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Fine-structure mapping and complementation analysis of nif (nitrogen fixation) genes in Klebsiella pneumoniae
Abstract:
Four hundred and eighty-nine independent Nif- strains containing 260 point, 130 millimicron-induced, and 99 deletion mutations in nif in the Klebsiella pneumoniae chromosome were isolated. Three hundred and ninety insertion and point mutations were mapped with millimicron-induced deletions carried on 44 plasmids derived from pTM4010, a recombinant R factor containing the his-nif region of K. pneumoniae. The 99 chromosomal deletions in the nif region were mapped with 69 derivatives of pTM4010 carrying insertion and point mutations in nif. Complementation analysis between 84 derivatives of pTM4010 carrying nif mutations and Rec- derivatives of the 390 Nif- mutants identified 14 genes. The nif mutations were ordered into 49 deletion groups with a gene order of his...nifQBALFMVSNEKDHJ. Complementation analysis of millimicron-induced, amber, frameshift, and deletion mutations indicates there are five polycistronic and two monocistronic operons: nifQ nifB, nifA nifL, nifF, nifM nifV nifS, nifN nifE, nifK nifD nifH, and nifJ. Transcription is from right to left in all polycistronic operons.
Insights
Researchers mapped nitrogen fixation (nif) mutations in Klebsiella pneumoniae, identifying 14 genes and their order. This study details the organization of nitrogen fixation operons, crucial for microbial processes.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Nitrogen fixation (nif) is a vital process for microbial life, converting atmospheric nitrogen into ammonia.
- Understanding the genetic organization of nif genes is crucial for optimizing nitrogen fixation in bacteria like Klebsiella pneumoniae.
Purpose of the Study:
- To isolate and characterize independent nitrogen fixation (nif) deficient (Nif-) mutants in Klebsiella pneumoniae.
- To map the location and order of these nif mutations within the Klebsiella pneumoniae chromosome.
- To determine the operon structure and gene organization of the nif gene cluster.
Main Methods:
- Isolation of 489 independent Nif- mutants (point, induced, and deletion mutations).
- Mapping of mutations using deletion plasmids and complementation analysis.
- Identification of 14 nif genes and their ordering into 49 deletion groups.
Main Results:
- Established a gene order: his...nifQBALFMVSNEKDHJ.
- Identified five polycistronic and two monocistronic operons within the nif gene cluster.
- Determined that transcription in polycistronic operons proceeds from right to left.
Conclusions:
- The study provides a detailed genetic map of the nif region in Klebsiella pneumoniae.
- The identified operon structure offers insights into the regulation and expression of nitrogen fixation genes.
- This foundational research contributes to understanding the complex machinery of biological nitrogen fixation.