Preparation of a fermented Sargassum extract, microbial dynamics involved, and its effect on Capsicum annuum

The study explored Sargassum valorization through the production of a fermented extract for its application as a crop biostimulant. The dried and ground Sargassum (S. natans and S. fluitans) was subjected to anaerobic fermentation utilizing the endogenous microorganisms already present in the seaweed. During the fermentation process, samples were periodically taken (5, 15, 20, 27, 30, and 35) for 16S rRNA and ITS paired-end amplicon metataxonomics. Microbiome profiling revealed distinct temporal microbiome shifts over the 35 days of fermentation, with Firmicutes, Bacteroidota, and Nectriaceae emerging as the core microbiome. Furthermore, microbial network analysis identified Clostridiaceae, Sporolactobacillaceae, and Pirellulaceae as dominant bacterial families, while Gibberella and Aspergillus showed up as prevalent fungal genera. Beta-diversity analyses showed a significant shift in microbial composition on Day 35. Extracts were screened for their antimicrobial properties against plant pathogens (Xanthomonas campestris pv. vesicatoria and Alternaria solani), however results indicated no antimicrobial effect. Plant growth trials were conducted using Capsicum annuum L. plants and the extracts were applied as foliar application sprays at 0.5-1% v/v concentrations under greenhouse conditions. All parameters measured (chlorophyll content, root and shoot length, and root and shoot weights were all significantly greater than Control-treated plants. Chlorophyll content, root length, shoot length, fresh root and shoot weight, and dry root and shoot weight all had significant increases of up to 28.82%, 60.13%, 15.95%, 67.95%, 53.90%, 82.05%, and 95.86% respectively. The result of the study promotes the usage of fermented Sargassum extracts as an organic biostimulant and aligns with sustainable agricultural practices.

The online version contains supplementary material available at 10.1007/s13205-026-04811-1.