Abstract

In our previous research, we constructed a Bacillus thuringiensis (Berliner) (Bacillales: Bacillaceae; Bt) strain (BMB171ΔhmgA), in which the loss of homogentisate 1, 2-dioxygenase (HmgA) activity promoted the melanin accumulation in the culture medium. However, further improvement in melanin yield by Bt strains has not been considered. Herein, based on the melanin synthesis pathway, we attempted to increase the melanin yield in Bt by adding a suitable concentration of L-tyrosine and increasing the expression levels of tyrosine aminotransferase (PhhC) and 4-hydroxyphenylpyruvate dioxygenase (HppD) using strong promoters. The results showed that the melanin yield of the engineered strain (Bt-2P) grown in medium supplemented with L-tyrosine was approximately 5.7 times higher than that of the original strain without L-tyrosine, suggesting that L-tyrosine addition and phhC or hppD overexpression were effective to improve the melanin yield in Bt. In addition, we tested the photoprotective effect of melanin on Autographa californica (Speyer) (Lepidoptera: Noctuidae) multiple nucleopolyhedrovirus (Lefavirales: Baculoviridae; AcMNPV) and Ralstonia solanacearum (Smith) Yabuuchi et al. (Burkholderiales: Burkholderiaceae) bacteriophage ФNK-7 against ultraviolet (UV) irradiation. The results implied that the titers of AcMNPV and bacteriophage ФNK-7 in the presence of melanin were approximately ten and four times higher than those without melanin under UV radiation, respectively. This indicated that the addition of melanin could effectively maintain the activities of the viruses. In conclusion, we reported strategies to increase the melanin yield in Bt and expanded the potential applications of melanin.

中文翻译：

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苏云金芽孢杆菌产生的黑色素的生产改进和光保护

摘要

在我们之前的研究中，我们构建了苏云金芽孢杆菌（Berliner）（芽孢杆菌目：芽孢杆菌科；Bt）菌株（BMB171Δ hmgA），其中尿黑酸1, 2-双加氧酶（HmgA）活性的丧失促进了培养基中黑色素的积累。然而，尚未考虑通过 Bt 菌株进一步提高黑色素产量。在此，基于黑色素合成途径，我们尝试通过添加合适浓度的L-酪氨酸并使用强启动子提高酪氨酸转氨酶（PhhC）和4-羟基苯基丙酮酸双加氧酶（HppD）的表达水平来提高Bt中黑色素的产量。结果表明，在添加L-酪氨酸的培养基中生长的工程菌株（Bt-2P）的黑色素产量比不含L-酪氨酸的原始菌株高约5.7倍，这表明添加L-酪氨酸和phhC或hppD过表达可有效提高 Bt 中的黑色素产量。此外，我们测试了黑色素对苜蓿银纹夜蛾（Speyer）（鳞翅目：夜蛾科）多重核多角体病毒（Lefavirales：杆状病毒科；AcMNPV）和青枯菌（Smith）Yabuuchi等人的光保护作用。 （伯克霍尔德氏菌目：伯克霍尔德氏菌科）噬菌体ФNK-7抵抗紫外线（UV）照射。结果表明，在紫外线照射下，有黑色素存在的情况下，AcMNPV 和噬菌体 ФNK-7 的滴度分别比没有黑色素的情况高约 10 倍和 4 倍。这表明黑色素的添加可以有效维持病毒的活性。总之，我们报告了提高 Bt 黑色素产量并扩大黑色素潜在应用的策略。