Why has the “nitrogenase plasmid” snubbed the pseudomonads?

Meganathan, R.

doi:10.1016/0022-5193(79)90213-3

“…The ability of the pseudomonads to fix atmospheric N 2 has not been appreciated [7,66,67] usually because of the following problems [39]: (a) mistaken or uncertain identification of the diazotroph; (b) lack of rigorous tests for diazotrophy in pseudomonads; and (c) multigeneric nature of the genus Pseudomonas as discussed above. Early attempts to find an N2-fixing pseudomonad were unsuccessful, due to the failure to recognise the 02 sensitivity or microaerobic character of its N2-fixing system.…”

Section: Diazotrophymentioning

confidence: 99%

N2-fixing pseudomonads and related soil bacteria

Chan

¹

1994

FEMS Microbiology Reviews

View full text Add to dashboard Cite

Pseudomonas-like organisms form a highly heterogeneous and ubiquitous group of bacteria. Recent identification of an authentic P~eudomonas genus should help to decrease difficulties which arose from taxonomic uncertainties. Further difficulties in recognising N2-fixing Pseudomonas species lie in the confirmation of diazotrophy. Optimised conditions are often needed for the detection of nitrogenase activity since it is controlled by specific environmental factors and physiological requirements. However, genetically constructed N2-fixing strains from authentic Pseudomonas species have demonstrated that at least some members of the genus possess mechanisms to accommodate and express nil (N z fixation) genes from a well-studied diazotroph, Klebsiella pneumoniae. Renowned for their catabolic versatility, pseudomonads can use a wide range of carbon and energy substrates. Hence, potential N2-fixing pseudomonads are conceivably less limited by carbon and energy sources available in the environment compared to other N2-fixing organisms. Pseudomonas species dominate in the rhizosphere of some plants from which isolates have been shown to be diazotrophic. Several strains are also chemolithotrophs, capable of using H 2 as energy and electron source and CO2 as carbon source. Besides assays for N2-fixing activity, DNA hybridisation to the well conserved molybdo-nitrogenase structural gene probe is an indicator of diazotrophy. However, absence of hybridisation to this probe, despite N 2 fixation activity, has been reported. Although the genetics of N 2 fixation in pseudomonads have hardly been studied, some nif genes have been shown to be plasmid-borne. Pseudomonas species are also predominant soil denitrifiers, reducing nitrate and nitrite to gaseous forms of nitrogen during anaerobic respiration. Hence, they play an important role in the global biological nitrogen cycle. Several diazotrophic species including a few pseudomonads can also denitrify. The potential contribution by Ne-fixing pseudomonads to the sinks and sources of soil nitrogen is considered small in the short term but essentially remains unclear in the absence of experimental data. Reliable rapid methods for their specific enumeration are indispensable for assessing their population dynamics and ascertaining their ecological significance.

show abstract

“…According to Palleroni [7], pseudomonads lack N2-fixing ability. The ability of the pseudomonads to fix atmospheric N 2 has not been appreciated [7,66,67] usually because of the following problems [39]: (a) mistaken or uncertain identification of the diazotroph; (b) lack of rigorous tests for diazotrophy in pseudomonads; and (c) multigeneric nature of the genus Pseudomonas as discussed above. Early attempts to find an N2-fixing pseudomonad were unsuccessful, due to the failure to recognise the 02 sensitivity or microaerobic character of its N2-fixing system.…”

Section: Diazotrophymentioning

confidence: 99%

N₂-fixing pseudomonads and related soil bacteria

Chan

¹

,

Barraquio

²

,

Knowles

³

1994

FEMS Microbiology Reviews

View full text Add to dashboard Cite

Pseudomonas-like organisms form a highly heterogeneous and ubiquitous group of bacteria. Recent identification of an authentic P~eudomonas genus should help to decrease difficulties which arose from taxonomic uncertainties. Further difficulties in recognising N2-fixing Pseudomonas species lie in the confirmation of diazotrophy. Optimised conditions are often needed for the detection of nitrogenase activity since it is controlled by specific environmental factors and physiological requirements. However, genetically constructed N2-fixing strains from authentic Pseudomonas species have demonstrated that at least some members of the genus possess mechanisms to accommodate and express nil (N z fixation) genes from a well-studied diazotroph, Klebsiella pneumoniae. Renowned for their catabolic versatility, pseudomonads can use a wide range of carbon and energy substrates. Hence, potential N2-fixing pseudomonads are conceivably less limited by carbon and energy sources available in the environment compared to other N2-fixing organisms. Pseudomonas species dominate in the rhizosphere of some plants from which isolates have been shown to be diazotrophic. Several strains are also chemolithotrophs, capable of using H 2 as energy and electron source and CO2 as carbon source. Besides assays for N2-fixing activity, DNA hybridisation to the well conserved molybdo-nitrogenase structural gene probe is an indicator of diazotrophy. However, absence of hybridisation to this probe, despite N 2 fixation activity, has been reported. Although the genetics of N 2 fixation in pseudomonads have hardly been studied, some nif genes have been shown to be plasmid-borne. Pseudomonas species are also predominant soil denitrifiers, reducing nitrate and nitrite to gaseous forms of nitrogen during anaerobic respiration. Hence, they play an important role in the global biological nitrogen cycle. Several diazotrophic species including a few pseudomonads can also denitrify. The potential contribution by Ne-fixing pseudomonads to the sinks and sources of soil nitrogen is considered small in the short term but essentially remains unclear in the absence of experimental data. Reliable rapid methods for their specific enumeration are indispensable for assessing their population dynamics and ascertaining their ecological significance. NUM347(a mbds.nrc.ca. distributed within any one genus, diazotrophic strains commonly exist in the genera of both archaeobacteria (eqv. archaebacteria [1]) and eubacteria. Free-living diazotrophs excluding photosynthetic bacteria and cyanobacteria are mostly heterotrophs with aerobic, microaerobic or anaerobic respiration when fixing N 2. Because of the high energy demand for N 2 fixation, free-liv-SSDI 01 68-6445(93)E0092-X

show abstract

“…Another reason was the demonstration by Line & Loutit (1973) that presumptive diazotrophic 'pseudomonas' colonies from New Zealand soil were syntrophic mixtures of pseudomonads with anaerobic diazotrophs resembling Clostridium butyricum. Despite occasional reports of the isolation of taxonomically unassigned diazotrophic pseudomonads, a 'dogma' arose that the genus Pseudomonas did not include diazotrophs (see, for example, Meganathan 1979). However, an authenticated P. saccharophila exhibits very 0 2-sensitive diazotrophy (Barraquio et al 1986).…”

Section: Kp Nif In Pseudomonadsmentioning

confidence: 99%

nifgenes in alien backgrounds

Postgate

¹

,

Dixon

²

,

Hill

³

et al. 1987

Phil. Trans. R. Soc. Lond. B

View full text Add to dashboard Cite

Since the original construction of diazotrophic Escherichia coli by conjugal transfer of nif genes from Klebsiella pneumoniae in 1972, the manipulation of nif genes into alien prokaryotic backgrounds has become routine: much of the basic genetics of the K. pneumoniae nif cluster was elucidated in an E. coli background. Gene transfers to new species and genera can give new information regarding the stability of nif genes and, particularly, conditions for their expression; recipients in which nif is partly expressed, or not expressed at all, are especially useful. Appropriate examples are discussed. New diazotrophic prokaryotes show little promise for practical exploitation but their construction should give forewarning of problems to be expected in the construction of diazotrophic eukaryotes, as well as hints concerning the ecology and evolution of diazotrophy.

show abstract

Why has the “nitrogenase plasmid” snubbed the pseudomonads?

Cited by 5 publications

References 26 publications

N2-fixing pseudomonads and related soil bacteria

N2-fixing pseudomonads and related soil bacteria

N₂-fixing pseudomonads and related soil bacteria

nifgenes in alien backgrounds

Contact Info

Product

Resources

About