SCIENCE TRIBUNE Thursday, September 6, 2001, Chandigarh, India
 

Story of a superbug
K. S. Parthasarathy
D
o you like cockroaches? I do. They have some special traits. They are very radiation-resistant. Deinococcus Radiodurans (DR) ó a bacterium ó beats cockroaches more convincingly in the game. They can survive enormous doses of radiation. DR is a lowly form of life. But biotechnologists can turn it into a superbug. If you look at living beings closely, we realise that we cannot consider any of them as lowly.

How safe are modern buildings?
Ved Parkash Takyar
A
ribbed RCC slab with a beam at the bottom is commonly called T-beam floors or flange floors. This is widely used in reinforced concrete practice because certain part/area of RCC flange on the beam also work as beam, with the result it reduces the depth of the beam and saves the quantity of steel considerably. The T-beams are economical and their simultaneous process of concreting along with the slab lead to homogeneity (monolithicness) if grouted with iron rods and by using vibrator.

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Story of a superbug
K. S. Parthasarathy

Do you like cockroaches? I do. They have some special traits. They are very radiation-resistant. Deinococcus Radiodurans (DR) ó a bacterium ó beats cockroaches more convincingly in the game. They can survive enormous doses of radiation. DR is a lowly form of life. But biotechnologists can turn it into a superbug. If you look at living beings closely, we realise that we cannot consider any of them as lowly.

Arther W. Anderson discovered DR for the first time in 1956 at Oregon Agricultural Experimental Station in Corvallis. He isolated the bacteria from a can of ground beef that had spoiled despite having been radiation-sterilised. Deinococcus Radiodurans literally means "strange berry that withstands radiation" Ever increasing fans of DR call it Conan the Bacterium.

These pink microbes with the weird smell of rotten cabbage often reside in cow patties and elephant dung. They stay equally cozy in nuclear waste or under the rocks in Antartica or the water shielding tanks of powerful cobalt-60 irradiators.

This toughests of organisms is believed to be two billion years old; it is one of the earliest forms of life on earth. DR is a truly remarkable organism. Dry it, dehydrate it for long periods or burn it with high doses of ultraviolet radiation, DR will pop back to life. Cook it with 15,000 gray of gamma radiation. (A radiation dose of five grays will kill man), you guessed it right, DR will shrug it off and live comfortably thereafter. Let us try the ultimate assault, an atomic blast, chances are that DR will thrive and rise from the ashes!

Currently, several laboratories are scrutinising the life of DR. DR has several traits. It endures many extremes. Besides high doses of ionising and ultraviolet radiation, it can withstand genotoxic chemicals and oxidative damage. DR possesses a clear external cell membrane, carotenoid pigments and enzymes to defend against oxygen toxicity. Researchers know that free radicals formed by radiation can damage DNA. Carotenoids are possibly free radical scavengers. The cell wall of DR is extremely complex. It contains three or more layers of amino acids and lipids. These may also protect DR from fatal doses of radiation.

The survival tactics of DR have been intriguing. Scientists at the Institute of Genomic Research (TIGR) in Rockville, Maryland and at the laboratories of the US Department of Energy had sequenced the entire collection of genes of DR. They observed something unique. DR seems to have thousands of genes that help it to clean up any damage caused by radiation to its DNA in a few hours. It is very smart. It throws out the damaged parts of the cell potentially preventing them from getting reincorporated into the genome. About 500 to 1000 unique genes appear to enable it to withstand radiation.

Michael Daly of the Uniformed Services University of Health Sciences at Bethesda, Maryland added a few genes to DR from a strain of E.coli particularly resistant to toxic form of mercury. The DR-e-coli beast acquired other interesting abilities. It can convert toxic mercury into a relatively harmless form of mercury.

For DR, toluene is a tasty meal. It works efficiently in the lab. It is yet to be tested in the field. The study has been published in Nature Biotechnology (January, 2000).

Radiation from plutonium and uranium kills conventional bacteria, which are capable of carrying out bio-remediation. But DR-E.coli beasts thrived well even when radioactive pollutants are present. They prevented the movement of uranium and plutonium. This is indeed a desirable stopgap arrangement till other clean-up technologies emerge. This may hopefully provide a safe and cheap tool to fix radioactive waste accumulated over the past several decades.

Dr Robert Richmond, a research biologist with National Agency for Space Administration, believes that DR beats most of the constraints for the survival of life on Mars. DR may be genetically altered to produce medicines for space travellers. An entire pharmacy is too heavy a payload!

Scientists are unlikely to leave the humble creature in peace. Its only mistake was it stayed happily inside that gamma-irradiated can of meat. The minor blemish of the superbug as noted earlier is that it smells like rotten cabbage, which even dedicated vegetarians cannot stand! Since many vegetarians believe that their numbers are increasing, we should do something about it. Idle biotechnologists may be asked to make DR sweet smelling. I suggest that they may add the genes of jasmine or sandalwood to the little beast to make it more acceptable.

Dr K.S.Parthasarathy is the Secretary of the Atomic Energy Regulatory Board
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How safe are modern buildings?
Ved Parkash Takyar

A ribbed RCC slab with a beam at the bottom is commonly called T-beam floors or flange floors. This is widely used in reinforced concrete practice because certain part/area of RCC flange on the beam also work as beam, with the result it reduces the depth of the beam and saves the quantity of steel considerably. The T-beams are economical and their simultaneous process of concreting along with the slab lead to homogeneity (monolithicness) if grouted with iron rods and by using vibrator. "Inverted beams" are not generally simultaneously casted along with the slab. Moreover the inverted beams act as a simple rectangular beam. In modern houses these hidden beams are generally casted in bigger rooms such as drawing rooms and lobbies. Because the slab beneath these beams remains in tension zone along with the beam (other than some part on both the ends) and this point is not covered while designing which often results in sheer cracks in the slab and becomes a source of leakage and dampness.

After laying RCC slab, loose shuttering in shape of "ROKE" with wooden planks or bricks is generally done on both sides above the slab for concreting the remaining part of the inverted beam. Generally, the concrete filling between such type of shuttering cannot be solidly grouted as in case of T-beam. In most cases of the inverted beams, the upper part of beam is casted after laying of the whole RCC slab or when concrete of slab is partially set. By this system of casting, the required strength of beam cannot be achieved because initial setting period of Portland cement is 30 minutes and final is 600 minutes. Moreover, the strength depends on other factors such as grading of bajri and sand, water cement ratio and compactness during laying etc.

In private residential houses, it has been seen that T-beams are rarely provided and the inverted (hidden) beams are commonly used and are not casted as per the designed depth. Inverted or flat beams are designed as simply supported beams by providing extra steel reinforcement at the bottom and at the top. But to keep the depth of beam up to the level of lean concrete for intermediate floors or up to the mud filling for laying tiles terracing, the designed depth is not often followed in residential houses. As a thumb rule the depth of inverted beam (ordinary simple beam) should not be less than 1/20 of the span unless sheer and other considerations prevail. Economical depth of a simple beam is 1/8 to 1/15 times the span in inches i.e. for simply supported beams, semi-continuous beams and continuous beams and moreover on the intensity of load.

With the same load and working stresses of concrete and steel, if the design depth of 20 ft span T-beam is calculated to 18", the depth of inverted beam (simply supported) will come to nearly 26". The depth of the beam can be reduced by providing extra steel reinforcement in compression zone i.e. at the top of beam. Such beams are called doubly reinforced beams and often these are designed as steel beams when the steel reinforcement on the upper side (compression zone) exceeds the bottom side (tension zone) reinforcement. These beams are called steel beams in which equal steel reinforcement is provided in tension and as well in compression zones with stirrups for sheer reinforcement which are rarely provided according to the design.

Because most construction of private residential houses is done on lumpsum contract or on per square foot rate, the petty contractors try to reduce the labour cost wherever they can. To avoid the extra expenditure on the shuttering and centering of T-beams, in most cases they prevail upon the owners to lay Inverted/flat beams with only one argument that the T-beams below insulation cannot be provided on the raised portion of beam and in absence of same, cracks occur in the tile terracing above the portion of beams on account of thermos expansion of steel in the beams. In most cases of inverted beams, required concrete cover is not provided around the M.S. Steel bars with only one interest to keep the depth at top with the lean concrete or mud filling. Moreover, due to overreinforcement of steel in the beam portion, the concrete is not solidly grouted. Due to thermos expansion of steel, cracks occur in the concrete of beams which further reduces the strength of inverted beams. If these cracks in the beams and tiles terracing are repaired these will again split which not only becomes a source of seepage of water in the roof but also makes the beam unsafe steadily. One can easily see the occurrence of dampness under the terrace floor roof through the cracks at the place of inverted beams. Once the water seeps through the cracks in the tile terracing, dampness will occur due to condensation also below the slab on account of atmosphere action. The inverted/flat beams are more or less a mental satisfaction of the contractors and the owners that the beams stand provided in the roof with sufficient steel.

Actually, the necessity of inverted beams should arise only when the clear head is restricted and not in view of underneath look of T-beam. The above mentioned minimum depth of inverted beam should not be reduced in any case in the interest to remain within the line of lean concrete of intermediate floors or up to mud filling for tile terracing. In private residential building, the above norm of minimum depth the simultaneously concreting of the slab with the upper part of inverted beam is not followed and that is why these beams do not attain required strength. Such beams have extra reinforcement work to some extent but do not possess the required factor of safety. Generally, the concrete in the upper portion of inverted beam is not laid between any frame of shuttering to keep the width and depth to the designed cross-sanctional area. In many cases concrete is rounded at the top of beam which further reduces the modulus of section of beam and thus the strength of beam is considerably reduced and such beam could not withstand against the jerks of earthquake, shattered and gave way under tremendous horizontal forces of earthquake which becomes a cause of disaster during recent earthquake in Gujarat.

It is suggested that as far as possible the inverted/flat beams should be avoided and provided only in compulsion i.e. in rare case to the designed crosssectional width and depth and their concreting should be done simultaneously along with the bottom slab which is only possible if their shuttering i.e. "Roke" on both the sides is managed strongly around the beam before laying of RCC Slab.
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Excreta of dinosaurs found

In a major discovery, scientists have found frozen remains of faecal (excreta) matter of prehistoric dinosaurs at Nand-Dongargaon at Pisdura near Nagpur in central India, a detailed study of which would now help in knowing their diet and metabolic process.

Dr Prasenjit Ghosh, a scientist at the Physical Research Laboratory (PRL) in Ahmedabad, told PTI today that the "excreta remains of dinosaurs were found by Geological Survey of India, Birbal Sahni Institute of Palaeobotany and PRL scientists last month from Nand-Dongargaon." Search for dinosaurs faecal matter was being done in areas and surroundings, where earlier their fossiled eggs and skeleton remains were found, he said.

"We have separated the organic materials from the coprolite (faecal) samples for carbon and nitrogen isotopes in order to get an idea about their diet and its type and metabolic process of digestion. Preliminary study has revealed that the species of dinosaurs were feeding on vegetation, specifically of C3 type (big trees like Neem and Papal) and their metabolic process was very similar to that of present day birds and reptiles," Dr Ghosh added.

Dr SK Bhattacharya, senior PRL scientist, who is guiding the study, said the investigated coprolites were poorly phosphatic, adding that the identity of producer of coprolites was based on circumstantial evidence showing a possible relationship between coprolites and their producers, dimensional and surface parameters, association of skeleton material and coprolite contents. PTI

 

Research launched on stem cells

The Department of Biotechnology (DBT) has launched three major programmes on stem cell research aimed at treating blindness and some types of brain disorders, and is hoping to allot "significant amount of funding" for this area of research in the 10th five year plan, a senior DBT official has said.

The LV Prasad Eye Institute in Hyderabad and the newly created National Brain Research Centre (NBRC) in New Delhi are among the beneficiaries of DBT funding. NK Vinayak, head of DBTís medical biotechnology division told PTI.

The availability of stem cells from legally aborted foetuses and unused embryos from test-tube baby clinics will help speed up research in this area, "that has great potential in future," Vinayak said.

The Indian Council of Medical Research guidelines allow use of aborted foetuses and less than 10-day old embryos in medical research. But transplantation of stem cells into humans is permitted only after animal trials when other forms of treatment are not available.

Doctors in test-tube baby clinics create several embryos and un-used embryos are flushed down the toilet. Vinayak said these could be put to use because embryonics cells are a rich source of stem cells, which, under proper conditions, have the ability to differentiate into tissues of choice.

According to Vinayak, technologies are now available to isolate, cultural, and maintain stem cells and also to modify these cells into specialised cell lines for transplantation purposes. "Industry is very much interested to collaborate in this work, Vinayak said. PTI

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