Population density measurement dilution

Analysis of the populations of two phenol-degrading bacteria P. putida BH and Comamonas sp. strain E6 introduced into an activated sludge system has been carried out by extraction of DNA, PCR amplification of the gyrB gene fragments using strain-specific primers, and quantification after electrophoresis by densitometry (Watanabe et al. 1998). Appropriate dilutions of the extracted DNA were used to maintain linearity between the measured intensity and population density. The initial inocula of 108 cells/ml fell to 104 cell/ml after 10 days and thereafter remained steady for a further 18 days. 

By feeding bacteria to the predator population at different dilution rates and measuring the steady state prey density in the second vessel it is therefore possible to relate X and H to each other. 

Jager etal. (1992) used a dilution unit in conjunction with laser diffraction measurement equipment. The combination could only determine, however, CSD by volume while the controller required absolute values of population density. For this purpose the CSD measurements were used along with mass flow meter. They were found to be very accurate when used to calculate higher moments of CSD. For the zeroth moment, however, the calculations resulted in standard deviations of up to 20 per cent. This was anticipated because small particles amounted for less then 1 per cent of volume distribution. Physical models for process dynamics were simplified by assuming isothermal operation and class II crystallizer behaviour. The latter implies a fast growing system in which solute concentration remains constant with time and approaches saturation concentration. An isothermal operation constraint enabled the simplification of mass and energy balances into a single constraint on product flowrate. 

Another indirect test measures the bacterial population density by determination of the enzyme adenosphine phosphor sulfate reductase, present in the bacteria. Measurement of this enzyme is again by color intensity, but uses a color interpretation card. The approximate population density can be determined with a detection threshold of 103 sulfate reducing bacteria per ml of liquid sample. Test results can be available within 15 minutes of sampling and show reasonable correlation with those from serial dilution tests. 

Not only osmotic pressure and light scattering data confirmed this model but other thermodynamic measurements as well, such as enthalpy of dilution and Donnan distribution for polyelectrolyte gels, were in excellent agreement [7]. Electrical transport phenomena, moreover, could be very satisfactorily explained by the concept of two counter-ion populations, one condensed and one non-condensed, which depended upon the chain charge density. For example, the very precise conductance data of Eisenberg and Sachs [8] could be accounted for in terms of the osmotically determined 0p. 

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