The role of iron in Mycobacterium smegmatis biofilm formation: The exochelin siderophore is essential in limiting iron conditions for biofilm formation but not for planktonic growth

Many species of mycobacteria form structured biofilm communities at liquid-air interfaces and on solid surfaces. Full development of Mycobacterium smegmatis biofilms requires addition of supplemental iron above 1 μM ferrous sulphate, although addition of iron is not needed for planktonic growth. Microarray analysis of the M. smegmatis transcriptome shows that iron-responsive genes - especially those involved in siderophore synthesis and iron uptake - are strongly induced during biofilm formation reflecting a response to iron deprivation, even when 2 μM iron is present. The acquisition of iron under these conditions is specifically dependent on the exochelin synthesis and uptake pathways, and the strong defect of an iron-exochelin uptake mutant suggests a regulatory role of iron in the transition to biofilm growth. In contrast, although the expression of mycobactin and iron ABC transport operons is highly upregulated during biofilm formation, mutants in these systems form normal biofilms in low-iron (2 μM) conditions. A close correlation between iron availability and matrix-associated fatty acids implies a possible metabolic role in the late stages of biofilm maturation, in addition to the early regulatory role. M. smegmatis surface motility is similarly dependent on iron availability, requiring both supplemental iron and the exochelin pathway to acquire it. © 2007 The Authors

Massive young stellar object W42-MME: The discovery of an infrared jet using VLT/NACO near-infrared images

We report on the discovery of an infrared jet from a deeply embedded infrared counterpart of 6.7 GHz methanol maser emission (MME) in W42 (i.e. W42-MME). We also investigate that W42-MME drives a parsec-scale H2 outflow, with detection of bow shock feature at ~0.52 pc to the north. The inner ~0.4 pc part of the H2 outflow has a position angle of ~18 deg and the position angle of ~40 deg is found farther away on either side of outflow from W42-MME. W42-MME is detected at wavelengths longer than 2.2 microns and is a massive young stellar object, with the estimated stellar mass of 19+-4 Msun. We map the inner circumstellar environment of W42-MME using VLT/NACO adaptive optics Ks and L' observations at resolutions ~0.2 arcsec and ~0.1 arcsec, respectively. We discover a collimated jet in the inner 4500 AU using the L' band, which contains prominent Br alpha line emission. The jet is located inside an envelope/cavity (extent ~10640 AU) that is tapered at both ends and is oriented along the north-south direction. Such observed morphology of outflow cavity around massive star is scarcely known and is very crucial for understanding the jet-outflow formation process in massive star formation. Along the flow axis, which is parallel to the previously known magnetic field, two blobs are found in both the NACO images at distances of ~11800 AU, located symmetrically from W42-MME. The observed W42-MME jet-outflow configuration can be used to constrain the jet launching and jet collimation models in massive star formation.Comment: 6 pages, 5 figures, Accepted for publication in The Astrophysical Journa

Cost and benefits of intermediate water storage structures: case study of diggies in Rajasthan

Water storageWater deliveryIrrigation schedulingWater controlIrrigation canalsWatercoursesFarmsCrop productionCost benefit analysis

Star Formation Activity in the Galactic HII Complex S255-S257

We present results on the star-formation activity of an optically obscured region containing an embedded cluster (S255-IR) and molecular gas between two evolved HII regions S255 and S257. We have studied the complex using optical, near-infrared (NIR) imaging, optical spectroscopy and radio continnum mapping at 15 GHz, along with Spitzer-IRAC results. It is found that the main exciting sources of the evolved HII regions S255 and S257 and the compact HII regions associated with S255-IR are of O9.5 - B3 V nature, consistent with previous observations. Our NIR observations reveal 109 likely young stellar object (YSO) candidates in an area of ~ 4'.9 x 4'.9 centered on S255-IR, which include 69 new YSO candidates. Our observations increased the number of previously identified YSOs in this region by 32%. To see the global star formation, we constructed the V-I/V diagram for 51 optically identified IRAC YSOs in an area of ~ 13' x 13' centered on S255-IR. We suggest that these YSOs have an approximate age between 0.1 - 4 Myr, indicating a non-coeval star formation. Using spectral energy distribution models, we constrained physical properties and evolutionary status of 31 and 16 YSO candidates outside and inside the gas ridge, respectively. The models suggest that the sources associated within the gas ridge are of younger population (mean age ~ 1.2 Myr) than the sources outside the gas ridge (mean age ~ 2.5 Myr). The positions of the young sources inside the gas ridge at the interface of the HII regions S255 and S257, favor a site of induced star formation.Comment: 46 pages, 14 figures, 5 tables. Accepted for publication in The Astrophysical Journa

New surveys of UBV photometry and absolute proper motions at intermediate latitude

A photometric and proper motion survey has been obtained in 2 directions at intermediate latitude: ($l=167.5^\circ$, $b=47.4^\circ$; $\alpha_{2000}=9^h41^m26^s$,$\delta_{2000}=+49^\circ53'27''$) and ($l=278^\circ$, $b=47^\circ$; $\alpha_{2000}=11^h42^m56^s$, $\delta_{2000}=-12^\circ31'42''$). The survey covers 7.13 and 20.84 square degrees, respectively. The limiting magnitude is about 18.5 in V for both directions. We have derived the density laws for stars (M$_{V}$ $\ge$ 3.5) as a function of distance from the galactic plane. The density laws for stars follow a sum of two exponentials with scale heights of 240 pc (thin disk) and 790 pc (thick disk), respectively. The local density of thick disk is found to be 6.1$\pm$3 % relative to the thin disk. The kinematical distribution of stars has been probed to distances up to 3.5 kpc above the galactic plane. New estimates of the parameters of velocity ellipsoid have been derived for the thick disk of the Galaxy. A comparison of our data sets with the Besan\c con model star count predictions has been performed, giving a good agreement in the magnitude range V = 13 to 18.Comment: 13 pages, 8 PS figures, To appear in A&

The molecular complex associated with the Galactic HII region Sh2-90: a possible site of triggered star formation

We investigate the star formation activity in the molecular complex associated with the Galactic HII region Sh2-90, using radio-continuum maps obtained at 1280 MHz and 610 MHz, Herschel Hi-GAL observations at 70 -- 500 microns, and deep near-infrared observation at JHK bands, along with Spitzer observations. Sh2-90 presents a bubble morphology in the mid-IR (size ~ 0.9 pc x 1.6 pc). Radio observations suggest it is an evolved HII region with an electron density ~ 144 cm^-3, emission measure ~ 6.7 x 10^4 cm^-6 pc and a ionized mass ~ 55 Msun. From Hi-GAL observations it is found that the HII region is part of an elongated extended molecular cloud (size ~ 5.6 pc x 9.7 pc, H_2 column density >= 3 x 10^21 cm^-2 and dust temperature 18 -- 27 K) of total mass >= 1 x 10^4 Msun. We identify the ionizing cluster of Sh2-90, the main exciting star being an O8--O9 V star. Five cold dust clumps (mass ~ 8 -- 95 Msun), four mid-IR blobs around B stars, and a compact HII region are found at the edge of the bubble.The velocity information derived from CO (J=3-2) data cubes suggests that most of them are associated with the Sh2-90 region. 129 YSOs are identified (Class I, Class II, and near-IR excess sources). The majority of the YSOs are low mass (<= 3 Msun) sources and they are distributed mostly in the regions of high column density. Four candidate Class 0/I MYSOs have been found; they will possibly evolve to stars of mass >= 15 Msun. We suggest multi-generation star formation is present in the complex. From the evidences of interaction, the time scales involved and the evolutionary status of stellar/protostellar sources, we argue that the star formation at the immediate border/edges of Sh2-90 might have been triggered by the expanding HII region. However, several young sources in this complex are probably formed by some other processes.Comment: 22 pages, 22 figures, accepted for publication in Astronomy and Astrophysic