Precursor-feeding and altered-growth conditions reveal novel blue pigment production by Rubrivivax benzoatilyticus JA2

Stable isotope-assisted metabolite profiling reveals new insights into L-tryptophan chemotrophic metabolism of Rubrivivax benzoatilyticus

Anoxygenic photosynthetic bacteria (APB) are metabolically versatile, capable of surviving with an extended range of carbon and nitrogen sources. This group of phototrophic bacteria have remarkable metabolic plasticity in utilizing an array of organic compounds as carbon source/electron donors and nitrogen sources with sophisticated growth modes. Rubrivivax benzoatilyticus JA2 is one such photosynthetic bacterium utilizes L-tryptophan as nitrogen source under phototrophic growth mode and produces an array of indolic compounds of biotechnological significance. However, chemotrophic L-tryptophan metabolism is largely unexplored and studying L-tryptophan metabolism under chemotrophic mode would provide new insights into metabolic potential of strain JA2. In the present study, we employed stable-isotopes assisted metabolite profiling to unravel the L-tryptophan catabolism in Rubrivivax benzoatilyticus strain JA2 under chemotrophic (dark aerobic) conditions. Utilization of L-tryptophan as a nitrogen source for growth and simultaneous production of indole derivatives was observed in strain JA2. Liquid chromatography mass spectrometry (LC-MS) analysis of exo-metabolite profiling of carbon labeled L-tryptophan (¹³C₁₁) fed cultures of strain JA2 revealed at least seventy labeled metabolites. Of these, only fourteen metabolites were confirmed using standards, while sixteen were putative and forty metabolites remained unidentified. L-tryptophan chemotrophic catabolism revealed multiple catabolic pathways and distinct differential catabolism of L-tryptophan under chemotropic state as compared to photo-catabolism of L-tryptophan in strain JA2.

Improved AP-3 production through combined ARTP mutagenesis, fermentation optimization, and subsequent genome shuffling

Ansamitocin (AP-3) is an ansamycins antibiotic isolated from Actinosynnema pretiosum and demonstrating high anti-tumor activity. To improve AP-3 production, the A. pretiosum ATCC 31565 strain was treated with atmospheric and room temperature plasma (ARTP). Four stable mutants were obtained by ARTP, of which the A. pretiosum L-40 mutant produced 242.9 mg/L AP-3, representing a 22.5% increase compared to the original wild type strain. With seed medium optimization, AP-3 production of mutant L-40 reached 307.8 mg/L; qRT-PCR analysis revealed that AP-3 biosynthesis-related gene expression was significantly up-regulated under optimized conditions. To further improve the AP-3 production, genome shuffling (GS) technology was used on the four A. pretiosum mutants by ARTP. After three rounds of GS combined with high-throughput screening, the genetically stable recombinant strain G3-96 was obtained. The production of AP-3 in the G3-96 strain was 410.1 mg/L in shake flask cultures, which was 44.5% higher than the L-40 production from the parental strain, and AP-3 was increased by 93.8% compared to the wild-type A. pretiosum. These results suggest that the combination of mutagenesis, seed medium optimization, and GS technology can effectively improve the AP-3 production capacity of A. pretiosum and provide an enabling methodology for AP-3 industrial production.

Tryptophan, a non-canonical melanin precursor: New L-tryptophan based melanin production by Rubrivivax benzoatilyticus JA2

Melanins are chemically diverse ubiquitous pigments found across the life forms synthesized via different biochemical pathways mainly from L-tyrosine or acetyl CoA. Though few reports suggest the possibility of tryptophan-based melanin synthesis, however, such tryptophan-based melanin and its biosynthesis remained a biochemical riddle. Here we report tryptophan-based melanin production by bacterium, Rubrivivax benzoatilyticus JA2. Aerobic cultures of strain JA2 produced brown pigment when grown on L-tryptophan-containing media. Purified pigment showed typical physico-chemical properties of melanin. Further, extensive spectroscopic studies revealed that pigment is an amorphous, indole-type polymer with stable free radical centers. Further, hydrolysis of the brown pigment revealed the presence of indole moiety, confirming the indolic nature of the pigment. Demonstration of in vitro and in vivo pigment synthesis directly from L-tryptophan or hydroxytryptophan confirms tryptophan-based melanin synthesis in strain JA2. Interestingly, canonical melanin biosynthetic inhibitors did not affect the pigment synthesis indicating possible non-canonical tryptophan-based melanin biosynthesis in strain JA2. Further, the exometabolite profiling and precursor feeding studies suggests that L-tryptophan converted to hydroxytryptophan/hydroxyindoles and their subsequent polymerization lead to the formation of melanin. The current study sheds light on biosynthetic diversity of melanins and L-tryptophan can be a potential precursor for melanin synthesis in life forms.