Thursday, 31 July 2008

GM and insecticides reduce mycotoxins in crops

European Corn Borer hatchlings
Food crops can become infested with insects which will reduce the yield of the crop - bad enough news for the farmer but it gets worse. A heavily chewed plant such as maize becomes susceptible to infection by fungi including aspergillus and that fungus can start to synthesise mycotoxins:
"How severely a maize plant is infected with fungi and whether this leads to mycotoxins being produced depends on a large number of factors. Humidity and temperature during the growing season, soil cultivation and the susceptibility of the variety in question all play a role, as does the time chosen for harvesting. The complex process, which is not fully understood, makes it difficult to control mycotoxin formation in individual cases and to reduce contamination reliably. Studies in Germany, for instance, have shown that mycotoxin levels vary widely between individual maize plants, even on the same site. There are many indications that stress – both for the maize and for the fungus – results in higher mycotoxin production"
As the infestation gets worse so the levels of mycotoxin get worse:
"But it is also clear that a heavy infestation of chewing pests leads to higher mycotoxin contamination. In many maize-growing regions of Europe the European corn borer is the main maize pest: the larvae bore their way into the maize plants, leaving holes through which Fusarium and other fungi can enter."
Mycotoxins can be extremely toxic so their levels are strictly controlled in food for both animals and humans.

Prevention of insect infestation effectively reduces the levels of mycotoxin in the crop, introducing a greater level of control over toxin levels.
"The more effectively the corn borer is controlled, the fewer chewing sites there are that can be used by the fungal pathogens to colonize the maize plant, in addition to the stigma route."

Certain genetically manipulated crops (e.g. Bt Maize) are effective at controlling insects without the aid of chemical insecticides and it has been shown that these crops also suffer from far lower levels of mycotoxin contamination:
"On all sites, the Bt maize varieties used showed the best results: only isolated corn borers were found in the crops. On almost all the trial fields the mycotoxin values measured were lower in the Bt maize plants than in the conventionally grown control plants."
The GM crop therefore benefits from both increased yield and lower toxin levels - two benefits for the price of a single modification.

Wednesday, 23 July 2008

Tea manufacture and Aspergillus

How tea works

Tea is the most widely drunk beverage in the world (Wiki) with over 3 million tonnes produced per year.
Many different types or grades are produced and I was intrigued to read this article which states:
"Poria Cocos Brick (Fu Tea) is the top grade in the ancient kind of brown tea. Being complete ferment tea, Poria Cocos Brick Tea is the most complex and unique brown tea which has the longest production processing cycle. It products Aspergillus Cristatus, brick-like in appearance, with flourishing golden flowers all over, dark and shining, red and strong tea soup, mellow to the taste with lasting scent."
Not making much sense but clearly indicating that Aspergillus is involved in the manufacture of this tea I decided to do a bit more research.

Some teas are fermented using enymes or crude extracts of fungi and Aspergillus is one of the best producers of those enzymes. This patent goes into this in much more detail:
"In fermentation, a microorganism (mold) is preferably co-present, in order to sufficiently obtain the flavor and physiological activity specific to fermented tea. An example of the microorganism that is used is mold. The mold that is used can be present in nature and examples are molds of Aspergillus sp. including Aspergillus awamori, Aspergillus saitoi, Aspergillus niger and Aspergillus orizae, Rhizopus sp. including Rhizopus delemar and also, other molds for processing food such as tempeh mold. From the viewpoint of exhibiting physiological activity, mold of Aspergillus sp. and Rhizopus sp. are preferably used. The type of mold that is used can be one type or a mixture of several types, but pure fermentation using one type of mold is preferable."
I was then intrigued as to how the mold is added to the tea, and where it comes from:

"Examples of the method of applying the mold to tea leaves and tea leave stems are the method of dry mixing tea leaves, tea leave stems and sporules of the mold as they are, the method of diluting the sporules of the mold by dry mixing together with a food diluent such as wheat flour, rice powder and barley flour and then mixing with tea leaves and tea leave stems, and the method of preparing a suspension of the sporules of mold in saline and then spraying onto the tea leaves and tea leave stems. The amount of mold is preferably 0.001 to 1 % by weight, more preferably 0.01 to 0.5 % by weight, based on the total amount of tea leaves and tea leave stems. When the amount of mold is less than 0.001 % by weight, fermentation tends to be insufficient. When the amount of mold is more than 1 % by weight, production costs tend to become too high.

These strains are easily available, as commercially available mold species such as koji for sake, koji for sweet sake, koji for shochu and koji for tempeh, and also, the fermented tea leaves can be left and reused as a mold starter.

Subsequently, the tea leaves and tea leave stems to which the mold is applied are spread on a bed in the fermenting chamber and then fermented. The temperature of the fermented substance when fermenting is preferably raised to 32°C or higher, more preferably 32 to 45°C, further preferably 35 to 42°C, within 25 hours after beginning fermentation. When such conditions are not satisfied, that is the temperature is not raised to a high temperature in short period of time, progression of fermentation tends to be insufficient. This temperature is preferably maintained for at least 5 hours, more preferably 5 to 100 hours, further preferably 5 to 10 hours."

So the use of Aspergillus is vital to the final taste and caffeine content of some fine teas. This is another example of the historical and ancient uses of Aspergillus to produce foods in the far east - more good uses for this mold with a bad image!

It is worth noting that most tea is NOT prepared using molds so readers worried about eating foods derived from molds can rest easy with their usual tea bags. Most tea is prepared by crushing, oxidising and drying.

Friday, 18 July 2008

Overcoming resistance to antifungals

Artwork by Nature - click here to go to journal
The latest copy of the journal 'Science' features a series of special articles on drug resistance in bacteria and fungi, a major area of research to attempt to improve the effectiveness of many of our antibiotics.
Antibiotic resistance has four main mechanisms, one of the least specific of which is to pump the antibiotic out of the bacterial cell as fast as possible - the active efflux pump. The same mechanism has been discovered in fungi and is discussed here in detail. One of the main things that make the efflux pump mechanism a threat to the use of antibiotics & antifungals is that it is pretty non-specific about which antibiotic/antifungal it removed from the cell interior - one type of pump can remove most of the azole antifungal drugs so the cell that possesses that pump automatically becomes resistant to a whole series of drugs all at the same time - also known as multidrug resistance.
One feature of reflux pump resistance is that the antifungal drug itself is remains active, it is just that it is removed from the cell too quickly for it to kill the cell.

The Science review looks at attempts to interfere with or destroy the efflux pumps thus allowing antifungal drugs to accumulate within the cells, killing them.
It turns out that there are a few possible strategies: stop the cell from making the pumps (transcritional/translational control) or switch off the pumping mechanism by using molecules that look like azole drugs which the pumping mechanism can 'grab hold' of but can't release, thus effectively blocking the pump.

More intriguingly a more thorough understanding of the function of these pumps has revealed that one of them, the plasma membrane proton pump (Pma1p) is important for both ensuring the cells remains healthy and is involved in the function of two other drug efflux pumps (ABC and MFS) . Interfering with that single pump attacks the fungal cells on more than one way - more encouragingly no resistance to inhibitors of that pump have been found, suggesting that the cell can find few ways around the loss of that pump. A two pronged attack involving a Pma1p inhibitor plus an antifungal drug could well prove to be an extremely effective combination in the war against fungi.

NB more good news - resistance mechanisms in bacteria are passed from pathogen to pathogen quite readily, rapidly leading to whole mixed populations of multidrug resistant bacteria. Such drug resistant transfer does not seem to happen as often in fungi such as Aspergillus and infections by drug resistant fungi are correspondingly uncommon.

Saturday, 12 July 2008

Biofuels development relies on Aspergillus

Biofuels - are they good for the environment?
There are numerous efforts underway to find new fuels to power devices that are currently powered by oil-based fuels - particularly as the oil supply comes under increasing demand and reserves start to taper off. Biofuels are one solution as these are made from plants and are therefore renewable - as long as the sun keeps shining! One strategy is to generate sugars from plant material and then ferment that sugar to produce ethanol - a burnable fuel made from plant material currently unused.

"It is estimated that more than a billion tons of lignocellulosic plant biomass could be utilized each year to produce liquid biofuels in North America alone." (ref)

Plant material is largely composed of cellulose and other complex sugars that need to be broken down into simple sugars before they can be fermented. Simple sugars are made by treating the plant material with enzymes called cellulases, and many efforts are being made to find the most efficient ways of carrying out this vital stage in biofuel production - the more sugar produced, the more fuel made.

Aspergillus is used as an enzyme production factory for several industries as it can produce many times the amount of enzyme normally available in the natural host organism for that enzyme - in this case Trichoderma reesei. In this paper a refinement is suggested for the enzyme production process in order to improve activity once produced in Aspergillus.

This report states that Aspergillus will play a major role in research into efficient ways to make biofuels by using Aspergillus to make the cellulases which will be the key to converting plant material into fuels that will eventually surely replace oil based fuels.

Wednesday, 2 July 2008

Anticancer drug developed from Aspergillus fumigatus

The Harvard team
Fumagillin is a secondary metabolite of Aspergillus fumigatus and belongs to that much-feared and maligned group of substances associated with fungi - mycotoxins.

This report follows the story of the discovery that this toxin might be useful.

First came a stroke of luck (and the ability to take advantage of that luck) reminiscent of the story of Fleming's discovery of penicillin.

"The fungus was discovered by Harvard’s Donald Ingber by accident while trying to grow cells that line blood vessels, or endothelial cells. The cells were affected by the mold in a way that prevented the growth of small blood vessels called capillaries."

The 'mycotoxin' was found to 'toxic' towards cancerous tumours as it prevented the growth of blood vessels in tumours, thus limiting their ability to grow (an activity referred to as anti-angiogenesis).

Having recognised this tremendously useful property a man-made version of the metabolite (TNP-470) was developed in the early 1990's by a company in Japan in an attempt to develop an anticancer drug. Unfortunately it was not successful:

"the drug would not stay in the body for very long and required continual infusions. It also affected the patients’ brain causing dizziness, depression, and other side-effects. Takeda Chemical Industries dropped it."

Years later we have developed the technology to encase drugs in molecular capsules that prevent them being broken down via stomach acid. An encapsulated version of TNP-470 was developed (now called to as Lodamin) and now it was found to be absorbed by the intestines and then go straight to the liver with no sign of side effects in mice.

Tests on mice show good activity against aggressive liver tumours but there are no reported results in humans yet.

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