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Applied and Environmental Microbiology, October 2008, p. 6306-6312, Vol. 74, No. 20
0099-2240/08/$08.00+0     doi:10.1128/AEM.00877-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Metabolic Microenvironmental Control by Photosynthetic Biofilms under Changing Macroenvironmental Temperature and pH Conditions{triangledown} ,{dagger}

Andrew Bissett,1* Andreas Reimer,2 Dirk de Beer,1 Fumito Shiraishi,2 and Gernot Arp2

Max Planck Institute for Marine Microbiology, Celsiusstraße 1, D-28359 Bremen, Germany,1 Geoscience Centre, University of Göttingen, Goldschmidtstraße 3, D-37077 Göttingen, Germany2

Received 17 April 2008/ Accepted 1 August 2008

Ex situ microelectrode experiments, using cyanobacterial biofilms from karst water creeks, were conducted under various pH, temperature, and constant-alkalinity conditions to investigate the effects of changing environmental parameters on cyanobacterial photosynthesis-induced calcification. Microenvironmental chemical conditions around calcifying sites were controlled by metabolic activity over a wide range of photosynthesis and respiration rates, with little influence from overlying water conditions. Regardless of overlying water pH levels (from 7.8 to 8.9), pH at the biofilm surface was approximately 9.4 in the light and 7.8 in the dark. The same trend was observed at various temperatures (4°C and 17°C). Biological processes control the calcium carbonate saturation state ({Omega}) in these and similar systems and are able to maintain {Omega} at approximately constant levels over relatively wide environmental fluctuations. Temperature did, however, have an effect on calcification rate. Calcium flux in this system is limited by its diffusion coefficient, resulting in a higher calcium flux (calcification and dissolution) at higher temperatures, despite the constant, biologically mediated pH. The ability of biological systems to mitigate the effects of environmental perturbation is an important factor that must be considered when attempting to predict the effects of increased atmospheric partial CO2 pressure on processes such as calcification and in interpreting microfossils in the fossil record.

* Corresponding author. Present address: CSIRO, Plant Industry, P. O. Box 1600, Canberra, ACT 2601, Australia. Phone: 61 (0)2 6246 4820. Fax: 61 (0)2 6246 5000. E-mail: Andrew.Bissett{at}csiro.au

{triangledown} Published ahead of print on 8 August 2008.

{dagger} Supplemental material for this article may be found at http://aem.asm.org/.

Applied and Environmental Microbiology, October 2008, p. 6306-6312, Vol. 74, No. 20
0099-2240/08/$08.00+0     doi:10.1128/AEM.00877-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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