Laccase activity in melanin-producing strains of Sinorhizobium meliloti

• Published in: FEMS microbiology letters 2002-03, Vol.209 (1), p.119-125
• Main Authors: Castro-Sowinski, S, Martinez-Drets, G, Okon, Y
• Format: Article
• Language: English
• Subjects: Azospirillum brasilense - physiology; Bacterial Proteins - antagonists & inhibitors; Bacterial Proteins - isolation & purification; Bacterial Proteins - metabolism; Bacteriology; Benzothiazoles; Biological and medical sciences; Biology of microorganisms of confirmed or potential industrial interest; Biotechnology; Cadmium; Copper - pharmacology; Edetic Acid - pharmacology; Enzyme Activation - drug effects; Enzymes; Ethylenediaminetetraacetic acids; Fundamental and applied biological sciences. Psychology; Genetics; Hydrazones - metabolism; Hydrogen-Ion Concentration; Inoculation; Isolation and description; Laccase; Melanin; melanins; Melanins - biosynthesis; Microbiology; Mission oriented research; Molecular Weight; Monophenol Monooxygenase - metabolism; Oryza - growth & development; Oryza - microbiology; Oxidoreductases - antagonists & inhibitors; Oxidoreductases - isolation & purification; Oxidoreductases - metabolism; Plant growth; plant nutrition; Rice; Sinorhizobia; Sinorhizobium meliloti; Sinorhizobium meliloti - enzymology; Sinorhizobium meliloti - physiology; Sodium dodecyl sulfate; Sodium Dodecyl Sulfate - pharmacology; Sodium lauryl sulfate; Species Specificity; Substrate Specificity; Sulfonic acid; Sulfonic Acids - metabolism; Symbiosis; Syringaldazine; Tyrosinase
• ISSN: 0378-1097; 1574-6968
• DOI: 10.1111/j.1574-6968.2002.tb11119.x

Laccase-like activity was detected in melanin-producing strains of Sinorhizobium meliloti mainly in cells at the stationary growth phase when copper was added to the medium. The laccase showed both syringaldazine and ABTS (2,2'-azino-bis-ethylbenzthiazoline-6-sulfonic acid) oxidase activities and was activated by the addition of 1.7 mM sodium dodecyl sulfate. Activity was totally inhibited by the addition of 1.0 mM EDTA, suggesting that the enzyme is a metal-dependent one. The enzyme was found to be cytosolic having an optimum pH of 5.0, an estimated molecular mass of 95 kDa and a Km of 4 micromolar for syringaldazine. Both laccase and tyrosinase activities were detected in melanin-producing S. meliloti strains. Plant growth-promoting (PGP) effect in rice by a laccase-producing S. meliloti strain when co-inoculated with Azospirillum brasilense Cd was observed. PGP effect by co-inoculation significantly increased plant yield compared to A. brasilense by itself. To the best of our knowledge this is the first report on laccase production in rhizobia and cooperation between Azospirillum and Sinorhizobium in rice.