A Preliminary Study on Indigenous Bacillus spp. Isolated from Acidic Soil as Agent of Bioinsecticide

Abstract

Bacillus spp. are the most abundant bacteria in the soil and release a wide range of benefits. Especially to produce the specific toxin for inhibiting mosquito life cycle. This study aimed to isolate Bacillus spp. from acidic soil and investigate its potential as a natural mosquito insecticide. The soil was collected from the oil palm plantation (KS) and secondary forest (HS) in Berambai, Samarinda, East Kalimantan. All samples were shaken and followed by a heat treatment technique. Furthermore, the dilution was spread onto Luria Bertani agar to obtain Bacillus spp. As a result, the soil physicochemical analysis showed the pH of HS was 5,38 ± 0,81 (acid), and KS was 4,41 ± 0,55 (very acid). The density of Bacillus spp. from HS and KS were 10.1×104 CFU/g and 1.1×104 CFU/g, respectively. Five selected isolates (T1HS4.1, T1KS4.2, T2HS6.1, T3KS4.1, and T3KS4.2) were grown on LB broth for culture starters (6%). Each culture starter was diluted into mosquito larvae water habitats to determine the mortality rate. The result showed that the highest mortality of mosquito larvae using A and B methods were 70% and 80% in isolate T3KS4.2, while another isolate T1HS4.1 showed zero mortality at 24 hours. Therefore, isolate T3KS4.2 produced the specific toxin that killed the larvae within 24 hours and presented the potential of indigenous Bacillus spp. as a bioinsecticide for mosquito larvae. Further, the molecular method is necessary to identify the species of Bacillus spp. potential like Bacillus thuringiensis as a natural mosquito insecticide.