D'Adamo Sarah, Jinkerson Robert E, Boyd Eric S, Brown Susan L, Baxter Bonnie K, Peters John W, Posewitz Matthew C
Department of Chemistry and Geochemistry, Colorado School of Mines, Golden, Colorado, United States of America.
Department of Microbiology and the Thermal Biology Institute, Montana State University, Bozeman, Montana, United States of America.
PLoS One. 2014 Jan 21;9(1):e85812. doi: 10.1371/journal.pone.0085812. eCollection 2014.
Although significant advances in H2 photoproduction have recently been realized in fresh water algae (e.g. Chlamydomonas reinhardtii), relatively few studies have focused on H2 production and hydrogenase adaptations in marine or halophilic algae. Salt water organisms likely offer several advantages for biotechnological H2 production due to the global abundance of salt water, decreased H2 and O2 solubility in saline and hypersaline systems, and the ability of extracellular NaCl levels to influence metabolism. We screened unialgal isolates obtained from hypersaline ecosystems in the southwest United States and identified two distinct halophilic strains of the genus Tetraselmis (GSL1 and QNM1) that exhibit both robust fermentative and photo H2-production activities. The influence of salinity (3.5%, 5.5% and 7.0% w/v NaCl) on H2 production was examined during anoxic acclimation, with the greatest in vivo H2-production rates observed at 7.0% NaCl. These Tetraselmis strains maintain robust hydrogenase activity even after 24 h of anoxic acclimation and show increased hydrogenase activity relative to C. reinhardtii after extended anoxia. Transcriptional analysis of Tetraselmis GSL1 enabled sequencing of the cDNA encoding the FeFe-hydrogenase structural enzyme (HYDA) and its maturation proteins (HYDE, HYDEF and HYDG). In contrast to freshwater Chlorophyceae, the halophilic Tetraselmis GSL1 strain likely encodes a single HYDA and two copies of HYDE, one of which is fused to HYDF. Phylogenetic analyses of HYDA and concatenated HYDA, HYDE, HYDF and HYDG in Tetraselmis GSL1 fill existing knowledge gaps in the evolution of algal hydrogenases and indicate that the algal hydrogenases sequenced to date are derived from a common ancestor. This is consistent with recent hypotheses that suggest fermentative metabolism in the majority of eukaryotes is derived from a common base set of enzymes that emerged early in eukaryotic evolution with subsequent losses in some organisms.
尽管最近在淡水藻类（如莱茵衣藻）的光致产氢方面取得了重大进展，但相对较少的研究关注海洋藻类或嗜盐藻类的产氢及氢化酶适应性。由于全球咸水资源丰富、在盐水和超盐体系中氢气和氧气的溶解度降低，以及细胞外氯化钠水平影响新陈代谢的能力，盐水生物在生物技术产氢方面可能具有几个优势。我们筛选了从美国西南部高盐生态系统中获得的单藻分离株，并鉴定出了四爿藻属的两个不同嗜盐菌株（GSL1和QNM1），它们表现出强大的发酵产氢和光致产氢活性。在缺氧驯化过程中，研究了盐度（3.5%、5.5%和7.0% w/v氯化钠）对产氢的影响，在7.0%氯化钠时观察到最高的体内产氢速率。这些四爿藻菌株即使在缺氧驯化24小时后仍保持强大的氢化酶活性，并且在长时间缺氧后相对于莱茵衣藻显示出更高的氢化酶活性。对四爿藻GSL1进行转录分析，使得能够对编码FeFe-氢化酶结构酶（HYDA）及其成熟蛋白（HYDE、HYDEF和HYDG）的cDNA进行测序。与淡水绿藻纲不同，嗜盐的四爿藻GSL1菌株可能编码单个HYDA和两个HYDE拷贝，其中一个与HYDF融合。对四爿藻GSL1中的HYDA以及串联的HYDA、HYDE、HYDF和HYDG进行系统发育分析，填补了藻类氢化酶进化方面现有的知识空白，并表明迄今为止测序的藻类氢化酶源自一个共同祖先。这与最近的假说一致，该假说认为大多数真核生物中的发酵代谢源自真核生物进化早期出现的一组共同的基础酶，随后在一些生物体中丢失。
