Evidence for Carbon Monoxide Insensitive Respiration in the Aerobic Nitrogen Fixing Bacteria Azotobacter vinelandii OP and Xanthobacter autotrophicus GZ 29

In intact cells of the non-gummy Azotobacter vinelandii OP CO-insensitivity of the respiratory activity increased with decreasing dissolved oxygen tension in the bacterial suspension. Upon changing from low to high aeration conditions the CO-sensitive respiration was restored. Measurement of the oxidative activity of small particles of A. vinelandii OP with NADH , ascorbate-DCPIP and ascorbate-TMPD as substrate in the presence and absence of CO indicated that the CO-insensitive site is probably identical with cytochrome a1, which preferably is reduced by elec­ trons from ascorbate-DCPIP. Small particles of the gum producing A. vinelandii NCIB 8660 appeared to be more sensitive towards CO with ascorbate DCPIP than the non-gummy A. vinelandii OP. In small particles the CO-insensitive DCPIP oxidase was present irrespective of the dissolved oxygen tension during cell growth. In intact cells, however, CO-insensitivity was only expressed at low dissolved oxygen tension when electrons are directed to cytochrome a1/o in the branched re­ spiratory chain. Intact cells of Xanthobacter autotrophicus GZ 29 exhibited a similar CO-insensitive respiration as A. vinelandii OP.