Skip to main content
  • ASM
    • Antimicrobial Agents and Chemotherapy
    • Applied and Environmental Microbiology
    • Clinical Microbiology Reviews
    • Clinical and Vaccine Immunology
    • EcoSal Plus
    • Eukaryotic Cell
    • Infection and Immunity
    • Journal of Bacteriology
    • Journal of Clinical Microbiology
    • Journal of Microbiology & Biology Education
    • Journal of Virology
    • mBio
    • Microbiology and Molecular Biology Reviews
    • Microbiology Resource Announcements
    • Microbiology Spectrum
    • Molecular and Cellular Biology
    • mSphere
    • mSystems
  • Log in
  • My alerts
  • My Cart

Main menu

  • Home
  • Articles
    • Current Issue
    • Accepted Manuscripts
    • Archive
    • Minireviews
    • JB Special Collection
    • JB Classic Spotlights
  • For Authors
    • Submit a Manuscript
    • Scope
    • Editorial Policy
    • Submission, Review, & Publication Processes
    • Organization and Format
    • Errata, Author Corrections, Retractions
    • Illustrations and Tables
    • Nomenclature
    • Abbreviations and Conventions
    • Publication Fees
    • Ethics Resources and Policies
  • About the Journal
    • About JB
    • Editor in Chief
    • Editorial Board
    • For Reviewers
    • For the Media
    • For Librarians
    • For Advertisers
    • Alerts
    • RSS
    • FAQ
  • Subscribe
    • Members
    • Institutions
  • ASM
    • Antimicrobial Agents and Chemotherapy
    • Applied and Environmental Microbiology
    • Clinical Microbiology Reviews
    • Clinical and Vaccine Immunology
    • EcoSal Plus
    • Eukaryotic Cell
    • Infection and Immunity
    • Journal of Bacteriology
    • Journal of Clinical Microbiology
    • Journal of Microbiology & Biology Education
    • Journal of Virology
    • mBio
    • Microbiology and Molecular Biology Reviews
    • Microbiology Resource Announcements
    • Microbiology Spectrum
    • Molecular and Cellular Biology
    • mSphere
    • mSystems

User menu

  • Log in
  • My alerts
  • My Cart

Search

  • Advanced search
Journal of Bacteriology
publisher-logosite-logo

Advanced Search

  • Home
  • Articles
    • Current Issue
    • Accepted Manuscripts
    • Archive
    • Minireviews
    • JB Special Collection
    • JB Classic Spotlights
  • For Authors
    • Submit a Manuscript
    • Scope
    • Editorial Policy
    • Submission, Review, & Publication Processes
    • Organization and Format
    • Errata, Author Corrections, Retractions
    • Illustrations and Tables
    • Nomenclature
    • Abbreviations and Conventions
    • Publication Fees
    • Ethics Resources and Policies
  • About the Journal
    • About JB
    • Editor in Chief
    • Editorial Board
    • For Reviewers
    • For the Media
    • For Librarians
    • For Advertisers
    • Alerts
    • RSS
    • FAQ
  • Subscribe
    • Members
    • Institutions
ENZYMES AND PROTEINS

Differential Accumulation of nifStructural Gene mRNA in Azotobacter vinelandii

Trinity L. Hamilton, Marty Jacobson, Marcus Ludwig, Eric S. Boyd, Donald A. Bryant, Dennis R. Dean, John W. Peters
Trinity L. Hamilton
1Department of Chemistry and Biochemistry and the Astrobiology Biogeocatalysis Research Center, Montana State University, Bozeman, Montana 59717
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
Marty Jacobson
2Department of Biochemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
Marcus Ludwig
3Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
Eric S. Boyd
1Department of Chemistry and Biochemistry and the Astrobiology Biogeocatalysis Research Center, Montana State University, Bozeman, Montana 59717
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
Donald A. Bryant
1Department of Chemistry and Biochemistry and the Astrobiology Biogeocatalysis Research Center, Montana State University, Bozeman, Montana 59717
3Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
Dennis R. Dean
2Department of Biochemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
  • For correspondence: deandr@vt.edu john.peters@chemistry.montana.edu
John W. Peters
1Department of Chemistry and Biochemistry and the Astrobiology Biogeocatalysis Research Center, Montana State University, Bozeman, Montana 59717
4Department of Microbiology, Montana State University, Bozeman, Montana 59717
  • Find this author on Google Scholar
  • Find this author on PubMed
  • Search for this author on this site
  • For correspondence: deandr@vt.edu john.peters@chemistry.montana.edu
DOI: 10.1128/JB.05100-11
  • Article
  • Figures & Data
  • Info & Metrics
  • PDF
Loading

ABSTRACT

Northern analysis was employed to investigate mRNA produced by mutant strains of Azotobacter vinelandiiwith defined deletions in the nifstructural genes and in the intergenic noncoding regions. The results indicate that intergenic RNA secondary structures effect the differential accumulation of transcripts, supporting the high Fe protein-to-MoFe protein ratio required for optimal diazotrophic growth.

TEXT

Biological nitrogen fixation occurs by the activity of nitrogenase, which exists as a complex metalloenzyme composed of two easily separable components. The Fe protein component (encoded by nifH) serves as the obligate electron donor to the MoFe protein component (encoded by nifDK), which contains the active site for dinitrogen reduction (12). In addition to the structural proteins, the nitrogenase enzyme requires extensive biosynthetic machinery consisting of enzymes, scaffolds, and carrier proteins to assemble the metalloclusters required for catalysis (3, 15). nifgenes are located in two clusters in the model diazotroph, Azotobacter vinelandii. The major nifcluster contains the structural genes and those for most of the biosynthetic machinery, which are organized in several contiguous operons (6), and a minor nifcluster contains the nifregulatory elements and the remaining, necessary biosynthetic genes (8). The major nifcluster in A. vinelandiiwas sequenced more than 3 decades ago and has been the subject of a number of gene deletion and mutation studies, which laid the groundwork for our current understanding of the operon structure and regulation of nif(6). The genes encoding the nitrogenase structural proteins, nifH, nifD, and nifK, are located in the major nifoperon and are cotranscribed from a single promoter, the nifHpromoter, along with nifT, nifY, orf1, and lrv(6). The nifHpromoter is efficient and is effectively regulated, driving the rapid and abundant expression of nitrogenase in the absence of fixed N and conversely an abrupt decline in nitrogenase component transcription in the presence of fixed N (16).

In vitrocharacterization of nitrogenase from a variety of microbial sources indicates that the highest nitrogenase activities are observed at high Fe protein-to-MoFe protein ratios. In line with these observations, Northern blot hybridization analyses have indicated differential expression of the nifstructural proteins (7), and immunoblotting has shown that the Fe protein occurs in significant excess compared to MoFe protein levels in cultures grown under diazotrophic conditions (2, 7). Moreover, global transcriptional analyses indicate that nifHmRNA accumulates at ∼3-fold-higher levels than nifDand nifKmessages in A. vinelandiigrown diazotrophically (4). Because the genes encoding the nitrogenase Fe protein and MoFe protein are cotranscribed in A. vinelandii, a mechanism must exist to control differential nifstructural gene transcript abundance.

In order to assess possible mechanisms resulting in the differential accumulation of nifstructural gene mRNA and nitrogenase component proteins, Northern blot hybridization analysis was performed, probing mRNAs for nifH. Wild-type A. vinelandiiand deletion strains were grown in fixed-N replete, modified Burk medium (17), and cells were derepressed to induce expression of nitrogenase as previously described (16). Deletion strains were constructed as previously described (1, 6, 13, 14). Samples for Northern blot hybridization were collected at 10-min intervals for 120 min. RNA extraction, glyoxylation, and electrophoresis were performed as described previously (10, 11). Transfer of RNA onto GeneScreen hybridization membranes and subsequent hybridization were performed according to the manufacturers' instructions (Dupont). Approximately 10 μg of RNA from each sample was analyzed by Northern blot hybridization using a nifH-specific, 32P-labeled probe, pMJH5, purified from Escherichia colias previously described (7). The results revealed differential accumulation of major transcripts that could correspond to nifH, nifHD, and nifHDKand a very minor transcript corresponding to the length of the entire operon, nifH, nifD, nifK, nifT, nifY, orf1, and lrv(Fig. 1A). The identity of the three most abundant transcripts was established in two ways. First, when a nifD-specific hybridization probe was used for Northern blot analysis, only the bands corresponding to putative nifHDand nifHDKtranscripts were detected (data not shown). In a second series of experiments, strains having defined deletions within the structural gene region were analyzed by Northern blot analysis using a nifHprobe (Fig. 1B). These results showed that a deletion within nifDhad no effect on the size of the accumulated nifHtranscripts but resulted in accumulation of smaller transcripts assigned to nifHDand nifHDK(DJ100) (Fig. 1B). Similarly, a deletion in nifKhad no effect on the size of the transcripts corresponding to nifHor nifHDbut resulted in the accumulation of a smaller transcript assigned to nifHDK(DJ13) (Fig. 1B). Strains that had deletions that spanned portions of nifHand nifD(DJ46) (Fig. 1B) or nifDand nifK(DJ33) (Fig. 1B) resulted in the accumulation of only two major transcripts, which suggested that elements leading to differential accumulation are likely to be located within the intergenic regions. A strain having a deletion of nifHthat encompassed the region corresponding to the nifH-specific probe showed no nifHhybridizing transcripts (DJ54) (Fig. 1B). These results are consistent with the aforementioned results showing that the major nifoperon produces three major transcripts that correspond to nifH, nifHD, and nifHDK.

Fig. 1.
  • Open in new tab
  • Download powerpoint
Fig. 1.

(A) Northern blot hybridization analysis of total RNA isolated from wild-type A. vinelandiiusing pMJH5, a nifH-specific probe. Cells were derepressed in N-free medium, and total RNA was extracted at 10-min increments from 0 to 120 min. The black arrow indicates the minor band resulting from the entire nifstructural gene operon. (B) Northern blot hybridization analysis of total RNA isolated from A. vinelandiistrains with deletions spanning regions of the structural genes indicated, performed by using pMJH5, a nifH-specific probe. Cells were derepressed in N-free medium, and total RNA was extracted 60 min after derepression. Nif+strains were capable of diazotrophic growth; Nif−strains were not.

It is interesting that during the transition to nitrogen-fixing conditions, the relative abundances of the three nifH-specific transcripts changed noticeably. For example, inspection of the time course shown in Fig. 1A revealed that in the early stage of nifderepression, the major accumulating mRNA corresponds to nifHDK. In contrast, as the cells enter steady-state, nitrogen fixation conditions (∼90 min following derepression), the relative amounts of shorter transcripts solely for nifHincreased in abundance relative to the longer transcripts. The elevated transcript levels for nifH, compared to nifDKexpression under steady-state nitrogen-fixing conditions, is in line with establishing and maintaining the high Fe protein-to-MoFe protein ratios required for optimal nitrogenase catalytic activity. It is not clear why there is an apparent increased capacity for expression of nifDrelative to that of nifK, because these genes encode subunits of the MoFe protein, which are required in equimolar amounts. However, it could be a mechanism to counteract potential differences in translation efficiencies for these transcripts or in the stabilities of nitrogenase protein subunits.

A closer analysis of the nucleotide sequences in the regions that separate the coding regions of the nifstructural gene operon revealed potential secondary structures between nifHand nifD, between nifDand nifK, and downstream from nifK(5, 19) (Fig. 2A). Free energy (ΔG) values of −29.0 and −26.9 kcal/mol were calculated for the structures between nifHand nifDand nifDand nifK, respectively (Fig. 2A). Additional structures predicted just downstream of nifKhad free energy values of −29.0 and −44.0 kcal/mol. Transcript profiling of A. vinelandiiunder Mo-dependent, nitrogen-fixing conditions (4) indicates a specific decrease in transcript sequences corresponding to a very small region that spans the putative mRNA secondary structure (Fig. 2A). Similar decreases in transcript abundance were observed for the regions corresponding to the predicted structures between nifDand nifKand downstream of nifK(data not shown). Conventionally, RNA structures have been probed individually, but the advent of whole-transcriptome sequencing has precipitated the need for high-throughput RNA structure probing to complement transcriptional profiling (9, 18). However, mapping the end of the most abundant message corresponding to nifHclearly indicates that transcript levels declined upstream of the first structure observed in the operon located between nifHand nifD(Fig. 2A). An inability to produce any detectable cDNA spanning the proposed secondary structure located within the nifH-nifDintergenic region provides strong evidence for the formation of a secondary structure within this region. This is further supported by the failure to detect cDNA sequence reads within the regions that define the putative secondary structures in the nifD-nifKintergenic region and downstream of nifK(data not shown).

Fig. 2.
  • Open in new tab
  • Download powerpoint
Fig. 2.

(A) Identification of RNA secondary structures between the nifstructural genes. ΔGvalues are given in kcal/mol. The transcript abundance of the intergenic region between nifHand nifDis plotted against the location of these genes in the genome. The box indicates the location of the RNA secondary structure. For detailed methods of transcriptional profiling, see reference 4. (B) Northern blot hybridization analysis of total RNA isolated from A. vinelandiimutant strain DJ81 using pMJH5, a nifH-specific probe. Cells were derepressed in N-free medium, and total RNA was extracted at 10-min increments from 0 to 120 min.

To examine the role of the intergenic regions in the differential accumulation of the nifstructural gene operon directly, a strain was constructed (DJ81) that had an 87-bp deletion spanning the proposed secondary structure located in the nifH-nifDintergenic region. Strain DJ81 was capable of diazotrophic growth at rates comparable to those of the wild type under typical laboratory culture conditions (6) (data not shown). Northern blot hybridization analysis of this strain revealed the accumulation of only two major nifHtranscripts, corresponding to nifHDand nifHDK, and a very minor transcript, which could correspond to nifH, nifD, nifK, nifT, nifY, orf1, and lrv(Fig. 2B). In this strain, no nifH-only transcripts were detected. As with the wild type (Fig. 1A), the first major accumulating mRNA during nifderepression of DJ81 corresponds to nifHDK, with the shorter nifHDtranscript accumulating later. This result provides further evidence that the secondary structures act as processing and/or mRNA stabilizing sites that increase the lifetime of specific segments of the primary transcripts.

In summary, the Northern analysis of multiple deletion mutants indicates definitively that all nifH-specific transcripts observed originate from the nifHpromoter and correspond to nifH, nifHD, nifHDK, and a small proportion of a full-length transcript representing the entire operon. The elimination of specific transcript segments in response to deletion of the intergenic regions clearly demonstrates the role of intergenic RNA secondary structures in differential accumulation of nifstructural gene mRNAs. The intergenic secondary structures could function as premature termination sites and/or sites of processing and stabilization. The changes in the relative abundances of nifH-specific transcripts that are observed to occur over the course of depression (Fig. 1A and 2B) seem to favor the latter or imply the involvement of trans-acting elements in controlling the ratios of these transcripts for optimal diazotrophic growth. In this regard, the differential accumulation of mRNA represents one mechanism for the production of the appropriate relative abundances of the nitrogenase components for optimal catalytic function. This mechanism may also be important in compensating for differences in translation efficiencies of the nifstructural genes or protein subunit stabilities.

ACKNOWLEDGMENTS

This work was supported by the NASA Astrobiology Institute, grant NNA08C-N85Ato J.W.P., NASA Astrobiology (Exobiology and Evolutionary Biology) AwardNNX09AM87G(to D.A.B.), and NSF MCB-071770(to D.R.D.). T.L.H. was supported by an NSF-Integrated Graduate Educational Research and Training fellowship grant, and E.S.B. was supported by a fellowship from the NASA Astrobiology Institute Postdoctoral Program.

FOOTNOTES

    • Received 15 April 2011.
    • Accepted 25 June 2011.
    • Accepted manuscript posted online 1 July 2011.
  • Copyright © 2011, American Society for Microbiology. All Rights Reserved.

REFERENCES

  1. 1.↵
    1. Brigle K. E.,
    2. et al
    . 1987. Site-directed mutagenesis of the nitrogenase MoFe protein of Azotobacter vinelandii. Proc. Natl. Acad. Sci. U. S. A.84:7066–7069.
    OpenUrlAbstract/FREE Full Text
  2. 2.↵
    1. Dingler C.,
    2. Kuhla J.,
    3. Wassink H.,
    4. Oelze J.
    . 1988. Levels and activities of nitrogenase proteins in Azotobacter vinelandiigrown at different dissolved oxygen concentrations. J. Bacteriol.170:2148–2152.
    OpenUrlAbstract/FREE Full Text
  3. 3.↵
    1. Dos Santos P. C.,
    2. Dean D. R.
    . 2011. Coordination and fine-tuning of nitrogen fixation in Azotobacter vinelandii. Mol. Microbiol.79:1132–1135.
    OpenUrlCrossRefPubMed
  4. 4.↵
    1. Hamilton T. L.,
    2. et al
    . 2011. Transcriptional profiling of nitrogen fixation in Azotobacter vinelandii. J. Bacteriol.193:4477–4486.
    OpenUrlAbstract/FREE Full Text
  5. 5.↵
    1. Hofacker I. L
    . 2003. Vienna RNA secondary structure server. Nucleic Acids Res.31:3429–3431.
    OpenUrlCrossRefPubMedWeb of Science
  6. 6.↵
    1. Jacobson M. R.,
    2. et al
    . 1989. Physical and genetic map of the major nifgene cluster from Azotobacter vinelandii. J. Bacteriol.171:1017–1027.
    OpenUrlAbstract/FREE Full Text
  7. 7.↵
    1. Jacobson M. R.,
    2. Premakumar R.,
    3. Bishop P. E.
    . 1986. Transcriptional regulation of nitrogen fixation by molybdenum in Azotobacter vinelandii. J. Bacteriol.167:480–486.
    OpenUrlAbstract/FREE Full Text
  8. 8.↵
    1. Joerger R. D.,
    2. Bishop P. E.
    . 1988. Nucleotide sequence and genetic analysis of the nifB-nifQregion from Azotobacter vinelandii. J. Bacteriol.170:1475–1487.
    OpenUrlAbstract/FREE Full Text
  9. 9.↵
    1. Kertesz M.,
    2. et al
    . 2010. Genome-wide measurement of RNA secondary structure in yeast. Nature467:103–107.
    OpenUrlCrossRefPubMedWeb of Science
  10. 10.↵
    1. Krol A. J.,
    2. Hontelez J. G.,
    3. Roozendaal B.,
    4. van Kammen A.
    . 1982. On the operon structure of the nitrogenase genes of Rhizobium leguminosarumand Azotobacter vinelandii. Nucleic Acids Res.10:4147–4157.
    OpenUrlCrossRefPubMed
  11. 11.↵
    1. McMaster G. K.,
    2. Carmichael G. G.
    . 1977. Analysis of single- and double-stranded nucleic acids on polyacrylamide and agarose gels by using glyoxal and acridine orange. Proc. Natl. Acad. Sci. U. S. A.74:4835–4838.
    OpenUrlAbstract/FREE Full Text
  12. 12.↵
    1. Peters J. W.,
    2. Szilagyi R. K.
    . 2006. Exploring new frontiers of nitrogenase structure and mechanism. Curr. Opin. Chem. Biol.10:101–108.
    OpenUrlCrossRefPubMed
  13. 13.↵
    1. Robinson A. C.,
    2. Burgess B. K.,
    3. Dean D. R.
    . 1986. Activity, reconstitution, and accumulation of nitrogenase components in Azotobacter vinelandiimutant strains containing defined deletions within the nitrogenase structural gene cluster. J. Bacteriol.166:180–186.
    OpenUrlAbstract/FREE Full Text
  14. 14.↵
    1. Robinson A. C.,
    2. Dean D. R.,
    3. Burgess B. K.
    . 1987. Iron-molybdenum cofactor biosynthesis in Azotobacter vinelandiirequires the iron protein of nitrogenase. J. Biol. Chem.262:14327–14332.
    OpenUrlAbstract/FREE Full Text
  15. 15.↵
    1. Rubio L. M.,
    2. Ludden P. W.
    . 2008. Biosynthesis of the iron-molybdenum cofactor of nitrogenase. Annu. Rev. Microbiol.62:93–111.
    OpenUrlCrossRefPubMedWeb of Science
  16. 16.↵
    1. Shah V. K.,
    2. Davis L. C.,
    3. Brill W. J.
    . 1972. Nitrogenase. I. Repression and derepression of the iron-molybdenum and iron proteins of nitrogenase in Azotobacter vinelandii. Biochim. Biophys. Acta256:498–511.
    OpenUrlPubMed
  17. 17.↵
    1. Strandberg G. W.,
    2. Wilson P. W.
    . 1968. Formation of the nitrogen-fixing enzyme system in Azotobacter vinelandii. Can. J. Microbiol.14:25–31.
    OpenUrlCrossRefPubMedWeb of Science
  18. 18.↵
    1. Underwood J. G.,
    2. et al
    . 2010. FragSeq: transcriptome-wide RNA structure probing using high-throughput sequencing. Nat. Methods7:995–1001.
    OpenUrlCrossRefPubMedWeb of Science
  19. 19.↵
    1. Zuker M
    . 2003. Mfold web server for nucleic acid folding and hybridization prediction. Nucleic. Acids Res.31:3406–3415.
    OpenUrlCrossRefPubMedWeb of Science
PreviousNext
Back to top
Download PDF
Citation Tools
Differential Accumulation of nifStructural Gene mRNA in Azotobacter vinelandii
Trinity L. Hamilton, Marty Jacobson, Marcus Ludwig, Eric S. Boyd, Donald A. Bryant, Dennis R. Dean, John W. Peters
Journal of Bacteriology Aug 2011, 193 (17) 4534-4536; DOI: 10.1128/JB.05100-11

Citation Manager Formats

  • BibTeX
  • Bookends
  • EasyBib
  • EndNote (tagged)
  • EndNote 8 (xml)
  • Medlars
  • Mendeley
  • Papers
  • RefWorks Tagged
  • Ref Manager
  • RIS
  • Zotero
Print

Alerts
Sign In to Email Alerts with your Email Address
Email

Thank you for sharing this Journal of Bacteriology article.

NOTE: We request your email address only to inform the recipient that it was you who recommended this article, and that it is not junk mail. We do not retain these email addresses.

Enter multiple addresses on separate lines or separate them with commas.
Differential Accumulation of nifStructural Gene mRNA in Azotobacter vinelandii
(Your Name) has forwarded a page to you from Journal of Bacteriology
(Your Name) thought you would be interested in this article in Journal of Bacteriology.
CAPTCHA
This question is for testing whether or not you are a human visitor and to prevent automated spam submissions.
Share
Differential Accumulation of nifStructural Gene mRNA in Azotobacter vinelandii
Trinity L. Hamilton, Marty Jacobson, Marcus Ludwig, Eric S. Boyd, Donald A. Bryant, Dennis R. Dean, John W. Peters
Journal of Bacteriology Aug 2011, 193 (17) 4534-4536; DOI: 10.1128/JB.05100-11
del.icio.us logo Digg logo Reddit logo Twitter logo CiteULike logo Facebook logo Google logo Mendeley logo
  • Top
  • Article
    • ABSTRACT
    • TEXT
    • ACKNOWLEDGMENTS
    • FOOTNOTES
    • REFERENCES
  • Figures & Data
  • Info & Metrics
  • PDF

Related Articles

Cited By...

About

  • About JB
  • Editor in Chief
  • Editorial Board
  • Policies
  • For Reviewers
  • For the Media
  • For Librarians
  • For Advertisers
  • Alerts
  • RSS
  • FAQ
  • Permissions
  • Journal Announcements

Authors

  • ASM Author Center
  • Submit a Manuscript
  • Article Types
  • Ethics
  • Contact Us

Follow #Jbacteriology

@ASMicrobiology

       

ASM Journals

ASM journals are the most prominent publications in the field, delivering up-to-date and authoritative coverage of both basic and clinical microbiology.

About ASM | Contact Us | Press Room

 

ASM is a member of

Scientific Society Publisher Alliance

 

American Society for Microbiology
1752 N St. NW
Washington, DC 20036
Phone: (202) 737-3600

Copyright © 2021 American Society for Microbiology | Privacy Policy | Website feedback

Print ISSN: 0021-9193; Online ISSN: 1098-5530