| The use of yeasts as biocontrol agents has distinct advantages, including their general lack of antibiotic production, ability to rapidly colonize wounds, stress tolerance, and compatibility with many chemicals and fungicides that are used in commercial settings. Problems with efficacy and viability are often due to the various abiotic stresses experienced by the yeast either during their forumulation or application, including oxidative stress, osmotic stress, heat stress, and cold stress. Collecting stress-tolerant yeast strains from extreme environments, such as Antarctica or seawater, has been an approach used to identify potential, stress tolerant, antagonists.Tibet is known for its harsh climate, so it is logical to expect that microorganisms collected there may be more tolerant to abiotic stresses than microbes collected from climates that are more temperate. Therefore, Tibet may represent an excellent source for obtaining abiotic stress tolerant biocontrol yeasts. The present study describes the selection of two antagonistic yeast from Tibet, one is Rhodotorula mucilaginosa (YC1), the other is Cryptococcus laurentii (LB2). C. laurentii (LB2) was selected to further study. The tests were conducted to exmine its safety, biocontrol activity at low temperature and primary mode of action. Then its deeper action mechanism was analyzed by comparative transcriptome method. Its effect on the fruit natural decay incidence and quality was also investigated.The main results are listed as follows:(1) Two yeasts with biocontrol activity at low temperature were isolated from Tibet region. They were identified as R. mucilaginosa and C. laurentii, respectively. Both of them were kept in China General Microbiological Culture Collection Center. Their serial number were CGMCC10223 and CGMCC10222.(2) The Tibetan C. laurentii (LB2) was selected for study. Its safety was tested by the acute oral toxicity test in rats. The result showed it was actually non-toxic.(3) The biocontrol activity of Tibetan C. laurentii was studied against the main postharvest decay of pear, apple, cherry tomato, orange and winter jujube at low temperature. The results showed its biocontrol efficacy was concentration dependant. The best biocontrol concentration was 1×108 cells/ml.(4) Its primary mode of action was investigated. The results indicated that competition for space and nutrient was the main mechanism of Tibetan C. laurentii against fruit decay, and the secretion of hydrolase and host resistance induction also were in its action. Besides, the reseaon why this yeast performed better stress resistance may be since there were more intracellular cryoprotectants, such as trehalose and proline. But it was not affected by the cell membrane fluidity.(5) Comparative transcriptome method was used to study the attributes of Tibetan C. laurentii for further exploring its mechanism. Based on the results at room temperature, compared with C. laurentii ZJU10 isolated before, there were totally 430 significantly differentially expressed genes in Tibetan C. laurentii (LB2). Among them,179 genes were up-ragulated and 251 genes were down-ragulated. But most of them may be related to their own charateristics. It was problematic to analyse the specialty of Tibetan C. laurentii. While the results from cold temperature of both yeasts showed the difference much more clearly. There were 176 significantly differentially expressed genes in Tibetan C. laurentii (LB2),126 genes up-regulated and 50 genes down-regulated. It meant that Tibetan C. laurentii (LB2) may have much more positive response to the cold temperature than C. laurentii ZJU10. Furthermore, the functions of 8 selected genes were mainly related to sulfur metabolism, zinc ion metabolism, cell defense mechanism, cell integrity and carbohydrate metabolism.(6) Tibetan C. laurentii had a good activity inhibiting the natural decay of fruit and had no negative effect on the quality of fruit. |
PDF Full Text Request