title: Evolutionary significance of an algal gene encoding an [FeFe]-hydrogenase with F-domain homology and hydrogenase activity in Chlorella variabilis NC64A.
abstract: [FeFe]-hydrogenases (HYDA) link the production of molecular H(2) to anaerobic metabolism in many green algae. Similar to Chlamydomonas reinhardtii, Chlorella variabilis NC64A (Trebouxiophyceae, Chlorophyta) exhibits [FeFe]-hydrogenase (HYDA) activity during anoxia. In contrast to C. reinhardtii and other chlorophycean algae, which contain hydrogenases with only the HYDA active site (H-cluster), C. variabilis NC64A is the only known green alga containing HYDA genes encoding accessory FeS cluster-binding domains (F-cluster). cDNA sequencing confirmed the presence of F-cluster HYDA1 mRNA transcripts, and identified deviations from the in silico splicing models. We show that HYDA activity in C. variabilis NC64A is coupled to anoxic photosynthetic electron transport (PSII linked, as well as PSII-independent) and dark fermentation. We also show that the in vivo H(2)-photoproduction activity observed is as O(2) sensitive as in C. reinhardtii. The two C. variabilis NC64A HYDA sequences are similar to homologs found in more deeply branching bacteria (Thermotogales), diatoms, and heterotrophic flagellates, suggesting that an F-cluster HYDA is the ancestral enzyme in algae. Phylogenetic analysis indicates that the algal HYDA H-cluster domains are monophyletic, suggesting that they share a common origin, and evolved from a single ancestral F-cluster HYDA. Furthermore, phylogenetic reconstruction indicates that the multiple algal HYDA paralogs are the result of gene duplication events that occurred independently within each algal lineage. Collectively, comparative genomic, physiological, and phylogenetic analyses of the C. variabilis NC64A hydrogenase has provided new insights into the molecular evolution and diversity of algal [FeFe]-hydrogenases.
authors.affiliation: Division of Environmental Science and Engineering, Colorado School of Mines, Golden, CO 80401, USA.
authors.forename: Jonathan E
authors.initials: JE
authors.lastname: Meuser
authors.forename: Eric S
authors.initials: ES
authors.lastname: Boyd
authors.forename: Gennady
authors.initials: G
authors.lastname: Ananyev
authors.forename: Devin
authors.initials: D
authors.lastname: Karns
authors.forename: Randor
authors.initials: R
authors.lastname: Radakovits
authors.forename: U M
authors.initials: UM
authors.lastname: Narayana Murthy
authors.forename: Maria L
authors.initials: ML
authors.lastname: Ghirardi
authors.forename: G Charles
authors.initials: GC
authors.lastname: Dismukes
authors.forename: John W
authors.initials: JW
authors.lastname: Peters
authors.forename: Matthew C
authors.initials: MC
authors.lastname: Posewitz
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D015687:Cell Hypoxia; D016825:Chlamydomonas reinhardtii / Q000201:enzymology / Q000235:genetics / Q000378:metabolism; D002708:Chlorella / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism; D003470:Culture Media; D018076:DNA, Complementary / Q000235:genetics; D018744:DNA, Plant / Q000235:genetics; D003624:Darkness; D019143:Evolution, Molecular; D005285:Fermentation; D015971:Gene Expression Regulation, Enzymologic / Q000235:genetics*; D018506:Gene Expression Regulation, Plant; D023281:Genomics; D006859:Hydrogen / Q000378:metabolism*; D006864:Hydrogenase / Q000235:genetics* / Q000378:metabolism*; D007506:Iron-Sulfur Proteins / Q000235:genetics* / Q000378:metabolism*; D008027:Light; D008969:Molecular Sequence Data; D009243:NAD / Q000378:metabolism; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018749:RNA, Plant / Q000235:genetics; D011994:Recombinant Proteins; D013997:Time Factors
chemical_list: D003470:Culture Media; D018076:DNA, Complementary; D018744:DNA, Plant; D007506:Iron-Sulfur Proteins; D010940:Plant Proteins; D018749:RNA, Plant; D011994:Recombinant Proteins; D009243:NAD; D002734:Chlorophyll; D006859:Hydrogen; C118830:iron hydrogenase; D006864:Hydrogenase; D010100:Oxygen