Characterization of sponge-associated actinobacteria with potential to promote plant growth on tidal swamps

Tidal swamps have become one of the highlighted topics in agricultural land development. Rice productivity in a tidal swamp is still low due to the high concentration of Fe, Al, and low pH. Siderophore-producing bacteria were known to alleviate the toxicity of heavy metals for plants. However, the potential of sponge-associated actinobacteria has been rarely reported in siderophore production. This work aimed to characterize the sponge-associated actinobacteria based on their tidal swamps characters and their potency to produce plant growth promoter on stressful tidal swamp imposed characters. The in vitro assay showed that, at the presence of Fe and Al, Car21t isolate produced a dry weight of mycelium reaching up to 289 mg and 204 mg in Yeast Malt Extract medium, respectively. Interestingly, all isolates were able to grow in relatively high salinity condition (7%). Indeed, under stress condition, inoculum of five actinobacteria isolates could produce Indole Acetic Acid and siderophore. These experimental results suggested that all potential isolates provided beneficial effects on the host plant, as evidenced by the rise of root length (9.86%), shoot length (9.44%), and root number (13.93%). Subsequently, our experimental data also indicated that these potential isolates belonged to the genus Streptomyces.