Effect of oxygen concentration on dinitrogen fixation and volatile fatty acid production by Clostridium butyricum growing in association with fungi on cellulose and on wheat straw

Abstract

Clostridium butyricum was grown with cellulolytic fungi on the substrates wheat straw and cellulose at a range of oxygen concentrations. The straw was not sterile and was inoculated with Sodaria alcina while the cellulose was sterile and was inoculated with Trichoderma harzianum as examples of cellulolytic organisms. The straw subsequently developed a mixed fungal population. Dinitrogen fixation was only significant at a reduced oxygen concentration: optima being 9.3 and 2.3% O2 for the straw and cellulose experiments, respectively. The efficiencies of N, fixation were 6 mg N per g straw decomposed and 2.3 mg N per g cellulose decomposed and N, fixation occurred only in the presence of significant cellulolysis. Both acetate and butyrate formation increased as the oxygen concentration decreased. With cellulose as a substrate, their formation correlated with a decrease in pH and an increase in final numbers of Cl. butyricum. The thickness of the anaerobic zone at the aerobic/anaerobic interface was linearly related to the square root of the oxygen concentration at the surface of the interface.