Screening And Identification Of Biocontrol Bacterial Strains Against Aflotoxin From Groundnut Geocarposphere And Diversity Reaserch

As the main source of edible oil, groundnut plays an important role in the national economy. In the wet condition, peanuts are easy invaded by fungi producing aflatoxin (AF) which is cancerogenic. AF can cause viral hepatitis, liver cirrhosis, liver cancer. It can stand high-temperature, and is hard to break down. It is harm to our health, also will impact on animal husbandry if mixed in the feed, which directly affect our national economy and the import and export trade.In this research, we launched an efficient way to screen biocontrol bacterial strains against aflotoxin from groundnut geocarposphere (the area 2 mm around the groundnut) firstly. 333 strains of biocontrol bacterial getting from groundnut geocarposphere were evaluated, and 195 strains which can inhibit Aspergillus Parasiticus were chosen to be purified. After purification, we get 227 strains. The highest mycelium inhibition ratio is 75.3% in GY (Glucose andYeast extract) medium, and 72.4% in PGY (with peanut extract) medium. Meanwhile, there are 8 strains whose ratio of inhibition of the NA formation can nearly reach 100% in GY medium and YGP2-1, YGP2-1 has the highest inhibition ratio of the NA formation——88%. And 50% of the strains which can inhibit the mycelial growth and 27% which can inhibit the aflatoxin production of Aspergillus parasiticus have better effects on the PGY medium than on the GY medium. Though with little difference in GY plate and PGY plate, 15 strains have a high inhibition ratio of the NA formation above 50%, and 18 strains have a high mycelium inhibition ratio above 60%.197 strains were chosen to do morphological identification, and the result showed that 101 strains are Gram-positive, including 34 bacterial strains which have brood cell, and others are gram-negative. Also, there are 100 strains of Gram-positive rod shaped bacteria, a strain of Gram-positive cocci, 37 strains of Gram- negative rod shaped bacteria and 59 strains of Gram-negative cocci. After molecular identification for 22 bacterial strains of them, they were identified as Bacillus sp. , Alcaligenes sp, Burkholderia sp. and Enterobacter sp. by 16S rDNA sequencing analysis. In futher studies, we confirmed there are 9 strains of Bacillus subtilis, 7 strains of Bacillus cereus, a strain of Bacillus pumilus, 2 strains of Alcaligenes faecalis, 2 strains of Burkholderia cepacia and a strain of Enterobacter cloacae.37 bacterial strains were chosen to research the activity by liquid PGY, and have discovered that ferment supernatant which was diluted 5/6 of 24 strains of the NA formation inhibition ratio by Aspergillus parasiticus NA mutant was above 70%, among them 9 bacterial strains of inhibition rate achieved 100%. Also there are 19 strains whose mycelium growth inhibition ratio were above 60%, and 9 strains were'above 90%.There are 9 bacterial strains whose ferment supernatant of NA inhibition rate were 80% when obverving anti-Aspergillus parasitic infection ability of supernatant in groundnut.The method of bacterial isolation and evaluation is so convenient and efficient in this research, and the activation test method combining with the practice may be very useful to industrial production, while, the bio-control bacteria lay a solid foundation for further study of aflatoxin.