The role of cytochrome b 1 in nitrate assimilation and nitrate respiration in Klebsiella aerogenes

Initial nitrogen enrichment conditions determines variations in nitrogen substrate utilization by heterotrophic bacterial isolates

Background

The nitrogen (N) cycle consists of complex microbe-mediated transformations driven by a variety of factors, including diversity and concentrations of N compounds. In this study, we examined taxonomic diversity and N substrate utilization by heterotrophic bacteria isolated from streams under complex and simple N-enrichment conditions.

Results

Diversity estimates differed among isolates from the enrichments, but no significant composition were detected. Substrate utilization and substrate range of bacterial assemblages differed within and among enrichments types, and not simply between simple and complex N-enrichments.

Conclusions

N substrate use patterns differed between isolates from some complex and simple N-enrichments while others were unexpectedly similar. Taxonomic composition of isolates did not differ among enrichments and was unrelated to N use suggesting strong functional redundancy. Ultimately, our results imply that the available N pool influences physiology and selects for bacteria with various abilities that are unrelated to their taxonomic affiliation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-017-0993-7) contains supplementary material, which is available to authorized users.

Genetic evidence that NarL function is not required for nitrate regulation of nitrate assimilation in Klebsiella pneumoniae M5al

We cloned the narL gene, required for nitrate induction of respiratory nitrate reductase synthesis, from Klebsiella pneumoniae. The E. coli narL gene product shares sequence similarity with the response regulator proteins of two-component regulatory systems. We found that narL(+)-containing plasmids restored nitrate regulation of anaerobic respiratory gene expression in appropriate Escherichia coli hosts. The K. pneumoniae narL region encoded a protein whose migration in Laemmli gels was indistinguishable from that of the narL product of E. coli. We constructed a narL::Km mutant of K. pneumoniae. This mutation abolished nitrate induction of respiratory nitrate reductase synthesis but had no effect on nitrate induction of assimilatory nitrate and nitrite reductase synthesis. We conclude that K. pneumoniae has distinct nitrate-responsive regulators for controlling respiratory and assimilatory gene expression.

Genetic regulation of nitrate assimilation in Klebsiella pneumoniae M5al

We isolated Mu dI1734 insertion mutants of Klebsiella pneumoniae that were unable to assimilate nitrate or nitrite as the sole nitrogen source during aerobic growth (Nas- phenotype). The mutants were not altered in respiratory (anaerobic) nitrate and nitrite reduction or in general nitrogen control. The mutations were linked and thus defined a single locus (nas) containing genes required for nitrate assimilation. beta-Galactosidase synthesis in nas+/phi(nas-lacZ) merodiploid strains was induced by nitrate or nitrite and was inhibited by exogenous ammonia or by anaerobiosis. beta-Galactosidase synthesis in phi(nas-lacZ) haploid (Nas-) strains was nearly constitutive during nitrogen-limited aerobic growth and uninducible during anaerobic growth. A general nitrogen control regulatory mutation (ntrB4) allowed nitrate induction of phi(nas-lacZ) expression during anaerobic growth. This and other results suggest that the apparent anaerobic inhibition of phi(nas-lacZ) expression was due to general nitrogen control, exerted in response to ammonia generated by anaerobic (respiratory) nitrate reduction.

Denitrification and nitrite reduction: Pseudomonas aeruginosa nitrite-reductase

Present knowledge of the different enzymatic steps of the denitrification chains in various bacteria, particularly Paracoccus denitrificans and Pseudomonas aeruginosa has been briefly reviewed. The question whether nitric oxide (NO), nitrous oxide (N2O) and other nitrogen derivatives are obligatory intermediates has been discussed. The second part is an extensive review of the structure and the function of a key enzyme in denitrification, cytochrome c551-nitrite-oxidoreductase from P. aeruginosa. Recent results on the stoichiometry of nitrite reduction have been discussed.

Isolation and analysis of mutants of Pseudomonas aeruginosa unable to assimilate nitrate

Pseudomonas aeruginosa can reduce nitrate to nitrite and evenutally to nitrogen gas by the denitrification pathway, thereby providing the organism with a mode of respiration and ATP generation in the absence of oxygen. P. aeruginosa can also reduce nitrate to nitrite through an assimilatory pathway that provides the cell with reduced nitrogen for biosyntheses. In order to establish whether this organism synthesizes a single nitrate reductase protein that functions in both pathways, or produces one for each pathway, we isolated mutants blocked in the assimilation of nitrate. These mutants are unaffected in the reduction of nitrate be the denitrification pathway, although they produce low or undectable levels of assimilatory nitrate reductase. On the basis of transductional analysis, the mutations were found to be distributed among four genes designated nasA, nasB, nasC, and nasD. Shifting a nasA mutant from anaerobic to aerobic growth eliminated the culture's ability to reduce nitrate, i.e. the anaerobic nitrate reductase cannot function in the presence of oxygen. Thus P. aeruginosa can synthesize two distinct proteins which reduce nitrate to nitrite: an assimilatory nitrate reductase and a dissimilatory nitrate reductase. If conditions of growth are fully aerobic, the latter is not synthesized and does not function. The former, synthesized under the control of at least four genes, is repressed by readily available nitrogen sources.

Energy conservation in chemotrophic anaerobic bacteria

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