Antimicrobial profile of Arthrobacter kerguelensis VL-RK_09 isolated from Mango orchards

Abstract An actinobacterial strain VL-RK_09 having potential antimicrobial activities was isolated from a mango orchard in Krishna District, Andhra Pradesh (India) and was identified as Arthrobacter kerguelensis. The strain A. kerguelensis VL-RK_09 exhibited a broad spectrum of in vitro antimicrobial activity against bacteria and fungi. Production of bioactive metabolites by the strain was the highest in modified yeast extract malt extract dextrose broth, as compared to other media tested. Lactose (1%) and peptone (0.5%) were found to be the most suitable carbon and nitrogen sources, respectively, for the optimum production of the bioactive metabolites. The maximum production of the bioactive metabolites was detected in the culture medium with an initial pH of 7, in which the strain was incubated for five days at 30 °C under shaking conditions. Screening of secondary metabolites obtained from the culture broth led to the isolation of a compound active against a wide variety of Gram-positive and negative bacteria and fungi. The structure of the first active fraction was elucidated using Fourier transform infrared spectroscopy, electrospray ionization mass spectrometry, 1H and 13C nuclear magnetic resonance spectroscopy. The compound was identified as S,S-dipropyl carbonodithioate. This study is the first report of the occurrence of this compound in the genus Arthrobacter.

Production of Amylase by Arthrobacter kerguelensis VL-RK_09 Isolated from Mango Orchards.

Objectives: To optimize the cultural parameters for improved production of amylase by Arthrobacter kerguelensis VL-RK_09 isolated from Mango orchards of Vissannapet, Krishna District, A.P., India. Methods: The strain A. kerguelensis was screened initially for amylase production on Inorganic salts starch agar medium (ISP-4). The enzyme assay was performed as per the procedure described by Bernfield (1955). One amylase unit equals to that amount of enzyme needed to release 1 mg of reducing sugar (maltose as standard) for 15 min at 37°C. Attempts were also made to optimize cultural parameters such as pH, temperature, carbon and nitrogen sources affecting the production of amylase by the strain. Results: Maximal yields of amylase were recorded after 4 days of incubation in Inorganic salts starch medium with initial pH 7.0 and temperature 35°C. ISP-4 broth amended with sorghum flour (2%) and yeast extract (0.5%) with initial pH 7.0 inoculated with Arthrobacter kerguelensis VLRK_ 09 and incubated at 30°C for 96 h resulted in improved production of amylase from initial 4.0 U to 10.4 U/mL. Conclusion: This is the first report on the production and optimization of amylase by A. kerguelensis and further studies on purification and characterization of the enzyme are in progress.