In this study, the removal of cadmium (Cd) by free-living Oscillatoria sp. was studied. Our results showed that maximal Cd removal efficiency (~60%) by the cyanobacterial culture was achieved within 12–24 h in the presence of 5.0 or 25.0 mg/L of Cd. The mechanisms underlying this phenomenon were explored by elemental analysis and FTIR-ATR spectroscopy. It was found that metal adsorption by negatively charged functional groups in the cyanobacterial biomass was the main mechanism used by Oscillatoria sp. to remove metal from the aqueous medium, followed by Cd bioaccumulation into living cells. Additionally, Cd-exposed microalgae showed increased oxidative stress (MDA formation), a decreased dehydrogenase activity, a higher amount of soluble carbohydrates and a decreased total carotenoid concentration, as compared to the control cells. These results suggest that Oscillatoria sp. improved its antioxidative defense system under stressful conditions, through carotenoid-mediated ROS quenching and induction of carbohydrate catabolism, in order to counteract the oxidative damage and preserve the photosynthetic machinery and cellular energetics. In fact, no significant reduction in Oscillatoria sp. cell density, total protein amount, and chlorophyll a content was observed after 24-h Cd exposure, even at the highest metal concentration tested (i.e., 25.0 mg/L). Hence, the presented results are the first to describe some new insights about the metabolic and physiological behavior of living Oscillatoria sp. during Cd remediation, and open up the possibility of finding an equilibrium that maximizes metal removal performance with an active cyanobacterial metabolism, to achieve a rewarding and sustainable management of industrial metal-polluted wastewater.

• A protease from a psychrotolerant yeast was characterized. • Protease production was dependent on temperature and medium composition. • Mass spectrometry analysis indicated that the protein belongs to the pepsin family. • We propose that the enzyme reported here could be Rodothorulapepsin.

Microbial proteases, especially aspartic proteases, are an essential group of enzymes produced from different microorganisms. Microbial proteases have several applications, mainly in the food, beverage, cosmetic, and pharmaceutical industries, due to their efficiency in the processing and in the manufacturing stages. The yeast Rhodotorula mucilaginosa CBMAI 1528 was isolated from the Antarctic environment and was previously reported to have higher extracellular aspartic protease production. In addition, advances in the operational conditions of bioreactors for enzyme production are important to reduce the gap associated with scaling−up processes. This is the first study that evaluates the influence of oxygen transference (k_La) on the protease production of R. mucilaginosa yeast. To that end, batch cultures were created in a stirred tank bioreactor using Sabouraud dextrose broth at 25 °C for 72 h under k_La values from 18 to 135 h⁻¹. The results show that k_La (121 h⁻¹) obtained at 500 rpm and 1.5 vvm plays an important role in protease production (124.9 U/mL) and productivity (6.784 U/L.h) as well as biomass (10.4 g/L), μ_max (0.14 h⁻¹) and Y_x/s (0.484 g/g). In conclusion, R. mucilaginosa showed high yield production in aerobic culture with the efficiency of protease expression and secretion influenced by k_La. In this sense, our results could be used for further industrial investment.

Background: The unsafe disposal of milk processing effluents has a negative impact on the environment due to their high content of nutrients and organic matter. Green alternatives can be applied to effectively manage and valorize these effluents, reducing their environmental footprint. Methods: The ability of the free-living cyanobacterium Oscillatoria sp. to grow in real cheese whey was evaluated as a potential strategy for integrating dairy wastewater treatment with biomass valorization. Autotrophic and mixotrophic cultures were maintained under controlled laboratory conditions and monitored over 28 days for growth, cell viability, biomass, pigment content, and physicochemical parameters, including pH, protein, carbohydrate, and chemical oxygen demand (COD). Results: Oscillatoria sp. successfully adapted to the initial acidic conditions of the effluent (pH 2.8–2.9), increasing the pH of the treated whey to levels suitable for industrial wastewater disposal (pH 6.0–9.0). A 5-fold increase in dehydrogenase activity was observed after a 28-day culture, with no signs of oxidative damage. Cyanobacterial biomass cultivated under mixotrophic conditions displayed a significant reduction (∼55%) in photosynthetic pigments, including chlorophyll a and total carotenoids, compared to autotrophic cultures. Notably, Oscillatoria sp. biomass increased by 2.3-fold under mixotrophy, compared to the autotrophic control. The higher biomass production was accompanied by a significant reduction in the whey COD from 35,250 mg/L to 8500 mg/L, along with a 65% and 80% decrease in protein and carbohydrate content, respectively. Conclusions: These findings provide new insights into the metabolic behavior of Oscillatoria sp. during cheese whey bioremediation, highlighting the potential of mixotrophic cyanobacteria for managing dairy wastewater management.