BIOLOGICAL CHARACTERISTICS AND PROBIOTIC PROPERTIES OF TWO KINDS OF BACILLUS STRAINS FROM YUNLONG HYBRID EPINEPHELUS
The biological characteristics and probiotic properties of Bacillus subtilis GM-2 and Bacillus licheniformis GM-39 was investigated,which were isolated from the intestine of Yunlong grouper(Epinephelus moara♀ ×Epinephelus lanceolatus♂).The biological characteristics were analyzed through the tolerance tests of artificial gastrointestinal fluid,pH,fish bile,hemolysis,and drug sensitivity,and the probiotic properties were studied respectively through the experiments of antibacterial activity,self-aggregation and hydrophobicity,adhesion,enzyme production activity,and antioxidant in vitro.The results showed that the survival rates of these Bacillus strains were more than 70％,80％,and 50％respectively,after treatment with artificial gastric solution,artificial intestinal solution,and 5％fish bile solution for 0～3 h.After treatment with physiological saline solutions with pH of 1.0,2.0,3.0,4.0 and 5.0 for 30 minutes,the survival rates of the two strains gradually increased from 0 to 87.83％and 88.25％,respectively.No hemolysis was observed in the blood agar plate test.The GM-39 was sensitive to 10 kinds of antibiotic sensitivity discs such as tetracycline and enrofloxacin,and GM-2 was sensitive to 8 kinds of antibiotic sensitivity discs such as tetracycline and 6 kinds of commonly used aquatic drugs such as enrofloxacin.The B.licheniformis GM-39 was sensitive to 10 kinds of antibiotic susceptibility discs such as tetracycline and 5 kinds of commonly used aquatic drugs such as enrofloxacin,and the B.subtilis GM-2 was sensitive to 8 kinds of antibiotic susceptibility discs such as tetracycline and 6 kinds of commonly used aquatic drugs such as enrofloxacin.The bacterial suspensions of these strains showed inhibitory effects on 6 indicator bacteria,such as Streptococcus agalactiae,Aeromonas hydrophila,and Vibrio parahaemolyticus,while the fermentation supernatants only showed inhibitory effects on 3 indicator bacteria,such as Escherichia coli and Staphylococcus aureus.The autoaggregation rates of these strains reached more than 30％,and the hydrophobicity rates were between 30％and 50％.The B.licheniformis GM-39 had a significantly stronger adhesion to mucin protein than B.subtilis GM-2.Both these strains can synthesize cellulase,amylase,protease,and lipase,but the enzyme-producing activity of B.licheniformis GM-39 is higher than that of B.subtilis GM-2.Both strains have the ability to scavenge DPPH free radicals,hydroxyl radicals,superoxide anion radicals,and reduction ability.B.subtilis GM-2 has stronger hydroxyl radical scavenging ability and reduction ability than B.licheniformis GM-39,and GM-39 has better DPPH free radical and superoxide anion radical scavenging ability than GM-2.Both these two bacillus have good tolerance,safety,antibacterial activity,adhesion,enzyme production activity,and antioxidant capacity,among which GM-39 has advantages over GM-2 in tolerance,enzyme production activity,and adhesion.Therefore,B.licheniformis GM-39 and B.subtilis GM-2 have potential for probiotic development,thus providing a scientific theoretical basis for their subsequent research as probiotic preparations.
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