Abstract
Haloarchaea produce C50 carotenoids such as bacterioruberin, which are of biotechnological in-terest. This study aimed to analyze the effect of different environmental and nutritional conditions on the cellular growth and dynamics of carotenoids accumulation in Haloferax mediterranei. The maximum production of carotenoids (40 µg·mL−1) was obtained during the stationary phase of growth, probably due to nutrient-limiting conditions (one-step culture). By seven days of culture, 1 mL culture produced 22.4 mg of dry weight biomass containing 0.18 % (w/w) of carotenoids. On the other hand, carbon-deficient cultures (low C/N ratio) were observed to be optimum for C50 bacterioruberin production by Hfx. mediterranei, but negatively affected the growth of cells. Thus, a two-steps process was evaluated for optimum carotenoids yield. In the first step, a nutri-ent-repleted culture medium enabled the haloarchaea to produce biomass, while in the second step, the biomass was incubated under osmotic stress and in a carbon-deficient medium. Under the conditions used, the obtained biomass contained 0.27% (w/w) of carotenoids after seven days, which accounts for 58.49 µg·mL−1 of carotenoids for a culture with turbidity 14.0.
Highlights
Received: 30 December 2020Halophilic archaea or haloarchaea are extremophilic microorganisms from the domain Archaea that grow optimally in culture media with high salt concentrations.The family Haloferacaceae in particular includes non-photosynthetic and mostly aerobic heterotrophs whose natural environments are usually hypersaline lakes and salt marshes [1].Haloarchaea produce highly valuable products of biotechnological interest, such as high temperature-resistant enzymes [2], polyhydroxyalkanoates [3], polyhydroxybutyrate [4], and carotenoids [5]
Following a lag phase of three days, an exponential phase was observed during days 3 to 5, with a generation time of around 32 h for cell growth, and the stationary phase was reached after five days of growth
The highest accumulation of carotenoids was observed during the stationary phase, when the biomass production in the culture had stopped possibly due to nutrient limitation
Summary
Received: 30 December 2020Halophilic archaea or haloarchaea are extremophilic microorganisms from the domain Archaea that grow optimally in culture media with high salt concentrations (up to 4 M).The family Haloferacaceae in particular includes non-photosynthetic and mostly aerobic heterotrophs whose natural environments are usually hypersaline lakes and salt marshes [1].Haloarchaea produce highly valuable products of biotechnological interest, such as high temperature-resistant enzymes [2], polyhydroxyalkanoates [3], polyhydroxybutyrate [4], and carotenoids [5]. BR is a C50 carotenoid that consists of a primary conjugated isoprenoid chain with thirteen conjugated carbon–carbon units and four hydroxyl groups arising from the terminal ends It improves the fluidity of the cell membrane and, due to its strong antioxidant properties, protects the cells from the harmful effects of radiation, as well as from osmotic stress [8]. C50 carotenoids show a higher antioxidant capacity than the C40 carotenoids, such as β-carotene, that are produced by most photosynthetic organisms [9]. This property can be explained by the higher number of pairs of conjugated double bonds, which makes these carotenoids remarkably interesting for the food and pharmaceutical industries [5]
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