Endophytic bacteria: co-existence and chemical warfare

Endophytic bacteria (EB) live within plant tissues without causing signs of disease. They may be horizontally or vertically
transmitted and can be considered to sit at the benign end of the spectrum between mutualists and pathogens. EB have
been reported to confer benefits to the host plant in terms of growth promotion and protection from pests and pathogens. In
order to maintain an endophytic lifestyle these bacteria must both interact with the host plant and other bacterial and fungal
endophytes without triggering defence mechanisms (co-operation), yet assist the plant in identifying and attacking
pathogens (chemical warfare). These ancient relationships are not only fascinating from an evolutionary perspective but
are potentially of great value for both sustainable crop production and as novel sources of bioactive natural products
including antimicrobials and antifungals.
In the past it was postulated that the states of symbiosis and pathogenesis were readily interchangeable, largely dependent
on environmental conditions. However, evidence from genomic studies do not support this, as symbionts tend to
demonstrate reduced genomes, lacking the necessary components required for pathogenesis. To date the majority of data
is from animal symbionts, and so it is important to analyse EB to determine whether this is also the case for plant
endosymbionts. If true, this has major implications for the application of these organisms in crop production and protection,
as biofertilisers, biopesticides, antifungals etc. (for both food and industrial crops), as co-operative adaptation may render
them inherently safer than predicted. Furthermore, chemical compounds may be isolated for application as antimicrobials
for human and animal health. A number of novel antibiotics have been isolated from EB over recent years, indicating that
EB remain a relatively untapped resource with high potential for discovery of novel bioactives.
This project will utilise the EB collection at IBERS developed in a previous BBSRC iCASE project BB/G017484/1 'Bacterial
endophytes in the energy crop Miscanthus'. Genomic analysis, mutagenesis and in planta screening will provide insight into
the adaptations required for an endophytic lifestyle. Concurrently, functional testing and subsequent chemical isolation and
characterisation will elucidate bioactive compounds produced by the EB for commercial application, e.g., as either crop
production/protection, or antimicrobial products. This project therefore addresses a number of BBSRC strategic priorities
including: Sustainably enhancing agricultural production; Food, nutrition and health; Bioenergy; and Combatting
antimicrobial resistance.