Microbial dolomite crusts from the carbonate platform off western India

Abstract The occurrence of Late Pleistocene dolomite crusts that occur at 64 m depth on the carbonate platform off western India is documented. Dolomite is the most predominant mineral in the crusts. In thin section, the crust consists of dolomitized microlaminae interspersed with detrital particles. Under scanning electron microscopy, these laminae are made up of tubular filaments or cellular structures of probable cyanobacterial origin. Dolomite crystals encrust or overgrow the surfaces of the microbial filaments and/or cells; progressive mineralization obliterates their morphology. Well-preserved microbial mats, sulphide minerals (pyrrhotite and marcasite) and the stable isotope composition of dolomite in the crusts indicate hypersaline and anoxic conditions during dolomite formation. The crusts are similar to dolomite stromatolites, and biogeochemical processes related to decaying microbial mats under anoxic conditions probably played an important role in dolomite precipitation. The dolomite is therefore primary and/or very early diagenetic in origin. The dolomite crusts are interpreted to be a composite of microbial dolomite overprinted by early burial organic dolomite. The results of this study suggest that a microbial model for dolomite formation may be relevant for the origin of ancient massive dolomites in marine successions characterized by cryptalgal laminites. The age of the crusts further suggests that the platform was situated at shallow subtidal depths during the Last Glacial Maximum.     

Evidence of Microbial Activity in the Formation of Manganese Wads at the Asahidake Hot Spring in Hokkaido, Japan

Abstract. Mt. Asahidake is an active volcano, with more than 90 active wells, in the Daisetsu volcanic group located in central Hokkaido, Japan. Wells along the Yukomanbetsu-sawa River showed high manganese concentrations and associated manganese deposits. These deposits consist of manganese oxides, and the concentration of iron is very low except for one sample collected from the upper reach of the river. Most of the wet samples showed basal diffraction characteristic of todorokite (9.6 Å). Cultivation tests showed that microorganisms were responsible for the oxidation of dissolved Mn²⁺ in the Asahidake hot spring. The dissolved Mn²⁺ concentration in the sterilized hot spring water was unchanged after four days, whereas the Mn²⁺ concentration in the sterilized hot spring water with a small amount of fresh manganese wad was decreased to zero after three days, and manganese oxide formed. This result implies that the activity of microorganism oxidizes dissolved Mn²⁺ and forms manganese oxide at the Asahidake manganese deposits. In addition to Komanoyu hot spring and Yunotaki Falls, this is the third report of microbial activity forming considerable deposits of manganese oxides in hot spring waters.     

南极菲尔德斯半岛生物体的微生物含量分析

于１９９３／１９９４年以平板培养法用５种基本培养基对南极菲尔德斯半岛地区的生物体作了微生物含量分析。所研究的海藻、苔藓、地衣、沙蚕、小红蛤、帽贝、鱼、企鹅和鲸等的体表和体内样本计３３个。分析和比较了各类生物体内外所含的陆源性细菌、海洋性细菌、肠细菌、真菌及耐酸细菌等的含量,在一定程度上,培养温度的提高可促进样本中原有的微生物迅速大量繁殖,表明低温仍是制约南极微生物的重要因子。     

Artemia parthenogenetica in Lake Hayward, Western Australia. II. Feeding biology in a shallow, seasonally stratified, hypersaline lake

Primary production in Lake Hayward, Western Australia, is dominated by benthic microbial communities, with limited planktonic primary production. This study investigated the question of howArtemia, commonly regarded as simple, obligate, non-selective filter feeders, were able to survive in this system. Bacteria (heterotrophic and autotrophic, filamentous and unicellular) were the major components in the diet of theArtemia in Lake Hayward. These bacteria were derived from bacterial aggregates in the water column and also from benthic mat material (both still attached to the substrate and from pieces floating in the water column). Benthic diatoms were a substantial dietary component of animals living in the unstratified shallow regions. Photosynthetic eukaryotic nanoplankton comprised a minor component of the diet of thisArtemia population. Gut contents of a large number of animals and the results of a simple laboratory test indicated that these animals utilise substrate-bound food resources. The results of the present study raises the question of the ecological significance of surface grazing by brine shrimps in other shallow, benthos dominated saline systems.     

Gas Production from an Ombrotrophic Bog-Effect of Climate Change on Microbial Ecology

Gases are produced from wetlands when plant biomass is degraded by microbial consortia, producing carbon dioxide aerobically and methane when oxygen is lacking. In anaerobic waterlogged situations, such as the catotelm of ombrotrophic bogs, this methane forms minute gas bubbles that severely reduce the hydraulic conductivity and hence the degradation of biomass due to the lack of nutrients. The bogs thus become carbon sinks, formed from the partially degraded biomass that accumulates as peat. The results of an investigation of an ombrotrophic bog, Mer Bleue, Ontario, Canada are summarized here, and the effects that climate change may have on such bogs are discussed. Any change of the water table in wetlands will have a substantial effect upon their ecology. If the water table should fall allowing bogs to become aerobic, most of the accumulated biomass carbon could be returned to the atmosphere by degradation to carbon dioxide, and as well, methane entrapped within the matrix would be released directly to the atmosphere. If on the other hand, the bogs are flooded, then the entrapped bubbles will coalesce allowing the gas to escape to the atmosphere, while at the same time the degradation of the peat will be enhanced.     

Pelagic ciliates (Protozoa, Ciliophora) of different brackish and freshwater lakes — a community analysis at the species level

The pelagic ciliate communities from 58 north German lakes differing in their origin (natural lakes and artificial ponds), morphology (from shallow ponds with a maximum depth of below 0.5 m to relatively deep lakes with a maximum depth of more than 10 m, surface areas from below 10 ha to more than 100 ha), trophic state (from mesotrophic to hypertrophic) and salinity (freshwater lakes and brackish water lakes) are described and compared at species level. Each lake was comprehensively sampled quarterly in the years 1996 and 1997, respectively. Applying a quantitative protargol stain, about 140 ciliate species could be identified and quantified in all investigated lakes. 35 species, mainly members of the Prostomatida and Oligotrichida, were found commonly in all types of lakes at all seasons and dominated the pelagic ciliate communities. 3 species were common in freshwaters, but never occurred in brackish lakes. In the brackish waters a mixture of common freshwater species and marine species was found with 13 species exclusively occurring in brackish waters. Lowest ciliate cell numbers were observed for deep freshwater lakes, highest cell numbers were determined for brackish waters. Highest species richness was found in artificial peat ponds with an average of 24 pelagic ciliate species in spring samples. The range of occurrence for the identified species was wide for most common species. However, the influence of some environmental factors could be enlightened.     

Carbon and nitrogen isotope excursions in mid-Pleistocene sapropels from the Tyrrhenian Basin: Evidence for climate-induced increases in microbial primary production

The modern Mediterranean Sea is oligotrophic, yet its sediment record contains layers of organic-carbon-rich sapropels at 21 ky (precessional) spacing that imply periods of elevated paleoproductivity that approached the high productivities of modern upwelling systems. Resolution to this paradox is provided by lines of evidence suggesting that the mode of primary productivity changed from one dominated by algae to one during times of sapropel deposition in which photosynthetic bacteria were important. We have made a high-resolution comparison of the organic carbon and nitrogen isotopic compositions of three sapropels and their background sediments in a 3-m sequence that corresponds to 1001 to 946 ka. Organic δ¹³C values systematically increase from − 26‰ to − 21‰ and δ¹⁵N values systematically decrease from 4‰ to < 0‰ as organic carbon mass accumulation rates increase in the sapropel layers. The increase in carbon isotope values mirrors the increases in primary productivity and associated organic matter export indicated by the increased mass accumulation rates. The decrease in nitrogen isotope values implies major contributions of nitrogen-fixing cyanobacteria to the total marine productivity. The precessional minima with which sapropels coincide were times of wetter climate that stratified the surface Mediterranean Sea, increased delivery of soil-derived phosphorus, and evidently amplified microbial primary production. Our high-resolution study reveals several relatively rapid excursions into and out of the high-productivity mode that suggest that sapropel deposition was a climate-sensitive surface-driven phenomenon that was not accompanied by basin-wide stagnation.     

基于低压静电场及高通量测序技术对中华管鞭虾(Solenocera crassicornis)保鲜过程中微生物群落影响分析

中华管鞭虾(Solenocera crassicornis)隶属于十足目、管鞭虾科、管鞭虾属, 主要分布于我国东南沿海。其富含多种必需氨基酸和矿物质, 高蛋白低脂肪, 但易受微生物污染而发生腐败变质, 需引用基于16S rRNA的高通量测序技术准确测定其微生物群落组成成分变化。以中华管鞭虾为试验材料, 采用高通量测序技术对虾肉的微生物群落碱基进行基因测序, 将产生的碱基序列通过OTU聚类、多样性及相关性分析手段研究了贮藏过程中电场处理后影响中华管鞭虾品质的微生物发育信息和群落组成变化规律。分组为新鲜样本(G0), 2 kV、3 kV及对照组贮藏中期(G1、G2、G3), 2 kV、3 kV、对照组贮藏末期(G4、G5、G6), 通过物种韦恩图、Alpha和Beta多样性以及物种组成分析, 研究不同强度电场环境对中华管鞭虾微生物群落组成的影响。结果表明, OTU聚类分析中优势菌群从属水平看为假交替单胞菌属(Pseudoalteromonas)、假单胞菌属(Pseudomonas)、嗜冷杆菌属(Psychrobacter)和热杀索丝菌属(Brochothrix)等, 其中假交替单胞菌属能够适应高盐浓度环境, 是中华管鞭虾微生物腐败主要致腐菌。贮藏中期微生物物种多样性顺序为3 kV组>2 kV组>对照组(0 kV), 电场能够有效抑制优势菌的生长; 贮藏末期3组物种结构相近, 此时电场对虾肉菌群结构无明显影响。PCoA主成分分析图中发现, 在坐标系中贮藏中期的G1、G2、G3组距离较为接近, 贮藏末期的G4、G5、G6组距离较为接近, 说明在同一贮藏期间的各组微生物种群结构类似。综上, 贮藏前中期低压静电场能够抑制优势菌的生长, 维持微生物物种间平衡并使其物种多样性较高, 且3kV更佳, 贮藏末期时由于优势菌更适应环境, 热杀索丝菌属和肉食杆菌属占比增加, 电场对物种多样性的影响不大。研究结果可为深入探讨影响中华管鞭虾贮藏保鲜效果的微生物群落组成和基础发育信息提供有效依据。