Glycerol ether lipids in sediments: sources, diversity and implications

Glycerol ether lipids are prominent membrane constituents in Archaea and Bacteria that are characterized by high potential for preservation in geological settings.During the past decade they were increasingly used in molecular proxies. For example,selected glycerol dialkyl glycerol tetraethers (GDGT) are used in ratios such as the TEX86 and BIT index for reconstructing past sea surface temperature (SST) and terrestrial input, respectively. However, the distribution and structural diversity of glycerol ether lipids in marine sediments has not yet been fully explored. In order to obtain a better understanding of the origin and fate of these lipids and to evaluate the potential impact on molecular proxies, a globally distributed set of samples was analyzed in this PhD thesis project. More than forty novel compounds were revealed and it could be shown that the diversity of glycerol ether lipids in marine sediments is much higher than previously recognized. Among the studied lipids, isoprenoid GDGTs were shown as the most dominant component in all analyzed sediments with over 70% of total ether lipids. A comparison of the lipid composition of core and intact polar isoprenoid GDGTs pointed to a potential impact of live benthic archaea and their intact lipids on the application of the TEX86 SST proxy. The same study suggested that recycling of fossil GDGTs from planktonic archaea by the benthic archaeal community could be an important process. In a set of peat sediments, two intact polar lipids of the orphan branched GDGTs were for the first time observed. These branched GDGTs that constitute the BIT index have in their intact form glucuronosyl and glucosyl headgroups. The two compounds accounted for 4-7% of total IPLs, suggesting that their producers represent a sizeable but not dominant component of the microbial community. The identification of these intact polar precursors of these orphan lipids provides important constraints for the search of their microbial sources. The presence of newly identified glycerol ether lipids with distinctive structures and ubiquitous distribution in all analyzed marine sediments provided potential phylogenetic biomarkers and a large reservoir for novel molecular proxies to be developed. A series of novel ether core lipids coexisting with corresponding isoprenoid GDGTs was identified in all analyzed sediments. The first series of compounds,accounting on average for 7% of total ether lipids, was identified as glycerol dibiphytanol diethers (GDDs) and is considered to represent either biosynthetic intermediates or degradation products of GDGTs. A second series was identified as hydroxylated GDGTs based on nuclear magnetic resonance (NMR) and mass spectral interpretation. Accordingly, a series of unknown IPLs that had been previously reported as a major component in samples of archaeal cultures, sediments, and the water column were then recognized to be glycosidic hydroxy-GDGTs. The widespread occurrence of IPLs of hydroxy-GDGTs suggests an important contribution of specific archaeal species with high activity in a wide range of geological settings. Several other groups of novel compounds were also tentatively identified based on interpretation of mass spectra. Specifically, extended H-shaped GDGTs, hybrid isoprenoid/branched GDGTs, and overly and sparsely branched GDGTs are characterized with a common feature of methylation series, containing compounds with one -CH2- unit difference between each other. It is expected that the information encoded in the distribution of the novel lipids can be used to develop molecular proxies indicating past environmental factors such as temperature and salinity and/or information pertaining to the composition and activity of extant microbial communities. An overall distribution of detected glycerol ether lipids in marine subsurface sediments was shown by the estimated relative abundance of 11 structural groups, and therefore reflects a general composition of ether lipid producing microbes contributing to the sedimentary record

Charm-strange baryon strong decays in a chiral quark model

The strong decays of charm-strange baryons up to N=2 shell are studied in a chiral quark model. The theoretical predictions for the well determined charm-strange baryons, $\Xi_c^*(2645)$, $\Xi_c(2790)$ and $\Xi_c(2815)$, are in good agreement with the experimental data. This model is also extended to analyze the strong decays of the other newly observed charm-strange baryons $\Xi_c(2930)$, $\Xi_c(2980)$, $\Xi_c(3055)$, $\Xi_c(3080)$ and $\Xi_c(3123)$. Our predictions are given as follows. (i) $\Xi_c(2930)$ might be the first $P$-wave excitation of $\Xi_c'$ with $J^P=1/2^-$, favors the $|\Xi_c'\ ^2P_\lambda 1/2^->$or$|\Xi_c'\ ^4P_\lambda 1/2^->$state. (ii)$\Xi_c(2980)$might correspond to two overlapping$P$-wave states$|\Xi_c'\ ^2P_\rho 1/2^->$and$|\Xi_c'\ ^2P_\rho 3/2^->$, respectively. The$\Xi_c(2980)$observed in the$\Lambda_c^+\bar{K}\pi$final state is most likely to be the$|\Xi_c'\ ^2P_\rho 1/2^->$state, while the narrower resonance with a mass$m\simeq 2.97$GeV observed in the$\Xi_c^*(2645)\pi$channel favors to be assigned to the$|\Xi_c'\ ^2P_\rho 3/2^->$state. (iii)$\Xi_c(3080)$favors to be classified as the$|\Xi_c\ S_{\rho\rho} 1/2^+>$state, i.e., the first radial excitation (2S) of$\Xi_c$. (iv)$\Xi_c(3055)$is most likely to be the first$D$-wave excitation of$\Xi_c$with$J^P=3/2^+$, favors the$|\Xi_c\ ^2D_{\lambda\lambda} 3/2^+>$state. (v)$\Xi_c(3123)$might be assigned to the$|\Xi_c'\ ^4D_{\lambda\lambda} 3/2^+>$,$|\Xi_c'\ ^4D_{\lambda\lambda} 5/2^+>$, or$|\Xi_c\ ^2D_{\rho\rho} 5/2^+>$state. As a by-product, we calculate the strong decays of the bottom baryons$\Sigma_b^{\pm}$,$\Sigma_b^{*\pm}$and$\Xi_b^*$, which are in good agreement with the recent observations as well.Comment: 15 pages, 9 figure

Low-mass Active Galactic Nuclei on the Fundamental Plane of Black Hole Activity

It is widely known that in active galactic nuclei (AGNs) and black hole X-ray binaries (BHXBs), there is a tight correlation among their radio luminosity ($L_R$), X-ray luminosity ($L_X$) and BH mass (\mbh), the so-called `fundamental plane' (FP) of BH activity. Yet the supporting data are very limited in the \mbh regime between stellar mass (i.e., BHXBs) and 10$^{6.5}$\,\msun\ (namely, the lower bound of supermassive BHs in common AGNs). In this work, we developed a new method to measure the 1.4 GHz flux directly from the images of the VLA FIRST survey, and apply it to the type-1 low-mass AGNs in the \cite{2012ApJ...755..167D} sample. As a result, we obtained 19 new low-mass AGNs for FP research with both \mbh\ estimates (\mbh \approx 10^{5.5-6.5}\,\msun), reliable X-ray measurements, and (candidate) radio detections, tripling the number of such candidate sources in the literature.Most (if not all) of the low-mass AGNs follow the standard radio/X-ray correlation and the universal FP relation fitted with the combined dataset of BHXBs and supermassive AGNs by \citet{2009ApJ...706..404G}; the consistency in the radio/X-ray correlation slope among those accretion systems supports the picture that the accretion and ejection (jet) processes are quite similar in all accretion systems of different \mbh. In view of the FP relation, we speculate that the radio loudness $\mathcal{R}$ (i.e., the luminosity ratio of the jet to the accretion disk) of AGNs depends not only on Eddington ratio, but probably also on \mbh.Comment: ApJ accepte