In this paper we present a new method for automated recognition of 12 microalgae that are most commonly found in water resources of Thailand. In order to handle some difficulties encountered in our problem such as unclear algae boundary and noisy background, we proposed a new method for segmenting algae bodies from an image background and proposed a new method for computing texture descriptors from a blurry texture object. Feature combination approach is applied to handle a variation of algae shapes of the same genus. Sequential Minimal Optimization (SMO) is used as a classifier. An experimental result of 97.22% classification accuracy demonstrates an effectiveness of our proposed method

Light plays a significant role in microalgae cultivation, significantly influencing critical parameters, including biomass production, pigment content, and the accumulation of metabolic compounds. This study was intricately designed to optimize light intensities, explicitly targeting enhancing growth, pigmentation, and antioxidative properties in the green microalga, Scenedesmus falcatus (KU.B1). Additionally, the study delved into the photosynthetic efficiency in light responses of S. falcatus. The cultivation of S. falcatus was conducted in TRIS-acetate-phosphate medium (TAP medium) under different light intensities of 100, 500, and 1000μmol photons m⁻²s⁻¹ within a photoperiodic cycle of 12h of light and 12h of dark. Results indicated a gradual increase in the growth of S. falcatus under high light conditions at 1000μmol photons m⁻²s⁻¹, reaching a maximum optical density of 1.330.03 and a total chlorophyll content of 22.670.2μg/ml at 120h. Conversely, a slower growth rate was observed under low light at 100μmol photons m⁻²s⁻¹. However, noteworthy reductions in the maximum quantum yield (Fv/Fm) and actual quantum yield (Y(II)) were observed under 1000μmol photons m⁻²s⁻¹, reflecting a decline in algal photosynthetic efficiency. Interestingly, these changes under 1000μmol photons m⁻²s⁻¹ were concurrent with a significant accumulation of a high amount of beta-carotene (919.8326.33mg/g sample), lutein (34.560.19mg/g sample), and canthaxanthin (24.000.38mg/g sample) within algal cells. Nevertheless, it was noted that antioxidant activities and levels of total phenolic compounds (TPCs) decreased under high light at 1000μmol photons m⁻²s⁻¹, with IC₅₀ of DPPH assay recorded at 218.004.24 and TPC at 230.8386.75mg of GAE/g. The findings suggested that the elevated light intensity at 1000μmol photons m⁻²s⁻¹ enhanced the growth and facilitated the accumulation of valuable carotenoid pigment in S. falcatus, presenting potential applications in the functional food and carotenoid industry.

The extensive use of glyphosate (N-(phosphonomethyl) glycine) herbicide in agriculture is accompanied by the risk of environmental contamination of aquatic ecosystems. In this study, the effects of glyphosate at different concentrations (50–500 µg ml-1) on three Chlorella species including Chlorella ellipsoidea, Chlorella sorokiniana and Chlorella vulgaris especially in relation to the biomass, pigment contents and photosynthetic efficiency were assessed. After treatment for 24 hr, the acute toxicity results showed that C. vulgaris (IC50 = 449.34 ± 6.20 µg ml-1) was more tolerant to glyphosate than C. ellipsoidea (IC50 = 288.23 ± 23.53 µg ml-1) and C. sorokiniana (IC50 = 174.28 ± 0.50 µg ml-1). After a 72-hr chronic toxicity treatment with glyphosate, glyphosate concentrations decreased to 400–500 µg ml-1 in C. ellipsoidea, 200–300 µg ml-1 in C. sorokiniana and 200–500 µg ml-1 in C. vulgaris respectively. During 24-hr acute toxicity exposure to glyphosate, the pigment contents and maximum quantum efficiency of photosystem II (Fv/Fm) decreased as the concentration of glyphosate increased. Overall, the biomass, pigment contents and photosynthetic efficiency presented a high positive correlation. It is worthwhile to mention that our study provides detailed information on the toxicity and sensitivity of these Chlorella species to glyphosate.

Sterols and squalene are essential biomolecules required for the homeostasis of eukaryotic membrane permeability and fluidity. Both compounds have beneficial effects on human health. As the current sources of sterols and squalene are plant and shark oils, microalgae are suggested as more sustainable sources. Nonetheless, the high costs of production and processing still hinder the commercialization of algal cultivation. Strain improvement for higher product yield and tolerance to harsh environments is an attractive way to reduce costs. Being an intermediate in sterol synthesis, squalene is converted to squalene epoxide by squalene epoxidase. This step is inhibited by terbinafine, a commonly used antifungal drug. In yeasts, some terbinafine-resistant strains overproduced sterols, but similar microalgae strains have not been reported. Mutants that exhibit greater tolerance to terbinafine might accumulate increased sterols and squalene content, along with the ability to tolerate the drug and other stresses, which are beneficial for outdoor cultivation. To explore this possibility, terbinafine-resistant mutants were isolated in the model green microalga Chlamydomonas reinhardtii using UV mutagenesis. Three mutants were identified and all of them exhibited approximately 50 percent overproduction of sterols. Under terbinafine treatment, one of the mutants also accumulated around 50 percent higher levels of squalene. The higher accumulation of pigments and triacylglycerol were also observed. Along with resistance to terbinafine, this mutant also exhibited higher resistance to oxidative stress. Altogether, resistance to terbinafine can be used to screen for strains with increased levels of sterols or squalene in green microalgae without growth compromise.