A total of 74 morphologically distinct bacterial colonies were selected during isolation of bacteria from different parts of tomato plant (rhizoplane, phylloplane and rhizosphere) as well as nearby bulk soil. The isolates were screened for plant growth promoting (PGP) traits such as production of indole acetic acid, siderophore, chitinase and hydrogen cyanide as well as phosphate solubilization. Seven isolates viz., NR4, NR6, RP3, PP1, RS4, RP6 and NR1 that exhibited multiple PGP traits were identified, based on morphological, biochemical and 16S rRNA gene sequence analysis, as species that belonged to four genera Aeromonas, Pseudomonas, Bacillus and Enterobacter. All the seven isolates were positive for 1-aminocyclopropane-1-carboxylate deaminase. Isolate NR6 was antagonistic to Fusarium solani and Fusarium moniliforme, and both PP1 and RP6 isolates were antagonistic to F. moniliforme. Except RP6, all isolates adhered significantly to glass surface suggestive of biofilm formation. Seed bacterization of tomato, groundnut, sorghum and chickpea with the seven bacterial isolates resulted in varied growth response in laboratory assay on half strength Murashige and Skoog medium. Most of the tomato isolates positively influenced tomato growth. The growth response was either neutral or negative with groundnut, sorghum and chickpea. Overall, the results suggested that bacteria with PGP traits do not positively influence the growth of all plants, and certain PGP bacteria may exhibit host-specificity. Among the isolates that positively influenced growth of tomato (NR1, RP3, PP1, RS4 and RP6) only RS4 was isolated from tomato rhizosphere. Therefore, the best PGP bacteria can also be isolated from zones other than rhizosphere or rhizoplane of a plant.

Humans have exploited natural resources for a variety of applications. Chitin and its derivative chitin oligosaccharides (CHOS) have potential biomedical and agricultural applications. Availability of CHOS with the desired length has been a major limitation in the optimum use of such natural resources. Here, we report a single domain hyper-transglycosylating chitinase, which generates longer CHOS, from Enterobacter cloacae subsp. cloacae 13047 (EcChi1). EcChi1 was optimally active at pH 5.0 and 40 °C with a Km of 15.2 mg ml−1, and k cat/Km of 0.011× 102 mg−1 ml min−1 on colloidal chitin. The profile of the hydrolytic products, major product being chitobiose, released from CHOS indicated that EcChi1 was an endo-acting enzyme. Transglycosylation (TG) by EcChi1 on trimeric to hexameric CHOS resulted in the formation of longer CHOS for a prolonged duration. EcChi1 showed both chitobiase and TG activities, in addition to hydrolytic activity. The TG by EcChi1 was dependent, to some extent, on the length of the CHOS substrate and concentration of the enzyme. Homology modeling and docking with CHOS suggested that EcChi1 has a deep substrate-binding groove lined with aromatic amino acids, which is a characteristic feature of a processive enzyme.

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