Low-frequency ultrasound and nitrogen limitation induced enhancement in biomass production and lipid accumulation of Tetradesmus obliquus FACHB-12

Investigating cultivation strategies for enhancing protein content in Auxenochlorella pyrenoidosa FACHB-5

This study investigated the influence of yeast extract addition, carbon source, and photoperiod on the growth dynamics of Auxenochlorella pyrenoidosa FACHB-5. Employing response surface methodology, the culture strategy was optimized, resulting in the following optimal conditions: yeast extract addition at 0.75 g L-1, glucose concentration of 0.83 g L-1, and a photoperiod set at Light: Dark = 18 h: 6 h. Under these conditions, the biomass reached 1.76 g L-1 with a protein content of 750.00 g L-1, containing 40 % of essential amino acids, representing a 1.52-fold increase. Proteomic analysis revealed that the targeted cultivation strategy up-regulated genes involved in microalgal protein synthesis. The combined effect of yeast extract and glucose enhanced both the glutamine synthetase-glutamate synthetase mechanism and the free amino acid content.

A modified cultivation strategy to enhance biomass production and lipid accumulation of Tetradesmus obliquus FACHB-14 with copper stress and light quality induction

In this study, a two-stage culture strategy was refined to concurrently enhance the growth and lipid accumulation of Tetradesmus obliquus. The results unveiled that, during the initial stage, the optimal conditions for biomass accumulation were achieved with 0.02 mg·L-1 Cu2+ concentration and red light. Under these conditions, biomass accumulation reached 0.628 g·L-1, marking a substantial 23.62 % increase compared to the control group. In the second stage, the optimal conditions for lipid accumulation were identified as 0.5 mg·L-1 Cu2+ concentration and red light, achieving 64.25 mg·g-1·d-1 and marking a 128.38 % increase over the control. Furthermore, the fatty acid analysis results revealed an 18.85 % increase in the saturated fatty acid content, indicating enhanced combustion performance of microalgae cultivated under the dual stress of red light and 0.5 mg·L-1 Cu2+. This study offers insights into the potential application of Tetradesmus obliquus in biofuel production.

Enhancing the growth of thermophilic Bacillus licheniformis YYC4 by low-intensity fixed-frequency continuous ultrasound

The effect of low-intensity fixed-frequency continuous ultrasound (LIFFCU) on the growth of Bacillus licheniformis YYC4 was investigated. The changes in morphology and activity of the organism, contributing to the growth were also explored. Compared with the control, a significant increase (48.95%) in the biomass of B. licheniformis YYC4 (at the logarithmic metaphase) was observed following the LIFFCU (28 kHz, 1.5 h and 120 W (equivalent to power density of 40 W/L)) treatment. SEM images showed that ultrasonication caused sonoporation, resulting in increased membrane permeability, evidenced by increase in cellular membrane potential, electrical conductivity of the culture, extracellular protein and nucleic acid, and intracellular Ca2+ content. Furthermore, LIFFCU action remarkably increased the extracellular protease activity, volatile components of the culture medium, microbial metabolic activity, and spore germination of the strain. Therefore, LIFFCU could be used to efficiently promote the growth of targeted microorganisms.

The growth and lipid accumulation of Scenedesmus quadricauda under nitrogen starvation stress during xylose mixotrophic/heterotrophic cultivation

In order to conquer the block of high cost and low yields which limit to realize the commercialization of microalgal biodiesel, the mixotrophic and heterotrophic cultivation of Scenedesmus quadricauda FACHB-1297 fed on xylose was separately studied employing six forms of media: phosphorus sufficient, phosphorus restricted, and phosphorus starvation were combined with nitrogen sufficient and nitrogen starvation conditions. The maximum lipid content (about 41% of dry weight) was obtained on the 5th day (heterotrophic cultivation) and 8th day (mixotrophic cultivation) under the nitrogen starved and phosphorus sufficient (N0&P) conditions, which was about twofold in comparison to the final lipid content on the sufficient nitrogen condition (control). Under mixotrophic and heterotrophic modes, the highest lipid production was achieved in the N0&P trial, with the value of 274.96 mg/L and 193.77 mg/L, respectively. Xylose utilization rate of 30-96% under heterotrophic modes was apparently higher than that of 20-50% in mixotrophic modes. In contrast, phosphorus uptake rate of 100% under mixotrophic cultivation was significantly more than that of 60-90% in heterotrophic cultivation. Furthermore, under the condition of heterotrophic cultivation using xylose as a carbon source, the phosphorus had a positive impact on microalgae cell synthesis and the lipid content enhanced with the augmentation in phosphorus concentrations. We suggested that sufficient phosphorus should be supplied for obtaining higher microalgal lipid production in the lack of nitrogen under xylose heterotrophic/mixotrophic condition. This was a highly effective way to obtain efficient microalgae lipid production.

New insights on the role of nitrogen in the resistance to environmental stress in an endosymbiotic dinoflagellate

Endosymbiotic dinoflagellates provide the nutritional basis for marine invertebrates, especially reef-building corals. These dinoflagellates are sensitive to environmental changes, and understanding the factors that can increase the resistance of the symbionts is crucial for the elucidation of the mechanisms involved with coral bleaching. Here, we demonstrate how the endosymbiotic dinoflagellate Durusdinium glynnii is affected by concentration (1760 vs 440 µM) and source (sodium nitrate vs urea) of nitrogen after light and thermal stress exposure. The effectiveness in the use of the two nitrogen forms was proven by the nitrogen isotopic signature. Overall, high nitrogen concentrations, regardless of source, increased D. glynnii growth, chlorophyll-a, and peridinin levels. During the pre-stress period, the use of urea accelerated the growth of D. glynnii compared to cells grown using sodium nitrate. During the luminous stress, high nitrate conditions increased cell growth, but no changes in pigments composition was observed. On the other hand, during thermal stress, a steep and steady decline in cell densities over time was observed, except for high urea condition, where there is cellular division and peridinin accumulation 72 h after the thermal shock. Our findings suggest peridinin has a protective role during the thermal stress, and the uptake of urea by D. glynnii can alleviate thermal stress responses, eventually mitigating coral bleaching events.

The Influence of Ultrasound on the Growth of Nannochloris sp. in Modified Growth Medium

The influence of ultrasound irradiation on the algal biomass productivity as well as its oil content and fatty acids profile, grown in a modified Zarrouk medium, i.e., deproteinized whey waste solution, was investigated. The algal samples (Nannochloris sp. 424-1 microalgae) were grown for 7 days in a thermostated incubator at 28 °C, shaken under continuous light. During this period, the algal biomass was subjected to induced stress by ultrasonic irradiation at different powers and sonication time. The obtained results demonstrate that ultrasound stressing of algae biomass has a positive effect on both the quantity of biomass and the oil obtained, also causing a shift in fatty acid composition by increasing the proportion of C16 and C18 polyunsaturated fatty acids. A low dosage level of exposure to the ultrasound led to algal biomass increase as well as lipid accumulation. For both types of irradiation modes which were investigated, daily and only initial irradiation, the beneficial effect of the ultrasound decreases as the exposure time increases and the excessive sonication becomes detrimental to microalgae growth.

Strategic thermosonication-mediated modulation of lactic acid bacteria acidification kinetics for enhanced (post)-fermentation performance

This study explored the feasibility of thermosonication (TS)-prestressed inoculum with different fermentation patterns for regulating microbial (post)-fermentation acidification kinetics. Through a Box-Behnken design, stimulative (20 min, 400 W, 33 kHz, 25 °C) and inhibitive (10 min, 600 W, 33 kHz, 20 °C) effects on the acidification capability of Lactobacillus plantarum A3 were achieved without observing greatly activated/inactivated strains growth, further confirmed by lactose fermentation performed by Streptococcus thermophilus and Lactobacillus bulgaricus. Lactic acid was the major contributing factor responsible for TS-induced acidification modifications corresponding to the potential fluctuations of CoA biosynthesis, fatty acid degradation and chain elongation pathways to TS prestress. Microscopy observations and quantitative extracellular substance assays showed palpable stress disturbance on microbes, but causing insignificant effects on product characteristics. This investigation demonstrated the potential of controlled sonication prestress strategies to achieve dual engineering effects on microbial metabolic behavior, for alleviating post-acidification problem or enhancing process efficiencies.