GROWTH AND REGULATION OF ENZYME-SYNTHESIS IN THE NITRILOTRIACETIC ACID (NTA)-DEGRADING BACTERIUM CHELATOBACTER-HEINTZII ATCC-29600

In the aerobic bacterium Chelatobacter heintzii, growth and regulation of enzymes involved in nitrilotriacetic acid (NTA) degradation have b een investigated in chemostat culture during cultivation with glucose, NTA or mixtures thereof. In batch culture mu(max) with NTA was 0.18 h (-1) and with glucose 0.22 h(-1). Growth yields for both substrates we re reduced at low dilution rates. During growth with NTA specific acti vity of the NTA monooxygenase (NTA-MO) exhibited a maximum at D = 0.03 h(-1) and gradually decreased with increasing dilution rates. In gluc ose-grown cells the specific activity as well as immunologically detec table NTA-MO protein was always close to the detection limit. During c ultivation with different mixtures of NTA and glucose at a dilution ra te of 0.06 h(-1), both substrates were utilized simultaneously, irresp ective of the NTA/glucose ratio and the presence of excess ammonia. Sy nthesis of both NTA-MO and iminodiacetic acid dehydrogenase became ind uced when NTA contributed to more than approximately 1-3% of the total carbon in the substrate mixture supplied. However, NTA was also degra ded when the proportion of NTA in the mixture was lower than 1%, which is consistent with the low constitutive level of expression for NTA-M O observed. Results are discussed with respect to NTA biodegradation d uring sewage treatment and in ecosystems.