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Volume 201, number 2 FEBS 3726 June 1986

Hypothesis dismutase: an essential role in the protection of the fixation process?

A. Puppo and J. Rigaud

Laboratoire de Biologie V&g&tale,UA CNRS 1114, FacuM des Sciences et des Techniques, 06034 Nice Cedex, France

Received 2 April 1986

The consumption process by cells is cytochrome c assay [6]; by comparison the SOD fraught with danger: in playing its classical role of content of Escherichia coli, used as control and electron acceptor to form a of water, ox- tested under the same experimental conditions, ygen can be partially reduced and generate several reaches only 14 units/mg of [6]. In the toxic intermediates [I]. The first one is the same way, SOD activity determined in the superoxide anion which is the precursor of more facultative anaerobe Klebsiella potent oxidants, including interconversion prod- pneumoniae using the - ucts derived from this radical [2]. A primary cytochrome c test exhibits 27 units/mg of protein defence is provided by [7]. Under the same conditions, the level of SOD (SOD) an scavenging superoxide anion appears significantly lower in five strains of Strep- with remarkable efficiency [3]. On the other hand, tococcus, a common facultative anaerobe (mean one of the most intriguing characteristics of value of 12.6 units/mg of protein) [7]. Thus it ap- nitrogen-fixing organisms is the rapid and irrever- pears that the SOD content of free-living nitrogen- sible inactivation by oxygen of the key enzyme of fixing is significantly higher than that en- this process: . At the cellular level, dif- countered in non-fixing ones. On the other hand, ferent strategies to ensure an adequate oxygen level the repression of nitrogenase by ammonium is compatible with an optimal nitrogenase activity associated with a decline in SOD activity have been described [4]. Unfortunately little infor- (measured by the -cytochrome c mation is available concerning the molecular test) of Azospirillum brasilense growing under mechanism involved in the protection of similar oxygen tensions [8]. nitrogenase against oxygen [5] and therefore we The situation of some blue-green algae capable propose here to consider the role of SOD. of fixing nitrogen appears even more complex However, to take into account a frequent variabili- since they contain an oxygen-evolving system ty in the measurement of SOD activities due to the associated with photosynthesis. The location of nature and the concentration of the detector nitrogenase in non-photosynthetic specialized molecule, the comparisons will be made only be- cells, the , is considered as a first tween assays realized under the same experimental strategy to limit the oxygen damage [9]. However, conditions. these cells, in which an oxygen diffusion barrier is Free-living bacteria like Azoiobacter, Azomonas found [4], are fitted with a SOD level which and Beijerinckia able to fix nitrogen exhibit high reaches 27% of that encountered in the vegetative SOD levels in the range of 32-86 units/mg of prd- ones having a functional photosynthetic system tein, determined by the xanthine oxidase- [lo]; in the two cases, the same xanthine oxidase-

Published by Elsevier Science Publishers B. V. (Biomedical Division) OOi45793/86/$3.50 0 1986 Federation of European Biochemical Societies 187 Volume 201, number 2 FEBS LETTERS June 1986

NBT assay has been used [lo]. On the other hand, ide, as suggested for another oxygen-sensitive en- in Gloeothece which fixes nitrogen aerobically zyme: succinate [ 181. even though it does not possess heterocysts, On the other hand, damage to other steps of the nitrogenase and SOD activities (xanthine oxidase- process may be prevented by cytochrome c test) are maximal at the same stage SOD. Thus its involvement in the protection of the of growth [ll]. -donating systems participating in nitrogen In the case of symbiotic associations, the fixation and in heterocysts total level of SOD in free-living is [IO] and of against oxidation in slightly higher than that of the corresponding soybean nodules [19] has been suggested. bacteroids [ 121, although the oxygen environment Moreover the symbiotic form of R. japonicum is strongly different (70 and 0.05 mmHg ~02, contains a group of heme with properties res~ctively). On the other hand, the exceptionally similar to cytochrome P-450 proteins 1201. Since high ability of Sesbania root and stem nodules to the role of this molecule as an oxygen activator is reduce atmospheric nitrogen [13] is on a par with well established, its presence can enhance the the presence in the corresponding bacteroids of superoxide anion production, thus contributing an significant SOD levels: 36 and 39 units/mg of explanation for the significant SOD content of the protein, respectively 1141. The SOD activity of bacteroids [12]. In symbiotic systems, the influence bacteroids extracted from French bean nodules, of SOD could occur during the first steps of infec- measured under the same conditions, is 12 units/mg tion by reference to its association with virulence in of protein 1121. All the tests concerning legume different strains of pathogenic bacteria such as have been performed with the same xan- Neisseria meningitidis [21] or Staphylococcus thine oxidase-NBT assay and their comparison is aureus [22] and with resistance to microbicidal ac- thus valid. As observed for Gloeothece, the tivities of the host cell in the case of Nocardia maximal activities of nitrogenase and SOD are asteroides [23]. encountered at the same stage of growth [14]. Anyhow, the correlation between high SOD Recently, the coordinate induction of SOD activity levels and nitrogen-fixing activity is a field which (measured by the xanthine oxidase-cytochrome c appears of great interest and may explain how assay) with derepression of nitrogen fixation has protect their nitrogen-fixing system been pointed out in the symbiotic system Alnus- from damage caused by oxygen. ~rankia fl5]. In the case of these slow growing ac- tinomycetes issued from Casuarinaceae, SOD (xanthine oxidase-NBT test) appears as a marker REFERENCES for the identification of strains [6]. All the above data strongly suggest that SOD is [l] Fridovich, I. (1978) Science 201, 875-880. involved in the protection of cellular components [2] Hailiwell, B. (1982) Trends Biochem. Sci. 7, 270-272. that are crucial to the overall process of dinitrogen [3] Halliwell, B. (1974) New Phytol. 73, 1075-1086. fixation. As SOD appears generally correlated with 141 Gallon, J.R. (1981) Trends Biochem. Sci. 6, 19-23. superoxide anion production, the high levels of iSI Wang, Z.C., Burns, A. and Watt, G.D. (1985) this enzyme can result either from higher superox- Biochemistry 24, 214-221. ide anion production by the metabolism of 161 Jurtshuk, P. jr, Liu, J.K. and Moore, E.R.B. nitrogen-fixing microorganisms or from their ac- (1984) Appl. Environ. Microbial. 47, 1185-I 187. tive respiration 1121. At which step(s) of the [71 Britton, L., MaIinowski, D.P. and Fridovich, I. nitrogen fixation process SOD action could be in- (1978) J. Bacterial. 134, 229-236. volved remains unknown. Although superoxide 181 Clara, R.W. and Knowles, R. (1983) Can. J. Microbial. 30, 1222-1228. anion has been implicated in the inhibition of Haystead, A., Robinson, R. and Stewart, W.D.P. nitrogen fixation in some cases [ 11,171, a direct in- [91 (1970) Arch. Mikrobiol. 74, 235-243. teraction with nitrogenase is not proved 151. If it 1101 Henry, L.E.A., Gogotov, I.N. and Hall, D.O. exists, the inactivation could be due to hydroxyl (1978) Biochem. J. 174, 373-377. radical produced by a Fenton reaction of the VII T&urn, S.R.D. and Gallon, J.R. (1979) J. Gen. reduced of nitrogenase with hydrogen perox- Microbial. 111, 3 13-326.

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[12] Dimitrijevic, L., Puppo, A. and Rigaud, J. (1984) [18] Brunori, M. and Rotilio, G. (1984) Methods Arch. Microbial. 139, 174-178. Enzymol. 105, 22-35. [13] Dreyfus, B.L. and Dommergues, Y.R. (1981) [19] Puppo, A., Dimitrijevic, L. and Rigaud, J. (1982) FEMS Microbial. Lett. 10, 313-317. Planta 156, 374-379. [14] Puppo, A., Dimitrijevic, L., Trinchant, J.C. and [20] Lambeir, A.M., Appleby, CA. and Dunford, Rigaud, J. (1986) submitted. H.B. (1985) Biochim. Biophys. Acta 828, 144-150. [15] Steele, D.B. and Stowers, M.D. (1985) in: Nitrogen [21] Hassan, H.M., Bhatti, A.R. and White, L.A. Fixation Research Progress (Evans, H.J. et al. eds) (1984) FEMS Microbial. Lett. 25, 71-74. p.439, Martinus Nijhoff, Dordrecht, Boston. [22] Kanafani, H. and Martin, S.E. (1985) J. Clin. 1161 Puppo, A., Dimitrijevic, L., Diem, H.G. and Microbial. 21, 607-610. Dommergues, Y.R. (1985) FEMS Microbial. Lett. [23] Beaman, B.L., Black, C.M., Doughty, F. and 30, 43-46. Beaman, L.V. (1985) Infect. Immun. 47, 135-141. [17] Buchanan, A.G. (1977) Can. J. Microbial. 23, 1548-1553.

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