Biomass, Volume 1, Issue 2 (December 2021) – 3 articles

Desmodesmus is a green microalgal genus that is frequently found in aquatic environments. Its high biomass productivity and potential as a source of lipids have attracted considerable attention. Although Desmodesmus is ubiquitous, it is difficult to identify; even within a small area, the diversity of the species and the fatty acids they produce are unknown. In this study, we performed scanning electron microscopy (SEM) and analyzed the genetic diversity of the internal transcribed spacer (ITS) region to accurately identify Desmodesmus in a local area of Japan (Saga City, Saga Pref.) and to assess its existence as a biological resource. In addition, we analyzed the fatty acid composition and content of the newly established strains. In total, 10 new strains were established, and 9 previously described species were identified. The presence of a cosmopolitan species indicated the global distribution of Desmodesmus. However, only regional species were found. One strain, dSgDes-b, did not form a clear clade with any described species in the phylogenetic analysis and had a characteristic ITS2 secondary structure. The cell wall of this strain exhibited a distinctive microstructure, and it produced docosahexaenoic acid (DHA); hence, the strain was described as a new species, Desmodesmus dohacommunis Demura sp. nov. Thus, useful information regarding the use of Desmodesmus as a bioresource was provided. Full article

This work focuses on a culture strategy that combines high biomass production and lipid accumulation in the green microalgae Raphidocelis subcapitata immobilized in alginate gel in order to obtain high lipid productivity for biodiesel production. The study of the effects of nitrogen and phosphorus deficiency on lipid accumulation and biomass production in immobilized microalgae showed that both conditions (N− and P−) promoted lipid accumulation in the microalgae. The lipid contents achieved under nitrogen (31.7% ± 3.2% (dcw)) and phosphorus (19.4% ± 1.9% (dcw)) deficiency conditions were higher than those obtained in the complete medium (control) (14.9% ± 1.5% (dcw)). The highest lipid productivity was recorded under nitrogen deficiency conditions (PL = 11.1 ± 1.1 mg/L/day). This indicated that nitrogen deficiency was more effective than phosphorus deficiency in terms of triggering lipid accumulation in the microalgae. However, the conditions for inducing lipid accumulation (N− or P−) resulted in slower growth. In order to address this issue and achieve high lipid productivity, a two-step culture strategy was used. Immobilized R. subcapitata was cultivated under optimal concentrations of nitrogen and phosphorus to achieve a high biomass concentration. Thereafter, the beads containing the microalgae were transferred to a culture medium under nitrogen deficiency conditions in order to induce lipid accumulation. The concentrations 1.5 g/L of NaNO₃ and 20 mg/L of K₂HPO₄ were determined as being the optimal concentrations for growth, and they produced the highest biomass production rates (µ_{m max} = 0.233 ± 0.023 day⁻¹ and µ_{m max} = 0.225 ± 0.022 day⁻¹ for NaNO₃ and K₂HPO₄, respectively) from all of the concentrations studied. With the two-step culture strategy, immobilized R. subcapitata accumulated 37.9 ± 3.8% of their dry weight in lipid and reached a lipid productivity value of PL = 40.3 ± 4.0 mg/L/day under nitrogen deficiency conditions. This value was approximately 3.6 times higher than that obtained in the direct culture of cells under nitrogen deficiency conditions (PL = 11.1 ± 1.1 mg/L/day). Full article

The conversion of abundant forest- and agricultural-residue-based lignocellulosic materials into high-quality bio-oil by the mild hydrothermal method has great potential in the field of biomass utilization. Some excellent research on biomass hydrothermal process has been completed, including temperature, time, catalyst addition, etc. Meanwhile, some research related to the biomass raw material tissue structure has been illustrated by adopting mode components (cellulose, hemicellulose, lignin, protein, lipid, etc.) or their mixtures. The interesting fact is that although some real lignocellulose has approximate composition, their hydrothermal products and distributions show individual differences, which means the interaction within biomass raw material components tremendously affected the reaction pathway. Unfortunately, to our knowledge, there is no review article with a specific focus on the effects of raw materials and their tissue structure on the lignocellulose hydrothermal process. In this review, research progress on the effects of model and mixed cellulose/hemicellulose/lignin effects on hydrothermal products is initially summarized. Additionally, the real lignocellulosic raw materials structure effects during the thermal process are summed up. This article will inspire researchers to focus more attention on wood fiber biomass conversion into liquid fuels or high-value-added chemicals, as well as promote the development of world energy change. Full article