Nipah worm (Namalycastis rhodochorde) belongs to the Polychaeta group that lived in the Nypa fruticans mangrove sediment in West Kalimantan. It has the potential to be cultivated because it has a high economic value in aquaculture. Feed aspect is an essential part of its cultivation, through improving the quality of feed by using probiotics isolated from its natural habitat, such as actinomycetes. These bacteria are known capable of producing secondary and primary metabolites. These metabolites are expected to increase immunity and biomass of worms. The purpose of this study was to isolate and determine the composition and characteristics of actinomycetes derived from mangrove sediment, gastrointestinal and faecal pellets of nipah worm that are potential as probiotic for feed formulation. Isolation and characterization of actinomycetes was conducted by pour plate method on SCA, ISP2, ISP3, ISP4, and ISP5 media; while characterization was by determining morphological characteristics of colonies, cell structure, and biochemical tests. Identification of the isolates referred to Bergey’s Manual of Determinative Bacteriology. The results showed that twelve isolates of actinomycetes had been found. Six isolates were from mangrove substrate, four isolates from fecal pellets and two isolates from the gastrointestinal tracts. All isolates were closely related to the genus Streptomyces.

The bacterial isolates NrLtF1, NrLtF4, NrLtF5, and NrLtG2 isolated from fecal pellets and gastrointestinal tract of nypha worms (Namalycastis rhodochorde) have cellulolytic, proteolytic activity and produce organic acids. The four isolates have the potency to be developed as probiotics in nypha worm cultivation feed. This study aims to determine the probiotics potency and identify the species of NrLtF1, NrLtF4, NrLtF5, and NrLtG2 isolate based on 16srDNA sequence. The probiotic potency was carried out by the acid tolerance assays on distilled water and 0.3% acid bile media, and the antimicrobial testing against Escherichia coli (MF exp21.12). Bacterial identification was carried out by sequencing of 16sDNA sequence based on GeneBank data. The results showed that the bacterial isolates of NrLtF1, NrLtF4, NrLtF5, and NrLtG2 were able to grow on 0.3% distilled water and acid bile media. However, only the NrLtF4 and NrLtF5 inhibited E. coli (MF exp21.12) with halo zones 30 mm and 18 mm, respectively. Blasting results of the 16srDNA sequences showed that the NrLtF1, NrLtF4, NrLtF5, and NrLtG2 were closely related to Bacillus wiedmannii, Brevibacterium sediminis, Bacillus proteolyticus, and Bacillus paramycoides. The nypha worm bacterial isolates have the potency to be developed as probiotics in nypha worm culture.