Isolation of thermophilic mannanase-producing bacteria useful for mannooligosaccharide (MOS) production

Mannanase is an enzyme that catalyzes random hydrolysis of mannosidic linkages in mannans, galactomannans, glucomannans, and galactoglucomannans. The aim of this research was to isolate the mannanolytic thermophilic bacterium useful for mannooligosaccharide (MOS) production. Thermophilic mannanase-producing bacteria were isolated from 6 soil samples collected from organic rice farm of Selaphum, Roi Et, Thailand. The bacteria were cultured using Luria-Bertani (LB) supernatant containing locust bean gum (LBG) and incubated at 60 °C for 1 hr before continued culturing at 37 °C for 47 hr. The mannanase activity was screened on LB agar containing LBG stained with iodine solution. The colonies that showed clear zone were selected. The isolates were cultured using LB supernatant containing LBG at 60 °C for 72 hr. Seven isolates exhibited the high amount of halo ratio were selected and named KS1, KS2, KS3, KS4, KS5, KS6 and KS7. Mannanase activity was also determined by DNS method using LBG (pH 7.0) as mannan source and cultured media as crude mannanase. Only KS1 and KS7 strains showed thermophilic mannanase and exhibited activities at 55–90 °C. KS1 and KS7 were identified by DNA sequencing and morphology. The results revealed that KS1 is Bacillus subtilis and KS7 is Bacillus amyloliquefaciens.