Useful Fungi

Fig. 1 - Mucor

From the microscopic yeasts to the largest mushrooms, many fungi have proved to be beneficial to both humans and the environment.

Members of the fungal kingdom, present in the soil, air, water and other living organisms, represent a wide range of species. Many are harmful, causing damage to crops and diseases in humans and animals. A large number of fungi, however, are of immense use, both to humans and to the environment in general.

Fungi as Decomposers

Many fungi play an important role in decomposing organic matter, and are thus instrumental in the cycling of minerals. In natural systems, for instance, species of Trichoderma, Phanerochaeta, Penicillium, Fusarium and Agaricus contain enzymes capable of digesting both the lignin and cellulose in dead forest trees and leaf litter. Valuable carbon, nitrogen and phosphorous are subsequently returned to the soil.

Some species of Rhizopus and Aspergillus can in fact decompose chemical pollutants such as aniline and benzene, while certain strains of Penicillium can degrade plasticisers, insecticides and herbicides. Moreover, the ability of fungi such as Cladosporium resinae to utilize hydrocarbons has been investigated as a possible solution to oil spillage issues.

The advantage of fungal, as opposed to bacterial, decomposition, is that most fungi develop far -reaching threads, or ‘hyphae’, which can penetrate and digest a larger area of organic waste than bacterial colonies. Examples include the hyphae of Mucor species (see figure 1), which grow quickly under favourable conditions, secreting hydrolytic enzymes as they spread over nutrient-rich organic matter.

Drugs from Fungi

Fig. 2 - Coralorrhiza

The most recognized fungus in the medical world is the Penicillium mould, found by Alexander Fleming in 1928 to inhibit the growth of bacteria. The antibiotic, Penicillin, was subsequently isolated from Penicillium chrysogenum and developed into workable concentrations by Howard Florey and Ernst Chain. Cephalosporium and Aspergillus species are also used in the production of antibiotics.

The fungus Tolypocladium inflatum is a source of the immunosuppressant drug Cyclosporin, used in bone marrow and organ transplants and instrumental in the treatment of autoimmune diseases. Other medicinal fungi include Aspergillus and Phoma species, which produce statins - drugs that assist in the reduction of low-density blood lipoproteins.

In addition, Claviceps pupurea, a fungus perhaps better known for the deadly disease ergotism, is often used in the treatment of migraines and blood pressure. Yeasts are also regularly used in genetic engineering procedures to produce recombinant vaccines such as the Hepatitis B Virus vaccine.

Fungi as Symbionts

The ability of some fungi to form symbiotic associations with plants is of great importance in ecosystems. Around eighty five per cent of plants acquire nutrients from mycorrhizal fungi associated with their root systems. The fungi, in turn, utilize some of the sugars produced by the plants in photosynthesis. Members of the Basidiomycetes family, for instance, form mycorrhizal soil associations with conifers.

Interestingly, some orchids tap into mycorrhizal fungi growing at the base of other plants to obtain their nutrients. An example of this phenomenon, known as myco-heterotrophy, can be observed in the Pacific Coralroot orchid (see figure 2). Lichens are another intriguing instance of fungi living symbiotically with plants. The plants in this case are members of the genus Trebouxia, a type of green alga. Each organism in this association depends on the other for survival.

Fungi and Food Production

The unicellular fungus, Saccharomyces cerevisciae, commonly known as yeast, has played a vital role in the manufacture of bread and alcohol for thousands of years. As yeasts feed off sugars in anaerobic respiration, they release carbon dioxide and ethanol. In bread making, the carbon dioxide produced helps the dough to rise, while any ethanol released is destroyed in the baking process.

When yeasts are used to produce wine, the carbon dioxide is either allowed to escape or retained to form sparkling beverages. The inability of yeasts to survive in high amounts of ethanol limits wine alcohol concentrations to around 15%. In beer making, brewer’s yeast ferments the sugars produced by germinated cereal grains such as barley, and the resulting ethanol is combined with hops to form the final product.

Other fungi involved in food production include Penicillium species, used in blue cheeses, Aspergillus oryzae, which grows on rice to produce soy sauce and the Japanese dish, koji, and Mucorales varieties, used to produce the food additive beta-carotene. Rhizopus oligosporus, a type of bread mould, is used to make the Indonesian dish, Tempeh, by fermenting leguminous seeds. Macroscopic fungi such as shiitake, agaricus and enoki mushrooms and truffles have also been cultivated and eaten for hundreds of years.

Biological Control

Some species of fungi have been introduced to agricultural crops as a form of biological control of insect pests. Many of these belong to the Hyphomycetes family, and target a range of insects, including thrips, caterpillars, aphids and mealy bugs.

Fungi, then, are an integral part of our natural and man-made surroundings. By contributing to the cycling of minerals, waste decomposition, food production and human medicine, they have consistently proved themselves to be an indispensable kingdom.

References

•                C.S.I.R.O., Australia, 2003, 'What do Fungi do?', fungibank.csiro.au

•                Fungi as Food Sources, singnet.com

•                Fungi as Saprobes, blue.com

•                Teh, J.S., 1973, ‘Utilisation of n-alkanes by Cladosporium resinae’, mendeley.com

•                University of Sydney, 2004, ‘Drugs From Fungi’, usyd.edu.au

Current C.N.S. Drug Development Issues

Neurones Involved in Alzheimer's Disease

Recent withdrawals from CNS drug development trials by major pharmaceutical companies have raised alarm bells in scientific and mental health circles.

Considering the ageing nature of world populations, and the fact that diseases of the central nervous system constitute 38.35% of the global economic health burden, investment in this area of medicine currently appears to be inadequate. A major reason for this is the excessive time needed to conduct clinical trials of new drugs in this field, the subjective and unpredictable effects of psychological medications and the difficulty in developing treatments that cross the blood-brain barrier.

Moreover, the stigma and lack of informed knowledge associated with psychological disorders such as depression and schizophrenia have further hindered investment in the development of new medications for these particular disorders. The following question therefore arises: should commercial considerations or ethical ones drive pharmaceutical companies?

The Withdrawal of Big Pharma Investment

In February, 2011, GlaxoSmithKline (GSK) announced it would no longer fund the development of psychiatric medicine, while pharmaceutical giant Pfizer is reducing its investment in this area by two billion dollars in the next two years. AstraZeneca (AZ), known for its antipsychotic drug Quetiapine, will also be ending its involvement in the development of future mental health medications.

According to Andrew Witty, CEO of GlaxoSmithKlein, ‘Pain, depression, and anxiety are areas where we believe the probability of success is relatively low, and we think the cost of attaining success is disproportionately high.’ This reflects a general predicament in CNS drug development, where there is an average wait of 13 years between drug discovery and market approval, around two years longer than for other drugs. In addition, only 8.2 percent of potential CNS drugs that begin human testing will reach the marketplace, compared with 15 percent for drugs overall.

Reasons for Uncertainties in CNS Drug Development

In March, 2011, the European College of Neuropsychopharmacology (ECNP) acknowledged these issues, and warned that this poses a particular threat to sufferers of depression, anxiety and addiction. Whereas drugs for other diseases are now being discovered with the help of protein biomarkers, the ECNP points out that there are few current biomarkers for psychiatric disorders. Drugs in this field have instead often been discovered by chance, a luxury few companies are now willing to accommodate.

This problem is exacerbated by the relatively low priority given to mental health by society in general, and the reluctance of industry to recognize, at the very least, the need for newer, improved versions of existing treatments. Moreover, the recent increase in regulatory measures such as the requirement for placebo controlled trials in children and double data entry has made the development of some psychiatric indications almost impossible.

Some success has been achieved in the bid to relax such prohibitive regulations. Pfizer and Johnson and Johnson, for instance, have been successful in convincing U.S. regulators to ease some of the safety restrictions required in clinical trials of their Alzheimer’s drugs. The F.D.A. has also formed the ‘Critical Path Initiative’, which re-assesses how medical products are being developed.

Psychiatric drugs do have one advantage over other CNS medications. While most medications treating mental illnesses such as schizophrenia and depression are small-molecule, lipid soluble compounds capable of crossing the blood-brain barrier, other CNS treatments currently cannot do this.

While scientists have discovered the genes responsible for many of these disorders, including Alzheimer’s disease, Huntington’s disease, and Parkinson’s disease, there is currently no way large enzymes can be delivered to the brain using gene therapy. In the case of Parkinson’s disease, L-Dopa, used to alleviate symptoms, can enter the brain, but provides only temporary relief.

Potential Solutions to the Blood- Brain Barrier Problem

William M. Pardridge has highlighted several areas where researchers are attempting to foil the barrier between the blood and the epithelial cells of the brain. One of these techniques, ‘trans-cranial’ drug delivery, involves the medication being injected or inserted into the brain itself. Problems with this have arisen, however, because diffusion rates from the site of delivery are not rapid enough.

Another possible solution is ‘blood-brain barrier disruption’, where solutes such as mannitol are used to shrink the brain’s endothelial cells, allowing various molecules to pass into the cerebral tissue. Trials to date, however, have revealed serious side effects associated with this treatment.

‘Trans- nasal’ drug delivery to the brain via the nasal cavity has also been considered, but it has been found that this only works for certain small molecules and in limited quantities. Another method, involving the use of molecules such as monoclonal antibodies to act as molecular ‘Trojan horses’, may help to carry genes and large proteins across the blood-brain barrier.

Limited success with this technique has occurred in trials on rats with experimental Parkinson’s disease. In these trials, plasmids containing dopamine-producing genes were first encapsulated in liposomes and then attached to monoclonal antibodies, which transported the genes into the brain. Similar ‘Trojan horse’ molecules are also being tested with nanocapsules containing glial growth factors or neurotransmitters. If successful, these treatments may help to repair damaged nerve cells in the brain and spinal cord.

Possible Answers to Funding and Trial Issues

In terms of the issues associated with CNS research and development, the ‘Coalition Against Major Diseases’ has been formed in the U.S. from drug companies, government agencies and other related organizations as a way of developing new guidelines for clinical trials. In addition, organizations such as the International Society for CNS Clinical Trials and Methodology (ISCTM) has recently convened to discuss the path forward in CNS drug development, with particular reference to recent results in Alzheimer trials.

The 2010 U.S. Health reform Act also provides for the funding of a Patient-Centered Outcomes Research Institute, aimed at improving the effectiveness of drug research, while the 'Critical Path Initiative', mentioned above, is also focussing on streamlining drug trial regulations. Organizations such as these are obviously vital in the light of recent developments in CNS drug research, which suggest that the major priority of pharmaceutical companies will always be their profit margins.

References

•                Goodwin, G. and Nutt, D., ‘ECNP Summit on the future of CNS drug research in Europe 2011’, ecnp.eu

•                Kaitlin, K., and Milne, P., 2011, ‘A Dearth of New Meds’, scientificamerican.com

•                Nierenberg, A., 2010, cnsspectrums.com, ‘The Perfect Storm: CNS Drug Development in Trouble’

•                Pardridge, W., ‘The Blood-Brain Barrier: Bottleneck in Brain Drug Development’, nih.gov

•                Ritter, A., 2011, ‘The Future of CNS DrugDevelopment’, pharmtech.com

Platypus Evolution and the Changing Ideas of Scientists

The Platypus

The platypus, once thought to have evolved after marsupials and placentals, is now generally agreed to belong to the most primitive mammalian order.

The platypus, Ornithorhynchus anatinus, displays unique features that have puzzled evolutionary scientists ever since the first specimen was sent to Britain in 1799. Possessing a combination of reptilian, mammalian and avian characteristics, the platypus and other monotremes are now considered to represent a separate evolutionary branch that arose between primitive reptile-like mammals (therians) and marsupial and eutherian (placental) mammals.

Recent biochemical findings, along with structural and physiological comparisons, have supported this idea. Some recent reports, however, appear to refute the interpretation that the platypus merely shares a common ancestor with all three vertebrate groups. Their inference, instead, is that there is a closer relationship between these organisms.

Similarities Between the Platypus and Reptiles

One of the reasons the platypus has been linked to reptiles, for instance, includes its ability to secrete reptilian-style venom from the spurs on its legs. Molecular studies have shown that this venom, consisting of b-defensin proteins, has a similar composition to snake venom. However, Dr. P.Z. Myers, of the University of Minnesota, argues that this similarity may simply be the result of convergent evolution rather than an indication of a close relationship between monotremes and reptiles.

Similarities Between the Platypus and Birds

The yolk-rich eggs laid by the platypus have also been used to suggest they are somehow part bird in nature. Myers and other scientists such as Dr. Ewan Birney , however, suggest that this may instead be due to a common ancestry between birds and monotremes rather than a close genetic linkage between the two groups. This may also offer an explanation for recently observed similarities between the sex chromosomes of monotremes and those of birds.

An example of this similarity can be found on the fifth X chromosome of the platypus, which contains the bird sex-determination gene DMRT1. The first X chromosome, however, has been found to resemble ancient therian chromosomes. These findings, along with the discovery of mammalian–like milk protein genes in the platypus, help to reinforce the notion that the platypus, although definitely a mammal, perhaps diverged from birds, reptiles and early therian mammals before marsupials and placentals evolved.

The Most Primitive Mammalian Order

Indeed, the fact that the platypus possesses ten sex chromosomes, as opposed to only two in other mammals, suggests its unique evolutionary status. The carbohydrate content in platypus and echidna milk also differs when compared to that of other mammals. Unlike marsupial and placental milk, which predominantly contain either lactose or galactose, monotreme milk has a high fucose content.

These distinctive features, combined with molecular studies made by researchers at the University of Nijmegen in 2005, support the ‘Therian hypothesis’, which maintains that monotremes diverged before the separation of marsupials and placentals. Previous studies of mitochondrial genes by Janke, Xu and Arnason in 1997 had in fact temporarily revived the ‘Marsupionta’ hypothesis, first proposed by William King Gregory in 1947, which held that monotremes and marsupials diverged after placental mammals.

Support for the Therian Hypothesis of Platypus Evolution

Analysis of nuclear genes by the University of Nijmegen scientists, however, has led them to estimate that monotremes diverged from therians between 231 and 217 million years ago, while marsupials separated from placentals as recently as 193-186 million years ago.

Fossil evidence does not clearly support this order of divergence, as the oldest monotreme fossil, Taenolophis trusleru, is estimated to be only 123 million years old, while an opalised tooth of Steropodon, found at Lightning Ridge, New South Wales, has been dated at 110 million years. On the other hand, Sinodelphys szalayi , the earliest known marsupial fossil, has been estimated to be approximately 125 million years old.

Morphological studies, however, do suggest the monotremes are a more primitive group than marsupials and placentals. Reasons for this conclusion include observed differences in mammary glands, dentition and inner ear architecture among the three groups. Perhaps the discovery of older fossil monotremes may help to reinforce this in the future.

References

•                AFP, 2008, 'Neither Fish nor Fowl: Platypus Genome Decoded', afp.google.com

•                Janke, A., Arnason, U., 1997,'The complete mitochondrial genome of the wallaroo (Macropus robustus) and the phylogenetic relationship among Monotremata, Marsupialia, and Eutheria', Proc. Natl. Acad. Sci. USA

•                Medical Research Council, 2008, 'Platypus Genome Unravelled', mrc.ac.uk

•                Myers, P.Z., 2008, 'Interpreting Shared Characateristics: The Platypus Genome', University of Minnesota, nature.com

•                University of California,2011, 'Monotremata: Fossil Record', ucmp.berkeley.edu

•                Van Rheede, et.al, 2005, 'The Platypus in its Place: Nuclear Genes and Indels Confirm the Sister Group Relation of Monotremes and Therians', University of Nijmegen, oxfordjournals.org

The Death Cap Mushroom and its Relatives

The Death Cap Mushroom

The Death Cap mushroom and other members of the genus Amanita contain a group of cyclic compounds capable of causing severe poisoning and even death.

The Death Cap mushroom, Amanita phalloides is reported to have resulted in more than 50% of all mushroom-related deaths in humans. Apart from containing the deadly compound, alpha amatoxin, the relatively innocuous appearance of the Death Cap also appears to be a contributing factor to this alarming statistic.

Two recent fatalities in Australia, for instance, have highlighted the tendency among people of Asian origin to mistake this deadly fungus for the harmless straw mushroom, a culinary delicacy in Asia. Both mushrooms are a yellowish-green in colour and have white gills.

Identifying Death Caps

One method of distinguishing the two mushrooms is to search for remnants of a ‘universal veil’, a thin film that covers the death cap when young. As the mushroom matures, the lower remains of the veil can be observed as a swelling at the base of the fungus.

This swelling, however, may be below ground level, and can therefore often only be detected by digging under the soil. Other indicators can be used to infer the identity of Death Caps, including the fact that they are often found near oak and other European tree species.

This is due to the mycorrhizal association that occurs between the underground filaments of the mushroom and the roots of these plants. In such an association, nutrients pass between the fungus and the plant roots in a mutually beneficial relationship.

Amatoxin and its Effects

Amatoxins, a group of cyclic octapeptides, are responsible for most of the toxic effects of the Death Cap and its relatives. Alpha amatoxin, in particular, targets the liver and kidneys by inactivating the enzyme RNA polymerase II. This inhibits protein synthesis and ultimately leads to cell death.

A sinister feature of alpha amatoxin is that a patient may not experience any symptoms for up to twelve hours after ingesting a poisonous mushroom. Vomiting, cramping and diarrhoea may then be experienced. Following this, the patient may feel as though he or she is recovering, but over the next two or three days the toxin continues to destroy the liver and kidneys and can result in death.

Other Mushrooms Containing Amatoxins

Amatoxins also occur in other members of the Amanita family, including the Destroying Angel (Amanita ocreata), the Fool’s Mushroom (Amanita verna), the European Destroying Angel (Amanita virosa), the Death Angel (Amanita bisporigera) and the East Asian Death Cap (Amanita subjunquilea).

In addition, amatoxins can be found in several related species such as the Deadly Galerina (Galerina autumnalis), the Deadly Parasol (Lepiota josserandii) and the Deadly Conocybe (Conocybe filaris). All of these species are considered to be extremely poisonous, and although injections of milk thistle extract may alleviate symptoms in some cases, there is no effective antidote to amatoxin poisoning.

As a consequence, although many Amanitas and their relatives are edible, mycologists advise avoiding all of them to avoid the risk of incorrectly identifying individual specimens.

The Fly Agaric and the Hallucinogenic Effects of Muscimol

Another member of the Amanaita family, the Fly Agaric (Amanita muscaria), pictured below, can produce severe vomiting and diarrhoea when ingested, along with mildly hallucinogenic effects. Often confused with the ‘magic mushrooms’ of the Psilocybe genus, Fly Agarics resemble the red and white spotted mushrooms of fairytale books.

Unlike the Death Cap, the damaging compound in the Fly Agaric is ibotenic acid, which can be converted in the body to the even more toxic muscimol. Muscimol affects the central nervous system and can result in confusion, convulsions, chills, sweating and delusions. Although these symptoms usually disappear after 24 hours, death from respiratory failure can occur in rare instances.

How to Avoid Amanita Poisoning

Identification is the key to avoiding the more toxic members of the Amanita family. The pale gills, white spores and basal collar, common to all Amanita species, should alert the mushroom collector to any potential culinary disasters.

Galerinas, which also contain deadly amatoxins, have a small, brown cap, tan gills and rusty-brown spores. Possessing a thin stalk, they may be found growing in small groups on rotting 

wood. Together with the Amanitas, they provide a persuasive argument for restricting one’s mushroom collecting to the supermarket.

References

David Fischer’s American Mushrooms

Elpel, T., 2011, Amanitaceae: The Deadly Amanita Family

Kozac, C., 1998, ‘Mushrooms of the San Mateo County Coast

Fly Agaric, James Broad

Determining the Vitamin C Content of Different Liquids

Orange Juice

Vitamin C, a water-soluble ion of ascorbic acid, is essential for normal growth, repair and development in humans. Unlike most other vertebrates, humans and some other primates are incapable of synthesizing their own vitamin C, with the result that it is a necessary requirement in our diet.

Vitamin C, a water-soluble ion of ascorbic acid, is essential for normal growth, repair and development in humans. Unlike most other vertebrates, humans and some other primates are incapable of synthesizing their own vitamin C, with the result that it is a necessary requirement in our diet.

In this activity the relative vitamin C content of a range of juices and drinks will be examined using a technique known as titration. Titration involves adding one reactant to another until an end point, often indicated by a colour change, is reached.

Vitamin C and its Reaction with the TriIodide Ion

In this experiment the end point will occur when a starch solution containing the beverage sample changes from clear to a bluish-black in the presence of iodine solution. The more vitamin C a sample contains, the greater the number of drops of iodine that will be required. This is due to the following reaction between the ascorbate ion and the triIodide (I3-) ion present in iodine solution:

C6H8O6 + I3- + H2O --> C6H6O6 + 3I- + 2H+

As long as the vitamin C (C6H8O6 ) is being oxidized to dehydro ascorbic acid (C6H6O6), the iodine is not available to react with the starch solution in the sample tested. When all of the vitamin C has reacted, however, any further added iodine reacts with the starch to form a blue-black complex, thus indicating the end-point of the reaction.

Vitamin C Comparison – Materials and Teaching Method

Step 1- Making up the Starch Solution

This step should be carried out by the teacher or laboratory technician prior to the lesson. The volume of starch solution prepared should be enough for around 6-7 groups of students.

Materials and Equipment Required:

•                1.5 litres near boiling water

•                6 teaspoons starch

•                Large 2 litre beaker or plastic bottle

Mix the starch with the hot water and pour into a large beaker or 2 litre plastic bottle. Allow the solution to cool.

Step 2 – Testing Selected Beverages With Iodine and Starch Solution

The following materials and equipment are required per group of four students:

•                Around 50ml starch solution

•                Dropper bottle or similar of Lugol’s iodine solution

•                Small beaker or jar

•                Teaspoon

•                Samples of beverages/juices such as different brands of orange juice, lemon juice, soft drinks, apple juice, milk, blackcurrant juice and cranberry juice

Students should be instructed to copy down the following directions, which could be followed by a teacher-led explanation:

•                Add 1 tsp starch solution to 20ml of the selected beverage in a small beaker.

•                Add drops of iodine to the beaker until the liquid remains blue-black in colour.

•                The liquid that takes the most drops to remain blue-black contains the most vitamin C.

A suitable results table should also be drawn up to include the following columns:’ liquid tested’, ‘number of drops of iodine needed to keep the solution a blue-black colour’ and ‘ranking of liquids in order of least vitamin C to most vitamin C’.

Typical results using these quantities range from about 4 drops of iodine in the liquids containing little to no vitamin C (such as soft drinks and milk) to around 20 drops in commercially prepared orange juices.

Vitamin C Comparison – Follow-Up Questions and Activities

The following questions could be written on the board after students write up the experiment and their observations:

1.             What is the scientific name for Vitamin C?

2.             Explain why starch solution is added to the liquids that are tested.

3.             Which of the liquids tested contained the most vitamin C? The least?

4.             Write the equation for the reaction that occurs between the iodine solution and the vitamin C in the liquids tested.

For more advanced students, an actual determination of vitamin C concentration can be conducted using a dissolved vitamin C tablet as a standard solution. Assuming the tablet contains 250 mg vitamin C (read the label to check this), the number of drops of iodine needed to reach the end-point can be compared to the results for other liquids.

If, for instance, 5 drops of iodine are needed to reach the end-point with the vitamin C solution and 10 drops are needed when a 20 ml orange juice sample is tested, the orange juice must contain twice as much vitamin C as the standard, that is, 500 mg per 20 ml. This can then be divided by 20 to arrive at a vitamin C concentration of 25 mg/ml.

References

•                University of Canterbury College of Science, 'Determination of Vitamin C Concentration by Titration', http://www.outreach.canterbury.ac.nz/chemistry/documents/vitaminc_iodine.pdf

•                Scharf, W. and Malerich, C.,Baruch College, New York, 'Determination of Vitamin C of Citrus Juices',http://www.baruch.cuny.edu/wsas/academics/natural_science/chm_1000/vitiamin_C.pdf