Fungal Competition Notes

Fungal Competition

• Fungal competition includes fungal-fungal and fungal-bacterial interactions.

Organisms Interacting with Fungi

• Fungi interact with a variety of organisms:
  • Plants
  • Animals
  • Bacteria
  • Other fungi
• These interactions can manifest as:
  • Endophytes
  • Pathogens
  • Lichens & Mycorrhizas
  • Facilitators
  • Grazers
  • Carriage and dispersal
  • Phagy
  • Endosymbionts
  • Helper bacteria
  • Inter- and Intra-specific interactions

Fungal Lifestyle

• Most basidiomycetes spend the majority of their lives as vegetative mycelium.

Fungi in the Environment

• Fungi rarely exist in isolation and compete with other organisms when they encounter them. Example: $H. fasciculare$ vs $P. velutina$.

Mechanisms of Competition

• Competition occurs when one organism inhibits another, potentially through allelopathy.
• Two main types of competition:
  • Interference: Direct inhibition.
  • Exploitation: One organism utilizes a resource, reducing its availability to others.

Competition for Resources

• For heterotrophic, mycelial, higher fungi colonizing solid organic resources (e.g., leaf and wood litter), competition for nutrients occurs through competition for space/territory.
• Interference and exploitation competition are often intertwined.

Types of Mycelial Interactions

• Interspecific mycelial interactions include:
  • Competition for nutrients
  • Competition for space, often involving combat

Fungal Competition in Organic Resources

• Primary resource capture (r-selected):
  • Good dispersal
  • Rapid spore germination
  • Rapid mycelial extension
  • Ability to utilize organic compounds available in uncolonized resources
• Secondary resource capture (combat):
  • Defending territory
  • Gaining occupied territory
  • Depends upon antagonistic mechanisms

Battle Fronts

• Interaction zone lines can be observed in wood.

Modes of Attack and Defence

• Antagonism at a distance
• Hyphal interference
• Mycoparasitism
• Gross mycelial contact

Types of Mycoparasitism

• Contact necrotroph: Parasite contacts the host hyphae, but does not penetrate. Host cytoplasm degenerates, and lysis may occur.
• Invasive necrotroph: Parasite penetrates and enters the host, leading to rapid degeneration of host cytoplasm and hyphal lysis.
• Intracellular biotroph: Entire thallus of the parasite enters the hypha of the host; host cell remains functional.
• Haustorial biotroph: A short haustorial branch from a parasite hypha penetrates the host; host cell remains functional.
• Fusion biotroph: Host and parasite are in intimate contact; micropore(s) form between the adpressed host and parasite hyphae, or from a short penetrative branch from the parasite hypha; host cell remains functional.

Examples of Mycoparasites

• $Spinellus fusiger$ on $Mycena$ sp.
• $Asterophora lycoperdoides$ on $Russula nigricans$
• $Pseudoboletus parasiticus$ on $Scleroderma citrinum$
• $Gomphideus roseus$ on $Suillus bovinus$
• $Tremella mesenterica$ on $S. hirsutum$
• $Asterophora parasitica$ on $Russula nigricans$

Morphological Responses During Antagonism

• Fungi exhibit morphological changes during antagonistic interactions.

Dynamics of Battles

• Fungal battles are dynamic, and changes occur with time.

Gene Expression Changes During Interactions

• Observed via Microarray analysis - ESTs changing in expression included genes involved in:
  • Overall biosynthetic processes
  • Ribosomal proteins
  • Metabolism and proteolysis
  • Membrane-associated functions
  • Cytoskeleton-associated genes
  • Cell division
  • Nucleic acid binding and transcription-related ESTs
  • Stress/protective responses
  • Signalling processes

Enzyme Activity and ROS

• Metabolic enzymes
• Cell-wall degrading
• Generation of ROS (Reactive Oxygen Species) – NADPH oxidases, laccase, peroxidases
• Extracellular detoxification and production of melanins – laccase, peroxidases
• Protection against ROS – catalase, DNA repair proteins

Secondary Metabolite Production

• Production of VOCs (Volatile Organic Compounds) and DOCs (Dissolved Organic Compounds).

Outcomes of Interactions

• Deadlock
• Replacement
• Partial replacement
• Reciprocal replacement

Change in Territory

• Time before replacement begins and speed of replacement depend on relative combative abilities.

Hierarchy of Combative Ability

• A hierarchy exists among fungi in terms of combative ability.
• Example: $P. velutina$, $H. fasciculare$, $L. betulina$ and $P. hydrophyllum$ > $P. impudicus$ and $M. platyphylla$ > $T. versicolor$ and $S. hirsutum$ > $A. gallica$, $L. turgidum$ and $X. hypoxylon$

Factors Affecting Outcome of Interactions

• Venue: soil, wood, agar
• Microclimate: temperature, moisture, gaseous regime
• Quantity and quality of resources: larger often prevails
• Presence of other microorganisms
• Grazing by invertebrates

Environmental Effects on Victors

• Victors vary depending on environment.
• Examples:
  • $T. versicolor$ v $D. concentrica$
    • 30% $CO<em>2$, 20% $O</em>2$
    • -1.3MPa
    • 20°C
  • $H. fasciculare$ v $P. radiata$
    • 30% $CO<em>2$, 5% $O</em>2$
    • -3.1MPa
    • 25°C

Grazing Affects Outcome of Interactions

• Grazing by collembola, nematodes, and woolice affects the outcome of interactions.
• Examples:
  • Ungrazed vs. grazed scenarios involving $H. fasciculare$, $R. bicolor$, and $P. velutina$

Multi-Species Interactions

• Three-way or more interactions are the norm in the natural environment.

Intransitive Interactions

• Intransitive interactions occur when A>B, B>C, but C>A. *Network diagram includes examples of:
  • Phallus impudicus
  • Megacollybia platyphylla
  • Hypholoma fasciculare
  • Phanerochaete velutina
  • Bjerkandera adusta
  • Stereum hirsutum
  • Psathyrella hydrophilum
  • Trametes versicolor
  • Stereum hirsutum
  • Vuilleminia comedens
  • Biscogniauxia sp.
  • Hypoxylon fragiforme

Relative Location Affects Outcome

• Relative location of interacting fungi influences the outcome of interactions.

Complex 3D Model Communities

• Fungal communities can be modeled in complex 3D structures.

Consequences of Fungal Fights

• Fungal fights alter:
  • Gene expression
  • VOCs
  • Enzyme activity
  • Mycelial search for new food supplies
  • Nutrient distribution and release
  • Decay rate / $CO_2$ evolution
  • Community structure, hence decay rate

Antagonistic Interactions

• Antagonistic interactions occur among fungi and other microbes.

Fungal-Bacterial Interactions

• Includes:
  • Fungal consumption of fixed N
  • Bacterial consumption of fungal enzyme products
  • Fungal lysis of bacterium
  • Bacterial lysis of fungus

Negative Interactions Between Fungi and Bacteria

• Some fungi are bacterivores, e.g., $Agaricus bisporus$ utilizes bacteria as a major source of N.
• Fungi that lyse bacteria appear to be attracted to bacterial colonies.
• Some bacteria are mycophages, e.g., $Streptomyces$ strains.
• Non-filamentous bacteria can also attack hyphae: $Collimonas$ strains attack hyphal tips; myxobacteria destroy yeasts and penetrate hyphae of soil fungi.

Bacterial Parasitism of Cultivated Mushrooms

• Bacterial parasitism of cultivated mushroom species has been known for almost 100 years.
• Examples:
  • Brown blotch disease of $Agaricus bisporus$, caused by $Pseudomonas tolaasii$
  • Soft rot of the cap and stipe, caused by $Burkholderia gladioli$ pv. $agricicola$ and $Janthinobacterium agaricidamnosum$
  • Mummy disease – $Pseudomonas$ species have been implicated

Fungal-Bacterial Competition

• Compete for simple carbon compounds
• Compete for products of extracellular digestion of lignocellulolysis
• Fungi can also use bacterial products

Mycostasis (Fungistasis)

• The majority of fungal spores that land on soil fail to germinate.
• Correlated with microbial activity.
• Alleviated if soil is sterilized.
• Alleviated if easily available energy sources are added.
• Therefore: effect is mediated by soil microbes:
  • Rapidly sequestering any soluble nutrients
  • Producing inhibitory metabolites
• Advantage: preventing germination until local microbial activity is reduced and substrates are available.

Viruses of Fungi

• Intracellular within the fungus
• Transmitted between hosts by cell-to-cell contact/fusion
• Can be disseminated within spores
• No natural vectors are known
• Effects: most cause few or no obvious symptoms; In plant pathogenic fungi, some lead to altered virulence

Negative Interactions Between Fungi and Protists

• Mycophages: Several testate amoeba, such as $Geococcus vulgaris$, fasten to the walls of fungal spores and hyphae and suck out the contents.
• In rumen: ciliate protozoa ingest $Neocallimastigomycota$ zoospores.
• Plasmodia of myxomycetes consume fungi.

Fungi and Amoeba Interactions

• $Dactylella passalopaga$ produces bulbous outgrowths which trap testate amoeba.
• Zoopagales (zygomycete) adhere to amoeba and feed on them.
• A dark septate root endophyte can control clubroot disease of Brassicacae.
• Some fungi colonize the fruit bodies of myxomycetes.