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Black soldier fly (Hermetia illucens L.) larvae are widely used in organic waste management. Its ability to digest organic compound was supported by the diversity of bacteria which produce various enzymes inside the larvae bodies. The exploration of potential bacteria in BSF larvae may have advantages for the agricultural field. This study aimed to screen cellulolytic, chitinolytic, phosphate solubilizing, and IAA-producing bacteria from BSF larvae. A total of 22 isolates were qualitatively screened using various media. Among the 22 isolates, five isolates showed positive results of cellulolytic activity; six isolates were able to digest chitin; nine isolates have positive result of IAA-producing test; and five isolates could solubilize phosphate in Pikovskaya’s agar. There were two isolates, B11 and B15, that gave positive result in three tests, those are on cellulolytic, phosphate solubilizing, and IAA producing test. Molecular identification of B11 showed that the isolate was similar to Bacillus altitudinis (100%) and B15 was closed to Klebsiella oxytoca (99.73%).

Abstract. Fadhilah QG, Santoso I, Yasman. 2021. The antagonistic activity of marine actinomycetes from mangrove ecosystem against phytopathogenic fungi Colletotrichum sp. KA. Biodiversitas 22: 642-649.  Marine actinomycetes from mangrove ecosystems are known to be potential antifungal-producing isolates against phytopathogenic fungi. The aim of this research was to obtain potential marine actinomycetes isolates against the phytopathogenic fungi Colletotrichum sp. KA. Screening of 15 marine actinomycetes isolates using a dual culture method with a plug technique showed that 80% of isolates have antagonistic activity, represented as a percentage of growth inhibition range from 47.96% to 84.94%. Among 12 potential isolates, six isolates (SM4, SM11, SM14, SM15, SM18, and SM20) were evaluated for delayed antagonistic activity with incubation periods of 6, 9, and 12 days using the plug and streak techniques. The results showed that the percentage of growth inhibition of selected isolates inclined to increase along with the incubation period prior to inoculation of Colletotrichum sp. KA. Delayed antagonist assays using the streak technique resulted in higher inhibition results compared to the plug technique. Furthermore, the non-delayed assays of the two selected isolates, SM11 and SM15, also inhibited Colletotrichum sp. KA 57.99% and 59.88%, respectively. The delayed antagonist assay with a shorter incubation period of the two selected isolates also showed an increased percentage of growth inhibition of Colletotrichum sp. KA. According to our research, the delayed antagonistic assay of marine actinomycetes isolates with a 12-day incubation period using a plug technique was representative to evaluate the percentage of growth inhibition.

Bacillus spp. are known as potential bacteria as biocontrol agent against fungal phytopathogen, such as Aspergillus niger. The Aspergillus niger can cause many problems, including in agriculture sector. Antagonist activity of 3 bacteria isolates Bacillus sp. KRG, KRT and LDR have been carried out against Aspergillus niger CP. Dual culture method for antagonist assay was performed using streak, disc, and pour plate technique. Result from the disc technique showed that there is no significant antagonist activity differences between all isolates KRG, KRT, and LDR (51.94 %, 61.24 %, and 54.53 %). The highest inhibition effect was shown clearly in pour plate technique with inhibition value almost 100 %. The LDR isolate was selected for further evaluation based on the physicochemical characters according to strong catalase activity and rapid fermentation. Antibiosis assay was performed in order to evaluate the antifungal compound produced by LDR isolate using agar and broth culture method. The filtrates from growth medium 7, 10 and 12 days fermentation were used for antibiosis assay against Asp. niger CP. The growth of Asp. niger CP was inhibited by 10- and 12-days filtrate fermentation in all the 2 methods used. The percentage of inhibition of isolates observed in agar culture were 84.41 % and 84.21 %. Biomass of Asp. niger CP reduced by 74.55 % and 85.54 %.

Marine actinomycetes are being explored to discover potential actinomycetes that produce antifungal compounds. In a previous study, marine actinomycetes isolates from the mangrove ecosystem were found to inhibit growth of the phytopathogenic fungi Colletotrichum siamense KA. In this study, the three of these isolates with the highest antagonistic activity—SM11, SM14, and SM15—were evaluated for their antifungal activity using antibiosis assay. The fermentation was performed in SCB:PDB medium (1:1) for 6, 9, and 12 days. The results showed that SM14 was the strongest potential isolate; it inhibited the growth of C. siamense KA on average up to 64.90% for 12 days on PDA filtrate medium. Molecular identification showed SM14 was closely related to Streptomyces sanyensis, but had differences in morphological and biochemical characteristics compared to SM11 or SM15. This indicated that the three isolates were different strains and may challenge further research on identifying and analyzing their antifungal compounds.