277 research outputs found
Transcriptional specificity after mycobacteriophage I3 infection
Transcriptional regulation following mycobacteriophage I3 infection has been investigated. For this purpose, RNA polymerase mutants (rif) of host bacterium, Mycobacterium smegmatis have been isolated and characterised. Phage growth inrifs and rifr cells in presence of rifampicin revealed the involvement of host RNA polymerase in phage genome transcription. This was confirmed by studies onin vivo RNA synthesis as well as by direct RNA polymerase assay after phage infection. Significant stimulation in RNA polymerase activity was seen following phage infection. The maximal levels were attained in about 60 min post infection and maintained throughout the phage development period. The stimulation of polymerase activity was most pronounced when the phage DNA was used as the template. RNA polymerases from uninfected and phage-infected Mycobacterium smegmatis have been purified to homogeniety. The enzyme purification was accomplished by a rapid procedure utilising affinity chromatography on rifampicin-Sepharose columns. Subunit structure analysis of the purified RNA polymerase from uninfected and phage-infected cells showed the presence of ╬▒ ,╬▓ , ╬▓ ' and ╧Г subunits similar to the other prokaryotic RNA polymerases. In addition, a polypeptide of 79, 000 daltons was associated with the enzyme after phage infection. The enzymes differed in their properties with respect to template specificity. Phage 13 DNA was the preferred template for the modified RNA polymerase isolated from infected cells which may account for the transcriptional switch required for phage development
Requirement for calcium ions in mycobacteriophage I3 DNA injection and propagation
Ca2+ ions are absolutely necessary for the propagation of mycobacteriophage I3 in synthetic medium. These ions are required for successful infection of the host and during the entire span of the intracellular development of the phage. A direct assay of the phage DNA injection using 32[p] labelled phage, shows that Ca2+ ions are necessary for the injection process. The injection itself is a slow process and takes 15 min to complete at 37°. The bacteria infected in presence of Ca2+ tend to abort if the ions are subsequently withdrawn from the growth medium. The effect of calcium withdrawal is maximally felt during the early part of the latent period; however, later supplementation of Ca2+ ions salvage phage production and the mature phage progeny appear after a delayed interval, proportional to the time of addition of Ca2+
Stimulation of valyl- and isoleucyl-tRNA synthetase reactions by polyamines
The aminoacylation of tRNA catalysed by valyl-tRNA synthetase (EC 6.1.1.9) and isoleucyl-tRNA synthetase (EC 6.1.1.5) from Mycobacterium smegmatis is dependent on the presence of divalent metal ions. Polyamines alone, in the absence of metal ions, do not bring about aminoacylation. In the presence of suboptimal concentrations of Mg2+, polyamines significantly stimulate the reaction. Of the cations tested, only Mn2+, Co2+ and Ca2+ can partially substitute for Mg2+ in aminoacylation, and spermine stimulates aminoacylation in the presence of these cations also. At neutral pH, spermine deacylates nonenzymatically aminoacyl tRNA. AMP and pyrophosphate-dependent enzymatic deacylation of aminoacyltRNA (reverse reaction) is also stimulated by spermine. The inhibitory effect of high concentration of KCl on aminoacylation is counteracted, by spermine. The low level of activity between pH 8.5-9.0 at 1.2 mM Mg2+ is restored to normal level on the addition of spermine. The inhibitory effect of high pH on aminoacylation in the presence of low concentration of Mg2+ is also prevntedvby spemine
Primary production
Studies on primary pruuuciion oj ine Indian Seas in general
and adjacent ecosystems such as estuaries, mangroves, mud banks
and coastal environments in particular are briefly discussed, in the
light oJ the data collected over the years by various Expeditions
and also by the investigations conducted in localised regions. The
results indicated that the general trend of primary production vary
both in space and time and also a seaward decrease in the
production. The factors affecting and favouring the primary
production of the Indian Seas is also presented. The annual
production rates of west coast and east coast andpotential estimates
of resources derivedfrom primary production is also discussed. The
annual carbon production for the EEZ of India has been com^puted
as 283 million tonnes and potential harvestable resources available
in this region derived as 5.5 million tonnes, based on primary
production. Future investigations on productivity through
chlorophyll analysis arc also projected
Phytoplankton
Investigations on phytoplankton of the Indian Seas has assumed
great significance during the last 5 decades. As these microscopic
organisms fluctuated in response to climatic changes,
water movements, seasonal variations, nutrient content of the water
etc. they form an important and convenient link in the assessment
of the stock of potential resources. The shelf and oceanic
waters of the Indian seas show fluctuations in the standing crop of
phytoplankton due to the effect of two monsoons. Available data
indicated that the waters along the west coast of India are more
fertile than that along the east coast mainly due to upwelling and
other favourable factors conducive to phytoplankton growth. Some
of the ecological factors contributing to the pattern of production of
phytoplankton are also briefly discussed
Influence of Thermal Effluents on the Growth Characteristics of Phytoplankton in the Waters of Tuticorin Bay
The paper reports the results of investigations conducted in 1990,
on the physico-chemical aspects of Tuticorin Bay waters in relation to
the abundance of phytoplankton. Selected species of phytoplankton were
experimental1y cultured to study the influence of thermal effluents. For
this purpose cultures ,vere raised in media collected from 4 stations.
showing different extents of pollution. Four species of nannoplankton,
namely. l sochrysis galbana (Haptophyceae), Dicrateria inornata
(chrysophyceae), Tetraselmis gracilis (Chloro-phyceae) and Chaetoceros
calcitrans (Bacillariophyceae) were grown in the water samples collected
from selected stations. The experiments showed stimulatory trend of
growth for the first 7-8 days and gradual inhibitory effect on the
multiplication in subsequent days. Among them, the phytoflagellates
(Jsochrysis, Dicrateria and Tetraselmis)showed good growth in the
samples of media collected from locations near to the pollution source.
The rate of production of both Tetraselmis and Dicrateria, which are
known to exist in the polluted waters, indicated enhanced growth in the
Bay waters. The growth of the diatom, Chaetoceros has been found to
be uniform except in the sample collected from the point nearest to the
source of pollution. Though the long-term effects of these samples have
not been studied, the experiments revealed the possible effects of.thermal
effiuents on the phytoplankton population in the waters of Tuticorin Bay
Quantitative ecology of phytoplankton in the Cochin backwater
A one-year study on the standing crop in terms of chlorophylls, primary
production and total-cell counts of four station grids has shown that there were
regional and seasonal variations in the magnitude of phytoplankton production in
the Cochin backwater. Statistically treated using a microcomputor, a multiple
regression relationship has been established between parameters within stations.
But th<^ Correlation coefBclent and Standard Regression coefficient have revealed
that the plankton production and the related parameters at all the stations were
independent of each other and the parameters varied from station to station. Probable
reasons are briefly discussed
Marine pollution - its effects on living resources with special reference to aquaculture
Due to large scale industrialisation and indiscriminate discharge of effluents with high BOD,
toxic chemicals and particulate matter reach the aquatic environment, either directly or indirectly.
Enrichment of the coastal waters through nutrients and minerals lead to immediate and long term
effects on the biota and fishery resources causing severe eutrophication or mass mortality. Among
a large variety of pollutants which reach the aquatic environment, the domestic sewage, agricultural
pesticides, industrial wastes, oil and oil dispersants, radioactive wastes and the polluted water from
the coconut retting zones causes deleterious effects in the inshore and fish fanning areas
Primary production in coastal waters
The data on primary production from the Bay of
Bengal and the Andaman Sea are very meagre. The
Danish Galathea Expedition during her round-the-
world cruise, made some measurements across the
Indian Ocean through the equatorial current system
and in the Bay of Bengal, of which two stations were
from the Andaman Sea. It was observed that in the
eastern part of Bay of Bengal, the lower bound ry of the
photosynthetic layer was between 84-99 ra and the
stations located on the shelf were characterised by a
high rate of production. In the Galathea report
(Steemann Nielsen and Jensen, 1957), it was concluded
that the monsoon shift has some influence on the rate of
production in the Bay of Bengal and that extensive
investigations during the different seasons are necessary
in order to get a true picture of the production of organic
matter
Productivity of the Exclusive Economic Zone of India
The factors governing phytoplankton production in the Indian Seas have been briefly discussed. The general
level of productivity of the Exclusive Economic Zone of India has been computed from primary production
measurements using radioactive carbon ("Q in different depth zones during different seasons. From this a
potential estimate of the harvestable resources has been derived. The annual carbon production for the EEZ
of India, comprising 2.02 million sq. km. has been estimated to be 283 million tonnes. The present exploitable
yield of living resources of the EEZ is estimated to be 5.5 million tonnes based on primary production. This
estimate is about 20% higher than the earlier estimates
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