Inhibitory effect of Enterobacter cloacae 3J1EC on Aspergillus flavus 3.4408 growth and aflatoxin production

Aspergillus flavus can easily infect major agricultural products and produce aflatoxin. In this study, we investigated the effect of the biocontrol bacterium Enterobacter cloacae 3J1EC on the growth of A. flavus strain 3.4408. The biocontrol bacterium played a key role in preventing infection by A. flavus. E. cloacae 3J1EC was found to inhibit the growth of A. flavus 3.4408 mycelial pellets and reduce the production of aflatoxin by 96.9%. We found differential expression between the control and the treatment groups in the transcriptome of A. flavus 3.4408. Gene ontology (GO) analysis indicated that E. cloacae 3J1EC induced the down-regulated expression of cellular component and molecular function, while its effects on the up-regulated expression indicated the relationship of biological process and molecular function. Thus, these results suggest that E. cloacae 3J1EC decreased aflatoxin production via down-regulated gene expression in terms of aflatoxin biosynthesis. In summary, E. cloacae 3J1EC can be employed as an alternative for the biological control of A. flavus 3.4408.

THE GROWTH KINETICS OF Bacillus sp. D2.2 AT DIFFERENT pH AND SALINITY

Isolate D2.2 is a bacterial isolate with 97% homology level with Bacillus sp. This isolate is a biocontrol bacterium capable of inhibiting the growth of Gram positive bacteria and Gram negative bacteria. The use of biocontrol bacteria is one solution of disease problem in cultivation organism. Prior to being applied to the field, D2.2 isolates need to go through a series of tests, one of which is growth kinetics testing under various environmental conditions, such as different degrees of pH and salinity. This is because environmental factors can affect the rapid growth of bacteria. The purpose of this study was to study the bacterial growth kinetics of D2.2 at different pH and salinity. The growth kinetics was observed by measuring optical density (OD) through a method of turbidimetry using a spectrophotometer at a wavelength of 625 nm to the stage of death. The results showed that the fastest growth rate was found at 20 ppt salinity with 0.179 h-1 and generation time of 5,588 hours. While in all pH treatments, generation time and growth rates achieved all treatments have the same pattern.