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Chaetomium Mould: Health Effects & Exposure Levels

Hello and welcome to this week's episode. Today I'm going to be talking to you about Chaetomium mould. And you're probably thinking why on earth is he talking about this strange sounding fungus? I'm going to be going into some of the history of this microorganism, and some of the health effects, and some of the impacts that this mould has, especially on water damaged building materials. Now, before we begin, I want to give you a bit of an overview of Chaetomium because this is a really special fungus. It was discovered and first written about by a German Professor of Zoology who had a special interest in actually ferns and entomology as well.

However, he first wrote about this fungus that he termed Chaetomium because of its unusual morphology or shape, and so it has a specific helmet-like, plume-like decoration on its fruiting body. And we'll see that in a minute. His name was Gustav Kunze, and he wrote about this in 1817. Now Chaetomium belongs to a family called Chaetomiaceae, and it is the division Ascomycetes. And we're going to be talking about the ascospores that this fungus produces in a second. Now one of the people that I follow on Instagram is called stylish streaking, and their Instagram page (https://www.instagram.com/stylish_streaking/) is quite beautiful for mycologists like myself and others who are interested in science and biology. And here is a picture at a hundred times magnification of Chaetomium down the microscope. And you can immediately see these black or dark colored melanized components, which are the plume of the helmet as Gustav Kunze talked about it. And they are hairy like, and they actually produce the ascus from where the ascospores come from.

And so that is particularly important. So I urge you to follow stylish streaking's Instagram page for more mycology and microscope images and general microbiology. Now we mustn't forget another one of the people that I follow actively on Instagram called chaetomium.queen (https://www.instagram.com/chaetomium.queen/), and she loves fungus probably as much as I do. And she also produces some beautiful micrographs showing in this particular image the perithecia, which are the things which contain or the ascus which contain the spores which are eventually released. And so certainly follow these two Instagram accounts if you want some other excellent reviews of some things that you see in the lab.

Now going to my lab, I have a beautiful pure strain of Chaetomium, and this is how it looks after it's grown for approximately five to seven days on potato dextrose agar. And you can see macroscopically on the surface of the Petri plate, it has a characteristic yellowy white coloring. And this is going to become particularly important when we move through to the next set of images I want to show you.

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And this is from a water damaged building, which I was called in to inspect at the beginning of winter a couple of months ago. And you can see this lovely timber fronted property, you can see that there is a slight slope in the street even in this photograph. And unfortunately what happened to this property is that the drains couldn't cope with the amount of rain water, and they overflowed, flooding inside this property. So the photograph on the left shows the spore trap pump on a tripod collecting spore traps and we're going to look down at some of these spore trap microscope images in the next slide on my Keynote. And you can see the inside of the wall void when some of the lath and plaster wall has been removed, at the base of the timber framing on the internal wall, you can actually see quite active mould growth within the wall.

And this is quite similar to the Petri plate culture from my own lab. But what happens when we take a spore trap inside this wall void? Well you can immediately see on the right hand side a whole bunch of spores. And right in the middle of the image I have shown you the Chaetomium ascospores, and these Chaetomium ascospores are usually described as being lemon shaped or football shaped. You can also see a whole bunch of other chains of Penicillium and Aspergillus spores as well. But you can also see a great big blue skin flake as well. Now if I take and move my slide on the microscope, I can find more clusters of Chaetomium, and this is really what I wanted to highlight because you need to see and appreciate that these Chaetomium spores are quite large relative to Aspergillus and Penicillium, but there's also an abundance of hyphal fragments.

These are the mycelium or the hyphae that ramify out of a spore after it germinates. That's how they get bigger over time. And so because the Chaetomium has these hairy like, plume appendages, this also gets broken down and we find a lot of these in spore trap samples, especially from heavily contaminated buildings. And I wanted to show this to you because the microscope images make this very real. Now what is Chaetomium mould? Well, where do you find it? It's found in the air, on soil and especially on plant material. And it is found in these locations because it produces a range of extracellular enzymes that allow it to break down the substrate and use it as a food source or a carbon source. And so it produces cellulase enzymes as well as others. And these preferentially like [eating] cellulose, and in the literature, the most common Chaetomium mould Species is usually referred to as Chaetomium globosum.

But there are many, many more. It loves cellulose, it degrades it and it can grow actually at quite high temperature. It produces a range of mycotoxins in three main classes. And it produces over 500 active metabolites, some of which are very useful and important in medicine and increasingly in pharmaceutical manufacture. And definitely in research. We'll be talking about some of these positive aspects of Chaetomium towards the end of this live stream. Now if I go to my dictionary of fungi, and I go to Chaetomium, I'm going to discover of course when it was first written about and appeared in the taxonomic literature, but more importantly, it's going to tell me that there are 95 known Species of Chaetomium. Although newer molecular methods put the number of Chaetomium sp. possibly up to 400, so there are a lot of strain variations out there probably because this fungus is adapted to grow at quite high temperatures.

Now it is definitely known to be an inhalant allergen. The ascospores, as I said, have a typical morphology of a lemon shape and they're brown in color. They're termed a melanized fungus. And again, this means that they are usually very adapted to withstanding the sunlight potential degradation from UV. Now what are some of the health effects of Chaetomium? Well, it is strongly linked to asthma and rhinitis, mainly due to the mycotoxins that are produced. And I should add too that emerging literatures on Chaetomium shows that a lot of the mycotoxins are exuded into this sticky mass. Now the perithecia of Chaetomium is often known to be sticky to retain the spore, but this is also termed guttation droplets. And think of these as droplets that are produced by the growing fungus in its natural habitat, whatever has high cellulose content.

And these then aerosolize and volatilize the mycotoxins inside, and these are the microbial volatile organic compounds. And eventually when the building dries out or if structural drying occurs with inadequate containment, there can be widespread dispersion within the property of not only the ascospores, but also the hyphal fragments and the 'plumes' as Professor Kunze talked about them throughout the property, and they're allergenic. Now wheeze and again rhinitis have been strongly correlated with Chaetomium and a wonderful paper by Vesper appeared in the literature talking about ERMI, which is the environmental relative mouldiness index. And there are 36 different water damage fungi indexed by the ERMI. And guess what? In homes of asthmatics, Chaetomium is one of the dominant fungi, which shows a huge peak in the ERMI. And that makes sense because we see this using classical microbiology and classical air spore techniques as well. Now I should also add that Chaetomium infections, the impact of this have largely been ignored in the literature, but increasingly, certainly due to the fact that in the Middle East there is an abundance of hot, arid deserts.

There has been an increasing amount of literature talking about Chaetomium eye infections, keratitis and also Chaetomium being linked to traumatic war injury wounds as well. So you don't just have to be on the battlefield to suffer from Chaetomium contamination if you are immunocompromised. Certainly those individuals undergoing chemotherapy or often bone marrow transplants, brain abscesses due to Chaetomium have definitely been recorded and that's a huge issue for any non-immunocompetent person. Now what about the relationship between Chaetomium and sick building syndrome? Well, we know sick building syndromes are these usually closed building structures where people spend a lot of time and they end up having adverse health symptoms when they spend time in those buildings, and these symptoms tend to diminish outside of the building.

Well this happens because of tight building practices, a lack of ventilation and the fact that fungi like Chaetomium love cellulose based building materials. And where are these cellulose based building materials? Well they are in particle board, they are on ceiling tiles and especially on plasterboard, especially if this plasterboard gets wet. And when does plasterboard get wet? Well not just after floods, not just after plumbing leaks, but if the property is particularly tightly built it may not ventilate properly and you may get a build up of condensation inside. Or worse, the cladding render external to the apartment may admit moisture or there may be problems with the wall wrap or other building defects introduced during construction, which impact on these cellulose based building materials. Now Chaetomium can be found growing also on stone and brick work. And of course I've already mentioned that it loves fiber-based materials and the adhesives used.

We're going to be talking about the fact that it loves wallpaper as well. I wanted to pull up a couple of plates from a paper, which the DOI number is linked at the bottom of this slide. And the one on the left hand side shows Chaetomium the third plate down, image down, and it shows it growing on cement. Now that's not a good thing because cement internal wall is often used increasingly in lightweight building construction and in tilt slab construction. So Chaetomium can definitely colonize and grow very happily on cement. Similarly, the fly-ash geopolymer used in gypsum plasterboard again, you can see the third row down in the column on the right hand side. You can see after four weeks Chaetomium colonizing the surface of this material and under the microscope they can see mould mycelium with the perithecia and also the ascospores.

Now what happens when it is deliberately inoculated onto samples of plywood and that plywood has then had a wallpaper attached to it? And again, you can see that after four weeks from an initial wetting event, the Chaetomium grows all over these typical building materials which are considered 'green building materials'. Now let's drill into the literature and look at what the growth rate or colonization ability is of Chaetomium onto typical building elements such as chipboard, plywood, gypsum, Masonite and MDF. And on the left hand top corner you can see an example of plywood being a composite manufactured timber. Now Chaetomium loves growing on chipboard and plywood, and growth is extremely rapid and dense after four weeks. So you don't want chipboard being used as the substrate in your bathroom or on suite bathroom or even in your kitchen area. And if you are having your home newly constructed, ask about the levels of chipboard and why they're being used.

And again, you can see the bottom left hand corner, a typical example of the gypsum wallboard or plasterboard as we call it here in Australia, and the growth on gypsum based materials is strong as well. And we can see on the Table what the colonization ability is. And again, if you reference the paper, which is given in the show notes for this live stream at the bottom, you'll be able to look at some of these building specific elements. And their bio deterioration [ability] caused by Chaetomium. Now MDF and Masonite are resistant to Chaetomium and that's a really good thing. So that's something that also should be considered when you're specifying the internal cabinetry as well and wall and floor finishes as well. Because some building materials are known to be much more resistant to fungal attack. And why wouldn't you use those over some of these other materials?

Now I should also say, how are you going to affect remediation if the building containing plywood and plasterboard does become wet? Well, going back to a ASTM IICRC S500, S520 and R520 Standard and Guideline, we already know that source removal of water damage building elements is the number one way to address mould remediation and water damage in the built environment. But in many cases remediators will look at chemical methods to disinfect the surfaces. And so the academic literature shows that Chaetomium is resistant to borax. That means it's resistant to Boracol. So if any remediator tells you that they are going to apply Boracol, which is a wood preservative pretreatment for the timber, not as a solution to treat mould after the fact, after it's been installed. Take heed of the fact that the academic literature already demonstrates that there is good evidence that this is not going to be effective in significantly reducing the viability of Chaetomium growth on timber or plasterboard.

However, wetting agents, those used in the cleaning product arena are shown to be very useful in removing Chaetomium mycelium, probably because these spores are quite large and they're more easily removed with physical removal methods. So that's what the academic literature says about this. And more recently bio deterioration of books and paper is an increasing topic that is published on. And museum collections are particularly susceptible to bio deterioration from microbes and they have discovered that UVGI, which stands for ultraviolet germicidal irradiation, at 254 nanometers is particularly effective at killing and reducing the growth rate of Chaetomium and other moulds. But it is again dose dependent, the distance from the UV light source. And the objects to be remediated is very important as well as the dwell time or how long the UVGI comes in contact with the material, and other factors such as the thickness of the material.

So the thinner the cellulase based paper containing objects are like tissue paper, that's going to be much easier to apply UVGI light to, rather than more dense hollow book contamination problems. Now, what are the acceptable levels of Chaetomium? Well, there's lots of conjecture out there about no, there aren't any published standards to, yes, there are lots of published standards. To there are lots and lots of guidelines which tell you what is considered low, medium, and high risk for the amount of mould spores in the air, especially inside buildings. And if we look at the World Health Organization guidelines, we quickly find out that from epidemiological studies, looking at things like how people have cough and wheeze and respiratory problems, there's lots and lots of literature which shows that we want the levels of mould spores to be about under 1000 colony forming units per cubic meter of air.

But importantly, the contribution of Chaetomium moulds to either the viable mould or the spores inside should be, as you can see from the table, they come under the other moulds category. And we really want these under 500 CFU per cubic meter. And so bear that in mind when you're interpreting lab reports on water damaged buildings. You want to find the line that talks about Chaetomium and you want to find out what the total numbers were for that particular fungus because as we know from the ERMI and also from other academic literature, that this is one of the really significant fungi inside buildings after water damage, and that caused asthma. Now what are some of the mycotoxins? Well, there are three main classes and I'm not going to get into a chemistry lesson about the mycotoxins from Chaetomium, but just bear in mind that there are three of them.

They are called Chaetoglobosin, Chaetoviridin and Chaetomugilin, and they have all different effects on various different cell lines, which you can drill into the academic literature to find out all about these mycotoxins. But just be aware that they're present. They are dispersed in the guttation droplets. They are inside the mould spores and the hyphal fragments, and of course all the micron and some micron dusts that can be generated in water damage building environments and during the remediation process as well, which can't be overlooked as well. Hence why proper containment and use of HEPA air extractors is fundamental.

Now is Chaetomium common? Well in mould affected buildings in Denmark, Chaetomium was discovered in 16% of samples taken from typical elements like linoleum inside cupboards and sampled from concrete. So this fungus is all around naturally, not just after water damage but usually in very low levels.

Of course with water damage it's going to reproduce on these cellulose containing materials. In the USA, 55 to 65% of plasterboard is contaminated with Chaetomium, and emerging literature is showing that a lot of these fungi are introduced during the manufacturing process of the plasterboard. And you can imagine the devastating impact that this has just on the whole supply chain of building elements into the construction industry. We will get to that in another live stream. Now do you know what's unique? Morphology. These flask shaped fruiting bodies contain all the spores which are then ejected at the right time of its life cycle, and then these grow or are dispersed within the building. But the fruiting bodies, those dark perithecia like the dark. So often you find Chaetomium growing in crevices and cracks and interstitial spaces, and of course hidden behind wall voids. So often they're missed during air sampling and if less destructive testing is undertaken [or isn't performed].

And this again is an emerging phenomena that we're seeing this written about in the literature, that Chaetomium is underestimated in terms of its indoor air quality impacts. And it is quite slow to become airborne because either the built structure needs to dry out so that these spores can be released because they're heavier than your typical Aspergillus and Penicillium spores, or they're already trapped on the sticky resin-like exudates that this fungus produces. Now it's not all bad though. Chaetomium loves biodiesel waste. So it is showing huge potential in biotechnology because it can grow on glycerol, and it makes something called an extracellular polysaccharide. Now this is a carbohydrate and it can be grown in large quantities via fermentation. And these extracellular polysaccharides show potent anticancer ability, and some of the earlier literature showed that they can interfere significantly with lung cancer cell line growth.

Now scientists have also discovered that the purified extract of the extracellular matter from the fermentation, when this is purified, it can cause cell death or apoptosis to a whole range of other cancer cell lines, but it's concentration dependent. And it can reduce cell viability, but really between 39 and 49%. Now that's really quite significant. So this is a benefit of the fungus. And the polysaccharide isn't just useful for its anticancer properties. It also kills bacteria. And so there's some lovely research showing the use of this fungus derived polysaccharide for killing common bacteria like E. coli and Staphylococcus aureus. And the Chaetoglobosin that is the mycotoxin has some good potential against ovarian cancer cell lines. As well, the fungal extract has shown to be very effective against another fungus. So it's antibacterial and anti-fungal against Exserohilum, which often colonizes the nasal and sinus passages in immunocompromised persons. And it would be fantastic if a polysaccharide from another fungus was discovered to be useful [for this purpose].

And so in closing, I just want to recap that Chaetomium loves cellulose. So any green building materials that become wet that have a high cellulose content, you can be pretty confident that they're going to grow Chaetomium. It produces these lovely lemon-shaped, melanin colored ascospores, which often remain trapped in these guttation droplets. Eventually they become dispersed into the air. They like growing in dark crevices and eventually the spores become liberated. They produce a range of different mycotoxins. They can grow on concrete, plasterboard. Things like MDF and Masonite don't show strong growth, but plywood definitely does and plasterboard. You can kill them with ultraviolet light, and detergent based cleaning materials may be much more effective than your classic boron based anti-fungal treatments. And they show significant potential in anticancer medicine, antibacterial applications, antifungal applications, and a whole range of emerging biotechnological and biodiesel uses. So Chaetomium can be beneficial as well as pathogenic to you and your family. In any case, thanks for watching this live stream. Post your comments below. I'll be sure to answer them. And next week I'll be going into further detail about other aspects of fungal biology. Bye for now. Enjoy your week.

Dr. Cameron Jones

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REFERENCES:

1. Fungicidal Effects of Ultraviolet Light(254 nm)Irradiation on Contaminated Museum Packing and Storing Materials. (2018). Biocontrol Science. 23(4):177-186. https://doi.org/10.4265/bio.23.177

2. Anticancer Activity of Polysaccharides Produced from Glycerol and Crude Glycerol by an Endophytic Fungus Chaetomium globosum CGMCC 6882 on Human Lung Cancer A549 Cells. (2018). Biomolecules. 8(4):171. doi: 10.3390/biom8040171

3. Antibacterial activity of a polysaccharide produced from Chaetomium globosum CGMCC 6882. International Journal of Biological Macromolecules. https://doi.org/10.1016/j.ijbiomac.2018.11.248

4. Quantitative PCR analysis of molds in the dust from homes of asthmatic children in North Carolina. (2007). Journal of Environmental Monitoring. 9: 826-830. https://pubs.rsc.org/en/content/articlelanding/2007/em/b704359g/unauth#!divAbstract

5. Growth and mycotoxin production by Chaetomium globosum. Mycopathologia. (2007). 164(1): 49-56. https://doi.org/10.1007/s11046-007-9023-x

6. Diversity and taxonomy of Chaetomium and chaetomium-like fungi from indoor environments. (2016). Studies in Mycology 84(C). https://www.sciencedirect.com/science/article/pii/S0166061616300197

7. Comparative characteristics of binders resistance for building composites to mold fungi. MATEC Web of Conferences 196, 04050 (2018). https://doi.org/10.1051/matecconf/201819604050. https://www.matec-conferences.org/articles/matecconf/pdf/2018/55/matecconf_rsp2018_04050.pdf

8. Penicillium expansum strain isolated from indoor building material was able to grow on gypsum board and emitted guttation droplets containing chaetoglobosins and communesins A, B and D.(2019). J Appl Microbiol. 2019 Jul 4. doi: 10.1111/jam.14369.

9. Indoor Chaetomium-like isolates: resistance to chemicals, fluorescence and mycotoxin production. Sisäilmastoseminaari 2017. http://publicatio.bibl.u-szeged.hu/12495/1/S%C3%ADsailmastoseminaari.pdf

10. Endophytic fungus strain 28 isolated from Houttuynia cordata possesses wide-spectrum antifungal activity. (2016). DOI:10.1016/j.bjm.2016.01.006

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