By means of single and mixed inoculation,this paper studied the interspecific competition between T.confusum and T.pretiosum on the factitious eggs of Corcyra cephaloica under different parasitoid densities,host densi...By means of single and mixed inoculation,this paper studied the interspecific competition between T.confusum and T.pretiosum on the factitious eggs of Corcyra cephaloica under different parasitoid densities,host densities and inoculated spaces.The results showed that for both singly and mixed inoculated groups,the parasitism increased with parasitoid density but decreased with host density,whereas the percentage of female progeny dropped with parasitoid density but enhanced with host density.No significant effect was observed on adult emergence for all parasitoid and host density treatments.In mixed inoculated group,the proportion of T.pretiosum in the progeny decreased with parasitoid density but increased with host density,and was more than 50% in all treatments,indicating that T.pretiosum had a stronger competitive ability than T.confusum.In the spaces ranging from 4 cm 3 to 102 cm 3,the parasitism decreased gradually in both singly and mixed inoculated groups.The percentage of female progeny and adult emergence had no significant difference among different inoculated spaces.In mixed inoculated group,the proportion of T.pretiosum in the progeny was more than 50% in all treatments except space 102 cm 3,but decreased with space,which suggested that T.confusum could improve their competitive ability through increasing their search areas and looking for more hosts.展开更多
The highly potent antitumor agent ansamitocin P3 is a macrolactam isolated from Actinosynnema pretiosum ATCC 31565. A 120-kb DNA fragment was previously identified as the ansamitocin biosynthetic gene cluster, and con...The highly potent antitumor agent ansamitocin P3 is a macrolactam isolated from Actinosynnema pretiosum ATCC 31565. A 120-kb DNA fragment was previously identified as the ansamitocin biosynthetic gene cluster, and contains genes for polyketide assembly, precursor synthesis, post-polyketide synthesis modification, and regulation. Within the biosynthetic gene cluster, asm8 encodes an 1117-amino-acid protein with a high degree of similarity to the large ATP-binding LuxR family-type regulators. In the current study, we determined that inactivation of asm8 by gene replacement in ATCC 31565 resulted in the complete loss of ansamitocin production, and that complementation with a cloned asm8 gene restored ansamitocin biosynthesis. Interestingly, the disruption of asm8 decreased the transcription of genes responsible for 3-amino-5-hydroxybenzoate (AHBA) formation, the starter unit required for ansamitocin biosynthesis. Subsequently, feeding of exogenous AHBA to the asm8 mutant restored ansamitocin biosynthesis, which showed that Asm8 is a specific positive regulator in AHBA biosynthesis. In addition, investigation of asm8 homologs identified two new ansamitocin producers, and inactivation of the asm8 homolog in A. pretiosum ATCC 31280 abolished ansamitocin production in this strain. Characterization of the positive regulator Asm8 and discovery of the two new ansamitocin producers paves the way for further improving production of this important antitumor agent.展开更多
文摘By means of single and mixed inoculation,this paper studied the interspecific competition between T.confusum and T.pretiosum on the factitious eggs of Corcyra cephaloica under different parasitoid densities,host densities and inoculated spaces.The results showed that for both singly and mixed inoculated groups,the parasitism increased with parasitoid density but decreased with host density,whereas the percentage of female progeny dropped with parasitoid density but enhanced with host density.No significant effect was observed on adult emergence for all parasitoid and host density treatments.In mixed inoculated group,the proportion of T.pretiosum in the progeny decreased with parasitoid density but increased with host density,and was more than 50% in all treatments,indicating that T.pretiosum had a stronger competitive ability than T.confusum.In the spaces ranging from 4 cm 3 to 102 cm 3,the parasitism decreased gradually in both singly and mixed inoculated groups.The percentage of female progeny and adult emergence had no significant difference among different inoculated spaces.In mixed inoculated group,the proportion of T.pretiosum in the progeny was more than 50% in all treatments except space 102 cm 3,but decreased with space,which suggested that T.confusum could improve their competitive ability through increasing their search areas and looking for more hosts.
基金supported by grants from the Ministry of Science and Technology of China (2012CB721005, 2012AA02A706, 2011ZX08009-001, 2012AA022107)the National Natural Science Foundation of China (31070070, 31121064)+1 种基金Ministry of Education of China (20110073110048)the SJTU-UM Collaborative Program
文摘The highly potent antitumor agent ansamitocin P3 is a macrolactam isolated from Actinosynnema pretiosum ATCC 31565. A 120-kb DNA fragment was previously identified as the ansamitocin biosynthetic gene cluster, and contains genes for polyketide assembly, precursor synthesis, post-polyketide synthesis modification, and regulation. Within the biosynthetic gene cluster, asm8 encodes an 1117-amino-acid protein with a high degree of similarity to the large ATP-binding LuxR family-type regulators. In the current study, we determined that inactivation of asm8 by gene replacement in ATCC 31565 resulted in the complete loss of ansamitocin production, and that complementation with a cloned asm8 gene restored ansamitocin biosynthesis. Interestingly, the disruption of asm8 decreased the transcription of genes responsible for 3-amino-5-hydroxybenzoate (AHBA) formation, the starter unit required for ansamitocin biosynthesis. Subsequently, feeding of exogenous AHBA to the asm8 mutant restored ansamitocin biosynthesis, which showed that Asm8 is a specific positive regulator in AHBA biosynthesis. In addition, investigation of asm8 homologs identified two new ansamitocin producers, and inactivation of the asm8 homolog in A. pretiosum ATCC 31280 abolished ansamitocin production in this strain. Characterization of the positive regulator Asm8 and discovery of the two new ansamitocin producers paves the way for further improving production of this important antitumor agent.
