Thursday, August 6, 2015

Juicing for fungi and oomycetes

Many fungi and oomycetes (fungus-like microbes often called water moulds) like to eat plants. Unfortunately for us, these plants basically include all of the ones we grow for food. Thus another front of the human-microbe war rages ever onward. In an effort to gain an edge against our dastardly eukaryotic cousins, scientists have compiled a whole lot of data on how plant-eating fungi and oomycetes go about their business. To grow these microorganisms in the laboratory, researchers have taken the quite reasonable approach of making appealing meals out of liquids extracted from plants. Popular plants used to grow and study fungi and oomycetes are corn, barley, and potatoes.

Here are some others that are perhaps not as well known:

Pea broth is essentially the outcome of the worst pea soup recipe you can imagine: nuke some frozen peas at 121°C for 15 minutes, strain the resulting sludge, then nuke it again to sterilize. We've used pea broth to grow oomycetes of the genus Phytophthora, which are responsible for the destruction of a wide range of plants including potatoes, oak trees, and cucumbers. A pea-based medium has also been used to grow the delightfully named fungus Botryotinia fuckeliana, which causes gray mold on a bunch of plants including peas. Karl Wilhelm Gottlieb Leopold Fuckel was a 19th century German botanist who focused his studies on fungi.

Phytophthora rotting out a potato (Source)

V8 vegetable juice is enjoyed by several fungi and oomycetes, including Thielaviopsis basicola (responsible for a plethora of plant diseases including a black carrot rot) and members of the genera Phytophthora (aforementioned destroyers of many plants) and Pythium (commonly found in soil and particularly good at killing seedlings). The blend of tomatoes, carrots, celery, beets, parsley, lettuce, watercress and spinach provides a convenient mixture that can support the growth of fungi capable of infecting plants or people. One thing V8 juice does particularly well is convince fungi they should make offspring via a process known as sporulation. Getting fungi to make spores is sometimes super annoying, but is necessary in order to understand how they spread between hosts (by producing spores that can be carried by wind/animal vectors/etc.) and acquire new abilities through sex. In particular, V8 juice has been used to study the sexual development of Cryptococcus neoformans, a fungus that causes disease in humans but also tends to live in old trees.

Oomycetes (Phytophthora and Pythium) can also be grown using straight up tomato juice (prepared fresh) or liquid squeezed from pulverized soybeans. This is useful since V8 juice can potentially be difficult to acquire in certain parts of the world. It also can address the issue of using a commercial product that could potentially be altered by the manufacturer unbeknownst to researchers who use it.

Phytophthora infecting a rhododendron leaf (Source)

Orange serum (the result of heating up orange juice and then filtering it to remove fruit particles and precipitates) provides a good growth medium for fungi that spoil citrus fruits (e.g. Penicillium digitatum). This stuff has also been used to grow the following:
  • Fungi living in association with Lophelia pertusa, a deep-sea cold-water coral notable for its ability to form large reef structures that serve as biodiversity hotspots in deep waters
  • Apparently harmless fungi living inside Norway spruce needles while they are still green and attached to a tree
  • Gremmeniella abietina, responsible for Scleroderris canker on coniferous trees

Anemones hanging out with Lophelia pertusa (white stuff) in the Gulf of Mexico (Source)

The liquid left over after boiling asparagus spears in water can support the growth of Fusarium oxysporum and Fusarium proliferatum, toxin-producing fungi capable of eating the roots and stalks of asparagus. I came across a paper from 1903 that mentioned using asparagus juice to grow species of Fusarium causing bulb rot in flowering plants such as crocuses. The juice has also been used to grow Cryptomyces pleomorpha, a mysterious fungus (it likely encompasses several bacteria and fungi thought to be different forms of the same organism) isolated from the blood of a cancer patient and briefly suspected to be carcinogenic.

It's not technically juice, but pureed carrots can be used to grow the fungi Gibberella fujikuroi (consumer of several plants including rice and corn, can also cause opportunistic infections in animals) and Gibberella zeae (damages wheat, barley, and other grains). Both species produce toxins (e.g. fumonisins and gibberellins) so even if infected plants can be harvested they're often not usable.

Gibberella zeae munching on some corn (Source)

Aschersonia placenta, a fungus that infects scale insects capable of spoiling tropical fruits such as durian and guava, grows particularly well on mushed up pumpkin. Citric acid-producing Aspergillus niger also likes to eat pumpkin juice, although optimal acid production is achieved when the fungus is fed a combination of pumpkin and molasses.


References

Beregoff-Gillow P. 1936. Cryptomyces pleomorpha has no etiological relation to carcinoma. Canadian Medical Association Journal 34(6):634-636. [Full text]

Galkiewicz JP, Stellick SH, Gray MA, Kellogg CA. 2012. Cultured fungal associates from the deep-sea coral Lophelia pertusa. Deep Sea Research Part I: Oceanographic Research Papers 67:12-20.

Gruner OC. 1935. Cryptomyces pleomorpha: A new organism isolated from the blood of a case of metastasized carcinoma of the breast. Canadian Medical Association Journal 32(1):15-19. [Full text]

Guo LY, Ko WH. 1993. Two widely accessible media for growth and reproduction of Phytophthora and Pythium species. Applied and Environmental Microbiology 59(7):2323-2325. [Full text]

Hilber UW, Hilber-Bodmer M. 1998. Genetic basis and monitoring of resistance of Botryotinia fuckeliana to anilinopyrimidines. Plant Disease 82(5):496-500. [Full text]

Ibrahim YB, Lim TK, Tang MK, Teng HM. 1993. Influence of temperature, pH and selected growth media on germination, growth and sporulation of Aschersonia placenta and Hypocrella raciborskii. Biocontrol Science and Technology 3(1):55-61.

Kent CR, Ortiz-Bermúdez P, Giles SS, Hull CM. 2008. Formulation of a defined V8 medium for induction of sexual development of Cryptococcus neoformans. Applied and Environmental Microbiology 74(20):6248-6253. [Full text]

Klittich C, Leslie JF. 1998. Nitrate reduction mutants of Fusarium moniliforme (Gibberella fujikuroi). Genetics 118(3):417-423. [Full text]

Majumder L, Khalil I, Munshi MK, Alam K, Rashid H, Begum R, Alam N. 2010. Citric acid production by Aspergillus niger using molasses and pumpkin as substrates. European Journal of Biological Sciences 2(1):01-08. [Full text]


Metcalf H. 1903. Cultural studies of a nematode associated with plant decay. Transactions of the American Microscopical Society 24:89-102. [First page]

Miller PM. 1955. V-8 juice agar as a general-purpose medium for fungi and bacteria. Phytopathology 45:461-462.

Müller MM, Valjakka R, Suokko A, Hantula J. 2001. Diversity of endophytic fungi of single Norway spruce needles and their role as pioneer decomposers. Molecular Ecology 10(7):1801-1810.

Ristaino JB, Madritch M, Trout CL, Parra G. 1998. PCR amplification of ribosomal DNA for species identification in the plant pathogen genus Phytophthora. Applied and Environmental Microbiology 64(3):948-954. [Full text]

Trail F, Xu H, Loranger R, Gadoury D. 2002. Physiological and environmental aspects of ascospore discharge in Gibberella zeae (anamorph Fusarium graminearum). Mycologia 94(2):181-189. [Full text]

Tuomivirta TT, Hantula J. 2005. Three unrelated viruses occur in a single isolate of Gremmeniella abietina var. abietina type A. Virus Research 110(1-2):31-39.

Waśkiewicz A, Irzykowska L, Karolewski Z, Bocianowski J, Goliński P, Weber Z. 2009. Mycotoxins biosynthesis by Fusarium oxysporum and F. proliferatum isolates of asparagus origin. Journal of Plant Protection Research 49(4):369-372.

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