DETECTION OF luc-TAGGED Arthrobacter IN SOIL

Katarina Björklöf, Annelie Möller*, Janet Jansson*, and Kirsten Jørgensen. Finnish

Environment Institute, Laboratory, Hakuninmaantie 4-6, FIN-00430 Helsinki, Finland and

* Department of Biochemistry, Stockholm University, S-10691 Stockholm, Sweden.

A Gram-positive 4-chlorophenol degrading Arthrobacter strain was isolated as previously described (Knutson, 1983). The luc marker gene was inserted by electroporation into the chromosome of this Arthrobacter sp. A6 strain using the mini-transposon vector pAM102. The expression of the luc -gene in vitro was lower in Arthrobacter sp. A6 than in the Gram-negative bacterium Pseudomonas fluorescens. The expression per cell measured as relative light units (RLU) depended on the aeration of the culture. Growing the luc-tagged Arthrobacter sp. A6 in the presence of kanamycin also lowered the signal from the luc gene. This strain was inoculated to a concentration of 10⁹ cells per g fresh weight to a clay soil containing low amounts of chlorophenols. The RLU signal was low already on day 0 and highly variable. Although the viability of the strain stayed constant in the soil over a 6 day period, the RLU decreased. Approximately of 25 % of the added RLU was detected immediately after inoculation. This was the case also for luc-tagged Pseudomonas inoculated into the same soil. Luciferase activities of about 20 times higher RLU per cell were detected in the organic bioremediated soil than in clay soil. It therefore seems that the method used for the isolation of the luciferase enzyme from the soils was not optimal for the clay soil.