热泉微生物驱动的氮循环研究进展及展望

热泉微生物是驱动热泉氮(N)循环的主导力量,开展热泉生态系统中驱动氮循环微生物种群构成及其与环境响应的研究,对于探索热泉中氮的生物地球化学循环、生命进化、生物修复等方面都具有重要的理论和应用价值。本文综合阐述了热泉生态系统驱动氮循环的功能微生物(如固氮菌、氨氧化菌、厌氧氨氧化菌、反硝化菌、异化硝酸盐还原菌)在系统发育学上的分布、功能基因的相对丰度、活性及其与环境因子(如温度、pH)的相关性等方面的研究现状和亟待解决的问题。并展望了热泉生境中驱动氮循环微生物未来的研究方向。     

Probing the role of Valine 185 of the D1 protein in the Photosystem II oxygen evolution

In Photosystem II (PSII), the Mn₄CaO₅-cluster of the active site advances through five sequential oxidation states (S₀ to S₄) before water is oxidized and O₂ is generated. The V185 of the D1 protein has been shown to be an important amino acid in PSII function (Dilbeck et al. Biochemistry 52 (2013) 6824–6833). Here, we have studied its role by making a V185T site-directed mutant in the thermophilic cyanobacterium Thermosynechococcus elongatus. The properties of the V185T-PSII have been compared to those of the WT*3-PSII by using EPR spectroscopy, polarography, thermoluminescence and time-resolved UV–visible absorption spectroscopy. It is shown that the V185 and the chloride binding site very likely interact via the H-bond network linking Tyr_Z and the halide. The V185 contributes to the stabilization of S₂ into the low spin (LS), S?=?1/2, configuration. Indeed, in the V185T mutant a high proportion of S₂ exhibits a high spin (HS), S?=?5/2, configuration. By using bromocresol purple as a dye, a proton release was detected in the S₁Tyr_Z?→?S₂^HSTyr_Z transition in the V185T mutant in contrast to the WT*3-PSII in which there is no proton release in this transition. Instead, in WT*3-PSII, a proton release kinetically much faster than the S₂^LSTyr_Z?→?S₃Tyr_Z transition was observed and we propose that it occurs in the S₂^LSTyr_Z?→?S₂^HSTyr_Z intermediate step before the S₂^HSTyr_Z?→?S₃Tyr_Z transition occurs. The dramatic slowdown of the S₃Tyr_Z?→?S₀Tyr_Z transition in the V185T mutant does not originate from a structural modification of the Mn₄CaO₅ cluster since the spin S?=?3?S₃ EPR signal is not modified in the mutant. More probably, it is indicative of the strong implication of V185 in the tuning of an efficient relaxation processes of the H-bond network and/or of the protein.     

Hydrogen and oxygen trapping at the H-cluster of [FeFe]-hydrogenase revealed by site-selective spectroscopy and QM/MM calculations

[FeFe]-hydrogenases are superior hydrogen conversion catalysts. They bind a cofactor (H-cluster) comprising a four-iron and a diiron unit with three carbon monoxide (CO) and two cyanide (CN^?) ligands. Hydrogen (H₂) and oxygen (O₂) binding at the H-cluster was studied in the C169A variant of [FeFe]-hydrogenase HYDA1, in comparison to the active oxidized (Hox) and CO-inhibited (Hox-CO) species in wildtype enzyme. ⁵⁷Fe labeling of the diiron site was achieved by in vitro maturation with a synthetic cofactor analogue. Site-selective X-ray absorption, emission, and nuclear inelastic/forward scattering methods and infrared spectroscopy were combined with quantum chemical calculations to determine the molecular and electronic structure and vibrational dynamics of detected cofactor species. Hox reveals an apical vacancy at Fe_d in a [4Fe4S-2Fe]^3 ? complex with the net spin on Fe_d whereas Hox-CO shows an apical CN^? at Fe_d in a [4Fe4S-2Fe(CO)]^3 ? complex with net spin sharing among Fe_p and Fe_d (proximal or distal iron ions in [2Fe]). At ambient O₂ pressure, a novel H-cluster species (Hox-O₂) accumulated in C169A, assigned to a [4Fe4S-2Fe(O₂)]^3 ? complex with an apical superoxide (O₂^?) carrying the net spin bound at Fe_d. H₂ exposure populated the two-electron reduced Hhyd species in C169A, assigned as a [(H)4Fe4S-2Fe(H)]^3 ? complex with the net spin on the reduced cubane, an apical hydride at Fe_d, and a proton at a cysteine ligand. Hox-O₂ and Hhyd are stabilized by impaired O₂^– protonation or proton release after H₂ cleavage due to interruption of the proton path towards and out of the active site.     

Taxonomic and functional ant diversity along a secondary successional gradient in a tropical forest

The taxonomic diversity (TD) of tropical flora and fauna tends to increase during secondary succession. This increase may be accompanied by changes in functional diversity (FD), although the relationship between TD and FD is not well understood. To explore this relationship, we examined the correlations between the TD and FD of ants and forest age in secondary forests at the α‐ and β‐diversity levels using single‐ and multi‐trait‐based approaches. Our objectives were to understand ant diversity patterns and to evaluate the role of secondary forests in the conservation of biodiversity and in the resilience of tropical forests. Ant assemblages were sampled across a chronosequence in the Lacandon region, Mexico. All species were characterized according to 12 functional ecomorphological traits relevant to their feeding behavior. We found that TD and FD were related to forest age at the alpha level, but not at the beta level. α‐functional richness and divergence increased linearly with species richness and diversity, respectively. Also, the relationship between taxonomic and functional turnover was linear and positive. Our results indicated that functional traits were complementary across the chronosequence. The increase in FD was mainly driven by the addition of rare species with relevant traits. The older secondary forests did not recover all of the functions of old growth forest but did show a tendency to recovery. Because older successional stages support more TD and FD, we suggest developing agriculture and forestry management practices that facilitate rapid post‐agricultural succession and thereby better preserve the functionality of tropical forests.     

Flow cytometry for assessing the efficacy of interspecific gynogenesis induction in sturgeon

The efficacy of ploidy analysis for separating progeny of Siberian sturgeon Acipenser baerii after induced gynogenesis was demonstrated using sperm of a paternal species differing in ploidy level from the maternal species. Gynogenesis was induced in tetraploid A. baerii with UV‐C irradiated sperm from the diploid sterlet Acipenser ruthenus and vice‐versa. The success of sperm UV irradiation and diploidy restoration by heat‐shock was estimated based on the ploidy level of progeny, confirmed by microsatellite parentage assignment. Hatching rates of interspecific gynogenotes were comparable with rates reported for gynogenesis induction using sperm and eggs of the same species. Juvenile mortality was similar to that observed in the control hybrids. The efficiency and reliability of this method may foster its use for production of gynogenotes in aquaculture, potentially allowing interspecific gynogenesis to replace intraspecific.     

Greater macroinvertebrate diversity and freshwater mussel density in meander margins of an Amazon river

Meanders are complex aquatic environments exhibiting different flow and sediment characteristics that influence macroinvertebrate distribution. Differences in macroinvertebrate composition, freshwater mussel density (mainly Castalia ambigua Lamarck, 1819) and habitat variables were investigated, using uni‐ and multivariate analyses, in two zones, the margin and thalweg, of the meanders of a 7‐km stretch of a morphologically unaltered tropical alluvial lowland river. Clear differences were found between meander zones, with greater taxonomic and functional diversity of macroinvertebrates and greater freshwater mussel densities in the meander margin. A total of 12 families of macroinvertebrates were exclusive to the meander margin, and macroinvertebrate indicators of zones were Philopotamidae and Leptoceridae (meander margin) and Chironomidae and Elmidae (meander thalweg). In the meander margin, there were no differences in macroinvertebrate abundance, and taxonomic and functional group diversity among areas with low, medium and high mussel density. Macroinvertebrate abundance did not vary between zones, but in both, abundance was associated with lower pH and higher electrical conductivity. Low shear velocity, which stabilises the river bed, high organic matter content and percentage silt in the meander margin were associated with higher taxonomic and functional macroinvertebrate diversity, as well as the presence of freshwater mussels. Natural unaltered meanders are spatially heterogeneous in both habitat and biodiversity and, similar to restored meanders, support greater macroinvertebrate taxonomic and functional diversity, as well as maintain freshwater mussel beds, mainly by stabilising the river bed. The meander margin may also be important for attracting mussel host fish that feed on macroinvertebrates and aid mussel dispersal. Thus, the meander margins, and other similar riparian habitats with low shear velocity, for example, side channels and pools, have potentially high conservation value and should be afforded due protection.     

北京植物园不同功能型植物叶经济谱

通过对北京植物园不同功能型植物的叶片光合参数、叶绿素荧光参数、叶面积、叶干质量以及叶氮含量等性状参数进行测定,分析了不同功能型植物的叶经济谱.结果表明: 生活型中草本植物、生活史中一年生植物、光合型中C4植物靠近叶经济谱中快速投资-收益型物种的一端,而生活型中乔木和灌木、生活史中多年生植物、光合型中C3植物位于缓慢投资-收益型物种的一端,表明不同功能型植物通过叶片性状间的权衡采取不同的环境适应策略,验证了不同功能型植物叶经济谱的存在.不同功能型植物叶片性状具有明显差异,其中不同生活型间的叶片比叶面积(SLA)、叶氮含量(N_mass)、最大净光合速率(A_mass)、光合氮利用效率(PNUE)均表现出草本植物>藤本植物>灌木>乔木;不同生活史间一年生植物的SLA、N_mass、A_mass、PNUE均显著高于多年生植物;不同光合型间植物的A_mass、PNUE、PSⅡ实际光化学效率(Φ_PSⅡ)均表现出C4>C3.N_mass、A_mass、SLA两两之间呈显著正相关,而PSⅡ有效光化学量子产量(F_v′/F_m′)与SLA呈显著负相关;PNUE与SLA呈显著正相关.     

黄顶菊入侵对土壤中主要功能细菌的影响

以我国北方大面积发生的入侵植物黄顶菊为研究对象,对黄顶菊根际土壤中可培养的主要功能细菌进行了分离筛选,通过rep-PCR聚类和多样性分析研究了其群落结构的变化,并利用16S rRNA序列比对,对主要优势菌群进行鉴定.结果表明: 相对于本地植物万寿菊和空白对照,黄顶菊显著增加了根际土壤中固氮菌、有机磷细菌、无机磷细菌和钾细菌的数量.rep-PCR分析显示,黄顶菊根际4种功能细菌的种群结构与本地植物和对照相比有显著差异,3种土壤中相同的聚类群极少.多样性分析表明,黄顶菊根际微生物物种多样性更加丰富,群落结构更加复杂,优势种群比较明显,生态多样性较高.对从3种土壤中分离得到的主要优势菌群的鉴定结果也进一步证明了这一结论.研究结果为阐明黄顶菊入侵的微生态机制提供了理论基础.