2,387 research outputs found
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 Ī¼M 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 Ī¼M 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 Ī¼M) 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. Ā© 2007 The Authors
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: (, ;
,) and
(, ; ,
). 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 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
6.13 % 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&
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
Multi-wavelength study of the star-formation in the S237 H II region
We present a detailed multi-wavelength study of observations from X-ray,
near-infrared to centimeter wavelengths to probe the star formation processes
in the S237 region. Multi-wavelength images trace an almost sphere-like shell
morphology of the region, which is filled with the 0.5--2 keV X-ray emission.
The region contains two distinct environments - a bell-shaped cavity-like
structure containing the peak of 1.4 GHz emission at center, and elongated
filamentary features without any radio detection at edges of the sphere-like
shell - where {\it Herschel} clumps are detected. Using the 1.4 GHz continuum
and CO line data, the S237 region is found to be excited by a radio
spectral type of B0.5V star and is associated with an expanding H{\sc ii}
region. The photoionized gas appears to be responsible for the origin of the
bell-shaped structure. The majority of molecular gas is distributed toward a
massive {\it Herschel} clump (M 260 M), which
contains the filamentary features and has a noticeable velocity gradient. The
photometric analysis traces the clusters of young stellar objects (YSOs) mainly
toward the bell-shaped structure and the filamentary features. Considering the
lower dynamical age of the H\,{\sc ii} region (i.e. 0.2-0.8 Myr), these
clusters are unlikely to be formed by the expansion of the H\,{\sc ii} region.
Our results also show the existence of a cluster of YSOs and a massive clump at
the intersection of filamentary features, indicating that the collisions of
these features may have triggered cluster formation, similar to those found in
Serpens South region.Comment: 21 pages, 14 figures, 1 table, Accepted for publication in The
Astrophysical Journa
Economics of Rice Production in Pyuthan District of Nepal
A research was conducted at Pyuthan district in order to access the profitability of rice production in Pyuthan during the summer season of 2018-2019. Altogether of 70 respondents were selected randomly and surveyed with semi-structured interview schedule. The results revealed that the average land holding was 0.45 hectare, and the average rice cultivation area was 0.34 hectare. On the basis of average rice cultivation area, farmers were categorized as small (39) and large (31). The cost and return was calculated among both the category. t- test was used to compare the mean costs of inputs between small and large farmers. Cost for agronomic operations was found far higher (more than 70%) in both the category in compared to the cost of inputs. Contribution of rice grains and straw to overall return was 72.65% and 27.35% respectively. Benefit Cost ratio was found greater among large farmers. The average B:C ratio was 1.51, which was fairly higher than 1.14 in Dang district indicating the investment of rice production is expected to deliver a positive net return to the farmers of the study area. In a nutshell, rice cultivation is an important enterprise that should be encouraged, considering the fact that it is a major staple crop
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