Francesca Raganati

As Streptomycetes might produce melanin to survive in stressful environmental conditions, like under metal exposure, supplementing metal ions to the growth medium could be a wise strategy for boosting the production of the pigment. The aim of this study was to test, for the first time, the possibility of boosting S. nashvillensis DSM40314 melanin biosynthesis by adding to the growth medium singularly or, at the same time, different concentrations (1.0, 1.5, and 2.0 g∙L⁻¹) of CuSO₄ or/and Fe₂(SO₄)₃. A maximum melanin production of 4.0 ± 0.1 g·L⁻¹ was obtained in shake flasks with a 2.0 g∙L⁻¹ coupled addition of the two metals, while the extracellular tyrosinase activities ranged values between 5.4 and 11.6 ± 0.1 U·L⁻¹. The pigments produced in different conditions were precipitated from the broth supernatants under acidic conditions, purified, and characterized by UV-VIS, FT-IR, and NMR analyses that determined structures like eumelanin pigments. Fermentation experiments in stirred tank reactors allowed to scale up the process in more controlled conditions, further boosting the pigment production up to 4.9 ± 0.1 g·L⁻¹, with an increase of about 22.0% compared to the results obtained in shake flasks.

This Special Issue, “Advances in Bioprocess Technology”, focuses on the latest advancements in sustainable bioprocess technologies

Although microalgae exploitation is very promising, process sustainability is undermined by biomass production and harvesting. Among the various bottlenecks of the production process, particular attention should be paid to the water footprint. Indeed, a huge volume of water is required in microalgae production. Water reuse can support both the water footprint and medium cost reduction, saving water and unconverted substrates. The present study reports preliminary results regarding the utilization of a water reuse strategy for two Chlorophyta microalgae under batch conditions. Growth parameters and chlorophyll content are monitored and the optimal amount of reused medium is assessed. The results show that 70% of the medium can be reused with no loss of specific growth rate and chlorophyll fraction for Pseudococcomyxa simplex in three consecutive batch cultivations. By contrast, a significant decline in Chlorella vulgaris growth was observed after the first cultivation in reused medium, across all tested conditions.

Biochemical engineering deals with the processing of biological or chemical materials using enzymes or living cells as biological catalysts