Biosensor-Assisted Adaptive Laboratory Evolution for Violacein Production

Violacein is a naturally occurring purple pigment, widely used in cosmetics and has potent antibacterial and antiviral properties. Violacein can be produced from tryptophan, consequently sufficient tryptophan biosynthesis is the key to violacein production. However, the complicated biosynthetic pathways and regulatory mechanisms often make the tryptophan overproduction challenging in Escherichia coli. In this study, we used the adaptive laboratory evolution (ALE) strategy to improve violacein production using galactose as a carbon source. During the ALE, a tryptophan-responsive biosensor was employed to provide selection pressure to enrich tryptophan-producing cells. From the biosensor-assisted ALE, we obtained an evolved population of cells capable of effectively catabolizing galactose to tryptophan and subsequently used the population to obtain the best violacein producer. In addition, whole-genome sequencing of the evolved strain identified point mutations beneficial to the overproduction. Overall, we demonstrated that the biosensor-assisted ALE strategy could be used to rapidly and selectively evolve the producers to yield high violacein production.

Review and New Evidence on the Molluscan Purple Pigment Used in the Early Late Bronze Age Aegean Wall Paintings

The production and use of the pigment extracted from the murex molluscs is discussed here in association with the purple textile dyeing industry in the Prehistoric Aegean. “True” purple has been identified in a number of archaeological finds dating from the early Late Bronze Age, found in old and recent excavations at three different but contemporary sites: Akrotiri and Raos on Thera, and Trianda on Rhodes. The chemical composition of the shellfish purple pigment either found in lump form or applied on wall paintings is discussed in relation to the archaeological context of several examined finds and with reference to Pliny’s purpurissum. The results of a comprehensive methodology combining new data obtained with molecular spectroscopies (microRaman and FTIR) and already reported data obtained with high performance liquid chromatography coupled with a diode array detector (HPLC–DAD) applied to samples of the murex purple finds are discussed in comparison to published data relating to few other instances of analytically proven murex purple pigment found in the Aegean over the timespan of its documented exploitation.

A Blue-Purple Pigment-Producing Bacterium Isolated from the Vezelka River in the City of Belgorod

Violacein is a biotechnologically significant secondary metabolite due to its antibacterial, antifungal, and other properties. Isolation, research, and identification of violacein producing strains are of interest for the development of biotechnological processes, in order to enhance the biosynthesis of this compound. The purpose of the present work was to study the properties of a newly isolated bacterium capable of synthesizing blue-purple pigment. An aboriginal bacterium was isolated from the coastal zone of the Vezelka River in the city of Belgorod. Based on chemical and spectrophotometric studies of the crude ethanol extract, the pigment was identified as violacein, and the isolate was assigned to the group of violacein-forming bacteria, which includes bacteria of the genera Chromobacterium, Iodobacter, Janthinobacterium, Duganella, Collimonas, and Massilia. Based on cultural, morphological, tinctorial, physiological, and biochemical properties, as well as analysis of the 16S rRNA gene sequence, the new isolated strain was assigned to the genus Janthinobacterium. The isolated strain is capable of suppressing the growth of a number of fungal and bacterial phytopathogens. For representatives of the genus Janthinobacterium, their inhibitory influence on cyanobacteria was shown for the first time.

Super-Sweet Purple Sweetcorn: Breaking the Genetic Link

Purple-pericarp supersweet sweetcorn currently does not exist as a horticultural product. Purple pericarp comprises the outer layers of the kernel, with the purple pigment being produced by anthocyanin. Unlike the aleurone layer which can also be pigmented, the pericarp is maternal tissue. Although standard purple sweetcorn based on mutations such as sugary1 (su1) and sugary enhancer (se1) are in existence, the development of purple supersweet sweetcorn based on the widely used shrunken2 (sh2) gene mutation is much more challenging. This is because there is an extremely close genetic linkage between the supersweet shrunken-2 mutation and the anthocyanin biosynthesis gene, anthocyaninless-1 (a1). As distance between these two genes is only 0.1 cM, the development of purple supersweet sweetcorn depends on breaking this close genetic link, which occurs at a very low frequency of 1 in 1000 meiotic crossovers. To make this possible, we crossed a white supersweet variety (a1a1sh2sh2) with a purple-pericarp Peruvian maize (A1A1Sh2Sh2) to obtain an initial heterozygous hybrid (A1a1Sh2sh2). The hybrid seed was sown and subsequently self-pollinated to produce seed segregating for the double recessive homozygote, sh2sh2 (1 in 4). These kernels present a visually distinctive phenotype, characterised by the seed’s shrunken appearance. Approximately 2760 sh2sh2 seeds were separated and resown. Due to the low frequency of linkage breakage, the majority of these plants (~99.9%) produced supersweet white cobs (a1a1sh2sh2). Three plants (0.1%) however, produced supersweet purple cobs (A1a1sh2sh2), due to a single low-frequency linkage break. These cobs will form the basis for a purple-pericarp supersweet sweetcorn breeding program.

Characterization of Ocimum tenuiflorum (Linn.) Morpho-types Using RAPD Markers

Ocimum tenuiflorum Linn. (Lamiaceae) is an aromatic plant with a lot of potential medicinally, industrially and domestically. There are different morpho-types of O. tenuiflorum, with different shades of purple pigment on their leaves. Very few studies have been done to study the genetic variation among O. tenuiflorum morpho-types. Thus, in the present study, four O. tenuiflorum morpho-types that varied in pigmentation were characterised using RAPD marker as a molecular tool. Eight different primers collectively amplified 64 bands in the four morpho-types analysed. The RAPD technique revealed that the varied amount of purple pigment in O. tenuiflorum morpho-types is not due to environmental factor alone. The UPGMA clustering algorithm based on RAPD data grouped the four morpho-types into two major groups, with O. tenuiflorum (T2) with very light purple leaves and stem morpho-type, more related to O. tenuiflorum (T3) that have deep purple leaves and stem. The result was able to show the phylogenetic relationships within the species. The low level of genetic diversity observed in O. tenuiflorum can be attributed to the mode of reproduction and the reproductive biology of the species, due to the fact that they are likely to be natural hybrids produced through cross pollination.