Tingwei Luo

Microbial production of recalcitrant dissolved organic matter: long-term carbon storage in the global ocean

The biological pump is a process whereby CO2 in the upper ocean is fixed by primary producers and transported to the deep ocean as sinking biogenic particles or as dissolved organic matter. The fate of most of this exported material is remineralization to CO2, which accumulates in deep waters until it is eventually ventilated again at the sea surface. However, a proportion of the fixed carbon is not mineralized but is instead stored for millennia as recalcitrant dissolved organic matter. The processes and mechanisms involved in the generation of this large carbon reservoir are poorly understood. Here, we propose the microbial carbon pump as a conceptual framework to address this important, multifaceted biogeochemical problem.

Natural and anthropogenic forcing on the dynamics of virioplankton in the Yangtze river estuary

Seasonal investigation of virus dynamics by flow cytometry was conducted in the Yangtze river estuarine area in April, August, November 2002 and February 2003, and a supplemental investigation in the inner estuary and downstream of the river was conducted in October 2005. The majority of the total viral abundance was bacteriophage and only 5.4% of the total was algal virus. Total viral abundance varied with season and location, ranging from 6.75×10 5 -1.68×10 7 particles/ml, and the virus:bacterium ratio (VBR) ranged from 1.52 to 72.02 with a mean of 8.7. In the present study, viral abundance peaked in both the summer and the winter, unlike the typical seasonal pattern reported in the literature, in which viral abundance peaks in the summer when bacterial hosts are also at their most abundant. However, the driving forces for the two peaks reported here were totally different, the summer viral abundance peak coupled with the development of bacterial hosts which were controlled largely by temperature year-round and by trophic state occasionally, while the winter one seemed to be multi-factor controlled. The host-phage interaction was no longer predominant in control of the winter viral abundance as bacterial abundance was lowest in this season. The winter low temperature would help maintain a high viral abundance as high temperatures might increase viral inactivation and viral decay; the VBR peak values actually occurred in the winter. More importantly, the high virus-containing freshwater discharge in winter due to a higher proportion of anthropogenic sewage relative to low natural flooding in winter run-off, turned out to be the first factor contributing to the high winter viral abundance and VBR values. In addition, the variation of intrusion of warm and relatively oligotrophic water from oceanic currents played a role alternating the distribution patterns of temperature, salinity and trophic conditions and consequently the distribution patterns of virus and bacteria seasonally and spatially. Dynamics of virus in the Yangtze river estuarine area is thus characterized by distinct seasonal and spatial variations due to natural forcing and by pronounced alternation of the regular patterns due to anthropogenic impacts.

Proliferating cell nuclear antigen (PCNA) as a marker of cell proliferation in the marine dinoflagellate Prorocentrum donghaiense Lu and the green alga Dunaliella salina Teodoresco

Proliferating cell nuclear antigen (PCNA) was detected in Prorocentrum donghaiense Lu and Dunaliella salina Teodoresco by enhanced chemiluminescence techniques with one mono-antibody. The observed band detected on western blots of P. donghaiense and D. salina had a molecular weight of 36–33 kDa rather than a PCNA-like protein with a size of 55 kDa reported in the dinoflagellates Crypthecodinium cohnii Biecheler and Gymnodinium catenatum Brav. The abundance of PCNA proteins was growth-stage dependent. Whole-cell immunoflurescence labeling showed that the PCNA antibody specifically stained the target proteins in P. donghaiense and D. salina, and PCNA is only present in the nucleus during the cell cycle. Synchronized cells of P. donghaiense show a cell cycle specific expression pattern with the highest expression in S phase and little expression in the G1 and G2/M phases. The results demonstrated that the PCNA-like proteins could be a marker for the estimation of marine phytoplankton growth rates. The different sizes of the PCNA-like proteins observed in dinoflagellates could be related to the variety of dinoflagellate chromosomal structure.

A marine inducible prophage vB_CibM-P1 isolated from the aerobic anoxygenic phototrophic bacterium Citromicrobium bathyomarinum JL354

A prophage vB_CibM-P1 was induced by mitomycin C from the epipelagic strain Citromicrobium bathyomarinum JL354, a member of the alpha-IV subcluster of marine aerobic anoxygenic phototrophic bacteria (AAPB). The induced bacteriophage vB_CibM-P1 had Myoviridae-like morphology and polyhedral heads (approximately capsid 60–100 nm) with tail fibers. The vB_CibM-P1 genome is ~38 kb in size, with 66.0% GC content. The genome contains 58 proposed open reading frames that are involved in integration, DNA packaging, morphogenesis and bacterial lysis. VB_CibM-P1 is a temperate phage that can be directly induced in hosts. In response to mitomycin C induction, virus-like particles can increase to 7 × 109 per ml, while host cells decrease an order of magnitude. The vB_CibM-P1 bacteriophage is the first inducible prophage from AAPB.

Comment on"Dilution limits dissolved organic carbon utilization in the deep ocean"

Arrieta et al. (Reports, 17 April 2015, p. 331) propose that low concentrations of labile dissolved organic carbon (DOC) preclude prokaryotic consumption of a substantial fraction of DOC in the deep ocean and that this dilution acts as an alternative mechanism to recalcitrance for long-term DOC storage. Here, we show that the authors’ data do not support their claims.

Seasonal Dynamics of the Bacterial Community in Lake Namco, the Largest Tibetan Lake

Seasonal variations of bacterial abundance and diversity in Lake Namco, the large and deep high altitude lake, were first investigated using flow cytometry enumeration and 16S rRNA gene clone library analysis. Bacterial abundance varied from 1.5 × 105 to 12.3 × 105 cells mL−1 and exhibited a seasonal pattern that correlated with water temperature and phytoplankton abundance rather than nutrient. This indicated that temperature had a strong effect on bacterial abundance in cold and oligotrophic Lake Namco. Bacterial diversity and community compositions varied in different months. Bacterial community structure changes coincide with the variations of dissolved organic carbon and total nitrogen contents. The three best-represented bacterial groups in libraries, the Actinobacteria, Cyanobacteria, and Beta-proteobacteria, had distinct temporal niches and dominated the bacterial communities in January, May, and June, respectively. Ice cover and nutrient appeared to be of important factors in structuring the seasonal variation of bacterial community composition in Lake Namco.

Horizontal and Vertical Distribution of Marine Virioplankton: A Basin Scale Investigation Based on a Global Cruise

Despite the fact that marine viruses have been increasingly studied in the last decade, there is little information on viral abundance and distribution on a global scale. In this study, we report on a global-scale survey covering the Pacific, Atlantic, and Indian Oceans on viral distribution using flow cytometry. Viruses were stained with the SYBR Green I, which targets only dsDNA viruses. The average viral abundance was 1.10±0.73×107 ml−1 in global surface oceans and decreased from the areas with high chlorophyll concentration (on average, 1.47±0.78×107 ml−1) to the oligotrophic subtropical gyres (on average, 6.34±2.18×106 ml−1). On a large-spatial-scale, viruses displayed significant relationships with both heterotrophic and autotrophic picoplankton abundance, suggesting that viral distribution is dependent on their host cell abundance. Our study provided a basin scale pattern of marine viral distributions and their relationship with major host cells, indicating that viruses play a significant role in the global marine ecosystem.

Estimating Primary Production of Picophytoplankton Using the Carbon-Based Ocean Productivity Model: A Preliminary Study

Picophytoplankton are acknowledged to contribute significantly to primary production (PP) in the ocean while now the method to measure PP of picophytoplankton (PPPico) at large scales is not yet well established. Although the traditional 14C method and new technologies based on the use of stable isotopes (e.g., 13C) can be employed to accurately measure in situ PPPico, the time-consuming and labor-intensive shortage of these methods constrain their application in a survey on large spatiotemporal scales. To overcome this shortage, a modified carbon-based ocean productivity model (CbPM) is proposed for estimating the PPPico whose principle is based on the group-specific abundance, cellular carbon conversion factor (CCF), and temperature-derived growth rate of picophytoplankton. Comparative analysis showed that the estimated PPPico using CbPM method is significantly and positively related (r2 = 0.53, P < 0.001, n = 171) to the measured 14C uptake. This significant relationship suggests that CbPM has the potential to estimate the PPPico over large spatial and temporal scales. Currently this model application may be limited by the use of invariant cellular CCF and the relatively small data sets to validate the model which may introduce some uncertainties and biases. Model performance will be improved by the use of variable conversion factors and the larger data sets representing diverse growth conditions. Finally, we apply the CbPM-based model on the collected data during four cruises in the Bohai Sea in 2005. Model-estimated PPPico ranged from 0.1 to 11.9, 29.9 to 432.8, 5.5 to 214.9, and 2.4 to 65.8 mg C m-2 d-1 during March, June, September, and December, respectively. This study shed light on the estimation of global PPPico using carbon-based production model.

Influence of temperature conditions on grain refinement of pure Cu solidified with low-voltage pulsed magnetic field

The influence of temperature conditions on the grain refinement of pure Cu solidified with low-voltage pulsed magnetic field (LVPMF) was investigated. With the pouring temperature (Tp) and mould temperature (Tm) increasing, the solidified microstructure of pure Cu was gradually changed from fine equiaxed grains to coarse columnar grains and then to the mixed structure of coarse equiaxed grains and columnar grains. Little change was observed from the microstructure of pure Cu solidified with and without LVPMF for the low Tp and Tm. But for the high Tp and Tm, applying LVPFM remarkably reduced the coarse columnar grains and obtained fine equiaxed grains. The grain refinement by LVPFM is considered to be caused by the electromagnetic flow. The smaller cooling rate resulted by higher Tp and Tm offers much acting time for LVPMF and thus better grain refinement can be achieved.

Distributions and relationships of virio- and picoplankton in the epi-, meso- and bathypelagic zones of the Western Pacific Ocean

&NA; Virio‐ and picoplankton mediate important biogeochemical processes and the environmental factors that regulate their dynamics, and the virus–host interactions are incompletely known, especially in the deep sea. Here we report on their distributions and relationships with environmental factors at 21 stations covering a latitudinal range (2–23° N) in the Western Pacific Ocean. This region is characterized by a complex western boundary current system. Synechococcus, autotrophic picoeukaryotes, heterotrophic prokaryotes and virus‐like particles (VLPs) were high (<2.4 × 102–6.3 × 104, <34–2.8 × 103, 3.9 × 104–1.3 × 106 cells mL−1 and 5.1 × 105–2.7 × 107 mL−1, respectively), and Prochlorococcus were low (<2.3 × 102–1.0 × 105 cells mL−1) in the Luzon Strait and the four most southerly stations, where upwelling occurs. Covariations in the abundances of VLPs with heterotrophic and autotrophic picoplankton, and their correlation (i.e. r2 = 0.63 and 0.52, respectively) suggested a strong host dependence in the epi‐ and mesopelagic zones. In the bathypelagic zone, only abiotic factors significantly influenced VLPs abundance variation (r2 = 0.12). This study shows that the dynamics of virio‐ and picoplankton in this Western Pacific are controlled by suite of complex and depth‐dependent relationship among physical and biological factors that in turn link the physical hydrography of the western boundary current system with microbial‐mediated biogeochemical processes.