Technical Improvements

Since the publication of the ‘MicroResp™’ paper (Campbell et al., 2003, AEM, 69, pp 3593-3599), the MicroResp™ system has undergone a few changes to optimise a few aspects and improve the data handling. 

Absorbance wavelength

During the early days we were using a wavelength filter of 590 nm as this was the closest filter we had available at the time.  The optimum wavelength for the indicator dye is 572 nm.  Due to the model of microplate reader used in our lab and the limitations of available filters, we are now using the 570 nm filter as the closest ‘optimum’ wavelength. 

Agar

We no longer use Noble Agar (Difco), this has been replaced with Purified Agar (Oxoid) because it has a lower absorbance and does not effect the wavelength of the indicator dye.

Absorbance to %CO2 formula

The formula used to convert absorbance reading to %CO2 has also changed as we found that the formula used for the curve fit, A+B/(1+D*Ai), gives a better fitting curve compared the original A+B*(R^Ai). 

Acknowledgements

The Macaulay MicroResp™ team held a workshop on 26-28 September 2005 to discuss “Development of methods for assessing below ground biodiversity as an indicator of soil quality and health”.  We would like to acknowledge the positive feedback and constructive comments from all participants which has helped to improve the manual and methods contained in it.  In particular we would like to acknowledge Nahia Gartzia Bengoetxea (NEIKER-Basque Institute) for highlighting the large improvement in using 570 nm filter as opposed to 590 nm.