Azotobacter Cysts

Abstract

Azotobacter is a genus of soil bacteria able to form cysts, which are dormant cells resistant to deleterious conditions. A cyst consists of a contracted oval cell, covered with a two‐layered capsule. Although many physiological and morphological studies about encystment were published decades ago, the biosynthetic pathways of the major components of the cyst (alginate, polyhydroxybutyrate and the phenolic lipids alkylresorcinols and alkylpyrones) and how they are regulated, remained largely unknown. More recent work elucidated their biosyntheses and the regulators controlling their formation and changes occurring during encystment, such as the loss of flagella. Among these regulators are the alternative sigma factors AlgU and RpoS, the global regulatory systems Gac/Rsm and the transcriptional regulators AlgR, ArpR and CydR. Lately, stress‐related proteins have been shown to contribute to the resistance of the cysts. A recent proteomic analysis confirmed many of the metabolic and structural changes observed and revealed new participants in the resistance mechanisms of the cysts.

Key Concepts

  • The encysting process results in a dormant cell more resistant to adverse conditions than the vegetative cell.
  • During the encysting process, a coordinated array of metabolic and morphological changes take place to produce a dormant cell.
  • The central body of the cyst is surrounded by a protective two‐layered capsule, which is composed of carbohydrates, proteins and lipids.
  • The exopolysaccharide alginate constitutes a structural part of the cyst envelope and is essential for desiccation resistance.
  • Several regulators of gene expression control the differentiation process, leading to the production of cyst.
  • Heat‐shock and LEA proteins prevent misfolding and aggregation of proteins exposed to stress (osmotic, freezing, heat, UV radiation, desiccation, etc.) in multiple organisms, including bacteria plants and animals.

Keywords: encystment; differentiation; dormancy; germination; capsule

Figure 1. Electron micrographs of an A. vinelandii vegetative cell (a); A vegetative cell negatively stained for visualisation of flagella (b); A cyst (c). Ex, exine; In, intine; Cb, central body; phb, polyhydroxybutyrate granules; f, flagella.
Figure 2. Diagram of the life cycle of A. vinelandii. The different development stages are depicted. The morphological changes are illustrated. The two cell types (vegetative cell and cyst) are shown with electron micrographs. The main biochemical and physiological changes occurring during the differentiation process are indicated. ARs, alkylresorcinols; APs, alkylpyrones; PHB, polyhydroxybutyrate; h, hours.
Figure 3. Model for the regulation of gene expression during encystment. Green lines: positive regulation; red lines: negative regulation. Dashed lines indicate unknown intermediates or unknown mechanism of regulation. Promoters are indicated as coloured rectangles.
close

References

Campos ME, Martínez‐Salazar JM, LLoret L, et al. (1996) Characterization of the gene coding for GDP‐mannose dehydrogenase (algD) from Azotobacter vinelandii. Journal of Bacteriology 178: 1793–1799.

Castañeda M, Guzmán J, Moreno S and Espín G (2000) The GacS sensor kinase regulates alginate and poly‐beta‐hydroxybutyrate production in Azotobacter vinelandii. Journal of Bacteriology 182: 2624–2628.

Castañeda M, Sanchez J, Moreno S, Núñez C and Espín G (2001) The global regulators GacA and σ2 form part of a cascade that controls alginate production in Azotobacter vinelandii. Journal of Bacteriology 183: 6787–6793.

Chowdhury‐Paul S, Pando‐Robles V, Jimenez‐Jacinto V, et al. (2018) Proteomic analysis revealed proteins induced upon Azotobacter vinelandii encystment. Journal of Proteomics 181: 47–59.

Cocótl‐Yañez M, Sampieri A, Moreno S, et al. (2011) Roles of RpoS and PsrA in cyst formation and alkylresorcinol in Azotobacter vinelandii. Microbiology 157: 1685–1693.

Cocótl‐Yañez M, Moreno S, Encarnación S, et al. (2014) A small heat shock protein (Hsp20) regulated by RpoS is essential for cyst desiccation resistance in Azotobacter vinelandii. Microbiology 160: 479–487.

Efuet ET, Pulakat L and Gavini N (1996) Investigations on the cell volumes of Azotobacter vinelandii by scanning electron microscopy. Journal of Basic Microbiology 36: 229–234.

Ertesvåg H, Doseth B, Larsen B, Skåjk‐Bræk G and Valla S (1994) Cloning and expression of an Azotobacter vinelandii mannuronan C‐5‐epimerase gene. Journal of Bacteriology 176: 2846–2853.

Ertesvåg H, Høidal HK, Hals IK, et al. (1995) A family of modular type mannuronan C‐5‐epimerase genes controls alginate structure in Azotobacter vinelandii. Molecular Microbiology 16: 719–731.

Ertesvåg H, Høidal HK, Schjerven H, Svanem BI and Valla S (1999) Mannuronan C‐5‐epimerases and their application for in vitro and in vivo design of new alginates useful in biotechnology. Metabolic Engineering 1: 262–269.

Funa N, Ozawa H, Hirata A and Horinouchi S (2006) Phenolic lipid synthesis by type III polyketide synthases is essential for cyst formation in Azotobacter vinelandii. Proceedings of the National Academy of Sciences of the USA 103: 6356–6361.

Gimmestad M, Steigedal M, Ertesvåg H, et al. (2006) Identification and characterization of an Azotobacter vinelandii type I secretion system responsible for export of the AlgE‐type mannuronan C‐5‐epimerases. Journal of Bacteriology 188: 5551–5560.

Gimmestad M, Ertesvåg H, Heggeset TM, et al. (2009) Characterization of three new Azotobacter vinelandii alginate lyases, one of which is involved in cyst germination. Journal of Bacteriology 191: 4845–4853.

Hernández‐Eligio A, Castellanos M, Moreno S and Espín G (2011) Transcriptional activation of the Azotobacter vinelandii polyhydroxybutyrate biosynthetic genes phbBAC by PhbR and RpoS. Microbiology 157: 3014–3023.

Hernández‐Eligio A, Moreno S, Castellanos M and Espín G (2012) RsmA post‐transcriptionally controls PhbR expression and polyhydroxybutyrate biosynthesis in Azotobacter vinelandii. Microbiology 158: 1953–1963.

Hitchins VM and Sadoff HL (1973) Sequential metabolic events during encystment of Azobacter vinelandii. Journal of Bacteriology 113: 1273–1279.

Høidal HK, Svanem BIG, Gimmestad M and Valla S (2000) Mannuronan C‐5 epimerases and cellular differentiation of Azotobacter vinelandii. Environmental Microbiology 2: 27–38.

Kennedy C, Rudnick P, MacDonald ML and Melton T (2005) Genus III. Azotobacter Beijerinck 1901, 567AL. In: Brenner DJ, Noel RK, Staley JT and Garrity GM (eds) Bergey's Manual of Systematic Bacteriology–The Proteobacteria, pp 384–402. Springer: New York, NY.

Kossler W and Kleiner D (1986) Degradation of the nitrogenase proteins during encystment of Azotobacter vinelandii. Archives of Microbiology 145: 287–289.

León R and Espín G (2008) FlhCD but not FleQ regulate flagella biogenesis in Azotobacter vinelandii and are under AlgU and CydR negative control. Microbiology 154: 1729–1738.

Lin LP and Sadoff HL (1968) Encystment and polymer production by Azotobacter vinelandii in the presence of beta‐hydroxybutyrate. Journal of Bacteriology 95: 2336–2343.

Lin LP and Sadoff HL (1969) Chemical composition of Azotobacter vinelandii cysts. Journal of Bacteriology 100: 480–486.

Lin LP, Pankratz S and Sadoff HL (1978) Ultrastructural and physiological changes occurring upon germination and outgrowth of Azotobacter vinelandii cysts. Journal of Bacteriology 135: 641–646.

Manchak J and Page WJ (1994) Control of polyhydroxyalkanoate synthesis in Azotobacter vinelandii strain UWD. Microbiology 140: 953–963.

Manzo J, Sánchez E, Velázquez C, et al. (2011) Post‐transcriptional regulation of the alginate biosynthetic gene algD by the Gac/Rsm system in Azotobacter vinelandii. Journal of Molecular Microbiology and Biotechnology 21: 147–159.

Martínez‐Salazar JM, Moreno S, Nájera R, et al. (1996) Characterization of the genes coding for the putative sigma factor AlgU and its regulators MucA, MucB, MucC, and MucD in Azotobacter vinelandii and evaluation of their roles in alginate biosynthesis. Journal of Bacteriology 178: 1800–1808.

Miyanaga A, Funa N, Awakawa T and Horinouchi S (2008) Direct transfer of starter substrates from type I fatty acid synthase to type III polyketide synthases in phenolic lipid synthesis. Proceedings of the National Academy of Sciences of the USA 105: 871–876.

Moreno J, González‐López J and Vela GR (1986) Survival of Azotobacter spp. in dry Soils. Applied and Environmental Microbiology 51: 123–125.

Moreno S, Nájera R, Guzmán J, Soberón‐Chávez G and Espín G (1998) Role of alternative sigma factor algU in encystment of Azotobacter vinelandii. Journal of Bacteriology 180: 2766–2769.

Moreno S, Ertesvag H, Valla S, et al. (2018) RpoS controls the expression and the transport of the AlgE1‐7 epimerases in Azotobacter vinelandii. Fems Microbiology Letters 365: fny210.

Muriel‐Millán LF, Moreno S, Romero Y, et al. (2015) The unphosphorylated EIIANtr protein represses the synthesis of alkylresorcinols in Azotobacter vinelandii. PLoS ONE 10: e0117184.

Muriel‐Millán LF, Moreno S, Gallegos‐Monterrosa R and Espín G (2017) Unphosphorylated EIIANtr induces ClpAP‐mediated degradation of RpoS in Azotobacter vinelandii. Molecular Microbiology 104: 197–211.

Noguez R, Segura D, Moreno S, et al. (2008) Enzyme I, NPr and IIA(Ntr) are involved in regulation of the poly‐beta‐hydroxybutyrate biosynthetic genes in Azotobacter vinelandii. Journal of Molecular Microbiology and Biotechnology 15: 244–254.

Núñez C, Moreno S, Soberón‐Chavez G and Espín G (1999) The Azotobacter vinelandii response regulator AlgR is essential for cyst formation. Journal of Bacteriology 181: 141–148.

Page WJ and Sadoff HL (1975) Relationship between calcium and uronic acids in encystment of Azotobacter vinelandii. Journal of Bacteriology 122: 145–151.

Reusch RN and Sadoff HL (1979) 5‐n‐Alkylresorcinols from encysting Azotobacter vinelandii: isolation and characterization. Journal of Bacteriology 139: 448–453.

Reusch RN and Sadoff HL (1981) Lipid metabolism during encystment of Azotobacter vinelandii. Journal of Bacteriology 145: 889–895.

Reusch RN and Sadoff HL (1983) Novel lipid components of the Azotobacter vinelandii cyst membrane. Nature 302: 268–270.

Rodríguez‐Salazar J, Moreno S and Espín G (2017) LEA proteins are involved in cyst desiccation resistance and other abiotic stresses in Azotobacter vinelandii. Cell Stress and Chaperones 22: 397–408.

Romero Y, Moreno S, Guzmán J, Espín G and Segura D (2013) The sigma factor RpoS controls alkylresorcinol synthesis through ArpR, a LysR‐type regulatory protein during encystment of Azotobacter vinelandii. Journal of Bacteriology 195: 1834–1844.

Romero Y, Guzmán J, Moreno S, et al. (2016) The GacS/A‐RsmA signal transduction pathway controls the synthesis of alkylresorcinol lipids that replace membrane phospholipids during encystment of Azotobacter vinelandii SW136. PLoS ONE 11: e0153266.

Ruppen ME, Garner G and Sadoff HL (1983) Protein turnover in Azotobacter vinelandii during encystment and germination. Journal of Bacteriology 156: 1243–1248.

Sadoff HL, Berke E and Loperfido B (1971) Physiological studies of encystment in Azotobacter vinelandii. Journal of Bacteriology 105: 185–189.

Sadoff HL (1975) Encystment and germination in Azotobacter vinelandii. Bacteriological Reviews 39: 516–539.

Segura D, Cruz T and Espín G (2003) Encystment and alkylresorcinol production by Azotobacter vinelandii strains impaired in poly‐β‐hydroxybutyrate synthesis. Archives of Microbiology 179: 437–443.

Segura D, Vite O, Romero Y, et al. (2009) Isolation and characterization of Azotobacter vinelandii mutants impaired in alkylresorcinol synthesis: alquilresorcinols are not essential for cysts desiccation resistance. Journal of Bacteriology 191: 3142–3148.

Setubal JC, dos Santos P, Goldman BS, et al. (2009) The genome sequence of Azotobacter vinelandii, an obligate aerobe specialized to support diverse anaerobic metabolic processes. Journal of Bacteriology 191: 4534–4545.

Socolofsky MD and Wyss O (1962) Resistance of Azotobacter cyst. Journal of Bacteriology 84: 119–124.

Steigedal M, Sletta H, Moreno S, et al. (2008) The Azotobacter vinelandii AlgE mannuronan C‐5‐epimerase family is essential for the in vivo control of alginate monomer composition and for functional cyst formation. Environmental Microbiology 10: 1760–1770.

Stevenson LH and Socolofsky MD (1966) Cyst formation and poly‐β‐hydroxybutyric acid accumulation in Azotobacter. Journal of Bacteriology 91: 304–310.

Stockall AM and Edwards C (1985) Changes in the respiratory activity during encystment of Azotobacter vinelandii. Journal of General Microbiology 131: 1403–1410.

Su CJ and Sadoff HL (1981) Unique lipids in Azotobacter vinelandii cysts: synthesis, distribution and fate during germination. Journal of Bacteriology 147: 91–96.

Su CJ, Cuhna A, Wernette CM, Reusch RN and Sadoff HL (1987) Protein synthesis during encystment of Azotobacter vinelandii. Journal of Bacteriology 169: 4451–4456.

Svanem BIG, Skjåk‐Bræk G, Ertesvåg H and Valla S (1999) Cloning and expression of three new Azotobacter vinelandii genes closely related to a previously described gene family encoding mannuronan C‐5‐epimerases. Journal of Bacteriology 181: 68–77.

Trejo A, Moreno S, Cocótl‐Yañez M and Espín G (2017) GacA regulates the PTSNtr‐dependent control of cyst formation in Azotobacter vinelandii. Fems Microbiology Letters 364: fnw278.

Vázquez A, Moreno S, Guzmán J, Alvarado A and Espín G (1999) Transcriptional organization of the Azotobacter vinelandii algGXLVIFA genes: characterization of algF mutants. Gene 232: 217–222.

Vela GR (1974) Survival of Azotobacter in dry soil. Applied Microbiology 28: 77–79.

Wu G, Cruz‐Ramos H, Hill S, et al. (2000) Regulation of cytochrome bd expression in the obligate aerobe Azotobacter vinelandii by CydR (Fnr). Sensitivity to oxygen species, and nitric oxide. Journal of Biological Chemistry 275: 4679–4686.

Further Reading

Berleman JE and Bauer CE (2004) Characterization of cyst cell formation in the purple photosynthetic bacterium Rhodospirillum centenum. Microbiology 150: 383–390.

Berleman JE, Hasselbring BM and Bauer CE (2004) Hypercyst mutants in Rhodospirillum centenum identify regulatory loci involved in cyst cell differentiation. Journal of Bacteriology 186: 5834–5841.

Carra S, Alberti S, Arrigo PA, et al. (2017) The growing world of small heat shock proteins: from structure to functions. Cell Stress and Chaperones 22: 601.

Castañeda M, Lopez‐Pliego L and Espín G (2016) Azotobacter vinelandii small RNAs: Their roles in the formation of cyst and other processes. In: Enguita FJ (ed.) Non‐coding RNAs and Inter‐kingdom Communication, pp 67–82. Springer International Publishing: Cham.

Dong Q and Bauer CE (2015) Transcriptome analysis of cyst formation in Rhodospirillum centenum reveals large global changes in expression during cyst development. BMC Genomics 16: 68.

Heulin T, De Luca G, Barakat M, et al. (2017) Bacterial adaptation to hot and dry deserts. In: Stan‐Lotter H and Fendrihan S (eds) Adaption of Microbial Life to Environmental Extremes, pp 75–98. Springer: Cham.

Marden JN, Dong Q, Roychowdhury S, Berleman J and Bauer CE (2011) Cyclic GMP controls Rhodospirillum centenum cyst development. Molecular Microbiology 79: 600–615.

Mulyukin AL, Suzina NE, Duda VI and EI'‐Registan GI (2008) Structural and physiological diversity among cystlike resting cells of bacteria of the genus Pseudomonas. Microbiology 77: 455–465.

Suzina NE, Mulyukin AL, Dmitriev VV, et al. (2006) The structural bases of long‐term anabiosis in non‐spore‐forming bacteria. Advances in Space Research 38: 1209–1219.

Tunnacliffe A, Hincha DK, Leprince O and Macherel D (2010) LEA proteins: versatility of form and function. In: Lubzens E, Cerda J and Clark M (eds) Dormancy and Resistance in Harsh Environments. Topics in Current Genetics, vol. 21. Springer: Berlin, Heidelberg.

Wang G and Maier RJ (2015) Bacterial histone‐like proteins: roles in stress resistance. Current Genetics 61: 489.

Contact Editor close
Submit a note to the editor about this article by filling in the form below.

* Required Field

How to Cite close
Segura, Daniel, Núñez, Cinthia, and Espín, Guadalupe(Jan 2020) Azotobacter Cysts. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0000295.pub3]