Novel New Zealand marine bioactive natural products for the control of Psa biovar 3

Abstract

Natural products (secondary metabolites), produced by living organisms to confer selective advantages via chemical-ecological interactions, have had extensive use in biodiscovery programmes and commercial applications. Such compounds are a unique source of chemical and structural novelty and thus provide relevant modes of biological activity unsurpassed by synthetic compounds. The marine environment has become recognised as an important natural product resource in recent years. Increasing interest is attributed to its high biodiversity, which is complemented by an elaborate chemical diversity in marine organisms. Of particular interest are those sessile and colonial marine organisms which utilise secondary metabolites for chemical defence.

Marine natural products represent unexplored potential for control of the causal agent of bacterial canker of kiwifruit, Pseudomonas syringae pv. actinidiae (Psa) biovar 3. Very few options are available to control the highly virulent pathogen, hence there is an urgent need to find alternative products which kill or inhibit Psa. Previous natural product discovery programmes informed the chance of discovering ‘hit’ activity is low. To increase the chance of success, this study focused on previous biomedicinal work examining related organisms with known activity against Pseudomonas aeruginosa and bacterial quorum sensing processes (known as ecologically guided discovery).

The study sought to identify bioactive compounds from marine organisms with biological activity against P. syringae pv. actinidiae biovar 3. Nineteen New Zealand macroalgae specimens collected in summer and winter were screened for preliminary biological activity against Psa biovar 3. Five candidates (26 percent) were identified with ‘hit’ activity; of which 16 percent was attributed to those targeted for screening and 10 percent is attributed to those selected at random. The secondary screening phase identified the presence of four brominated ions in Vidalia colensoi, m/z 278.8, 308.8, 421.8, and 311.9, as likely to represent biologically active compounds of interest against Psa. There is currently no evidence to suggest these ions represent previously isolated compounds. Hence, Vidalia colensoi is the species of highest priority to further explore chemically. The elicitor screening phase informed that further considerations are to be made for an effective higher order screening method to examine the macroalgae for elicitor activity against Psa biovar 3.

In summary, the findings of this study suggest than ecologically guided discovery approach effectively directed the selection of species with ‘hit’ activity against Psa biovar 3 and thus fast tracked the initial discovery phase. Secondly, the discovery of four previously unidentified brominated ions with potential biological activity against Psa suggests they may represent structurally novel compounds with commercial patentability and marketability. Lastly, the elicitor screening findings provided important preliminary information for optimisation of higher level screening process to explore elicitor activity as a mode of action against Psa biovar 3.