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Microbiology 148 (2002), 2293-2298
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Microbiology (2002), 148, 2293-2298.
© 2002 Society for General Microbiology

Research Paper

Evidence for protection of nitrogenase from O2 by colony structure in the aerobic diazotroph Gluconacetobacter diazotrophicus

Z. Donga,1, C. D. Zelmer2, M. J. Cannyb,1, M. E. McCullyb,1, B. Luit2, B. Pan2, R. S. Faustino3, G. N. Pierce3 and J. K. Vessey2

Department of Biology, Carleton University, Ottawa, ON, CanadaK1S 5B61
Department of Plant Science, University of Manitoba, Winnipeg, MB, CanadaR3T 2N22
Department of Physiology, University of Manitoba, Winnipeg, MB, CanadaR3E 3J73

Author for correspondence: J. K. Vessey. Tel: +1 204 474 8251. Fax: +1 204 474 7528. e-mail: k_vessey{at}umanitoba.ca

Gluconacetobacter diazotrophicus is an endophytic diazotroph of sugarcane which exhibits nitrogenase activity when growing in colonies on solid media. Nitrogenase activity of G. diazotrophicus colonies can adapt to changes in atmospheric partial pressure of oxygen (pO2). This paper investigates whether colony structure and the position of G. diazotrophicus cells in the colonies are components of the bacterium’s ability to maintain nitrogenase activity at a variety of atmospheric pO2 values. Colonies of G. diazotrophicus were grown on solid medium at atmospheric pO2 of 2 and 20 kPa. Imaging of live, intact colonies by confocal laser scanning microscopy and of fixed, sectioned colonies by light microscopy revealed that at 2 kPa O2 the uppermost bacteria in the colony were very near the upper surface of the colony, while the uppermost bacteria of colonies cultured at 20 kPa O2 were positioned deeper in the mucilaginous matrix of the colony. Disruption of colony structure by physical manipulation or due to ‘slumping’ associated with colony development resulted in significant declines in nitrogenase activity. These results support the hypothesis that G. diazotrophicus utilizes the path-length of colony mucilage between the atmosphere and the bacteria to achieve a flux of O2 that maintains aerobic respiration while not inhibiting nitrogenase activity.

Keywords: Acetobacter diazotrophicus, diffusion resistance, N2 fixation, nitrogen, oxygen

Abbreviations: CLSM, confocal laser scanning microscopy; DAI, days after inoculation; pO2, partial pressure of oxygen

a Present address: Department of Biology, St Mary’s University, Halifax, NS, Canada B3H 3C3.

b Present address: Division of Plant Industry, CSIRO, GPO 1600, Canberra, ACT 2601, Australia.






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