Nitrogen Fixation by Sulphate-reducing Bacteria

Abstract

SUMMARYNitrogen fixation has been obained with strains of Desulfovibrio vulgaris and D . gigas, organisms hitherto believed to be incapable of using molecular nitrogen. Fixation has been demonstrated by increases in total nitrogen and by uptake of 15N2. Fixation of N, may be widespread in this genus of the sulphate-reducing bacteria. I N T R O D U C T I O NThe research reported here was begun as a result of Postgate's comment (19653) in a review that 'Most strains of Desulfovibrio do not fix nitrogen'. Enriched cultures from the mud of Lake Mendota, Wisconsin, not completely free of contaminating bacteria, readily fixed N, ; however, the pure cultures intended as negative controls, Desulfovibrio vulgaris NCIB 8303 HILDENBOROUGH and D. gigas NCIB 9332, also fixed in some experiments. Accordingly, the attempt to purify the new isolates was discontinued in favour of a more thorough examination of this unexpected development. The results, reported briefly at the Colloquium on Nitrogen Fixation held at Sanibd Island, Florida (Silver, 1967), are given in more detail here. MATERIALS A N D METHODSCultures. The culture of Desulfovibrio vulgaris strain NCIB 8303 (HILDENBOROUGH) originally was obtained from Sister M. Regina Lanigan, Rosary Hill College (Buffalo, N.Y.); later, subcultures of this same strain were obtained from Professors L. L. Campbell (University of Illinois) and J. R. Postgate (University of Sussex). The purity of the cultures was routinely checked by examination in a phase microscope and inoculation of Postgate's medium A (1951). These subcultures are designated by the letters R, C and P after the strain number 8303. Crude cultures of this organism were isolated from Lake Mendota mud using the technique described by Postgate with 0.02 yo thioglycollate and 0.01 % ascorbic acid added. In the nitrogen fixation * Present address :

Nitrogen cycle feedbacks as a control on euxinia in the mid-Proterozoic ocean

“…Phosphate input from weathering is an obvious candidate driver for periods of nitrogen fixation (therefore euxinia) during the Proterozoic, one which could conceivably have been enhanced (above the previous non-biologically enhanced rate) by colonization of the land surface 37 towards the end of the Neoproterozoic. In a similar speculative vein, the basic idea that sulphate-reducing bacteria spent an appreciable fraction of their evolutionary past in an environment experiencing bioavailable nitrogen stress is circumstantially supported by the observation that sulphate reducers are capable of facultative nitrogen fixation 33 . It is even conceivable that nitrogen fixation under euxinic conditions could produce a negative d 15 N signature 34 which future geochemical data may record, and which would work in the same direction as our semiquantitative isotopic predictions.…”

Benthic Dinitrogen Fixation Traversing the Oxygen Minimum Zone Off Mauritania (NW Africa)

“…Sequences clustering with known organisms using iron and sulfur as electron acceptors, namely Pelobacter carbinolicus (Lovley et al, 1995) and the species Caldicellulosiruptor saccharolyticus, which hydrolyses a variety of polymeric carbohydrates (Rainey et al, 1994), were found in low (2%) abundance (at 46, 90, 412, and 1,108 m). Sequences closely related to sulfate-reducing bacteria of the genus Desulfovibrio, such as Desulfovibrio desulfuricans (Steenkamp and Peck, 1981;Lobo et al, 2007), Desulfovibrio vulgaris (Riederer-Henderson and Wilson, 1970;Muyzer and Stams, 2008), and Desulfovibrio salexigens (Postgate and Campbell, 1966;van Niel et al, 1996) were detected at all stations. Archaeal genes, which could potentially harbor diazotrophic methanogens, were not detected.…”

“…Only N 2 fixing prokaryotes (diazotrophs) have the capability to convert N 2 to bioavailable N, i.e., ammonium, and make it available for nondiazotrophic organisms (Ward and Bronk, 2001;Gruber, 2008). Diazotrophs can be detected using molecular tools such as the nifH gene, the key functional marker encoding a subunit of the nitrogenase reductase enzyme (Sisler and ZoBell, 1951;Riederer-Henderson and Wilson, 1970;Zehr and Turner, 2001).…”

“…Both microbial processes are often coupled in organic-rich sediments (Bertics and Ziebis, 2010;Bertics et al, 2013;Gier et al, 2016). Additionally, many sulfate reducers carry the nifH gene (Zehr and Turner, 2001;Muyzer and Stams, 2008;Fulweiler et al, 2013;Gier et al, 2016) and actively fix N 2 in culture (Riederer-Henderson and Wilson, 1970), indicating that these bacteria may play a role in supplying bioavailable N to the benthic community Sohm et al, 2011;Fulweiler et al, 2013).…”

Nutrient enrichment in tropical wetlands: shifts from autotrophic to heterotrophic nitrogen fixation

“…Sulfate-reducing bacteria can fix N and diazotrophy is widespead among mezophilic sulfur reducing bacteria (Riederer-Henderson and Wilson 1970;Postgate and Kent 1985;Welsh et al 1996b;Steppe and Paerl 2002). The abundance and activity of sulfur reducing bacteria is driven by anoxia, the presence of sulfates and high C availability.…”