Ecophysiology of phototrophic sulfur bacteria in lakes: Vertical distribution of planktonic populations

The study of purple and green sulfur bacterial populations in nature is of interest for the following reasons: (1) high quantities of biomass, with low species diversity can be collected; (2) study of planktonic life permits one to understand the mechanisms, structural as well as physiological, used to maintain their vertical position without sinking; and (3) they are capable of sulfur oxidations and reductions that act as important intermediates in the global sulfur cycle. Purple and green photosynthetic bacteria, moreover, may be responsible for certain geological deposits. Planktonic phototrophic sulfur bacteria were analyzed in relation to their vertical distribution in the water column. Factors, including competition for light, that determine their sedimentation rates and the numerical changes in species and populations were assessed

Superwind evolution: the young starburst-driven wind galaxy NGC 2782

We present results from a 30 ksec Chandra observation of the important starburst galaxy NGC 2782, covering the 0.3-10keV energy band. We find evidence of a superwind of small extent, that is likely in an early stage of development. We find a total of 27 X-ray point sources within a region of radius 2$D_{25}$ of the galaxy centre and which are likely associated with the galaxy. Of these, 13 are ULXs ($L_{X}\geq 10^{39}~ erg s ^{-1}$) and a number have likely counterparts. The X-ray luminosities of the ULX candidates are $1.2-3.9\times10^{39}~ erg s ^{-1}$. NGC2782 seems to have an unusually large number of ULXs. Central diffuse X-ray emission extending to ~ 3kpc from the nuclear region has been detected. We also find an X-ray structure to the south of the nucleus, coincident with H{\alpha} filaments and with a 5 GHz radio source. We interpret this as a blow-out region of a forming superwind. This X-ray bubble has a total luminosity (0.3-10 keV) of $5\times10^{39}erg s ^{-1}$ (around $15\%$ of the total luminosity of the extended emission), and an inferred wind mass of $1.5\times10^{6}$ M$_\odot$. We also discuss the nature of the central X-ray source in NGC2782, and conclude that it is likely a low-luminosity AGN (LLAGN), with a total X-ray luminosity of $L_{X}=6\times10^{40}~erg s ^{-1}$ with strong Fe line emission at 6.4 keV.Comment: 14 pages, 14 figures, 3 tables. Accepted for publication in MNRA

Newtonian gravity and resonance on de-Sitter branes

A dS brane on the boundary between two five-dimensional spacetimes is determined. We consider asymmetric scenarios with AdS${}_5$ vacua at each side of the dS brane; and as a result, a resonant mode inside of the spectrum of the gravitational fluctuations is found. We analyze the deviations to the Newton potential generated by the gravitational excitations, finding that, for scenarios with large values of the cosmological constants, the contribution of the resonant mode is exponentially suppressed. However, when one of the vacua is null, the resonant mode belongs to the light states set of the gravitational fluctuations and five-dimensional gravity is recovered on the dS brane.Comment: 6 pages, 2 figure

Sulfur cycling and metabolism of phototrophic and filamentous sulfur bacteria

Phototrophic sulfur bacteria taken from different habitate (Alum Rock State Park, Palo Alto salt marsh, and Big Soda Lake) were grown on selective media, characterized by morphological and pigment analysis, and compared with bacteria maintained in pure culture. A study was made of the anaerobic reduction of intracellular sulfur globules by a phototrophic sulfur bacterium (Chromatium vinosum) and a filamentous aerobic sulfur bacterium (Beggiatoa alba). Buoyant densities of different bacteria were measured in Percoll gradients. This method was also used to separate different chlorobia in mixed cultures and to assess the relative homogeneity of cultures taken directly or enriched from natural samples (including the purple bacterial layer found at a depth of 20 meters at Big Soda Lake.) Interactions between sulfide oxidizing bacteria were studied