CO2 Saturation and Trophic Shift Induced by Microbial Metabolic Processes in a River-Dominated Ocean Margin (Tropical Shallow Lagoon,Chilika, India)

An effort has been made for the first time in Asia's largest brackish water lagoon, Chilika, to investigate the spatio-temporal variability in primary productivity (PP), bacterial productivity (BP), bacterial abundance (BA), bacterial respiration (BR) and bacterial growth efficiency (BGE) in relation to partial pressure of CO₂ (pCO₂) and CO₂ air–water flux and the resultant trophic switchover. Annually, PP ranged between 24 and 376 µg C L^?1 d^?1 with significantly low values throughout the monsoon (MN), caused by light limitation due to inputs of riverine suspended matter. On the contrary, BP and BR ranged from 11.5 to 186.3 µg C L^?1 d^?1 and from 14.1 to 389.4 µg C L^?1 d^?1, respectively, with exceptionally higher values during MN. A wide spatial and temporal variation in the lagoon trophic status was apparent from BP/PP (0.05–6.4) and PP/BR (0.10–18.2) ratios. The seasonal shift in net pelagic production from autotrophy to heterotrophy due to terrestrial organic matter inputs via rivers, enhanced the bacterial metabolism during the MN, as evident from the high pCO₂ (10,134 µatm) and CO₂ air–water flux (714 mm m^?2 d^?1). Large variability in BGE and BP/PP ratios especially during MN led to high bacteria-mediated carbon fluxes which was evident from significantly high bacterial carbon demand (BCD >100% of PP) during this season. This suggested that the net amount of organic carbon (either dissolved or particulate form) synthesized by primary producers in the lagoon was not sufficient to satisfy the bacterial carbon requirements. Lagoon sustained low to moderate autotrophic–heterotrophic coupling with annual mean BCD of 231% relative to the primary production, which depicted that bacterioplankton are the mainstay of the lagoon biogeochemical cycles and principal players that bring changes in trophic status. Study disclosed that the high CO₂ supersaturation and oxygen undersaturation during MN was attributed to the increased heterotrophic respiration (in excess of PP) fuelled by allochthonous organic matter. On a spatial scale, lagoon sectors such as south sector, central sector and outer channel recorded “net autotrophic,” while the northern sector showed “net heterotrophic” throughout the study period.     

Nitrogen uptake and the importance of internal nitrogen loading in Lake Balaton

1. The importance of various forms of nitrogen to the nitrogen supply of phytoplankton has been investigated in the mesotrophic eastern and eutrophic western basin of Lake Balaton.
2. Uptake rates of ammonium, urea, nitrate and carbon were measured simultaneously. The uptake rates were determined using N and C methodologies, and N2‐fixation was measured using the acetylene‐reduction method. The light dependence of uptake was described with an exponential saturation equation and used to calculate surface‐related (areal) daily uptake.
3. The contribution of ammonium, urea and nitrate to the daily nitrogen supply of phytoplankton varied between 11 and 80%, 17 and 73% and 1 and 15%, respectively. N2‐fixation was negligible in the eastern basin and varied between 5 and 30% in the western region of the lake. The annual external nitrogen load was only 10% of that utilized by algae.
4. The predominant process supplying nitrogen to the phytoplankton in the lake is the rapid recycling of ammonium and urea in the water column. The importance of the internal nutrient loading is emphasized.     

Terrestrial and marine perspectives on modeling organic matter degradation pathways

Organic matter (OM) plays a major role in both terrestrial and oceanic biogeochemical cycles. The amount of carbon stored in these systems is far greater than that of carbon dioxide (CO₂) in the atmosphere, and annual fluxes of CO₂ from these pools to the atmosphere exceed those from fossil fuel combustion. Understanding the processes that determine the fate of detrital material is important for predicting the effects that climate change will have on feedbacks to the global carbon cycle. However, Earth System Models (ESMs) typically utilize very simple formulations of processes affecting the mineralization and storage of detrital OM. Recent changes in our view of the nature of this material and the factors controlling its transformation have yet to find their way into models. In this review, we highlight the current understanding of the role and cycling of detrital OM in terrestrial and marine systems and examine how this pool of material is represented in ESMs. We include a discussion of the different mineralization pathways available as organic matter moves from soils, through inland waters to coastal systems and ultimately into open ocean environments. We argue that there is strong commonality between aspects of OM transformation in both terrestrial and marine systems and that our respective scientific communities would benefit from closer collaboration.     

氟微量元素矿化液对葡糖基转移酶及乳酸脱氢酶的影响

目的 采用氟与微量元素联合制成以钙、磷为基础,含有氟和微量元素的矿化液,探讨该矿化液对致龋毒力因子－－变形链球菌和远缘链球菌的胞外葡糖基转移酶（ＧＴＦ）和乳酸脱氢酶（ＬＤＨ）的影响。方法 选用国际标准菌株ＡＴＣＣ Ｓ．ｍｕｔａｎｓ ２５１７５和Ｓ．Ｓｏｂｒｉｎｕｓ６７１５为实验菌珠,采用厌氧菌的连续培养技术培养细菌,用微量酶化学分析方法检测矿化液对ＧＴＦ和ＬＤＨ酶活性的影响,用菌液的吸光度（ＡＢＳ）来描述。结果 无氟矿化液对ＧＴＦ酶活性无明显的抑制作用（Ｐ〉０．０５）,而含氟矿化液和氟微量元素矿化液对ＧＴＦ酶活性有明显抑制作用（Ｐ〈０．０１）,两两比较,万２以氟微量元素矿化液的作用最强;氟微量元素矿化液对ＬＤＨ酶活性具有明显的抑制作用（Ｐ〈０．０１）,而无氟矿化液和含氟矿化液对其无明显的统计学意义（Ｐ〉０．０５     

High rates of denitrification and nitrate removal in cold seep sediments

We measured denitrification and nitrate removal rates in cold seep sediments from the Gulf of Mexico. Heterotrophic potential denitrification rates were assayed in time-series incubations. Surficial sediments inhabited by Beggiatoa exhibited higher heterotrophic potential denitrification rates (32 μ N reduced day⁻¹) than did deeper sediments (11 μ N reduced day⁻¹). Nitrate removal rates were high in both sediment horizons. These nitrate removal rates translate into rapid turnover times (<1 day) for the nitrate pool, resulting in a faster turnover for the nitrate pool than for the sulfate pool. Together, these data underscore the rigorous nature of internal nitrogen cycling at cold seeps and the requirement for novel mechanisms to provide nitrate to the sediment microbial community.     

Veränderungen im Phosphatgehalt des Wassers in einem Prielsystem im Wattengebiet nahe der Nordstrander Bucht (östliche Nordsee) im Verlauf einer Tide Changes in the Phosphate Content of Water in a Tidal Channel through the Wadden Sea near Nordstrander Bight (Eastern North Sea) during a Tidal Cycle

The total phosphate content of the water in a well delimited region of the Wadden Sea (26.8 km²) was determined by multiplying the concentration by the water volume during each phase of the tide. When the weather is moderate, sharp but stable gradients are observed from the shore to the open sea resulting from the remineralization processes that occur most rapidly near the shore.     

Dissolved silica affects the bulk iron redox state and recrystallization of minerals generated by photoferrotrophy in a simulated Archean ocean

Chemical sedimentary deposits called Banded Iron Formations (BIFs) are one of the best surviving records of ancient marine (bio)geochemistry. Many BIF precursor sediments precipitated from ferruginous, silica-rich waters prior to the Great Oxidation Event at ~2.43 Ga. Reconstructing the mineralogy of BIF precursor phases is key to understanding the coevolution of seawater chemistry and early life. Many models of BIF deposition invoke the activity of Fe(II)-oxidizing photoautotrophic bacteria as a mechanism for precipitating mixed-valence Fe(II,III) and/or fully oxidized Fe(III) minerals in the absence of molecular oxygen. Although the identity of phases produced by ancient photoferrotrophs remains debated, laboratory experiments provide a means to explore what their mineral byproducts might have been. Few studies have thoroughly characterized precipitates produced by photoferrotrophs in settings representative of Archean oceans, including investigating how residual Fe(II)_aq can affect the mineralogy of expected solid phases. The concentration of dissolved silica (Si) is also an important variable to consider, as silicate species may influence the identity and reactivity of Fe(III)-bearing phases. To address these uncertainties, we cultured Rhodopseudomonas palustris TIE-1 as a photoferrotroph in synthetic Archean seawater with an initial [Fe(II)_aq] of 1 mM and [Si] spanning 0–1.5 mM. Ferrihydrite was the dominant precipitate across all Si concentrations, even with substantial Fe(II) remaining in solution. Consistent with other studies of microbial iron oxidation, no Fe-silicates were observed across the silica gradient, although Si coprecipitated with ferrihydrite via surface adsorption. More crystalline phases such as lepidocrocite and goethite were only detected at low [Si] and are likely products of Fe(II)-catalyzed ferrihydrite transformation. Finally, we observed a substantial fraction of Fe(II) in precipitates, with the proportion of Fe(II) increasing as a function of [Si]. These experimental results suggest that photoferrotrophy in a Fe(II)-buffered ocean may have exported Fe(II,III)-oxide/silica admixtures to BIF sediments, providing a more chemically diverse substrate than previously hypothesized.     

Coastal connectivity and spatial subsidy from a microbial perspective

The transfer of organic material from one coastal environment to another can increase production in recipient habitats in a process known as spatial subsidy. Microorganisms drive the generation, transformation, and uptake of organic material in shallow coastal environments, but their significance in connecting coastal habitats through spatial subsidies has received limited attention. We address this by presenting a conceptual model of coastal connectivity that focuses on the flow of microbially mediated organic material in key coastal habitats. Our model suggests that it is not the difference in generation rates of organic material between coastal habitats but the amount of organic material assimilated into microbial biomass and respiration that determines the amount of material that can be exported from one coastal environment to another. Further, the flow of organic material across coastal habitats is sensitive to environmental change as this can alter microbial remineralization and respiration rates. Our model highlights microorganisms as an integral part of coastal connectivity and emphasizes the importance of including a microbial perspective in coastal connectivity studies.     

壳聚糖及其衍生物在口腔疾病防治中的研究进展

壳聚糖是一种天然高分子多糖,在食品、纺织、美容、医疗等行业被广泛应用。在口腔医学领域,壳聚糖及其衍生物因多种优良的生物学性能,如抗菌性能、载药功能、再矿化性能和成骨作用等,被广泛应用于多种口腔常见疾病的预防和治疗。文中介绍了壳聚糖的生物学性能、壳聚糖常见衍生物,与壳聚糖及其衍生物在口腔疾病防治方面的最新应用研究进展。