strains are delivered to the soil directly surrounding the germinating seed, enhancing
their potential to colonise and compete on the emerging roots. This strategy mimics
the vertical transmission of strains seen by other eukaryotic hosts, such as leafcutter
ants. Plants also release approximately 20% of the carbon that they fix during
photosynthesis into the soil via their roots (Bais et al. 2006; Chaparro et al. 2013).
This root exudate contains a huge variety of carbohydrates, proteins and organic
acids which can all act as substrates or inhibitors for different microbial species (Bais
et al. 2006). For example, secretion of the tricarboxylic acid intermediate, malic acid,
by the plant species Arabidopsis thaliana has been shown to enhance the recruitment
of the bacterial species Bacillus subtilis to roots when plants are infected with a foliar
pathogen (Rudrappa et al. 2008). An increased release of malic acid from the roots
initiates the movement of B. subtilis towards A. thaliana and promotes the subsequent formation of biofilms by this bacterial species on the plant roots (Rudrappa
et al. 2008). In turn, B. subtilis is capable of priming the plant host’s immune system,
reducing the severity of infections (Rudrappa et al. 2008). Understanding the role of
individual root exudates, like malic acid, as well as the genetics underlying their
production and release from roots could enable crop breeders to create new plant
lines that are more effective at attracting protective bacteria (Zhang et al. 2015; Ryan
et al. 2009).
Thus, understanding how organisms interact with protective microbes in natural
systems could provide the inspiration to develop novel methods of disease control
for the benefit of human health, agriculture and conservation. Major challenges
include unpicking the complexity of microbiomes and understanding the factors
that contribute to microbial community variation and stability over time. New
technologies could further enable the exploration of defensive mutualisms involving
underexplored microbes, such as fungi and viruses, which could also open up novel
avenues for disease prevention into the future.
Sarah Worsley
23 Defensive Microbiomes: A Widespread Phenomenon in Nature
507
their potential to colonise and compete on the emerging roots. This strategy mimics
the vertical transmission of strains seen by other eukaryotic hosts, such as leafcutter
ants. Plants also release approximately 20% of the carbon that they fix during
photosynthesis into the soil via their roots (Bais et al. 2006; Chaparro et al. 2013).
This root exudate contains a huge variety of carbohydrates, proteins and organic
acids which can all act as substrates or inhibitors for different microbial species (Bais
et al. 2006). For example, secretion of the tricarboxylic acid intermediate, malic acid,
by the plant species Arabidopsis thaliana has been shown to enhance the recruitment
of the bacterial species Bacillus subtilis to roots when plants are infected with a foliar
pathogen (Rudrappa et al. 2008). An increased release of malic acid from the roots
initiates the movement of B. subtilis towards A. thaliana and promotes the subsequent formation of biofilms by this bacterial species on the plant roots (Rudrappa
et al. 2008). In turn, B. subtilis is capable of priming the plant host’s immune system,
reducing the severity of infections (Rudrappa et al. 2008). Understanding the role of
individual root exudates, like malic acid, as well as the genetics underlying their
production and release from roots could enable crop breeders to create new plant
lines that are more effective at attracting protective bacteria (Zhang et al. 2015; Ryan
et al. 2009).
Thus, understanding how organisms interact with protective microbes in natural
systems could provide the inspiration to develop novel methods of disease control
for the benefit of human health, agriculture and conservation. Major challenges
include unpicking the complexity of microbiomes and understanding the factors
that contribute to microbial community variation and stability over time. New
technologies could further enable the exploration of defensive mutualisms involving
underexplored microbes, such as fungi and viruses, which could also open up novel
avenues for disease prevention into the future.
Sarah Worsley
23 Defensive Microbiomes: A Widespread Phenomenon in Nature
507