Steady-state bioassay

Recently, Hudson et al. (2000) reported the smallest phosphate concentrations to date for any aquatic system (27 pM) in a study using a new, steady-state bioassay technique for estimating orthophosphate concentrations. In phosphate-limited aquatic systems, accurate determination of orthophosphate is critical because it is the only form of phosphorus that can be directly assimilated by primary producers (e.g., Cembella et al., 1984a,b). The standard phosphomolybdate blue method for phosphate determination falls short of this goal, and is widely thought to overestimate... 

Continuous culture systems have been widely used to culture microorganisms for industrial and research purposes (Kubitschek 1970 Tempest 1970 Veldkamp 1976 Rhee 1980). In recent years, these culture techniques have found their way into the bioassay methods of ecotoxicology and allelopathy (Rhee 1980). The early development of a continuous culture system can be traced back to the work of Novik and Szilard (1950 a,b) who developed the first chemostat. In a continuous culture system, nutrients are supplied to the cell culture at a constant rate and to maintain a constant volume, an equal volume of cell culture is removed. This allows the cell population to reach a steady state, where the growth rate and the total number of cells/ml of culture remains constant. Two kind of continuous culture systems can be distinguished turbidostat and chemostat. ... 

Destruction of nitric oxide by superoxide in the buffers is more likely to account for the short half-life of nitric oxide in vitro. Superoxide dismutase (15-100 U/ml) substantially increased the apparent half-life of EDRF, strongly suggesting that superoxide contributes to the short biological half-life of nitric oxide. In the perfusion cascade bioassay system, the buffers are bubbled with 95% oxygen, contain 11 mM glucose as well as trace iron plus copper contamination and are incubated under the weak ultraviolet (UV) radiation of fluorescent lights. These are prime conditions for the autoxidation of glucose to form small amounts of superoxide in sufficient amounts to account for the short half-life of nitric oxide in nanomolar concentrations. The rate of reaction between superoxide and nitric oxide is 6.7 X 10 M sec L The shortest half-life of nitric oxide measured is approximately 6 sec. To achieve a half-life of 6 sec, the steady state concentration of superoxide would only need to be 17 pM, calculated as ln(2)/ (6 sec X 6.7 X 10 M" sec )-... 

Steady state kinetic analyses can be as diverse as the range of biocatalysts themselves. Rate enhancements brought about by any one biocatalyst are usually assessed by means of a bioassay. 

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