are exploited commercially (Podile and Kishore 2006) and hold great promise for sustainable agriculture. A number of PGPR strains have been identified and applied for use as plant growth promoters but the search for better PGPR strains suitable for development of effective formu- lations (longer shelf life) continues. Different carrier-based chitin/chitosan-supplemented formulations (Manjula and Podile 2001, 2005) were effective against several phyto- pathogens and also significantly increased plant growth. Chitin is a major structural polysaccharide and is abundant in the cell walls of the majority of fungi. The b 1 ? 4 glycosidic bonds in the chitin are responsible for cell wall integrity and, therefore, are a sensitive target for chitin-degrading enzymes. Chitin degradation is an important attribute of several of the successful microbial agents used in biological control of fungal pathogens. We have shown the extensive damage caused to major fungal pathogens of groundnut by chitinolytic biocontrol strains and the partially purified enzymes (Podile and Prakash 1996; Manjula and others 2004; Manjula and Podile 2005), and exploited the chitinolytic potential of the biocontrol PGPR strains to improve both the shelf life and effective- ness of the formulations (Manjula and Podile 2001, 2005; Kishore and others 2005a, b). The chitinolytic bacterial strains isolated from the phylloplane of groundnut were effective as PGPR when applied on the seeds (Kishore and S. N. Das Á S. Dutta Á A. Kondreddy Á N. Chilukoti Á S. V. S. R. N. Pullabhotla Á S. Vadlamudi Á A. R. Podile (&) Department of Plant Sciences, School of Life Sciences, University of Hyderabad, Hyderabad 500 046, India e-mail: arpsl@uohyd.ernet.in; apparaopodile@yahoo.com 123 J Plant Growth Regul (2010) 29:409–418 DOI 10.1007/s00344-010-9152-1