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Cell cycle dysregulation of globally important SAR11 bacteria resulting from environmental perturbation – Microbiology Research


  • Giovannoni, S. J., Thrash, J. C. & Temperton, B. Implications of streamlining theory for microbial ecology. ISME J. 8, 1553–1565 (2014).

    Article 
    PubMed 
    PubMed Central 

    Google Scholar
     

  • McCutcheon, J. P. & Moran, N. A. Extreme genome reduction in symbiotic bacteria. Nat. Rev. Microbiol. 10, 13–26 (2011).

    Article 
    PubMed 

    Google Scholar
     

  • Morris, R. M. et al. SAR11 clade dominates ocean surface bacterioplankton communities. Nature 420, 806–810 (2002).

    Article 
    CAS 
    PubMed 

    Google Scholar
     

  • Schattenhofer, M. et al. Latitudinal distribution of prokaryotic picoplankton populations in the Atlantic Ocean. Environ. Microbiol. 11, 2078–2093 (2009).

    Article 
    CAS 
    PubMed 

    Google Scholar
     

  • Giovannoni, S. J. SAR11 Bacteria: the most abundant plankton in the oceans. Ann. Rev. Mar. Sci. 9, 231–255 (2017).

    Article 
    PubMed 

    Google Scholar
     

  • Giovannoni, S. J. et al. Genome streamlining in a cosmopolitan oceanic bacterium. Science 309, 1242–1245 (2005).

    Article 
    CAS 
    PubMed 

    Google Scholar
     

  • Grote, J. et al. Streamlining and core genome conservation among highly divergent members of the SAR11 clade. mBio 3, e00252-12 (2012).

  • Noell, S. E. & Giovannoni, S. J. SAR11 bacteria have a high affinity and multifunctional glycine betaine transporter. Environ. Microbiol. 21, 2559–2575 (2019).

    Article 
    CAS 
    PubMed 

    Google Scholar
     

  • Clifton, B. E., Alcolombri, U., Uechi, G.-I., Jackson, C. J. & Laurino, P. The ultra-high affinity transport proteins of ubiquitous marine bacteria. Nature 634, 721–728 (2024).

    Article 
    CAS 
    PubMed 
    PubMed Central 

    Google Scholar
     

  • Grzymski, J. J. & Dussaq, A. M. The significance of nitrogen cost minimization in proteomes of marine microorganisms. ISME J. 6, 71–80 (2012).

    Article 
    CAS 
    PubMed 

    Google Scholar
     

  • Gibson, D. G. et al. Creation of a bacterial cell controlled by a chemically synthesized genome. Science 329, 52–56 (2010).

    Article 
    CAS 
    PubMed 

    Google Scholar
     

  • Lachance, J.-C., Rodrigue, S. & Palsson, B. O. Minimal cells, maximal knowledge. eLife 8, e45379 (2019).

    Article 
    PubMed 
    PubMed Central 

    Google Scholar
     

  • Moger-Reischer, R. Z. et al. Evolution of a minimal cell. Nature 620, 122–127 (2023).

  • Cottrell, M. T. & Kirchman, D. L. Transcriptional control in marine copiotrophic and oligotrophic bacteria with streamlined genomes. Appl. Environ. Microbiol. 82, 6010–6018 (2016).

    Article 
    CAS 
    PubMed 
    PubMed Central 

    Google Scholar
     

  • Noell, S. E., Hellweger, F. L., Temperton, B. & Giovannoni, S. J. A reduction of transcriptional regulation in aquatic oligotrophic microorganisms enhances fitness in nutrient-poor environments. Microbiol. Mol. Biol. Rev. 87, e0012422 (2023).

    Article 
    PubMed 

    Google Scholar
     

  • Tripp, H. J. et al. SAR11 marine bacteria require exogenous reduced sulphur for growth. Nature 452, 741–744 (2008).

    Article 
    CAS 
    PubMed 

    Google Scholar
     

  • Tripp, H. J. et al. Unique glycine-activated riboswitch linked to glycine-serine auxotrophy in SAR11. Environ. Microbiol. 11, 230–238 (2009).

    Article 
    CAS 
    PubMed 
    PubMed Central 

    Google Scholar
     

  • Carini, P., Steindler, L., Beszteri, S. & Giovannoni, S. J. Nutrient requirements for growth of the extreme oligotroph ‘Candidatus Pelagibacter ubique’ HTCC1062 on a defined medium. ISME J. 7, 592–602 (2013).

    Article 
    CAS 
    PubMed 

    Google Scholar
     

  • Carlson, C. A. et al. Seasonal dynamics of SAR11 populations in the euphotic and mesopelagic zones of the northwestern Sargasso Sea. ISME J. 3, 283–295 (2009).

    Article 
    CAS 
    PubMed 

    Google Scholar
     

  • Becker, J. W., Hogle, S. L., Rosendo, K. & Chisholm, S. W. Co-culture and biogeography of Prochlorococcus and SAR11. ISME J. 13, 1506–1519 (2019).

    Article 
    CAS 
    PubMed 
    PubMed Central 

    Google Scholar
     

  • Dethlefsen, L. & Schmidt, T. M. Performance of the translational apparatus varies with the ecological strategies of bacteria. J. Bacteriol. 189, 3237–3245 (2007).

    Article 
    CAS 
    PubMed 
    PubMed Central 

    Google Scholar
     

  • Roller, B. R. K., Stoddard, S. F. & Schmidt, T. M. Exploiting rRNA operon copy number to investigate bacterial reproductive strategies. Nat. Microbiol. 1, 16160 (2016).

    Article 
    CAS 
    PubMed 
    PubMed Central 

    Google Scholar
     

  • Schwalbach, M. S., Tripp, H. J., Steindler, L., Smith, D. P. & Giovannoni, S. J. The presence of the glycolysis operon in SAR11 genomes is positively correlated with ocean productivity. Environ. Microbiol. 12, 490–500 (2010).

    Article 
    CAS 
    PubMed 

    Google Scholar
     

  • Carini, P., White, A. E., Campbell, E. O. & Giovannoni, S. J. Methane production by phosphate-starved SAR11 chemoheterotrophic marine bacteria. Nat. Commun. 5, 4346 (2014).

    Article 
    CAS 
    PubMed 

    Google Scholar
     

  • Lankiewicz, T. S., Cottrell, M. T. & Kirchman, D. L. Growth rates and rRNA content of four marine bacteria in pure cultures and in the Delaware estuary. ISME J. 10, 823–832 (2016).

    Article 
    CAS 
    PubMed 

    Google Scholar
     

  • Henson, M. W., Lanclos, V. C., Faircloth, B. C. & Thrash, J. C. Cultivation and genomics of the first freshwater SAR11 (LD12) isolate. ISME J. 12, 1846–1860 (2018).

    Article 
    CAS 
    PubMed 
    PubMed Central 

    Google Scholar
     

  • Lanclos, V. C. et al. Ecophysiology and genomics of the brackish water adapted SAR11 subclade IIIa. ISME J. 17, 620–629 (2023).

    Article 
    CAS 
    PubMed 
    PubMed Central 

    Google Scholar
     

  • Willis, L. & Huang, K. C. Sizing up the bacterial cell cycle. Nat. Rev. Microbiol. 15, 606–620 (2017).

    Article 
    CAS 
    PubMed 

    Google Scholar
     

  • Olsson, J. A., Nordström, K., Hjort, K. & Dasgupta, S. Eclipse–synchrony relationship in Escherichia coli strains with mutations affecting sequestration, initiation of replication and superhelicity of the bacterial chromosome. J. Mol. Biol. 334, 919–931 (2003).

    Article 
    CAS 
    PubMed 

    Google Scholar
     

  • Levin, P. A., Shim, J. J. & Grossman, A. D. Effect of minCD on FtsZ ring position and polar septation in Bacillus subtilis. J. Bacteriol. 180, 6048–6051 (1998).

    Article 
    CAS 
    PubMed 
    PubMed Central 

    Google Scholar
     

  • Sundararajan, K. et al. The bacterial tubulin FtsZ requires its intrinsically disordered linker to direct robust cell wall construction. Nat. Commun. 6, 7281 (2015).

    Article 
    CAS 
    PubMed 

    Google Scholar
     

  • Dubarry, N., Willis, C. R., Ball, G., Lesterlin, C. & Armitage, J. P. In vivo imaging of the segregation of the 2 chromosomes and the cell division proteins of Rhodobacter sphaeroides reveals an unexpected role for MipZ. mBio 10, e02515-18 (2019).

  • Pelletier, J. F. et al. Genetic requirements for cell division in a genomically minimal cell. Cell 184, 2430–2440.e16 (2021).

    Article 
    CAS 
    PubMed 

    Google Scholar
     

  • Fujikawa, N. et al. Structural and biochemical analyses of hemimethylated DNA binding by the SeqA protein. Nucleic Acids Res. 32, 82–92 (2004).

    Article 
    CAS 
    PubMed 
    PubMed Central 

    Google Scholar
     

  • Boye, E. & Løbner-Olesen, A. The role of dam methyltransferase in the control of DNA replication in E. coli. Cell 62, 981–989 (1990).

    Article 
    CAS 
    PubMed 

    Google Scholar
     

  • Blair, J. A. et al. Branched signal wiring of an essential bacterial cell-cycle phosphotransfer protein. Structure 21, 1590–1601 (2013).

    Article 
    CAS 
    PubMed 
    PubMed Central 

    Google Scholar
     

  • Krupka, M., Sobrinos-Sanguino, M., Jiménez, M., Rivas, G. & Margolin, W. Escherichia coli ZipA organizes FtsZ polymers into dynamic ring-like protofilament structures. mBio 9, e01008-18 (2018).

  • Pichoff, S., Du, S. & Lutkenhaus, J. Roles of FtsEX in cell division. Res. Microbiol. 170, 374–380 (2019).

    Article 
    CAS 
    PubMed 
    PubMed Central 

    Google Scholar
     

  • Corrales-Guerrero, L. et al. MipZ caps the plus-end of FtsZ polymers to promote their rapid disassembly. Proc. Natl Acad. Sci. USA 119, e2208227119 (2022).

    Article 
    CAS 
    PubMed 
    PubMed Central 

    Google Scholar
     

  • Letzkus, M., Trela, C. & Mera, P. E. Three factors ParA, TipN, and DnaA-mediated chromosome replication initiation are contributors of centromere segregation in Caulobacter crescentus. Mol. Biol. Cell 35, ar68 (2024).

    Article 
    PubMed 
    PubMed Central 

    Google Scholar
     

  • Freel, K. C. et al. New SAR11 isolate genomes and global marine metagenomes resolve ecologically relevant units within the Pelagibacterales. Nat. Commun. 17, 328 (2025).

    Article 
    PubMed 
    PubMed Central 

    Google Scholar
     

  • Oren, A. A plea for linguistic accuracy – also for Candidatus taxa. Int. J. Syst. Evol. Microbiol. 67, 1085–1094 (2017).

    Article 
    PubMed 

    Google Scholar
     

  • Cooper, S. & Helmstetter, C. E. Chromosome replication and the division cycle of Escherichia coli B/r. J. Mol. Biol. 31, 519–540 (1968).

    Article 
    CAS 
    PubMed 

    Google Scholar
     

  • Jun, S., Si, F., Pugatch, R. & Scott, M. Fundamental principles in bacterial physiology—history, recent progress, and the future with focus on cell size control: a review. Rep. Prog. Phys. 81, 056601 (2018).

    Article 
    PubMed 
    PubMed Central 

    Google Scholar
     

  • Skarstad, K., Steen, H. B. & Boye, E. Escherichia coli DNA distributions measured by flow cytometry and compared with theoretical computer simulations. J. Bacteriol. 163, 661–668 (1985).

    Article 
    CAS 
    PubMed 
    PubMed Central 

    Google Scholar
     

  • Fu, H., Uchimiya, M., Gore, J. & Moran, M. A. Ecological drivers of bacterial community assembly in synthetic phycospheres. Proc. Natl Acad. Sci. USA.117, 3656–3662 (2020).

    Article 
    CAS 
    PubMed 
    PubMed Central 

    Google Scholar
     

  • Amin, S. A. et al. Interaction and signalling between a cosmopolitan phytoplankton and associated bacteria. Nature 522, 98–101 (2015).

    Article 
    CAS 
    PubMed 

    Google Scholar
     

  • Daniel, R. M. & Danson, M. J. Temperature and the catalytic activity of enzymes: a fresh understanding. FEBS Lett. 587, 2738–2743 (2013).

    Article 
    CAS 
    PubMed 

    Google Scholar
     

  • Løbner-Olesen, A., Skarstad, K., Hansen, F. G., von Meyenburg, K. & Boye, E. The DnaA protein determines the initiation mass of Escherichia coli K-12. Cell 57, 881–889 (1989).

    Article 
    PubMed 

    Google Scholar
     

  • Bremer, H. & Churchward, G. Deoxyribonucleic acid synthesis after inhibition of initiation of rounds of replication in Escherichia coli B/r. J. Bacteriol. 130, 692–697 (1977).

    Article 
    CAS 
    PubMed 
    PubMed Central 

    Google Scholar
     

  • Dai, K. & Lutkenhaus, J. The proper ratio of FtsZ to FtsA is required for cell division to occur in Escherichia coli. J. Bacteriol. 174, 6145–6151 (1992).

    Article 
    CAS 
    PubMed 
    PubMed Central 

    Google Scholar
     

  • Luo, H., Csűros, M., Hughes, A. L. & Moran, M. A. Evolution of divergent life history strategies in marine Alphaproteobacteria. mBio 4, e00373-13 (2013).

  • Smith, D. P. et al. Proteomic and transcriptomic analyses of ‘Candidatus Pelagibacter ubique’ describe the first PII-independent response to nitrogen limitation in a free-living Alphaproteobacterium. mBio 4, e00133–12 (2013).

    Article 
    PubMed 
    PubMed Central 

    Google Scholar
     

  • Zheng, H. et al. General quantitative relations linking cell growth and the cell cycle in Escherichia coli. Nat. Microbiol. 5, 995–1001 (2020).

    Article 
    CAS 
    PubMed 
    PubMed Central 

    Google Scholar
     

  • Lee, C. Characterizing Growth Promoters and Inhibitors of SAR11 Pelagibacter sp. HTCC7211. BSc thesis, Oregon State Univ. (2013).

  • Braakman, R. et al. Global niche partitioning of purine and pyrimidine cross-feeding among ocean microbes. Sci. Adv. 11, eadp1949 (2025).

  • Monod, J. The growth of bacterial cultures. Annu. Rev. Microbiol. 3, 371–394 (1949).

    Article 
    CAS 

    Google Scholar
     

  • Held, N. A. et al. Nutrient colimitation is a quantitative, dynamic property of microbial populations. Proc. Natl Acad. Sci. USA 121, e2400304121 (2024).

    Article 
    CAS 
    PubMed 
    PubMed Central 

    Google Scholar
     

  • Schaechter, M., MaalØe, O. & Kjeldgaard, N. O. Dependency on medium and temperature of cell size and chemical composition during balanced growth of Salmonella typhimurium. Microbiology 19, 592–606 (1958).

    CAS 

    Google Scholar
     

  • Si, F. et al. Mechanistic origin of cell-size control and homeostasis in bacteria. Curr. Biol. 29, 1760–1770.e7 (2019).

    Article 
    CAS 
    PubMed 
    PubMed Central 

    Google Scholar
     

  • Guo, X. et al. Automated determination of ammonium at nanomolar levels in seawater by coupling lab-in-syringe with highly sensitive light-emitting-diode-induced fluorescence detection. Molecules 30, 1288 (2025).

  • Moran, M. A. et al. The ocean’s labile DOC supply chain. Limnol. Oceanogr. 67, 1007–1021 (2022).

    Article 
    CAS 

    Google Scholar
     

  • Seymour, J. R., Amin, S. A., Raina, J.-B. & Stocker, R. Zooming in on the phycosphere: the ecological interface for phytoplankton–bacteria relationships. Nat. Microbiol. 2, 17065 (2017).

    Article 
    CAS 
    PubMed 

    Google Scholar
     

  • Paerl, H. W. Why does N-limitation persist in the world’s marine waters? Mar. Chem. 206, 1–6 (2018).

    Article 
    CAS 

    Google Scholar
     

  • Sarmento, H. & Gasol, J. M. Use of phytoplankton-derived dissolved organic carbon by different types of bacterioplankton: use of phytoplankton-derived DOC by bacterioplankton. Environ. Microbiol. 14, 2348–2360 (2012).

    Article 
    CAS 
    PubMed 

    Google Scholar
     

  • Brüwer, J. D. et al. In situ cell division and mortality rates of SAR11, SAR86, Bacteroidetes, and Aurantivirga during phytoplankton blooms reveal differences in population controls. mSystems 8, e0128722 (2023).

    Article 
    PubMed 

    Google Scholar
     

  • Margolin, W. FtsZ and the division of prokaryotic cells and organelles. Nat. Rev. Mol. Cell Biol. 6, 862–871 (2005).

    Article 
    CAS 
    PubMed 
    PubMed Central 

    Google Scholar
     

  • Barrows, J. M., Sundararajan, K., Bhargava, A. & Goley, E. D. FtsA regulates Z-ring morphology and cell wall metabolism in an FtsZ C-terminal linker-dependent manner in Caulobacter crescentus. J. Bacteriol. 202, e00693-19 (2020).

  • Wu, K. J. et al. Characterization of conserved and novel septal factors in Mycobacterium smegmatis. J. Bacteriol. 200, e00649-17 (2018).

  • Oh, H.-M. et al. Complete genome sequence of ‘Candidatus Puniceispirillum marinum’ IMCC1322, a representative of the SAR116 clade in the Alphaproteobacteria. J. Bacteriol. 192, 3240–3241 (2010).

    Article 
    CAS 
    PubMed 
    PubMed Central 

    Google Scholar
     

  • Coelho, J. T. et al. Culture-supported ecophysiology of the SAR116 clade demonstrates metabolic and spatial niche partitioning. ISME J. 19, wraf124 (2025).

    Article 
    CAS 
    PubMed 
    PubMed Central 

    Google Scholar
     

  • Cho, J.-C. & Giovannoni, S. J. Parvularcula bermudensis gen. nov., sp. nov., a marine bacterium that forms a deep branch in the α-Proteobacteria. Int. J. Syst. Evol. Microbiol. 53, 1031–1036 (2003).

    Article 
    CAS 
    PubMed 

    Google Scholar
     

  • Dang, H., Li, T., Chen, M. & Huang, G. Cross-ocean distribution of Rhodobacterales bacteria as primary surface colonizers in temperate coastal marine waters. Appl. Environ. Microbiol. 74, 52–60 (2008).

    Article 
    CAS 
    PubMed 

    Google Scholar
     

  • Follows, M. J., Dutkiewicz, S., Grant, S. & Chisholm, S. W. Emergent biogeography of microbial communities in a model ocean. Science 315, 1843–1846 (2007).

    Article 
    CAS 
    PubMed 

    Google Scholar
     

  • Aumont, O., Ethé, C., Tagliabue, A., Bopp, L. & Gehlen, M. PISCES-v2: an ocean biogeochemical model for carbon and ecosystem studies. Geosci. Model Dev. 8, 2465–2513 (2015).

    Article 
    CAS 

    Google Scholar
     

  • Stock, C. A. et al. Ocean biogeochemistry in GFDL’s Earth System Model 4.1 and its response to increasing atmospheric CO2. J. Adv. Model. Earth Syst. 12, e2019MS002043 (2020).

  • Ross, A. C. et al. A high-resolution physical–biogeochemical model for marine resource applications in the northwest Atlantic (MOM6-COBALT-NWA12 v1.0). Geosci. Model Dev. 16, 6943–6985 (2023).

    Article 
    CAS 

    Google Scholar
     

  • Martinez-Gutierrez, C. A., Uyeda, J. C. & Aylward, F. O. A timeline of bacterial and archaeal diversification in the ocean. Elife 12, RP88268 (2023).

  • Hyun, J. C. & Palsson, B. O. Reconstruction of the last bacterial common ancestor from 183 pangenomes reveals a versatile ancient core genome. Genome Biol. 24, 183 (2023).

    Article 
    PubMed 
    PubMed Central 

    Google Scholar
     

  • Staley, J. T. & Konopka, A. Measurement of in situ activities of nonphotosynthetic microorganisms in aquatic and terrestrial habitats. Annu. Rev. Microbiol. 39, 321–346 (1985).

    Article 
    CAS 
    PubMed 

    Google Scholar
     

  • Henson, M. W. et al. Expanding the diversity of bacterioplankton isolates and modeling isolation efficacy with large-scale dilution-to-extinction cultivation. Appl. Environ. Microbiol. 86, e00943-20 (2020).

  • Paysan-Lafosse, T. et al. InterPro in 2022. Nucleic Acids Res. 51, D418–D427 (2023).

    Article 
    CAS 
    PubMed 

    Google Scholar
     

  • Jones, P. et al. InterProScan 5: genome-scale protein function classification. Bioinformatics 30, 1236–1240 (2014).

    Article 
    CAS 
    PubMed 
    PubMed Central 

    Google Scholar
     

  • Thrash, C. Pangenomic analyses files. figshare https://doi.org/10.6084/M9.FIGSHARE.30087295.V1 (2025).

  • UniProt Consortium. UniProt: the universal protein knowledgebase in 2025. Nucleic Acids Res. 53, D609–D617 (2025).

    Article 

    Google Scholar
     

  • Ahmad, S. et al. The UniProt website API: facilitating programmatic access to protein knowledge. Nucleic Acids Res. 53, W547–W553 (2025).

    Article 
    PubMed 
    PubMed Central 

    Google Scholar
     

  • Rappé, M. S., Connon, S. A., Vergin, K. L. & Giovannoni, S. J. Cultivation of the ubiquitous SAR11 marine bacterioplankton clade. Nature 418, 630–633 (2002).

    Article 
    PubMed 

    Google Scholar
     

  • Henson, M. W. et al. Artificial seawater media facilitate cultivating members of the microbial majority from the Gulf of Mexico. mSphere 1, e00028-16 (2016).

  • Sodium phosphate. Cold Spring Harb. Protoc. 2006, db.rec8303 (2006).

  • Cheng, C. & Thrash, J. C. sparse-growth-curve: a computational pipeline for parsing cellular growth curves with low temporal resolution. Microbiol. Resour. Announc. 10, e00296-21 (2021).

  • Lanclos, V. C. et al. New isolates refine the ecophysiology of the Roseobacter CHAB-I-5 lineage. ISME Commun. 5, ycaf068 (2025).

    Article 
    PubMed 
    PubMed Central 

    Google Scholar
     

  • Cheng, C. Thrash-lab/SAR11_cell_cycle: V1.0.0. Zenodo https://doi.org/10.5281/ZENODO.17703344 (2025).

  • Stokke, C., Flåtten, I. & Skarstad, K. An easy-to-use simulation program demonstrates variations in bacterial cell cycle parameters depending on medium and temperature. PLoS ONE 7, e30981 (2012).

    Article 
    CAS 
    PubMed 
    PubMed Central 

    Google Scholar
     

  • Michelsen, O., Teixeira de Mattos, M. J., Jensen, P. R. & Hansen, F. G. Precise determinations of C and D periods by flow cytometry in Escherichia coli K-12 and B/r. Microbiology 149, 1001–1010 (2003).

    Article 
    CAS 
    PubMed 

    Google Scholar
     

  • Thrash, C. Epimicroscopy images of SAR11. figshare https://doi.org/10.6084/M9.FIGSHARE.29396375.V1 (2025).

  • Messer, W. The bacterial replication initiator DnaA. DnaA and oriC, the bacterial mode to initiate DNA replication. FEMS Microbiol. Rev. 26, 355–374 (2002).

    CAS 
    PubMed 

    Google Scholar
     

  • Katayama, T., Ozaki, S., Keyamura, K. & Fujimitsu, K. Regulation of the replication cycle: conserved and diverse regulatory systems for DnaA and oriC. Nat. Rev. Microbiol. 8, 163–170 (2010).

    Article 
    CAS 
    PubMed 

    Google Scholar
     

  • Boye, E. & Løbner-Olesen, A. Bacterial growth control studied by flow cytometry. Res. Microbiol. 142, 131–135 (1991).

    Article 
    CAS 
    PubMed 

    Google Scholar
     

  • Stokke, C., Waldminghaus, T. & Skarstad, K. Replication patterns and organization of replication forks in Vibrio cholerae. Microbiology 157, 695–708 (2011).

    Article 
    CAS 
    PubMed 

    Google Scholar
     



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