Antifungal Natural Products Originating from Endophytic and Rhizospheric Microbes Isolated from Coastal Vegetation

Candida infections severely impact patients who are immunocompromised. Currently, there are limited options to treat fungal infections, especially drug-resistant-fungal infections. Therefore, investigating alternative or repurposed antifungals is paramount. Endophytic microbes (EMs) and rhizospheric microbes (RMs) emerge as promising reservoirs of bioactive natural compounds. Interestingly, plants that have adapted to various environmental conditions harbour a plethora of microbes producing a variety of bioactive natural products that can be assessed for potential antifungal activity. To date, EMs and RMs residing in coastal plants and their associated antifungals have not been extensively studied or reviewed. Therefore, this comprehensive review will focus on antifungal natural products, extracted from coastal-vegetation-associated microbiota to draw the attention of research in this field. A comprehensive literature search was conducted by examining both Scopus and Google Scholar databases during the period of 2013-2024 related to the following coastal vegetation: mangroves, sand dune plants, salt marsh plants, and seagrasses. To date, 65 novel antifungal compounds derived from coastal-plant EMs and RMs have been identified. Mangroves were found to be the most prominent host harbouring antifungal-producing EMs and RMs compared with other coastal plants. Coastal-plant-associated fungal partners were the most prominent producers of antifungals compared to their bacterial counterparts. Fifty-four fungal-EM/RM derived antifungals have been reported to demonstrate activities against plant pathogenic fungi as well as human fungal pathogens. Most of the bacterial-derived antifungals (11 antifungals) have previously been reported to have antifungal activity against Candida albicans.

Evaluation of Streptomyces sp. strain g10 for suppression of Fusarium wilt and rhizosphere colonization in pot-grown banana plantlets

Streptomyces sp. strain g10 exhibited strong antagonism towards Fusarium oxysporum f.sp. cubense (Foc) races 1, 2 and 4 in plate assays by producing extracellular antifungal metabolites. Treating the planting hole and roots of 4-week-old tissue-culture-derived 'Novaria' banana plantlets with strain g10 suspension (10(8) cfu/ml), significantly (P < 0.05) reduced wilt severity when the plantlets were inoculated with 10(4) spores/ml Foc race 4. The final disease severity index for leaf symptom (LSI) and rhizome discoloration (RDI) was reduced about 47 and 53%, respectively, in strain g10-treated plantlets compared to untreated plantlets. Reduction in disease incidence was not significant (P < 0.05) when plantlets were inoculated with a higher concentration (10(6) spores/ml) of Foc race 4. Rhizosphere population of strain g10 showed significant (P = 0.05) increase of more than 2-fold at the end of the 3rd week compared to the 2nd week after soil amendment with the antagonist. Although the level dropped, the rhizosphere population at the end of the 6th week was still nearly 2-fold higher than the level detected after 2 weeks. In contrast, the root-free population declined significantly (P = 0.05), nearly 4-fold after 6 weeks when compared to the level detected after 2 weeks. Neither growth-inhibiting nor growth-stimulating effects were observed in plantlets grown in strain g10-amended soil.