红树林生态系统微生物驱动的氮素循环过程研究进展

微生物驱动的氮循环过程在红树林生态系统物质循环、净化外来污染物、维持生态系统平衡等方面起重要作用。相较于其他自然生态系统,因红树林处于沿海陆地交界地带,其氮循环过程及其相关微生物的种类丰富,受交错复杂的环境因素影响与调控。本文梳理了红树林土壤性质及特性,综述了红树林生态系统中由微生物驱动的固氮、氮素矿化、硝化、厌氧氨氧化、反硝化、异化硝酸盐还原为铵等主要的氮循环过程,并讨论了氮循环与其他循环的耦合过程。最后讨论pH、盐度、季节、螃蟹活动、红树林树种等环境因素对氮循环过程及其相关微生物丰度、多样性的影响。本综述以期为红树林湿地生态系统的保护和修复提供理论参考。     

Cyanobacterial diversity in the phyllosphere of a mangrove forest

The cyanobacterial community colonizing phyllosphere in a well-preserved Brazilian mangrove ecosystem was assessed using cultivation-independent molecular approaches. Leaves of trees that occupy this environment (Rhizophora mangle,Avicennia schaueriana and Laguncularia racemosa) were collected along a transect beginning at the margin of the bay and extending upland. The results demonstrated that the phyllosphere of R. mangle and L. racemosa harbor similar assemblages of cyanobacteria at each point along the transect. A. schaueriana, found only in the coastal portions of the transect, was colonized by assemblages with lower richness than the other trees. However, the results indicated that spatial location was a stronger driver of cyanobacterial community composition than plant species. Distinct cyanobacterial communities were observed at each location along the coast-to-upland transect. Clone library analysis allowed identification of 19 genera of cyanobacteria and demonstrated the presence of several uncultivated taxa. A predominance of sequences affiliated with the orders Nostocales and Oscillatoriales was observed, with a remarkable number of sequences similar to genera Symphyonemopsis/Brasilonema (order Nostocales). The results demonstrated that phyllosphere cyanobacteria in this mangrove forest ecosystem are influenced by environmental conditions as the primary driver at the ecosystem scale, with tree species exerting some effect on community structure at the local scale.     

宏基因组测序分析东寨港红树林淤泥和水体微生物的多样性

为深入了解海南东寨港红树林生态系统微生物多样性及其在氮、磷、硫等代谢循环中的功能特点,本研究采用宏基因组测序,从物种注释与丰度、群落功能及多样性指数等角度,分析红树林淤泥和水体生境中微生物群落结构及生态功能的特异性。结果显示,在淤泥中检测到53个门、909个属的微生物类群,有3个占比超过1%的优势门类,其中变形杆菌门为83.78%,处于绝对优势,其下的12个优势属全部来自变形杆菌门;不动杆菌属是聚磷微生物的主要类群,其在淤泥中含量是水体的107.7倍,硫氧化单胞菌属、脱硫杆菌属是硫化物代谢的主要菌属,主要存在于淤泥生境当中。在水体中检测到64个门、1 522个属,包括13个优势门类、7个优势属;Nitrospinae和硝化螺旋菌门是亚硝酸盐氧化代谢的关键类群,两者在水体中占比分别是淤泥中的28.1倍和6.8倍。多样性评估得知,水体样品中的Shannon Wiener指数和Simpson指数均高于淤泥样品,两样品在属分类学单元上的Simpson指数趋近于1,表明红树林生态系统具有非常高的微生物多样性,水体生境的微生物多样性高于淤泥;亚硝酸盐的微生物代谢循环主要发生在水体生境中,微生物对磷的富集作用和硫化合物的氧化还原代谢主要发生在淤泥生境中。本研究有助于认识东寨港红树林湿地生境中的微生物资源状况,为保护红树林生态系统和开发利用其中的微生物资源提供依据。     

典型红树林生态系统藻类多样性及其在生态过程中的作用

藻类是红树林生态系统重要的生物类群, 根据生态习性可分为浮游植物、底栖微藻和大型藻类三个生态类群, 它们在红树林生态系统生物多样性、初级生产、元素循环等方面起着重要作用。但在红树林生态系统中, 关注重点多集中在红树植物和动物, 对其中的藻类重视不够, 且多数研究集中在近20年以及亚洲的红树林区。事实上, 红树林生态系统藻类非常丰富, 其多样性研究有助于深入揭示红树林生态系统的结构与功能。本文介绍了红树林生态系统藻类的组成类群及其重要性, 重点对红树林区浮游植物、底栖硅藻和大型海藻的种类组成、地理分布及其与初级生产力、水质污染、元素循环、碳库形成等生态过程中的作用的研究动态和进展等进行了总结。根据已有研究, 红树林区浮游植物和底栖硅藻的种类数一般为几十到上百种, 其中硅藻在种类和数量上都占绝对优势, 它们是重要的初级生产者、饵料生物和水质污染指示生物; 红树林区底栖大型藻类主要由红藻、绿藻、褐藻、蓝藻组成, 绿藻的种类较多, 红藻在数量上占优势; 藻类是红树林湿地碳库的重要贡献者, 在红树林湿地生态系统碳汇和碳循环中起重要作用。红树林生态系统是个高度动态和异质的系统, 今后应加强红树林藻类多样性的长周期、大尺度变化及不同生境藻类的综合研究, 关注大陆径流和潮汐对藻类多样性和蓝碳的影响, 借助沉积物藻类记录, 探明红树林区藻类的长周期变化, 反演气候变化和人类活动对红树林生态系统的影响过程和机制。     

红树林湿地硫酸盐还原菌的多样性及其参与驱动的元素耦合机制

红树林生态系统是热带和亚热带地区重要的滨海湿地,具有营养物质形态多样化和高效动态变化的特征,是驱动碳、氮、硫等元素循环的热区。硫酸盐还原菌(sulfate-reducing prokaryotes,SRPs)是地球最古老的微生物生命形式之一,在推动早期地球地质演化以及现代生物地球化学循环中发挥关键作用,但其在红树林湿地还缺乏全面深入研究。本文基于Genome Taxonomy Database中原核生物基因组的挖掘,系统总结了硫酸盐还原菌的类群,梳理了近年来国内外红树林中硫酸盐还原菌的分布情况及影响其分布的因素,分析了硫酸盐还原菌在红树林生态系统的碳、氮、硫及铁等元素地球化学循环中的作用,并对硫酸盐还原菌未来的研究方向进行了展望,以期为深入研究硫酸盐还原菌参与驱动的元素生物地球化学循环及其耦合机制提供参考。     

滨海盐渍化土壤中蓝细菌多样性及分布

【目的】蓝细菌在贫瘠土壤的固氮、固碳中发挥着重要作用,然而土壤盐渍化对蓝细菌多样性及群落结构的影响还不清楚。本研究以莱州湾南岸及黄河口海水入侵盐渍化土壤为例,研究蓝细菌的多样性、群落结构及丰度沿盐度梯度的分布情况。【方法】利用自动核糖体间隔基因分析(ARISA)技术与群落相似性分析(ANOSIM)探究蓝细菌群落的差异与空间分布格局;通过16S rRNA基因克隆文库、测序与系统进化分析解析了3个典型盐度梯度样品中蓝细菌的群落组成;实时定量PCR测定蓝细菌16S rRNA拷贝数(丰度);BEST多元分析探寻影响蓝细菌分布的主要环境因子。【结果】蓝细菌在莱州湾南岸盐土中分布广泛,其群落结构在低(0.63%?1.27%)、中(1.55%?2.00%)、高盐度(2.39%?5.11%)样品组之间差异显著(P=0.03),而在不同含水量样品组间则不显著(P=0.09)。总体来看,群落结构主要受土壤盐度与含水量这两个因子联合控制(P=0.02)。低盐样品中蓝细菌多样性和丰富度最低,并以Halomicronema和Acaryochloris为优势类群。Leptolyngbya在中、高盐土中占优势。Arthrospira与Geitlerinema仅在低盐土中检测到,而Oscillatoria则仅出现在高盐土中。随盐度升高蓝细菌丰度呈下降趋势,低盐土样中蓝细菌丰度(2.14×105 copies/g干土)显著高于中盐土(1.25×105 copies/g干土)(P<0.05);高盐度土为1.20×105 copies/g干土。【结论】盐渍化程度是调控莱州湾南岸滨海土壤中蓝细菌群落结构与丰度的最重要环境因子,可能对滨海土壤微生物碳氮循环产生重要影响。     

Mangrove and coral reef sponge faunas: untold stories about shallow water Porifera in the Caribbean

Sponge faunas from coral reefs and mangrove ecosystems in the Caribbean have mostly been studied from an ecological perspective, with researchers considering the effects of physical and biological factors on their species distribution. To discern evolutionary patterns, this study analyzed the systematic composition, taxonomic diversity, and ecological properties (reproductive strategies, size, shape, endosymbiosis) of mangrove and reef sponge assemblages from seven distant Caribbean localities. Species composition was compared by use of cluster analysis (Sørensen’s), and taxonomic diversity by use of the biodiversity index average taxonomic distinctness (AvTD). Mangrove and reef-associated sponge faunas were found to be statistically dissimilar, with the AvTD values suggesting stronger taxonomic bias toward specific groups in mangroves, irrespective of geographic distance. Most Demospongiae orders have 30–50% more species in coral reefs than in mangroves. The richest reef genera (Agelas, Aplysina, Callyspongia, Petrosia, and Xestospongia) rarely colonize contiguous mangrove formations. The distribution and diversity of suprageneric taxa suggest that coral reef sponge assemblages might represent an older fauna. This historical interpretation would place mangrove subtidal habitats as the youngest marine ecosystem, rather than a below-optimum ecosystem. Life history traits support a biological split discussed here from the perspective of distinct evolutionary histories and different environmental conditions.     

Effects of maternal genotypic identity and genetic diversity of the red mangrove Rhizophora mangle on associated soil bacterial communities: A field‐based experiment

Loss of plant biodiversity can result in reduced abundance and diversity of associated species with implications for ecosystem functioning. In ecosystems low in plant species diversity, such as Neotropical mangrove forests, it is thought that genetic diversity within the dominant plant species could play an important role in shaping associated communities. Here, we used a manipulative field experiment to study the effects of maternal genotypic identity and genetic diversity of the red mangrove Rhizophora mangle on the composition and richness of associated soil bacterial communities. Using terminal restriction fragment length polymorphism (T‐RFLP) community fingerprinting, we found that bacterial community composition differed among R. mangle maternal genotypes but not with genetic diversity. Bacterial taxa richness, total soil nitrogen, and total soil carbon were not significantly affected by maternal genotypic identity or genetic diversity of R. mangle. Our findings show that genotype selection in reforestation projects could influence soil bacterial community composition. Further research is needed to determine what impact these bacterial community differences might have on ecosystem processes, such as carbon and nitrogen cycling.     

Processes of organic carbon in mangrove ecosystems

In addition to carbon accumulation in plants, processes of organic carbon in mangrove ecosystems include origins of sediment organic carbon, carbon fluxes between mangroves and their adjacent systems (coastal waters and atmosphere), and cycling processes. Sediment organic carbon originates from suspending solids in coastal waters, mangrove plants and benthic algae. In mangroves with low organic carbon content in sediments, tidal seawater is the main origin of sediment organic carbon, while in mangroves with high sediment organic carbon contents, sediment organic carbon mainly originates from mangrove plants. Due to tidal flush, there is large material exchange between mangrove ecosystems and their adjacent coastal waters. In China, exports of organic carbon in litter falls and dissolved organic carbon from mangroves to their adjacent coastal waters have not been documented. Processes of mangrove litter falls, including production, decomposition, export and animal consumption, determine linkages among organic carbon among mangrove plants, secondary production and coastal ocean. Consumers especially benthic animals may influence organic carbon in mangrove ecosystems, because (1) their consumption rates are high, and their selective feeding on some food sources will change the relative quantities of export, bury and mineralization of organic carbon from different origins; (2) their consumption is much more than assimilation, resulting in the changes in sizes, forms and qualities of non-assimilated organic matters, and then the changes in availability of export, consumption or mineralization of organic carbon. Respiration and sulfate reduction are important mineralization processes of organic carbon in mangrove sediments. Mineralization rates of organic carbon in mangrove sediments are influenced by quantities, activities and particle sizes of organic matters, and other factors such as forest ages, root activities and animal burrowing activities. Researches on processes of mangrove organic carbon should be based on open systems, and ecological processes of organic carbon should be coupled with vegetation restoration.     

Processes of organic carbon in mangrove ecosystems

In addition to carbon accumulation in plants, processes of organic carbon in mangrove ecosystems include origins of sediment organic carbon, carbon fluxes between mangroves and their adjacent systems (coastal waters and atmosphere), and cycling processes. Sediment organic carbon originates from suspending solids in coastal waters, mangrove plants and benthic algae. In mangroves with low organic carbon content in sediments, tidal seawater is the main origin of sediment organic carbon, while in mangroves with high sediment organic carbon contents, sediment organic carbon mainly originates from mangrove plants. Due to tidal flush, there is large material exchange between mangrove ecosystems and their adjacent coastal waters. In China, exports of organic carbon in litter falls and dissolved organic carbon from mangroves to their adjacent coastal waters have not been documented. Processes of mangrove litter falls, including production, decomposition, export and animal consumption, determine linkages among organic carbon among mangrove plants, secondary production and coastal ocean. Consumers especially benthic animals may influence organic carbon in mangrove ecosystems, because (1) their consumption rates are high, and their selective feeding on some food sources will change the relative quantities of export, bury and mineralization of organic carbon from different origins; (2) their consumption is much more than assimilation, resulting in the changes in sizes, forms and qualities of non-assimilated organic matters, and then the changes in availability of export, consumption or mineralization of organic carbon. Respiration and sulfate reduction are important mineralization processes of organic carbon in mangrove sediments. Mineralization rates of organic carbon in mangrove sediments are influenced by quantities, activities and particle sizes of organic matters, and other factors such as forest ages, root activities and animal burrowing activities. Researches on processes of mangrove organic carbon should be based on open systems, and ecological processes of organic carbon should be coupled with vegetation restoration.     

Long-Term Nitrogen Amendment Alters the Diversity and Assemblage of Soil Bacterial Communities in Tallgrass Prairie

Anthropogenic changes are altering the environmental conditions and the biota of ecosystems worldwide. In many temperate grasslands, such as North American tallgrass prairie, these changes include alteration in historically important disturbance regimes (e.g., frequency of fires) and enhanced availability of potentially limiting nutrients, particularly nitrogen. Such anthropogenically-driven changes in the environment are known to elicit substantial changes in plant and consumer communities aboveground, but much less is known about their effects on soil microbial communities. Due to the high diversity of soil microbes and methodological challenges associated with assessing microbial community composition, relatively few studies have addressed specific taxonomic changes underlying microbial community-level responses to different fire regimes or nutrient amendments in tallgrass prairie. We used deep sequencing of the V3 region of the 16S rRNA gene to explore the effects of contrasting fire regimes and nutrient enrichment on soil bacterial communities in a long-term (20 yrs) experiment in native tallgrass prairie in the eastern Central Plains. We focused on responses to nutrient amendments coupled with two extreme fire regimes (annual prescribed spring burning and complete fire exclusion). The dominant bacterial phyla identified were Proteobacteria, Verrucomicrobia, Bacteriodetes, Acidobacteria, Firmicutes, and Actinobacteria and made up 80% of all taxa quantified. Chronic nitrogen enrichment significantly impacted bacterial community diversity and community structure varied according to nitrogen treatment, but not phosphorus enrichment or fire regime. We also found significant responses of individual bacterial groups including Nitrospira and Gammaproteobacteria to long-term nitrogen enrichment. Our results show that soil nitrogen enrichment can significantly alter bacterial community diversity, structure, and individual taxa abundance, which have important implications for both managed and natural grassland ecosystems.     

CYANOBACTERIAL BUOYANCY REGULATION: THE PARADOXICAL ROLES OF CARBON1

In stratified lakes, dominance of the phytoplankton by cyanobacteria is largely the result of their buoyancy and depth regulation. Bloom-forming cyanobacteria regulate the gas vesicle and storage polymer contents of their cells in response to interactive environmental factors, especially light and nutrients. While research on the roles of nitrogen and phosphorus in cyanobacterial buoyancy regulation has reached a consensus, evaluations of the roles of carbon have remained open to dispute. We investigated the various effects of changes in carbon availability on cyanobacterial buoyancy with continuous cultures of Microcystis aeruginosa Kuetz. emend. Elenkin (1924), a notorious bloom-former. Although CO₂ limitation of photosynthesis can promote buoyancy in the short term by preventing the collapse of turgor-sensitive gas vesicles and/or by limiting polysaccharide accumulation, we found that sustained carbon limitation restricts buoyancy regulation by limiting gas vesicle as well as polysaccharide synthesis. These results provide an explanation for the positive effects of bicarbonate enrichment on cyanobacterial nitrogen uptake and bloom formation in lake experiments and may help to explain the pattern of cyanobacterial dominance in phosphorus-enriched, low-carbon lakes.     

Classification trees as a tool for predicting cyanobacterial blooms

Nutrient enrichment of aquatic ecosystems caused dramatic increase in the frequency, magnitude and duration of cyanobacterial blooms. Such blooms may cause fish kills, have adverse health effects on humans and contribute to the loss of biodiversity in aquatic ecosystems. Some 50 eutrophic to hypereutrophic ponds from the Brussels Capital Region (Belgium) were studied between 2003 and 2009. A number of the ponds studied are prone to persistent cyanobacterial blooms. Because of the related health concerns and adverse effects on ecological quality of the affected ponds, a tool for assessment of the risk of cyanobacterial bloom occurrence was needed. The data acquired showed that cyanobacteria have threshold relationships with most of the environmental factors that control them. This is negatively reflected on the predictive capacity of conventional statistical methods based on linear relationships. Therefore, classification trees designed for the treatment of complex data and non-linear relationships were used to assess the risk of cyanobacterial bloom occurrence. The main factors determining cyanobacterial bloom development appeared to be phytoplankton biomass, pH and, to a lesser degree, nitrogen availability. These results suggest that to outcompete eukaryotic phytoplankters cyanobacteria need the presence of environmental constraints: carbon limitation, light limitation and nitrogen limitation, for which they developed a number of adaptations. In the absence of constraints, eukaryotic phytoplankters appear to be more competitive. Therefore, prior build up of phytoplankton biomass seems to be essential for cyanobacterial dominance. Classification trees proved to be an efficient tool for the bloom risk assessment and allowed the main factors controlling bloom development to be identified as well as the risk of bloom occurrence corresponding to the conditions determined by these factors to be quantified. The results produced by the classification trees are consistent with those obtained earlier by probabilistic approach to bloom risk assessment. They can facilitate planning management interventions and setting restoration priorities.     

Cyanobacteria and cyanotoxins: the influence of nitrogen versus phosphorus

The importance of nitrogen (N) versus phosphorus (P) in explaining total cyanobacterial biovolume, the biovolume of specific cyanobacterial taxa, and the incidence of cyanotoxins was determined for 102 north German lakes, using methods to separate the effects of joint variation in N and P concentration from those of differential variation in N versus P. While the positive relationship between total cyanobacteria biovolume and P concentration disappeared at high P concentrations, cyanobacteria biovolume increased continually with N concentration, indicating potential N limitation in highly P enriched lakes. The biovolumes of all cyanobacterial taxa were higher in lakes with above average joint NP concentrations, although the relative biovolumes of some Nostocales were higher in less enriched lakes. Taxa were found to have diverse responses to differential N versus P concentration, and the differences between taxa were not consistent with the hypothesis that potentially N(2)-fixing Nostocales taxa would be favoured in low N relative to P conditions. In particular Aphanizomenon gracile and the subtropical invasive species Cylindrospermopsis raciborskii often reached their highest biovolumes in lakes with high nitrogen relative to phosphorus concentration. Concentrations of all cyanotoxin groups increased with increasing TP and TN, congruent with the biovolumes of their likely producers. Microcystin concentration was strongly correlated with the biovolume of Planktothrix agardhii but concentrations of anatoxin, cylindrospermopsin and paralytic shellfish poison were not strongly related to any individual taxa. Cyanobacteria should not be treated as a single group when considering the potential effects of changes in nutrient loading on phytoplankton community structure and neither should the N(2)-fixing Nostocales. This is of particular importance when considering the occurrence of cyanotoxins, as the two most abundant potentially toxin producing Nostocales in our study were found in lakes with high N relative to P enrichment.     

基于克隆文库法研究古尔班通古特沙漠蓝藻多样性

该研究采用克隆文库法研究古尔班通古特沙漠藻类生物结皮中蓝藻多样性及分布。在古尔班通古特沙漠不同区域采集10份藻类结皮代表性土样,分别构建古尔班通古特沙漠蓝藻16S rRNA和psbA基因克隆文库,并进行系统发育分析,对蓝藻多样性和丰度与环境因子进行关联分析,研究蓝藻分布特点及影响因子。结果显示:(1)16S rRNA基因系统发育树中包括具有明确分类地位的蓝藻有6科10属(占总克隆文库的94.85%)和一个未分类蓝藻属,其中颤藻属(Oscillatoria)和微鞘藻属(Microcoleus)分别占克隆文库的42.54%和37.16%,为古尔班通古特沙漠蓝藻优势属;psbA基因系统发育树中仅鉴定有蓝藻类群4科4属,但优势属与前者结果一致。(2)10个样点藻类结皮中所含蓝藻种类不尽相同,但每个采样点都出现颤藻属和微鞘藻属,证明这二者是古尔班通古特沙漠藻类结皮中的优势属;且样点Gur2和Gur17中蓝藻种类较多,Gur3、Gur5和Gur9中种类较少,但Gur2、Gur3、Gur5和Gur17相对地理位置较近,表明地理位置不是影响蓝藻分布的主要因素。(3)RDA(Redundancy analysis)分析结果显示,微生物量氮(MBN)和土壤有机碳(SOC)对蓝藻多样性影响程度最大,其次是硝态氮(NO~-_3-N)、微生物量碳(MBC),全磷(TP)和全钾(TK)对其影响程度最小。研究表明,古尔班通古特沙漠不同区域沙漠蓝藻多样性和土壤理化性质具有空间异质性,综合分析可得沙漠中南部藻类结皮土壤营养最为丰富,蓝藻多样性较高,而东部和西部土壤营养较为贫瘠,蓝藻丰富度和多样性较低。     

Application of a nifH microarray to assess the impact of environmental factors on free-living diazotrophs in a glacier forefield

Glacier forefield environments are exposed to extreme and fluctuating climatic and nutritional conditions. The high diversity of free-living diazotrophic communities found in these environments indicates that nitrogen fixers are able to efficiently cope with such conditions. In this study, a nifH microarray was used to monitor changes in diazotrophic populations in the field over a season, in the presence or absence of plants and in 2 glacier forefields characterized by a different bedrock type (siliceous or calcareous), as well as at different temperatures (10 °C, 15 °C) and under different nitrogen fertilization regimes (0, 10, 40 kg N·ha(-1)·year(-1)) in laboratory systems. Population structures responded highly dynamically to environmental changes. Plant presence had the strongest impact, which decreased toward the end of the season and with high amounts of nitrogen fertilization. Temperature and nitrogen fertilization increases indirectly affected diazotrophic communities through their positive impact on plant growth. These results indicate strong carbon limitation in young glacier forefield soils. Phylotypes related to the genus Methylocystis strongly responded to environmental variations. These methanotrophic microorganisms, which are able to retrieve nitrogen and carbon from the atmospheric pool, are particularly adapted to the extreme nutritional conditions found in glacier forefields.     

Phylogeny of culturable cyanobacteria from Brazilian mangroves

The cyanobacterial community from Brazilian mangrove ecosystems was examined using a culture-dependent method. Fifty cyanobacterial strains were isolated from soil, water and periphytic samples collected from Cardoso Island and Bertioga mangroves using specific cyanobacterial culture media. Unicellular, homocytous and heterocytous morphotypes were recovered, representing five orders, seven families and eight genera (Synechococcus, Cyanobium, Cyanobacterium, Chlorogloea, Leptolyngbya, Phormidium, Nostoc and Microchaete). All of these novel mangrove strains had their 16S rRNA gene sequenced and BLAST analysis revealed sequence identities ranging from 92.5 to 99.7% when they were compared with other strains available in GenBank. The results showed a high variability of the 16S rRNA gene sequences among the genotypes that was not associated with the morphologies observed. Phylogenetic analyses showed several branches formed exclusively by some of these novel 16S rRNA gene sequences. BLAST and phylogeny analyses allowed for the identification of Nodosilinea and Oxynema strains, genera already known to exhibit poor morphological diacritic traits. In addition, several Nostoc and Leptolyngbya morphotypes of the mangrove strains may represent new generic entities, as they were distantly affiliated with true genera clades. The presence of non-ribosomal peptide synthetase, polyketide synthase, microcystin and saxitoxin genes were detected in 20.5%, 100%, 37.5% and 33.3%, respectively, of the 44 tested isolates. A total of 134 organic extracts obtained from 44 strains were tested against microorganisms, and 26% of the extracts showed some antimicrobial activity. This is the first polyphasic study of cultured cyanobacteria from Brazilian mangrove ecosystems using morphological, genetic and biological approaches.     

Identification and regulation of novel compatible solutes from hypersaline stromatolite-associated cyanobacteria

Cyanobacteria are able to survive in various extreme environments via the production of organic compounds known as compatible solutes. In particular, cyanobacteria are capable of inhabiting hypersaline environments such as those found in intertidal regions. Cyanobacteria in these environments must possess regulatory mechanisms for surviving the changing osmotic pressure as a result of desiccation, rainfall and tidal fluxes. The objective of this study was to determine the compatible solutes that are accumulated by cyanobacteria from hypersaline regions, and specifically, the stromatolite ecosystems of Shark Bay, Western Australia. Previously, the cyanobacterial populations associated with these stromatolites were characterized in two separate studies. Compatible solutes were extracted from isolated cyanobacteria here and identified by nuclear magnetic resonance. As the media of isolation contained no complex carbon source, the solutes accumulated were likely synthesized by the cyanobacteria. The data indicate that from this one habitat taxonomically distinct cyanobacteria exposed to varying salinities accumulate a range of known compatible solutes. In addition, taxonomically similar cyanobacteria do not necessarily accumulate the same compatible solutes. Glucosylglycerol, a compatible solute unique to marine cyanobacteria was not detected; however, various saccharides, glycine betaine, and trimethylamine-N-oxide were identified as the predominant solutes. We conclude that the cyanobacterial communities from these hypersaline stromatolites are likely to possess more complex mechanisms of adaptation to osmotic stress than previously thought. The characterization of osmoregulatory properties of stromatolite microorganisms provides further insight into how life can thrive in such extreme environments.     

Multi-functional pollution mitigation in a rehabilitated mangrove conservation area

Many mangroves were forced to act as informal pollution mitigation zones and double up as conservation areas. Long-term data are presented for a high-profile mangrove reserve acting as such a mitigation zone in urban Thailand. Efficient mineralization of organic wastes by mangrove soil in a semi-engineered and hydraulically contained zone made it possible not to compromise the reserve's natural status. The data demonstrate that the treatment zone could process organic waste with an eight-fold efficiency in comparison to previous reports. Clones of microbial taxa critically novel for mangrove ecosystems were recovered (anammox bacteria and archaeal ammonia oxidizers), suggesting their significant presence. Community structures of nitrogen-cycling and other taxa of natural and hypernutrified soils did not differ substantially. It is suggested that waste nitrogen removal may have occurred through bacterial and archaeal nitrification, conventional denitrification and anammox process. The article addresses the issue of multi-functional use of ever-shrinking habitats available for wildlife conservation. Data on key microbial, floral and faunal communities demonstrate that the mangrove exhibited stability under the major nutrient load. Supply of additional nutrients correlated with an enhancement of mangrove growth and diversity of selected key invertebrates/vertebrates which increase conservation potential of the reserve. Serving to determine ecologically safe nutrification limits, the study suggests that a successful rehabilitation of an urban mangrove to its near-natural status is feasible.