Pedosphere 28(1): 144--156, 2018
ISSN 1002-0160/CN 32-1315/P
©2018 Soil Science Society of China
Published by Elsevier B.V. and Science Press
Vigna radiata var. GM4 Plant Growth Enhancement and Root Colonization by a Multi-Metal-Resistant Plant GrowthPromoting Bacterium Enterobacter sp. C1D in Cr(VI)-Amended Soils
Gangavarapu SUBRAHMANYAM1,2,3, Rakesh Kumar SHARMA1, Gattupalli Naresh KUMAR4, Gattupalli ARCHANA1
1Department of Microbiology and Biotechnology Centre, The Maharaja Sayajirao University of Baroda, Vadodara 390002 (India)
2Department of Biomedical Science, Nitte University Center for Science Education and Research (NUCSER), Nitte University, Deralakatte, Mangalore 575018 (India)
3Central Muga Eri Research and Training Institute, Central Silk Board, Lahdoigarh 785700 (India)
4Department of Biochemistry, Faculty of Science, The Maharaja Sayajirao University of Baroda, Vadodara 390002 (India)
      Contamination of agricultural soils by heavy metals has become a major concern due to their toxic effects on plant growth, symbiosis and consequently the yields of crops. In the present study, to enhance plant growth in Cr(VI)-amended soils, novel metalresistant plant growth-promoting bacteria (PGPB) were isolated from a soil contaminated with industrial waste effluent. One of the bacterial isolates, identified as Enterobacter sp. C1D by 16S rRNA gene sequencing, was found to be multi-metal resistant in nature with excellent plant growth-promoting (PGP) traits. Mung bean (Vigna radiata var. GM4) inoculation with Enterobacter sp. C1D significantly (P < 0.01) increased root and shoot length, shoot and root weight, and chlorophyll content in a range of Cr(VI) treatments. Plant tolerance towards Cr(VI) measured as effective concentration showed higher values with Enterobacter sp. C1Dtreated plants compared to un-inoculated plants. Root colonization study was also carried out using green fluorescence protein-labeled Enterobacter sp. C1D under a hydroponic system. Confocal laser scanning microscopy of the plant roots showed heavy bacterial loads on the surface of the plant root specifically at the root tip and the point of root hair/lateral root formation. The results of PGP traits showed that elevated indole acetic acid levels and 1-aminocyclopropane-1-carboxylate deaminase activity enabled Enterobacter sp. C1D to enhance V. radiata growth in Cr(VI)-amended soils, whereby it significantly increased plant tolerance towards elevated Cr(VI) concentrations.
Key Words:  chromium(VI),Enterobacter sp. C1D,heavy metal,metal toxicity,plant tolerance
Citation: Subrahmanyam G, Sharma R K, Kumar G N, Archana G. 2018. Vigna radiata var. GM4 plant growth enhancement and root colonization by a multi-metal-resistant plant growth-promoting bacterium Enterobacter sp. C1D in Cr(VI)-amended soils. Pedosphere. 28(1):144-156.
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