Environmental factors and microbial inoculum size, and their effect on biodefluorination of sodium monofluoroacetate (1080)

Abstract

The effect of inoculum size and the environmental factors of pH, temperature and soil moisture on the biodefluorination of sodium monofluoroacetate (1080) by seven microorganisms (four bacterial species and three fungi) was studied. In the presence of 1080 as the sole carbon source, the effect of pH on 1080 defluorination varied among the organisms. Generally, the optimum pH for 1080 defluorination by soil bacteria ( Pseudomonas acidovorans and P. fluorescens 1) was at neutral to alkaline pH and the maximum defluorination by fungi ( Fusarium oxysporum and Penicillium restriction) was at pH 5. Most organisms grew on nutrient agar at a pH range of 5–8. The optimal temperature for 1080 defluorination varied with different microorganisms and with different organic carbon sources. On agar, all seven isolates grew best in the temperature range of 28–30°C. The highest rate of 1080 defluorination in soil for all the isolates occurred at fluctuating temperatures (minimum = 11°C, maximum = 24°C) and at soil moisture contents of 8–15%, while the lowest rates occurred at a soil moisture content of 30%. The defluorination rate of 1080 when it was present as the sole carbon source decreased as the inoculum size decreased. In soil the rate of reduction in 1080 defluorination did not appear to be directly proportional to the microbial inoculum size and the rate varied with different microorganisms. Some microorganisms, e.g. P. fluorescens 1, had their highest rate of defluorination activity at a low inoculum density, i.e. (10 5 cells ml −1 in 1080 solution and 10 7 cells ml −1 in soil).