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press-release wrote:25 May 2004 11:28:28 -0000

 

Bio-remediation Without Caution

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press-release ISIS Director m.w.ho

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ISIS Press Release 25/05/04

Bio-remediation Without Caution

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A bacterium living inside plants could be improved for

cleaning up environmental pollutants without genetic

modification. Prof. Joe Cummins and Dr. Mae-Wan Ho reveal

that this seemingly beneficial development is beset with

danger, as the bacterium concerned is a known pathogen.

 

Sources for this report are available in the ISIS members

site http://www.i-sis.org.uk/full/BWCFull.php. Full details

here http://www.i-sis.org.uk/membership.

 

Water soluble and highly volatile organic environmental

pollutants, such as benzene, toluene, ethylbenzene and

xylene compounds, chlorinated solvents and nitrotoluene

ammunition wastes, are being cleaned up using plants in

combination with microorganisms that naturally live inside

the plants (endophytes).

 

Endophyte bacteria live within the tissue of the plant

without harming it. They are found in most plant species,

and many can colonize the vascular system. The highest

densities of bacteria are usually found in the roots, less

in the stem, and least in the leaves. The plants take up the

pollutants through their roots, and the bacteria break these

down within the roots or in other parts of the plant.

 

This natural process is inefficient because the compounds

tend to get transported up the plant faster than the

bacteria can break them down. Once transported up, the

plants metabolize the contaminants, and some of the

metabolites as well as the contaminant can be toxic. For

example, trichloroethane is metabolized into trichloroacetic

acid, both of which are toxic. Worse still, plants tend to

release volatile pollutants and their metabolites into the

atmosphere via evaporation from the leaves, which turns bio-

remediation into bio-pollution.

 

A recent article in Nature Biotechnology reports how this

clean up process could be greatly improved by engineering an

endophyte bacterium Burkholderia cepacia, a natural resident

of the yellow lupine. Researchers from Linburgs University

in Diepenbeek, Belgium and Brookhaven National Laboratory in

New York, USA, created a strain of B. cepacia that has

enhanced ability to degrade toluene within the plant,

enabling the plant to tolerate high levels of toluene, and

also substantially reduced the amount of toluene released

into the atmosphere.

 

 

The engineered strain of bacterium carries marker genes for

kanamycin resistance and nickel resistance and is derived

from the natural endophyte. By adding to this endophyte

strain a toluene-degrading plasmid from another strain of B.

cepacia that normally lives in the soil through natural

conjugation (bacterial reproduction) between the strains, a

new endophyte strain is created that can live in the plant

and degrade toluene taken up by the plant.

 

 

Plants inoculated with the engineered bacterium grew much

better than plants that were not inoculated; or else

inoculated either with the control strain lacking the

plasmid, or with the strain that normally lives in the soil.

More impressively, the plants inoculated with the engineered

bacterium reduced toluene evaporation into the atmosphere to

about 50% of the control. This looks very promising, as the

researchers point out, the experiment could have been done

without any genetic modification. The plasmid containing all

the toluene degrading enzymes belonged to a natural soil

bacterium, and an endophyte host without the marker genes

could easily have been used to receive the plasmid by

conjugation.

 

A non-GM bacterial endophytic strain created in this way may

well be the very first really useful and beneficial product

from the industry. So what’s wrong?

 

The research paper did not deal with safety. What

metabolites of toluene are generated in the plant, and will

they be toxic? How will the plants be disposed of? There are

three lupine species cultivated for fodder - blue, white and

yellow - and there are a also a number of wild species. The

wild species contain alkaloid chemicals that are very toxic

to cattle and sheep while the cultivated species are edible

for farm animals, provided care is taken to treat the seeds

in such a way as to remove the toxins. Lupines thrive on

poor soil and provide ground cover and green manure as well

as fodder for animals.

 

More importantly, the research report failed to mention that

B. cepacia has the ability to cause fatal disease in humans.

 

 

The groundwater of Wichita, Kansas was found to be polluted

with the chemical solvents dichloroethylene and

trichloroethylene, and was cleaned up using a natural strain

of B. cepacia. But no special public health measures or

follow up seemed to have been implemented after the clean

up.

 

The United States Environmental Protection Agency (EPA) has

considered the problems associated with approval of B.

cepacia as a plant pesticide, for, not only is the bacterium

used to fight plant pests but is itself a pest as it is a

disease agent in humans. EPA, through a Scientific Advisory

Panel (SAP), reviewed B. cepacia as a plant pesticide and

acknowledged that it is linked to human disease. The SAP

risk assessment peculiarly noted " Bc [b. cepacia] has been

referred to as an opportunistic human pathogen. However, as

might be expected, the strains registered or proposed for

use as biopesticides were isolated from the soil or plant

roots, rather than from human patients " .

 

In reality, the SAP comment offered cold comfort because the

B. cepacia strains isolated from patients proved essentially

undistinguishable from strains isolated from the roots of

crops such as corn. The American Phytopathological Society

produced a useful review of the risks from plant disease or

human disease along with the benefits in cleaning up

chemical pollution and fighting some plant diseases.

Unfortunately, there has been no clear and simple way to

differentiate between the ‘evil’ and the beneficial strains

of B. cepacia, and no way of preventing the two from

exchanging genes.

 

B. cepacia has an unusual genetic makeup; it has a

relatively large amount of DNA (about twice that of E. coli)

and unlike most bacteria, which usually have a single

chromosome, B. cepacia strains have as many as five large

replicons (chromosomes) and the different chromosomes are

rich in insertion sequences that allow for extensive gene

exchange between different strains, and insertion of disease

related genes from other bacterial species. B. cepacia is a

prominent cause of death among cystic fibrosis patients, the

bacterium frequently reaches epidemic proportion among such

patients and an epidemic related strain was identified in

soil samples in USA. It is believed to be a complex species

made up of seven distinct genomic subspecies all of which

are capable of infecting humans; and all of the disease-

related subspecies were isolated from maize rhizosphere

(root zone). The disease is difficult to contain because

disease bacteria may be replenished continually from the

soil and plant material.

 

Hospital acquired B. cepacia epidemics appeared among

patients with diabetes, malignancy, heart failure and

chronic obstructive pulmonary disease. One such B. cepacia

outbreak appeared in an intensive pediatric care unit, and

B. cepacia infection was common among renal transplant

patients. Different B. cepacia clones showed different

infectivity among cystic fibrosis patients and patients with

different complaints. Antibiotic resistant B. cepacia

infection was the most common cause of death among lung

transplants for cystic fibrosis patients. B. cepacia causes

feared infections because the strains tend to be antibiotic

resistant. Bacteria isolated from different infections were

found to be resistant to all seven tested antibiotics but

were sensitive to treatment with honey.

 

Do lupines pose a threat to people with compromised immune

systems or cystic fibrosis? Yellow lupines, and perhaps the

other commercial species as well, contain potentially

disease-causing B. cepacia endophytes so their presence in

hospitals and homes of compromised people is unwise. The

bacteria may be transferred by direct contact with broken

plant stems or petals along with the dust and debris

associated with the plant; a gift of lupines could be fatal.

 

There is clearly a large literature on the threat of B.

cepacia infection and its death toll among compromised

patients. The existing evidence indicates that the bacterial

infections may pass from the ecosystem to the hospital ward

and there seems no way of ensuring that the B. cepacia

strains used in biotechnology are unable to infect

compromised humans.

 

 

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