Heterotrophic bacteria are organic and inorganic decomposer functioning to inhibit pathogenic bacteria in the waters. This research is aimed at understanding the heterotrophic population in Siak River estuary and the antagonism of heterotrophic bacteria against pathogenic bacteria (Vibrio sp, Aeromonas sp dan Pseudomonas sp), identified based on their genotype and phenotype. The research was conducted from July to October 2017 in the estuary of Siak River using a survey method. Estuary water sample was used to classify the heterotrophic bacteria. The antagonism test of 25 isolated bacteria resulted in 10 isolates potential in inhibiting the growth of pathogenic bacteria (Vibrio sp, Pseudomonas sp and Aeromonas sp). The mean of the biggest transparent zone of Vibrio sp. bacterium was 1P11 isolate by 20.3 mm and the smallest one was 1P19 by 5 mm, and for the Aeromonas sp bacterium. Its largest transparent zone diameter was 2P20 isolate for 9.3 mm and 1P12 (3.3 mm) for the smallest one. Further, the Pseudomonas sp biggest transparent zone was 1P12 isolate (17mm) and the smallest ones were 1P11 and 2P22 (8.3 mm). The result of molecular identification with 16S rRNA and BLAST analysis showed that there was a relationship between 10 heterotrophic isolated bacteria and that of Bacillus genus; Bacillus cereus (1P11, 1P12, 1P14, 1P15, 1P19, 2P20, 2P21, 2P23), Bacillus toyonensis (2P22) and Virgibacillus salarius (1P18).
Heterotrophic bacteria, Isolation, Antagonism test, Identification, PCR.
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