Bioluminescence induction response and survival of the bioreporter bacterium Pseudomonas fluorescens HK44 in nutrient-deprived conditions

Pseudomonas fluorescens HK44 is a bioluminescent bioreporter synthesizing light in the presence of naphthalene or salicylate. Upon immobilization, HK44 is useful as an in situ or on-line biosensor of bioavailable naphthalene and salicylate in waste streams or contaminated fields. The bioreporting efficacy of alginate/SrCl₂-immobilized HK44 was investigated in simulated groundwater with different pH regimes. When induced with complex (salicylate plus auxiliary energy supplements) and simple (salicylate as the sole energy supplement) inducer solutions, the specific light response was steadier at pH 6 than at pH 7 in a 35-day study. There was no bioluminescence response from cells incubated in groundwater samples with pH below 6. The rate of the luminescence reaction was stable at pH 6 irrespective of the type of inducer solution, indicating the robust physiological status of the bioreporter bacteria. In addition, the quantity of light synthesized was at least one order of magnitude higher with complex inducer solution than with simple inducer solution. The numbers of viable and cultivable cells remained constant in groundwater at pH 6 and 7 (approx. 10⁷ g⁻¹ beads). The numbers decreased by four orders of magnitude (10⁷ to 10³) to zero in groundwaters with pH below 6. This study suggested that HK44 is useful for long-term biosensor applications in moderately acidic to neutral groundwater conditions. Received: 6 August 1996 / Received revision: 12 December 1996 / Accepted: 4 January 1997