Tuesday, 29 November 2011

Aspergillus and Bacteria Team Up

Bacteria and fungi have often been traditionally suspected as being foes competing for the same food resources in their natural environment. Many antibiotics (e.g. Penicillin) for example are antibacterial substances synthesised by fungi, thought by many to be one way that fungi can beat their bacterial competitors to a meal.

It has now been suggested that that impression is too simplistic. Ingham et .al. has shown that Aspergillus fumigatus, a fungus important for the degradation of dead plant material (e.g. compost heaps) and which has an important impact on human health (e.g. aspergillosis), seems to work closely with a highly motile bacterium Paenibacillus vortex.

Paenibacillus is very able at moving over solid surfaces and forms characteristic swarms

Paenibacillus is very adept at moving but cannot travel across gaps, whereas Aspergillus is more than capable of bridging gaps. Aspergillus tends to use up all available nutrients in one place and then stop and sporulate. It then requires 'help' to transport its spores to another substrate and the best known of these is via air currents but that may not be available and is a wasteful process with many spores landing in areas where growth is not possible.

Aspergillus growing across gaps
Paenibacillus is demonstrated in this paper to be able to transport Aspergillus fumigatus spores from locations where there are few nutrients available to new areas where nutrients are plentiful, and where there are antibiotics present which will inhibit the growth of competing bacteria. The speed of movement is around 8cm per hour. 
  • Paenibacillus will not do this for other particles similar in size to Aspergillus spores.
  • Other swarming bacteria where tested and were found not to transport A. fumigatus spores.
  • Paenibacillus will not transport the spores of other fungi similar to A. fumigatus as efficiently as they do for A. fumigatus.
P. vortex flagella 'gripping' A. fumigatus spores during transport
It seems that we are left with a conclusion that P. vortex and A. fumigatus have developed a cooperative symbiotic relationship whereby the efficient spread of each is reliant on the other and each expends energy on behalf of the other when there is no apparent direct advantage for itself.

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