Photo-fermentational hydrogen production of Rhodobacter sp. KKU-PS1 isolated from an UASB reactor

Electronic Journal of Biotechnology

Volumn 18, Issue 3, 2015, Pages 221-230

  Assawamongkholsiri, Thitirut ^a   Reungsang, Alissara ^a  

^a KHON KAEN UNIVERSITY   (Thailand)

Author keywords

nifD; nifH; Photo fermentation; Purple non sulfur bacteria

Indexed keywords

BACTERIA; CARBON; FERMENTATION; METHANE; POLYMERASE CHAIN REACTION;

CENTRAL COMPOSITE DESIGNS; NIFD; NIFH; PHOTO FERMENTATION; PHOTO-HYDROGEN PRODUCTIONS; PURPLE NON-SULFUR BACTERIA; RESPONSE SURFACE METHODOLOGY; SUBSTRATE CONVERSION EFFICIENCY;

HYDROGEN PRODUCTION;

DINITROGENASE DENOTED ALPHA; DINITROGENASE REDUCTASE; HYDROGEN; MALIC ACID; NITROGEN; OXIDOREDUCTASE; UNCLASSIFIED DRUG;

ARTICLE; BACTERIAL STRAIN; BACTERIUM ISOLATE; CARBON SOURCE; CONTROLLED STUDY; ENZYME ASSAY; ENZYME SUBSTRATE; FERMENTATION OPTIMIZATION; FERMENTATION TECHNIQUE; ILLUMINATION; NONHUMAN; NUCLEOTIDE SEQUENCE; PH; PHOTO HYDROGEN PRODUCTION FERMENTATION; POLYMERASE CHAIN REACTION; RHODOBACTER; RNA SEQUENCE; SEQUENCE ANALYSIS; STRAIN IDENTIFICATION; TEMPERATURE SENSITIVITY; UPFLOW REACTOR;

PHOTOBACTERIA; PROTEOBACTERIA; RHODOBACTER SP.;

EID: 84930251175     PISSN: None     EISSN: 07173458     Source Type: Journal    
DOI: 10.1016/j.ejbt.2015.03.011     Document Type: Article

References (83)

1. Marbán G, Valdés-Solís T. Towards the hydrogen economy? Int J Hydrog Energy 2007;32:1625–37. http://dx.doi.org/10.1016/j.ijhydene.2006.12.017.
2. Hay JXW, Wu TY, Juan JC, Jahim JM. Biohydrogen production through photo fermentation or dark fermentation using waste as a substrate: Overview, economics, and future prospects of hydrogen usage. Biofuels Bioprod Biorefin 2013;7:334–52. http://dx.doi.org/10.1002/bbb.1403.
3. Mudhoo A, Kumar S. Effects of heavy metals as stress factors on anaerobic digestion processes and biogas production from biomass. Int J Environ Sci Technol 2013;10: 1383–98. http://dx.doi.org/10.1007/s13762-012-0167-y.
4. Liu BF, Ren NQ, Xie GJ, Ding J, Guo WQ, Xing DF. Enhanced bio-hydrogen production by the combination of dark- and photo-fermentation in batch culture. Bioresour Technol 2010;101:5325–9. http://dx.doi.org/10.1016/j.biortech.2010.02.024.
5. Su H, Cheng J, Zhou J, Song W, Cen K. Combination of dark- and photo-fermentation to enhance hydrogen production and energy conversion efficiency. Int J Hydrog Energy 2009;34:8846–53. http://dx.doi.org/10.1016/j.ijhydene.2009.09.001.
6. Malandra L, Wolfaardt G, Zietsman A, Viljoen-Bloom M. Microbiology of a biological contactor for winery wastewater treatment. Water Res 2003;37:4125–34. http://dx.doi.org/10.1016/j.memsci.2009.07.013.
7. Lameloise M, Matinier H, Fargues C. Concentration and purification of malate ion from a beverage industry waste water using electrodialysis with homopolar membranes. J Membr Sci 2009;343:73–81. http://dx.doi.org/10.1016/S0043-1354(03)00339-7.
8. Wu TY, Hay JXW, Kong LB, Juan JC, Jahim JMD. Recent advances in reuse of waste material as substrate to produce biohydrogen by purple non-sulfur (PNS) bacteria. Renew Sustain Energy Rev 2012;16:3117–22. http://dx.doi.org/10.1016/j.rser.2012.02.002.
9. Laocharoen S, Isolation Reungsang A. Characterization and optimization of photo-hydrogen production conditions by newly isolated Rhodobacter sphaeroides KKU-PS5. Int J Hydrog Energy 2014;39:10870–82. http://dx.doi.org/10.1016/j.ijhydene.2014.05.055.
10. Kim MS, Kim DH, Cha J. Culture conditions affecting H2 production by phototrophic bacterium Rhodobacter sphaeroides KD131. Int J Hydrog Energy 2012;37:14055–61. http://dx.doi.org/10.1016/j.ijhydene.2012.06.085.
11. Kim DH, Cha J, Kang S, Kim MS. Continuous photo-fermentative hydrogen production from lactate and lactate-rich acidified food waste. Int J Hydrog Energy 2013;38:6161–6. http://dx.doi.org/10.1016/j.ijhydene.2012.12.072.
12. Akkose S, Gunduz U, Yucel M, Eroglu I. Effects of ammoniumion, acetate and aerobic conditions on hydrogen production and expression levels of nitrogenase genes in Rhodobacter sphaeroides O.U.001. Int J Hydrog Energy 2009;34:8818–27. http://dx.doi.org/10.1016/j.ijhydene.2009.08.040.
13. Chen CY, Lu WB, Wu JF, Chang JS. Enhancing phototrophic hydrogen production of Rhodopseudomonas palustris via statistical experiment design. Int J Hydrog Energy 2007;32:940–9. http://dx.doi.org/10.1016/j.ijhydene.2006.09.021.
14. Shi XY, Yu HQ. Continuous production of hydrogen from mixed volatile fatty acids with Rhodopseudomonas capsulata. Int J Hydrog Energy 2006;31:1641–7. http://dx.doi.org/10.1016/j.ijhydene.2005.12.008.
15. Ozmihci S, Kargi F. Bio-hydrogen production by photo-fermentation of dark fermentation effluent with intermittent feeding and effluent removal. Int J Hydrog Energy 2010;35:6674–80. http://dx.doi.org/10.1016/j.ijhydene.2010.04.090.
16. Argun H, Kargi F, Kapdan IK. Light fermentation of dark fermentation effluent for bio-hydrogen production by different Rhodobacter species at different initial volatile fatty acid (VFA) concentrations. Int J Hydrog Energy 2008;33:7405–12. http://dx.doi.org/10.1016/j.ijhydene.2008.09.059.
17. Wang YZ, Liao Q, Zhu X, Tian X, Zhang C. Characteristics of hydrogen production and substrate consumption of Rhodopseudomonas palustris CQK 01 in an immobilized-cell photobioreactor. Bioresour Technol 2010;101:4034–41. http://dx.doi.org/10.1016/j.biortech.2010.01.045.
18. Imhoff JF, Hiraishi A, Su LJ. Anoxygenic phototrophic purple bacteria. In: Brenner DJ, Krieg NR, Staley JT, Garrity GM, editors. Bergey's Manual of Systematic Bacteriology. The Proteobacteria, part A, 2nd ed.New York: Springer-Verlag; 2005. p. 119–32.
19. Budiman PM, Wu TY, Ramanan RN, Hay JXW. Treatment and reuse of effluents from palm oil, pulp, and paper mills as a combined substrate by using purple nonsulfur bacteria. Ind Eng Chem Res 2014;53:14921–31. http://dx.doi.org/10.1021/ie501798f.
20. Belila A, Fazaa I, Hassen A, Ghrabi A. Anoxygenic phototrophic bacterial diversity within wastewater stabilization plant during ‘red water’ phenomenon. Int J Environ Sci Technol 2013;10:837–46. http://dx.doi.org/10.1007/s13762-012-0163-2.
21. Basak N, Das D. The prospect of purple non-sulfur (PNS) photosynthetic bacteria for hydrogen production: The presence state of the art. World J Microbiol Biotechnol 2007;23:31–42. http://dx.doi.org/10.1007/s11274-006-9190-9.
22. Dasgupta CN, Gilbert JJ, Lindblad P, Heidorn T, Borgvang SA, Skjanes K, et al. Recent trends on the development of photobiological processes and photobioreactors for the improvement of hydrogen production. Int J Hydrog Energy 2010;35:10218–38. http://dx.doi.org/10.1016/j.ijhydene.2010.06.029.
23. Igarashi RY, Seefeldt LC. Nitrogen fixation: The mechanism of the Mo-dependent nitrogenase. Crit Rev Biochem Mol Biol 2003;38:351–84. http://dx.doi.org/10.1080/10409230390242380.
24. Hu Y, Ribbe MW. Nitrogenase assembly. BiochimBiophys Acta Bioenerg 2013;1827: 1112–22. http://dx.doi.org/10.1016/j.bbabio.2012.12.001.
25. Tan JW, Thong KL, Arumugam ND, Cheah WL, Lai YW, Chua KH, et al. Development of a PCR assay for the detection of nifH and nifD genes in indigenous photosynthetic bacteria. Int J Hydrog Energy 2009;34:7538–41. http://dx.doi.org/10.1016/j.ijhydene.2009.04.029.
26. Chen CY, Liu CH, Lo YC, Chang JS. Perspectives on cultivation strategies and photobioreactor designs for photo-fermentative hydrogen production. Bioresour Technol 2011;102:8484–92. http://dx.doi.org/10.1016/j.biortech.2011.05.082.
27. Akroum-Amrouche D, Abdi N, Lounici H, Mameri N. Effect of physico-chemical parameters on biohydrogen production and growth characteristics by batch culture of Rhodobacter sphaeroides CIP 60.6. Appl Energy 2011;88:2130–5. http://dx.doi.org/10.1016/j.apenergy.2010.12.044.
28. Akkerman I, Janssen M, Rocha J, Wijffels RH. Photobiological hydrogen production: Photochemical efficiency and bioreactor design. Int J Hydrog Energy 2002;27:1195–208. http://dx.doi.org/10.1016/S0360-3199(02)00071-X.
29. Chen CY, Lee CM, Chang JS. Hydrogen production by indigenous photosynthetic bacterium Rhodopseudomonas palustris WP3-5 using optical-fiber-illuminating photobioreactors. Biochem Eng J 2006;32:33–42. http://dx.doi.org/10.1016/j.bej.2006.08.015.
30. Chen CY, Lee CM, Chang JS. Feasibility study on bioreactor strategies for enhanced photohydrogen production from Rhodopseudomonas palustris WP3-5 using optical-fiber-assisted illumination systems. Int J Hydrog Energy 2006;31: 2345–55. http://dx.doi.org/10.1016/j.ijhydene.2006.03.007.
31. Basak N, Jana AK, Das D. Optimization of molecular hydrogen production by Rhodobacter sphaeroides O.U.001 in the annular photobioreactor using response surface methodology. Int J Hydrog Energy 2014;39:11889–901. http://dx.doi.org/10.1016/j.ijhydene.2014.05.108.
32. O-Thong S, Prasertsan P, Intrasungkha N, Dhamwichukorn S, Birkeland NK. Optimization of simultaneous the thermophilic fermentative hydrogen production and COD reduction from palm oil mill effluent by Thermoanaerobacterium-rich sludge. Int J Hydrog Energy 2008;33:1221–31. http://dx.doi.org/10.1016/j.ijhydene.2007.12.017.
33. Stanbury PF, Whitaker A, Hall SJ. Principles of Fermentation Technology. 2nd ed. New Delhi, India: Aditya Book (P) Ltd; 1997 93–122.
34. Annadurai G, Balan SM, Murugesan T. Box-Behnken design in the development of optimized complex medium for phenol degradation using Pseudomonas putida (NICM 2174). Bioprocess Eng 1999;21:415–21. http://dx.doi.org/10.1007/PL00009082.
35. Teh CY, Wu TY, Juan JC. Optimization of agro-industrial wastewater treatment using unmodified rice starch as a natural coagulant. Ind Crop Prod 2014;56:17–26. http://dx.doi.org/10.1016/j.indcrop.2014.02.018.
36. Biebl H, Pfennig N. Isolation ofmembers of the family Rhodosprillaceae. In: Starr MP, Stolp H, Trüper HG, Balows A, Schlegel HG, editors. The Prokaryotes, vol. 1. New York: Springer; 1981. p. 267–73.
37. Edwards T, Rogall T, Blocker H, Emde M, Bottger EC. Isolation and direct complete nucleotide determination of entire genes. Characterization of a gene coding for 16S ribosomal RNA. Nucleic Acids Res 1989;17:7843–53. http://dx.doi.org/10.1093/nar/17.19.7843.
38. Khamtib S, Plangklang P, Reungsang A. Optimization of fermentative of hydrogen production from hydrolysate of microwave assisted sulfuric acid pretreated oil palm trunk by hot spring enriched culture. Int J Hydrog Energy 2011;36: 14204–16. http://dx.doi.org/10.1016/j.ijhydene.2011.05.117.
39. Altschul SF, Madden TL, Schaffer AA, Zhang J, Zhang Z, Miller W, et al. Gapped BLAST and PSI-BLAST: A new generation of protein database search programs. Nucleic Acids Res 1997;25:3389–402. http://dx.doi.org/10.1093/nar/25.17.3389.
40. Thompson JD, Gibson TJ, Plewniak F, Jeanmougin F, Higgins DG. The CLUSTAL_X windows interface: Flexible strategies for multiple sequence alignment aided by quality analysis tools. Nucleic Acids Res 1997;25:4876–82. http://dx.doi.org/10.1093/nar/25.24.4876.
41. Saito N, Nei M. The neighbor-joining method: A new method for reconstructing phylogenetic trees. Mol Biol Evol 1987;4:406–25.
42. Felsenstein J. Confidence limits on phylogenies: An approach using the bootstrap. Evolution 1985;39:783–91. http://dx.doi.org/10.2307/2408678.
43. Lee JZ, Klaus DM, Maness PC, Spear JR. The effect of butyrate concentration on hydrogen production via photo fermentation for use in a Martian habitat resource recovery process. Int J Hydrog Energy 2007:3301–7. http://dx.doi.org/10.1016/j.ijhydene.2007.05.029.
44. Tao Y, He Y, Wu Y, Liu F, Li X, Zong W, et al. Characteristics of a new photosynthetic bacterial strain for hydrogen production and its application in wastewater treatment. Int J Hydrog Energy 2008;33:963–73. http://dx.doi.org/10.1016/j.ijhydene.2007.11.021.
45. Lazaro CZ, Varesche MBA, Silva EL. Effect of inoculum concentration, pH, light intensity and lighting regime on hydrogen production by phototrophic microbial consortium. Renew Energy 2015;75:1–7. http://dx.doi.org/10.1016/j.renene.2014.09.034.
46. Box GEP, Hunter WG, Hunter JS. Statistics for Experimenters. New York: Wiley; 1978.
47. Lay JJ. Modeling and optimization of anaerobic digested sludge converting starch to hydrogen. Biotechnol Bioeng 2000;68:269–78. http://dx.doi.org/10.1002/(SICI)1097-0290(20000505)68:3b269::AID-BIT5N3.0.CO;2-T.
48. Hay JXW, Wu TY, Teh CY, Jahim JM. Optimized growth of Rhodobacter sphaeroides O.U.001 using response surface methodology (RSM). J Sci Ind Res 2012;71:149–54.
49. Bianchi L, Mannelli F, Viti C, Adessi A, Philippis RD. Hydrogen-producing purple non-sulfur bacteria isolated from the trophic lake Averno (Naples, Italy). Int J Hydrog Energy 2010;35:12216–23. http://dx.doi.org/10.1016/j.ijhydene.2010.08.038.
50. Khamtib S, Reungsang A. Biohydrogen product ion from xylose by Thermoanaerobacterium thermosaccharolyticum KKU 19 isolated from hot spring sediment. Int J Hydrog Energy 2012;37:12219–28. http://dx.doi.org/10.1016/j.ijhydene.2012.06.038.
51. Owen WF, Stuckey DC, Healy JB, Young LY, McCarty PL. Bioassay for monitoring biochemical methane potential and anaerobic toxicity. Water Res 1979;13:485–92. http://dx.doi.org/10.1016/0043-1354(79)90043-5.
52. Fangkum A, Reungsang A. Biohydrogen production from sugarcane bagasse hydrolysate by elephant dung: Effects of initial pH and substrate concentration. Int J Hydrog Energy 2011;36:8687–96. http://dx.doi.org/10.1016/j.ijhydene.2010.05.119.
53. Saraphirom P, Reungsang A. Biological hydrogen production from sweet sorghum syrup by mixed cultures using an anaerobic sequencing batch reactor (ASBR). Int J Hydrog Energy 2011;36:8765–73. http://dx.doi.org/10.1016/j.ijhydene.2010.08.058.
54. Zheng XJ, Yu HQ. Inhibitory effects of butyrate on biological hydrogen production with mixed anaerobic cultures. J Environ Manage 2005;74:65–70. http://dx.doi.org/10.1016/j.jenvman.2004.08.015.
55. Khanal SK, ChenWH, Li L, Sung S. Biological hydrogen production: Effect of pH and intermediate products. Int J Hydrog Energy 2004;29:1123–31. http://dx.doi.org/10.1016/j.ijhydene.2003.11.002.
56. Zhang H, Bruns MA, Logan BE. Biological hydrogen production by Clostridium acetobutylicum in an unsaturated flow reactor. Water Res 2006;40:728–34. http://dx.doi.org/10.1016/j.watres.2005.11.041.
57. Uyar B, Eroglu I, Yucel M, Gunduz U. Photofermentative hydrogen production from volatile fatty acids present in dark fermentation effluents. Int J Hydrog Energy 2009;34:4517–23. http://dx.doi.org/10.1016/j.ijhydene.2008.07.057.
58. Van Niel CB. The culture, general physiology, morphology, and classification of the non-sulfur purple and brown bacteria. Bacteriol Rev 1944;8:1–118.
59. Imhoff JF. Anoxygenic Photosynthetic Bacteria: Taxonomy and Physiology of Purple Bacteria and Green Sulfur Bacteria. In: Blankenship RE, Madigan MT, Bauer CE, editors. USA: Kluwer Academic Publishers; 1995. p. 1–14.
60. Danyal K, Dean DR, Hoffman BM, Seefeldt LC. Electron transfer within nitrogenase: Evidence for a deficit-spending mechanism. Biochemistry 2011;50:9255–63. http://dx.doi.org/10.1021/bi201003a.
61. Seefeldt LC, Yang ZY, Duval S, Dean DR. Nitrogenase reduction of carbon-containing compounds. Biochim Biophys Acta Bioenerg 2013;1827:1102–11. http://dx.doi.org/10.1016/j.bbabio.2013.04.003.
62. Spatzal T, Aksoyoglu M, Zhang L, Andrade SL, Schleicher E,Weber DC, et al. Evidence for interstitial carbon in nitrogenase FeMo cofactor. Science 2011;334:940. http://dx.doi.org/10.1126/science.1214025.
63. Xie GJ, Liu BF, Xing DF, Ding J, Nan J, Ren HY, et al. The kinetic characterization of photofermentative bacterium Rhodopseudomonas faecalis RLD-53 and its application for enhancing continuous hydrogen production. Int J Hydrog Energy 2012;37: 13718–24. http://dx.doi.org/10.1016/j.ijhydene.2012.02.168.
64. Holt JG, Krieg NR, Sneath PHA, Staley JT. Bergey's Manual of Determinative Bacteriology. Baltimore: Williams and Wilkins; 1994.
65. Chen CY, Chang JS. Enhancing phototropic hydrogen production by solid-carrier assisted fermentation and internal optical-fiber illumination. Process Biochem 2006;41:2041–9. http://dx.doi.org/10.1016/j.procbio.2006.05.005.
66. Fang HHP, Liu H, Zhang T. Phototrophic hydrogen production from acetate and butyrate in wastewater. Int J Hydrog Energy 2005;30:785–93. http://dx.doi.org/10.1016/j.ijhydene.2004.12.010.
67. Merugu R, Girisham S, Reddy SM. Bioproduction of hydrogen by Rhodobacter capsulatus KU002 isolated from leather industry effluents. Int J Hydrog Energy 2010;35:9591–7. http://dx.doi.org/10.1016/j.ijhydene.2010.06.057.
68. Mongi F, Edward C, William H, Gwang-Hoon G, Almadidy A. Influence of culture parameters on biological hydrogen production by Clostridium saccharoperbutylacetonicum ATCC 27021. World J Microbiol Biotechnol 2005;21:855–62. http://dx.doi.org/10.1007/s11274-004-5972-0.
69. Kim MS, Kim DH, Cha J, Lee JK. Effect of carbon and nitrogen sources on photofermentative H2 production associated with nitrogenase, uptake hydrogenase activity, and PHB accumulation in Rhodobacter sphaeroides KD131. Bioresour Technol 2012;116:179–83. http://dx.doi.org/10.1016/j.biortech.2012.04.011.
70. Cai J, Wang G. Hydrogen production by a marine photosynthetic bacterium, Rhodovulum sulfidophilum P5, isolated from a shrimp pond. Int J Hydrog Energy 2012;37:15070–80. http://dx.doi.org/10.1016/j.ijhydene.2012.07.130.
71. Wang YZ, Liao Q, Zhu X, Li J, Lee DJ. Effect of culture conditions on the kinetics of hydrogen production by photosynthetic bacteria in batch culture. Int J Hydrog Energy 2011;36:14004–13. http://dx.doi.org/10.1016/j.ijhydene.2011.04.005.
72. Franchi E, Tosi C, Scolla G, Penna GD, Rodríguez F, Pedroni PM. Metabolically engineered Rhodobacter sphaeroides RV strains for improved biohydrogen photo production combined with disposal of food wastes. Mar Biotechnol 2004;6: 552–65. http://dx.doi.org/10.1007/s10126-004-1007-y.
73. Pandey A, Srivastava N, Sinha P. Optimization of hydrogen production by Rhodobacter sphaeroides NMBL-01. Biomass Bioenergy 2012;37:251–6. http://dx.doi.org/10.1016/j.biombioe.2011.12.005.
74. Han H, Liu B, Yang H, Shen J. Effect of carbon sources on the photobiological production of hydrogen using Rhodobacter sphaeroides RV. Int J Hydrog Energy 2012;37:12167–74. http://dx.doi.org/10.1016/j.ijhydene.2012.03.134.
75. Basak N, Das D. Photo fermentative hydrogen production using purple non-sulfur bacteria Rhodobacter sphaeroides O.U.001 in an annular photobioreactor: A case study. Biomass Bioenergy 2009;33:911–9. http://dx.doi.org/10.1016/j.biombioe.2009.02.007.
76. Suwansaard M, Choorit W, Zeilstra-Ryalls JH, Prasertsan P. Isolation of anoxygenic photosynthetic bacteria from Songkhla Lake for use in a two-staged biohydrogen production process from palm oil mill effluent. Int J Hydrog Energy 2009;34: 7523–9. http://dx.doi.org/10.1016/j.ijhydene.2009.05.077.
77. Willison JC, Madern D, Vignais PM. Increased photoproduction of hydrogen by non-autotrophic mutants of Rhodopseudomonas capsulata. Biochem J 1984;219: 593–600.
78. Klasson KT, Lundback KMO, Clausen EC, Gaddy JL. Kinetics of light limited growth and biological hydrogen production from carbon monoxide and water by Rhodospirillum rubrum. J Biotechnol 1993;29:177–88. http://dx.doi.org/10.1016/0168-1656(93)90049-S.
79. Kim NJ, Lee JK, Lee CG. Pigment reduction to improve photosynthetic productivity of Rhodobacter sphaeroides. J Microbiol Biotechnol 2004;14:442–9.
80. Asada Y, Miyake J. Photobiological hydrogen production. J Biosci Bioeng 1999;88: 1–6. http://dx.doi.org/10.1016/S1389-1723(99)80166-2.
81. Kim MS, Baek JS, Lee JK. Comparison of H2 accumulation by Rhodobacter sphaeroides KD131 and its uptake hydrogenase and PHB synthase deficient mutant. Int J Hydrog Energy 2006;31:121–7. http://dx.doi.org/10.1016/j.ijhydene.2004.10.023.
82. Kawagoshi Y, Oki Y, Nakano I, Fujimoto A, Takahashi H. Biohydrogen production by isolated halotolerant photosynthetic bacteria using long-wavelength light-emitting diode (LW-LED). Int J Hydrog Energy 2010;35:13365–9. http://dx.doi.org/10.1016/j.ijhydene.2009.11.121.
83. Li X, Wang YH, Zhang SL, Chu J, Zhang M, Huang MZ, et al. Enhancement of phototrophic hydrogen production by Rhodobacter sphaeroides ZX-5 using a novel strategy — Shaking and extra-light supplementation approach. Int J Hydr