IDENTIFICATION AND CHARACTERIZATION OF A NEW BACTERIUM (S-9 ISOLATE) AND ITS MANNER OF INDUCING ABNORMAL GROWTH OF SEEDLINGS
WM PARK and CW PYUN
Graduate School of Biotechnology, Korea University, Seoul 136-701, Korea
Background and objectives
Some bacteria can induce abnormal growth of their host plants. Overgrowth or proliferation of organs can be caused by certain species of Agrobacterium, Pseudomonas and Rhizobium which could synthesize some plant-growth regulators. Barea et al.  found that among 50 bacterial isolates obtained from the rhizospheres of various plants, 86, 58 and 90% produced auxins, gibberellins and kinetin-like substances, respectively. Some fluorescent pseudomonads can produce secondary metabolites . Soybean sprout, which is an etiolated soybean seedling, grown in the dark for 7 days, is a popular food for Koreans. Hypocotyls of some soybean sprouts develop short and thick. It is thought that the reason for this abnormal growth may be due to a bacterium growing on the surface of the sprout tissue producing bacterial metabolites which affect plant growth. The present research was carried out to identify and characterize the causal bacterium.
Results and conclusions
The S-9 isolate inducing short and thick hypocotyls of young seedlings was isolated from soybean sprouts. It could induce the symptoms on a wide range of dicotyledonous plants (eight families; 13 genera; 15 species tested), however it could not affect the growth of plants of the Gramineae. The S-9 isolate did not affect germination of seeds or produce necrotic symptoms on the infected seedlings. Microsections of tissue of inoculated hypocotyl showed that the cells were short in length and thick in diameter. Through morphological and biochemical tests, the S-9 isolate was identified as Pseudomonas fluorescens biovar 1. The S-9 isolate and other fluorescent pseudomonads, P. aureofaciens (ATCC 13985), P. chlororaphis (ATCC 9446), P. fluorescens (KCTC1767), P. fluorescens biovar 1 (ATCC 13525), P. fluorescens biovar 11 (ATCC 17816), P. putida (ATCC 12633) and P. syringae pv. syringae (ATCC 19310), were inoculated to radish seeds. Only S-9 isolate induced the symptom, while seven species did not affect growth of radish seedlings. Antiserum against S-9 isolate did not react with other isolates of pseudomonads. The RAPD patterns of the S-9 was very different from those of other pseudomonads. Even with the isolates ATCC 13525 and KCTC 1767, belonging to P. fluorescens, the RAPD patterns differed from those of S-9. This result suggests that S-9 may be a new strain of pseudomonad. The plasmid isolation was carried out, but no plasmid was detected in the S-9 isolate. Extracts of the infected abnormal hypocotyl sap and the bacterial cultured medium by methanol and ethyl acetate produced similar symptom on dicotyledonous seedlings. The symptom-inducing material was purified by TLC, silica gel column.
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