Adaptive response and enhancement of N-methyl-N'-nitro-N-nitrosoguanidine mutagenesis by chloramphenicol in Streptomyces fradiae

Implication of mutagenesis and precursor supplementation towards the enhancement of lipstatin (an antiobesity agent) biosynthesis through submerged fermentation using Streptomyces toxytricini

In the present study, lipstatin production was studied from different mutants of Streptomyces toxytricini which were developed using ultraviolet radiation (exposure time 30 s, 1, 2, 5 and 10 min), ethyl methane sulfonte, methyl methane sulfonate (MMS) and N-methyl-N'-intro-N-nitrosoguanidine (NTG) treatments (50, 100, 200, 500, 1000 µM, respectively). Highest yielding mutants were provided precursor supplementation of citric acid, thiamine and biotin (each 1 g/L) at idiophase for further enhancement in the production of lipstatin. Screened mutants produced biomass in the range of 5.8-7.16 g/L which were lesser than control. Screened mutants also exhibited pellet morphology in submerged culture. Out of these mutants, NTG8 mutant produced highest amount of lipstatin (1383.25 mg/L) with 9.606 mg/L/h productivity. Precursor supplementation to this mutant further increased the production to 2387.81 mg/L. Mutant was validated in 5 L bioreactor and lipstatin production was enhanced to 2519.34 mg/L.

Genetic engineering combined with random mutagenesis to enhance G418 production in Micromonospora echinospora

G418, produced by fermentation of Micromonospora echinospora, is an aminoglycoside antibiotic commonly used in genetic selection and maintenance of eukaryotic cells. Besides G418, M. echinospora produces many G418 analogs. As a result, the G418 product always contains impurities such as gentamicin C1, C1a, C2, C2a, gentamicin A and gentamicin X2. These impurities are less potent but more toxic than G418, but the purification of G418 is difficult because it has similar properties to its impurities. G418 is an intermediate in the gentamicin biosynthesis pathway. From G418 the pathway proceeds via successive dehydrogenation and aminotransferation at the C-6′ position to generate the gentamicin C complex, but genes responsible for these steps are still obscure. Through disruption of gacJ, which is deduced to encode a C-6′ dehydrogenase, the biosynthetic impurities gentamicin C1, C1a, C2 and C2a were all removed, and G418 became the main product of the gacJ disruption strain. These results demonstrated that gacJ is in charge of conversion of the 6′-OH of G418 into 6′-NH2. Disruption of gacJ not only eliminates the impurities seen in the original strain but also improves G418 titers by 15-fold. G418 production was further improved by 26.6 % through traditional random mutagenesis. Through the use of combined traditional and recombinant genetic techniques, we produced a strain from which most impurities were removed and G418 production was improved by 19 fold.

Application of a combined approach involving classical random mutagenesis and metabolic engineering to enhance FK506 production in Streptomyces sp. RM7011

FK506 production by a mutant strain (Streptomyces sp. RM7011) induced by N-methyl-N'-nitro-N-nitrosoguanidine and ultraviolet mutagenesis was improved by 11.63-fold (94.24 mg/l) compared to that of the wild-type strain. Among three different metabolic pathways involved in the biosynthesis of methylmalonyl-CoA, only expression of propionyl-CoA carboxylase (PCC) pathway led to a 1.75-fold and 2.5-fold increase in FK506 production and the methylmalonyl-CoA pool, respectively, compared to those of the RM7011 strain. Lipase activity of the high FK506 producer mutant increased in direct proportion to the increase in FK506 yield, from low detection level up to 43.1 U/ml (12.6-fold). The level of specific FK506 production and lipase activity was improved by enhancing the supply of lipase inducers. This improvement was approximately 1.88-fold (71.5 mg/g) with the supplementation of 5 mM Tween 80, which is the probable effective stimulator in lipase production, to the R2YE medium. When 5 mM vinyl propionate was added as a precursor for PCC pathway to R2YE medium, the specific production of FK506 increased approximately 1.9-fold (71.61 mg/g) compared to that under the non-supplemented condition. Moreover, in the presence of 5 mM Tween 80, the specific FK506 production was approximately 2.2-fold (157.44 mg/g) higher than that when only vinyl propionate was added to the R2YE medium. In particular, PCC expression in Streptomyces sp. RM7011 (RM7011/pSJ1003) together with vinyl propionate feeding resulted in an increase in the FK506 titer to as much as 1.6-fold (251.9 mg/g) compared with that in RM7011/pSE34 in R2YE medium with 5 mM Tween 80 supplementation, indicating that the vinyl propionate is more catabolized to propionate by stimulated lipase activity on Tween 80, that propionyl-CoA yielded from propionate generates methylmalonyl-CoA, and that the PCC pathway plays a key role in increasing the methylmalonyl-CoA pool for FK506 biosynthesis in RM7011 strain. Overall, these results show that a combined approach involving classical random mutation and metabolic engineering can be applied to supply the limiting factor for FK506 biosynthesis, and vinyl propionate could be successfully used as a precursor of important methylmalonyl-CoA building blocks.

Assessing the potential of an induced-mutation strategy for avermectin overproducers

Mutant libraries of avermectin-producing Streptomyces avermitilis strains were constructed by different mutagenesis strategies. A metric was applied to assess the mutation spectrum by calculating the distribution of average phenotypic distance of each population. The results showed for the first time that a microgravity environment could introduce larger phenotype distribution and diversity than UV and N-methyl-N-nitro-N-nitrosoguanidine (NTG) could.

Converging concepts: adaptive response, preconditioning, and the Yerkes-Dodson Law are manifestations of hormesis

The adaptive response in toxicology and environmental mutagenesis, preconditioning in biomedicine and the Yerkes-Dodson Law in psychology have dominating research themes with widespread and significant scientific and societal implications. This paper suggests that these apparently independent biological dose-response phenomena are manifestations of the common and more general biphasic dose-response relationship concept called hormesis. These three types of dose-response, as well as the hormesis concept, may represent the same general type of adaptation, which were discovered independently in different biological disciplines, amongst which there has been little communication. This intellectual isolation, due principally to progressively greater disciplinary specialization, resulted in the evolution of different terminologies for dose-response phenomena with strikingly similar quantitative features. This lack of recognition of converging dose-response concepts across disciplines has important implications since it limits the recognition of a common and basic biological concept while minimizing collaborations by investigators in related areas. The paper concludes that the broadly recognized biological adaptive responses, as described by the concepts of adaptive response, preconditioning and the Yerkes-Dodson Law, are special cases of the more general hormesis dose-response concept.

Induction of the alkA gene of Escherichia coli in gram-negative bacteria

A broad-host-range plasmid containing a fusion of the alkA and lacZ genes of Escherichia coli was introduced into various aerobic and facultative gram-negative bacteria--33 species belonging to 19 genera--to study the induction of expression of the alkA gene by alkylating agents. The bacteria included species of the families Enterobacteriaceae, Pseudomonadaceae, Rhizobiaceae, Vibrionaceae, Neisseriaceae, Rhodospirillaceae, and Azotobacteraceae. Results obtained show that all bacteria tested, except Aeromonas hydrophila, Agrobacterium tumefaciens, Hafnia alvei, Rhizobium meliloti, Salmonella enteritidis, Xanthomonas campestris, and those of the genus Rhodobacter, are able to induce the alkA gene of E. coli in the presence of N-methyl-N'-nitro-N-nitrosoguanidine. All these data indicate that the adaptive response to alkylating agents is present in bacterial species of several families and that the Ada box sequence must be widely conserved.

Polyclonal antibodies against O6-methylguanine-DNA methyltransferase in adapted bacteria

The similarity of the adaptive response and the methyltransferase component in bacterial strains from different phylogenic groups was investigated. An adaptive response with induction of transferase activity was found for the first time in the soil bacteria P. aeruginosa and X. maltophilia. Polyclonal antibodies against the E. coli ada protein were used to investigate the structural similarity of the transferases from several bacterial strains with adaptive responses and inducible transferase activity. These antibodies cross-reacted with transferase from M. luteus and P. aeruginosa but not with proteins from other related bacteria, and not with human transferase. The phylogenic relationships of bacteria with adaptive responses suggest that the response likely was present in the common ancestor of eubacteria. The restricted antibody cross-reactivity may reflect the dual role of the E. coli ada protein not only in DNA repair but in positive gene regulation.

Dihydropteridine reductase from Escherichia coli

A dihydropteridine reductase from Escherichia coli was purified to apparent homogeneity. It is a dimeric enzyme with identical subunits (Mr 27000) and a free N-terminal group. It can use NADH (Vmax./Km 3.36 s-1) and NADPH (Vmax./Km 1.07 s-1) when 6-methyldihydro-(6H)-pterin is the second substrate, as well as quinonoid dihydro-(6H)-biopterin (Vmax./Km 0.69 s-1), dihydro-(6H)-neopterin (Vmax./Km 0.58 s-1), dihydro-(6H)-monapterin 0.66 s-1), 6-methyldihydro-(6H)-pterin and cis-6,7-dimethyldihydro-(6H)-pterin (Vmax./Km 0.66 s-1) when NADH is the second substrate. The pure reductase has a yellow colour and contains bound FAD. The enzyme also has pterin-independent NADH and NADPH oxidoreductase activities when potassium ferricyanide is the electron acceptor.

DNA binding and mutagenicity of ethyl methanesulfonate in wild-type and uvrB cells of Salmonella typhimurium

The extent of DNA ethylation and the influence of excision repair on ethyl methanesulfonate (EMS) mutagenesis of Salmonella typhimurium were examined. The relationship between the dose to DNA and the exposure concentration of EMS was linear. EMS induction of his+ revertants followed exponential kinetics and did not parallel the increase in total DNA ethylation. Mutant induction was influenced by the cells' nucleotide excision repair ability. Although mutagenized to a larger extent than the wild-type (uvr+) strain at high doses, the uvrB strain was more resistant to the mutagenic effect of low doses of EMS.