Endophytic bacteria: co-existence and chemical warfare

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Endophytic bacteria (EB) live within plant tissues without causing signs of disease. They may be horizontally or verticallytransmitted and can be considered to sit at the benign end of the spectrum between mutualists and pathogens. EB havebeen reported to confer benefits to the host plant in terms of growth promotion and protection from pests and pathogens. Inorder to maintain an endophytic lifestyle these bacteria must both interact with the host plant and other bacterial and fungalendophytes without triggering defence mechanisms (co-operation), yet assist the plant in identifying and attackingpathogens (chemical warfare). These ancient relationships are not only fascinating from an evolutionary perspective butare potentially of great value for both sustainable crop production and as novel sources of bioactive natural productsincluding antimicrobials and antifungals.In the past it was postulated that the states of symbiosis and pathogenesis were readily interchangeable, largely dependenton environmental conditions. However, evidence from genomic studies do not support this, as symbionts tend todemonstrate reduced genomes, lacking the necessary components required for pathogenesis. To date the majority of datais from animal symbionts, and so it is important to analyse EB to determine whether this is also the case for plantendosymbionts. 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 renderthem inherently safer than predicted. Furthermore, chemical compounds may be isolated for application as antimicrobialsfor human and animal health. A number of novel antibiotics have been isolated from EB over recent years, indicating thatEB 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 'Bacterialendophytes in the energy crop Miscanthus'. Genomic analysis, mutagenesis and in planta screening will provide insight intothe adaptations required for an endophytic lifestyle. Concurrently, functional testing and subsequent chemical isolation andcharacterisation will elucidate bioactive compounds produced by the EB for commercial application, e.g., as either cropproduction/protection, or antimicrobial products. This project therefore addresses a number of BBSRC strategic prioritiesincluding: Sustainably enhancing agricultural production; Food, nutrition and health; Bioenergy; and Combattingantimicrobial resistance.