Biomass yield, oil productivity and fatty acid profile of Chlorella lobophora cultivated in diverse eutrophic wastewaters

Phylogenetic Analysis, Pulse-Amplitude-Modulated (PAM) Fluorometry Measuring Parameter Optimization, and Cell Wall Disintegration of Chlorella vulgaris K-01

Chlorella is a rich source of nutrients. In addition to its nutritional value, it exhibits versatile biological activities. New strains have been extensively identified and investigated in recent years to expand the potential of Chlorella. The accurate measurement of pulse-amplitude-modulated (PAM) fluorometry parameters and effective microalgal cell lysis are foundational for advanced studies of novel Chlorella species. In this study, ribosomal small subunit (SSU)-internal transcribed spacer (ITS) phylogenetic analysis and internal transcribed spacer 2 (ITS2) secondary structure analysis were employed to identify a new Chlorella species. The dark adaptation time, the duration of the saturation pulse, the intensity of actinic light, and the duration of actinic light exposure for PAM fluorometry measurements were optimized. Different conditions of ultrasonication and high-pressure homogenization (HPH) for microalgal cell lysis were compared. Chlorella vulgaris K-01 was identified. The suitable duration for dark adaptation, the saturation pulse, and the actinic light were 15 min, 200 milliseconds, and 30 s, respectively. The suitable intensity of actinic light was 191 μE/(m2·s). For microalgal cell lysis, HPH could achieve 98.65% cell lysis efficiency at 30 kpsi (207 MPa), whereas ultrasonication attained an efficiency of 45.47% (300 W for 30 min). These results facilitate further study on the physiology and the composition of Chlorella vulgaris K-01.

A critical review of soil algae as a crucial soil biological component of high ecological and economic significance

Aero-terrestrial algae are ecologically and economically valuable bioresources contributing to carbon sequestration, sustenance of soil health, and fertility. Compared to aquatic algae, the literature on subaerial algae is minimal, including studies of distinctive habitats such as forest soils, agricultural fields, deserts, polar regions, specific subaerial zones, artificial structures, and tropical soils. The primary goal here was to identify the gaps and scope of research on such algae. Accordingly, the literature was analyzed per sub-themes, such as the "nature of current research data on terrestrial algae," "methodological approaches," "diversity," "environmental relationships," "ecological roles," and "economic significance." The review showed there is a high diversity of algae in soils, especially members belonging to the Cyanophyta (Cyanobacteria) and Chlorophyta. Algal distributions in terrestrial environments depend on the microhabitat conditions, and many species of soil algae are sensitive to specific soil conditions. The ecological significance of soil algae includes primary production, the release of biochemical stimulants and plant growth promoters into soils, nitrogen fixation, solubilization of minerals, and the enhancement and maintenance of soil fertility. Since aero-terrestrial habitats are generally stressed environments, algae of such environments can be rich in rare metabolites and natural products. For example, epilithic soil algae use wet adhesive molecules to fix them firmly on the substratum. Exploring the ecological roles and economic utility of soil and other subaerial algae could be helpful for the development of algae-based industries and for achieving sustainable soil management.

Synergistic integration of wastewaters from second generation ethanol plant for algal biofuel production: an industrially relevant option

The present study provides an integrated method for utilizing the wastewaters from second generation (2G) ethanol pretreatment plant for microalgal biomass and lipid production. The study was conducted using a mixture of wastewaters (referred as MW; pH 4.3) generated after washing of acidic and alkaline-soaked lignocellulosic biomass prior to pretreatment process. The growth studies indicated that the thermotolerant strain of Chlorella pyrenoidosa (C. pyrenoidosa) M18 exhibited higher cell proliferation in wastewater as compared to freshwater. About 20-25% enhancement in biomass (509 mg L^-1 d^-1 ± 3.09) and lipid productivity (146 mg L^-1 d^-1 ± 1.34) was observed in MW. The total chlorophyll content and variable fluorescence by maximum fluorescence (Fv/Fm) ratio of strain cultivated in MW were 10.32 µg mL^-1 and 0.75, respectively. The use of MW also enhanced the content of saturated and monounsaturated fatty acids in total lipid. The exhausted wastewater medium obtained after harvesting the auto-flocculated biomass was also reused up to three successive growth cycles. The recycled medium without any nutrient addition could be used for two subsequent rounds with enhanced biomass (520 mg L^-1 d^-1 ± 4.07) and lipid (157.71 mg L^-1 d^-1 ± 1.09) productivities. This synergistic approach of cultivating thermotolerant microalgae with wastewater from 2G pretreatment plant provides an economical setup for development of commercial algal biofuel technology.