Isolation And Characterization Of Banana Residue-Degrading Strains And Their Degrading Characteristics

China is one of the biggest banana cultivation countries, the cultivation area of bananas is increasing annually, and the rise in banana output can set the improvement of farmers’ economic income in motion, but the treatment of banana residue worry is very difficult. It usually takes a great deal of manpower to uproot the underground bulb of banana, namely the real stem, and to assure the good harvest next year. Plenty of excavated bulbs have been piled up around the farmland over years to let them decompose naturally, which may result in serious environmental pollution and the proliferation and diffusion of banana pathogens in the farmland to affect the banana output indirectly. Therefore, microbial biodegradation of bulb was studied in this paper to accelerate the rate of converting the hard-to-use macromolecule into available micromolecule and facilitate further resource utilization of bulb in other fields.Rotten banana bulbs for the isolation of banana bulb-degrading strains were collected from Hainan provience, China. Enrichment culture technique was used to isolate banana bulb-degrading strains. Activity measurement of several kinds of enzymes and banana bulb degradation experiment were also conducted. Results are as follows:First, Target microbes were concentrated and cultured with the liquid medium of banana bulb powders as the sole carbon source. Strains with quicker growth-rate, including7bacteria and2fungi were selected for further study. The activities of cellulose, hemicellulose and lignin enzymes of the selected4bacteria and2fungi were determined. The results showed that these6strains all possess the corresponding enzyme abilities. Among all bacterial strains, the highest CMC and filter paper enzyme activities were shown in bacterial strain bd-7and the values were81.10U/mL and34.61U/mL, respectively. Among all fungal strains, strain Z2possessed the highest CMC and filter paper enzyme activities and the values were141.21U/mL and50.24U/mL respectively. Among all the stains, the highest xylanase activity (293.22U/mL) and xylanase activity (256.71U/mL) were shown in bacterial strain bd-7and fungal strain Z2, respectively. The highest Lip and Mnp enzyme activities were shown in the bacterial strain bd-48with the values of8.39U/L and23.78U/L, respectively. However, the activity of fungal lignin enzyme was relatively low.Second, Sterile banana bulb degradation rates of different microbes were used to investigate their degradation abilities. The degradation rates of the tested microbes were53.14%,50.64%,36.26%and52.81%for bacterial strain bd-7, bd-12, bd-30and bd-48,18.44%and51.09%for fungal strain Z1and Z2, respectively. The combination degradation rate of Z2with each of the bacteria strains were further determined, that is fungal strain Z2with bacterial strain bd-7, bd-12, bd-30and bd-48, respectively. The results showed that the banana bulb degradation rates were significantly increased in the combination groups and the values were63.24%,67.31%,59.79%and62.51%, respectively. There is a10-30%higher degradation rate of the combination groups compared to that of the single strains. Contents of cellulose, hemicellulose and lignin were also measured during the biodegradation process. Bacterial strain bd-7and bd-48exhibited a better degradation ability of cellulose, hemicellulose and lignin compared to the other strains. The degradation rates of cellulose、hemicellulose and lignin were33.77%,82.83%and18.64%for strain bd-7,and36.91%,83.03%and30.10%for strain bd-48, respectively. A significant enhancement of cellulose-degrading rate was significantly enhanced when combaining with the fungus. The cellulose degrading-rate for fungal strain Z2combained with bacterial strain bd-30reached51.76%. However, the enhancement of degradation rates for hemicellulose and lignin were not shown.Third, the surface structures of the degraded banana bulb samples were observed by scanning electron microscope. Compared with control sample inoculated with sterile water, the surface structures of samples inoculated with microbes were rougher and more irregular, and had more amounts of disintegration fragments.Fourth, to better evaluate the degradation effects of these strains in the natural field, the degradation experiment for bacterial strain bd-7, bd-12, bd-30, bd-48and fungal strain Z2with using non-sterilized banana bulbs were conducted. After treating for30days, bacterial strain bd-48showed the strongest degradation effect and the degradeing-rate was33.22%. However, their practical application need further study.Fifth, bacterial strain bd-7, bd-48and fungul strain Z2were identified. Results showed that bacterial strain bd-7and bd-48were related to the Bacillus sp. lineage and closely clustered with the type strain Bacillus methylotrophicusT with a16S rDNA sequence similarity score of100%and99.9%respectively. The fungul strain Z2was preliminarily identified as Aspergillus fumigatus based on its morphological, physiological, and biochemical properties, as well as ITS sequence.