Regulation of biosynthesis of monensins on chemically defined medium

Addition ofL-valine andDL-isoleucine to the cultivation medium ofStreptomyces cinnamonensis was found to affect the ratio of synthesized monensins A and B. In the presence ofL-valine monensin A is synthesized predominantly, whereas in the presence ofDL-isoleucine the production of monensin B increases.     

氨基酸前体对棘白霉素B发酵合成的影响

以构巢曲霉(Aspergillus nidulans)发酵生产酯肽类化合物棘白霉素B,研究棘白霉素B己肽环结构的前体性氨基酸对产物的代谢影响,显示出脯氨酸、鸟氨酸、苏氨酸在发酵48 h 补入,对发酵代谢有促进作用.利用响应面统计学方法进行前体及有机氮源配方优化,得出优化配方:脯氨酸4.55 mg/mL,鸟氨酸1.85 mg/mL,苏氨酸0.97 mg/mL,棉籽粉2.62％,摇瓶发酵水平达到3 270μg/mL,较原水平提高30.2％.新工艺在50 L罐上放大,发酵水平进一步提高至3 520 μg/mL,显示出良好的工业应用前景.     

Effect of penicillin precursors on antibiotic biosynthesis in various strains]

The regularities of biosynthesis of 6-aminopenicillanic acid (6-APA), benzylpenicillin (BP) and phenoxymethylpenicillin (PMP) by the strains under the investigation did not significantly differ. In the absence of the precursor both the strains mainly synthesized 6-APA. Phenylacetic acid (PAA) and phenoxyacetic acid (POAA) provided directed biosynthesis: the fungus synthesized BP or PMP depending on the precursor nature. When the amount of the precursors was not sufficient, 6-APA was synthesized along with the penicillins. PAA proved to be a more active precursor than POAA. When both precursors were present in the fermentation broth, only BR was synthesized. An important distinction of strain 316A was its increased sensitivity to PAA especially in the initial period. After an increase in the PAA concentration the growth rate of strain 316A lowered to a greater extent than that of strain 284A. This was likely to determine the higher levels of penicillin production by strain 316A in the presence of POAA, a nontoxic precursor. A procedure for supplying the precursors was developed. Under the laboratory conditions it provided high levels of the penicillin production.     

Enhanced anaerobic biotransformation of carbon tetrachloride with precursors of vitamin B12 biosynthesis

Relatively low concentrations of Vitamin B₁₂ are known to accelerate the anaerobic biotransformation of carbon tetrachloride (CT) and chloroform (CF). However, the addition of vitamin B₁₂ for field-scale bioremediation is expected to be costly. The present study considered a strategy to generate vitamin B₁₂ by addition of biosynthetic precursors. One of the precursors, porphobilinogen (PB) involved in the formation of the corrin ring, significantly increased the CT biotransformation rates by 2.7−, 8.8- and 10.9-fold when supplemented at 160, 500 and 900 μM, respectively. A positive control with 10 μM of vitamin B₁₂ resulted in a 5.9-fold increase in the CT-bioconversion rate. PB additions provided high molar yields of inorganic chloride (57% of CT organochlorine), comparable to that obtained with vitamin B₁₂ supplemented cultures. The primary substrate, methanol, known to induce vitamin B₁₂ production in methanogens and acetogens, was required for PB to have a significant impact on CT conversion. The observation suggests that PB’s role was due to stimulating vitamin B₁₂ biosynthesis. The present study therefore provides insights on how to achieve vitamin B₁₂ enhanced rates of CT bioremediation through the use of less complex compounds that are precursors of vitamin B₁₂. Although PB is a costly chemical, its large impact points to corrin ring formation as the rate-limiting step.     

Propionate and the production of monensins inStreptomyces cinnamonensis

Variants resistant to propionate were prepared from a mutant strain of Streptomyces cinnamonensis producing predominantly monensin A. Using selected resistants the production of monensins (in media with higher concentrations of propionate) was examined. Stimulation of monensin synthesis by propionate was observed with 70% of the resistants studied. Propionate did not influence the ratio between monensin A and B production.     

Effect of inorganic phosphorus on the biosynthesis of polymyxin B]

A synthetic medium containing optimal levels of the sources of carbon, nitrogen and inorganic phosphorus and providing satisfactory yields of polymyxin B was developed for 2 strains of Bac. polymyxa 933 and VK-153. The consumption of phosphorus in the medium by the strains and the antibiotic biosynthesis levels depended on the form of phosphorus added to the medium. Optimal biosynthesis of polymyxin B was observed at lower concentration levels of soluble soluble phosphorus in the medium than the bacterial growth.     

Effect of plant stilbene precursors on the biosynthesis of resveratrol in Vitis amurensis Rupr. Cell cultures

The biosynthesis of resveratrol after the application of a precursor for biosynthesis, i.e., phenylalanine (Phe), has been studied. The application of Phe has been shown to increase significantly the expression of the phenylalanine-ammonia-lyase (PAL) and stilbene synthase (STS) genes and enhance the production of resveratrol by 8.5 times. Data on resveratrol production after the addition of Phe and coumaric acid (CA) were compared with known analogs.     

Supply of precursors for carotenoid biosynthesis in plants

Carotenoids are isoprenoids of industrial and nutritional interest produced by all photosynthetic organisms, including plants. Too often, the metabolic engineering of plant carotenogenesis has been obstructed by our limited knowledge on how the endogenous pathway interacts with other related metabolic pathways, particularly with those involved in the production of isoprenoid precursors. However, recent discoveries are providing new insights into this field. All isoprenoids derive from prenyl diphosphate precursors. In the case of carotenoids, these precursors are produced predominantly by the methylerythritol 4-phosphate (MEP) pathway in plants. This review focuses on the progress in our understanding of how manipulation of the MEP pathway impacts carotenoid biosynthesis and on the discoveries underlining the central importance of coordinating the supply of MEP-derived precursors with the biosynthesis of carotenoids and other derived isoprenoids.     

Characterization of leukotriene A4 and B4 biosynthesis

We have studied LTA4 and LTB4 synthesis in a cell-free system from RBL-1 cells. All the enzymes leading to the formation of LTB4 from arachidonic acid are localized in the soluble fraction (100,000 x g supernatant) of these cells. The formation of LTA4 and LTB4 is complete by 10 min. When we varied the arachidonic acid concentration from 1 to 300 microM, the synthesis of LTB4 leveled off at 30 microM and of LTA4 at 100 microM while 5-HETE had not reached a plateau at 300 microM. This enzyme system has the capacity to generate relatively large amounts of 5-HETE and LTA4 and only a relatively small amount of LTB4. Therefore, the rate limiting step is not the 5-lipoxygenase, the first step in the pathway, but the conversion of LTA4 to LTB4. This is in contrast to cyclooxygenase pathway where the first step is rate limiting. A second addition of arachidonic acid at submaximal concentration for LTA4 synthesis did not produce any additional LTA4 or LTB4. Further study of this phenomenon showed that the 5-lipoxygenase and LTA-synthase were inactivated with time by preincubation with arachidonic acid and that peroxy fatty acids seem to be the inactivating species.     

Synthesis of probable and improbable precursors for porphyrin biosynthesis.

Insights into details of the biomechanism by which porphobilinogen (1) cyclotetramerizes to uroporphyrinogen III (2) as well as promising synthetic applications are provided by investigation of this reaction in vitro. The cyclotetramerization of newly prepared norporphobilinogen (5) proved to be extemely specific due to strong conformation control. Advantage was taken of this finding by preparing a N,N,N,N-tetramethyl-porphyrinogen (13a) for the first time. Protected derivatives of the linear tetramer of porphobilinogen (20c) which is regarded as an intermediate of the cyclotetramerization were gained by total synthesis and their transformations investigated.     

Novel insights into biosynthesis and uptake of rhamnolipids and their precursors

Applied Microbiology and Biotechnology - The human pathogenic bacterium Pseudomonas aeruginosa produces rhamnolipids, glycolipids with functions for bacterial motility, biofilm formation, and...     

Studies on antibiotic biosynthesis by protoplasts and resting cells of Streptomyces echinatus. Part II. Effect of chromophore precursors

Washed cell and protoplast suspensions from Streptomyces echinatus A8331, which produces the quinoxaline antibiotic echinomycin, have been used to study the effects of analogues of the natural chromophore upon antibiotic biosynthesis. Addition of quinoline-2-carboxylic acid caused a decrease in the labelling of echinomycin from L-[methyl-14C]methionine and an increase in labelled chloroform-extractable material. Quinoxaline-2-carboxylic acid increased the incorporation of radioactivity into both fractions. Thieno[3,2-b]pyridine-5-carboxylic acid, 6-methylquinoline-2-carboxylic acid, and quinoline-2-carboxylic acid (also to a lesser extent 7-chloroquinoxaline-2-carboxylic acid) increased markedly the incorporation of radioactivity into chloroform-extractable material and virtually abolished echinomycin synthesis. Autoradiographs of extracts from suspensions supplemented with the latter four analogues revealed bis-substituted metabolites not found in unsupplemented cultures. When protoplast suspensions were incubated with L-[U-14C]serine, L-[U-14C]valine, or DL-[benzene ring-U-14C]tryptophan, quinoline-2-carboxylic acid, thieno[3,2-b]pyridine-5-carboxylic acid, and 6-methylquinoline-2-carboxylic acid directed the synthesis of antibiotically active bis derivatives at the expense of echinomycin. When analogues of quinoxaline-2-carboxylic acid previously found unsuitable for incorporation by growing cultures were tested in protoplast suspensions, only isoquinoline-3-carboxylic acid caused a large increase in the incorporation of radioactivity from L-[methyl-14C]methionine into chloroform-extractable material. With DL-[benzene ring-U-14C]tryptophan as the radiolabel, benzotriazoline-2-acetic acid and 6-bromoquinoxaline-2-carboxylic acid as well as isoquinoline-3-carboxylic acid sharply reduced the labelling of echinomycin.     

Effect of phosphorus on polymyxin B biosynthesis by B. polymyxa 1538 on media of varying makeup]

The effect of phosphorus on biosynthesis of polymyxin B by B. polymyxa 1538 was studied and its optimal concentration in the synthetic and two complex media was determined. Correlation between the culture growth and consumption of the main components, on the one hand, and concentration of phosphorus in the medium, on the other hand, was found. It was shown that the effect of phosphorus on biosynthesis of polymyxin B did not depend on the carbon source in the medium and aeration conditions.