Comparison of monocultures and a mixed culture of three Chlorellaceae strains to optimize biomass production and biochemical content in microalgae grown in a greenhouse

Abstract

Light and temperature are important environmental conditions affecting microalgal growth in outdoor culture. It is essential to evaluate microalgae strains growing under outdoor conditions where they are subjected to variable environmental parameters. The present study investigated three Chlorellaceae strains (Micractinium sp. MACC-728, Chlorella sorokiniana MACC-438, and C. sorokiniana MACC-452) and a mixed culture combining these three strains. Cultures were grown in 2-L bioreactors in a greenhouse over 3 months to assess the effects of high temperature and light on their growth, macromolecule content, and antioxidant and plant-stimulating bioactivities. The most influential environmental parameters on growth were average air temperature and the sum of photosynthetically active radiation, followed by maximum air temperature. The most affected growth parameter was daily change in cell number. Chlorella sorokiniana MACC-438 produced the lowest biomass and was most affected by the high temperature and light conditions. Micractinium sp. produced the highest biomass and was least affected, suggesting it was the most suitable strain for outdoor cultivation. The mixed Chlorellaceae culture performed well in biomass production, exceeding C. sorokiniana monocultures but significantly underyielding in lipid content. Antioxidant activity and the root-stimulating activity varied with strain and culture age. Micractinium sp. had the highest but most variable antioxidant and plant-stimulating activity. Bioactivity in the mixed culture was more consistent, remaining high regardless of culture age and environmental conditions. Thus, mixed cultures of productive strains could be a useful strategy to ensure stable and high-quality biomass production in outdoor cultivation with fluctuating environmental conditions.

Photosynthesis Monitoring in Microalgae Cultures Grown on Municipal Wastewater as a Nutrient Source in Large-Scale Outdoor Bioreactors

“…These naturally produced compounds are a variety of biologically active molecules that can positively affect plant growth as well as the efficiency of nutrient use and increase plant tolerance to abiotic stresses. In this respect, microalgae strains showing biostimulating features have been studied as these microorganisms can be produced in controlled mass cultures and their metabolic plasticity provides the possibility to modulate biomass composition which is one of the critical aspects in the production of biostimulants [ 57 , 58 , 59 , 60 , 61 , 62 ]. Recently, the pilot production trial of Scenedesmus and Chlorella biomass with biostimulating features was realized using brewery [ 63 ] or municipal WW [ 37 , 64 ] as sources of nutrients which significantly reduced the costs of biomass production.…”

“…Recently, the pilot production trial of Scenedesmus and Chlorella biomass with biostimulating features was realized using brewery [ 63 ] or municipal WW [ 37 , 64 ] as sources of nutrients which significantly reduced the costs of biomass production. Biotests also showed that Micractinium is a valuable strain with biostimulating activity for agricultural use based on its auxin-like activity [ 61 ]. Downstream processes, e.g., dissolved air flotation, centrifugation, sonication, and enzymatic hydrolysis, are being optimized to prepare biomass extracts in DEMO scale for field or greenhouse hydroponic application.…”

Photosynthetic activity measured in-situ in microalgae cultures grown in large-scale raceway ponds

“…The plant biostimulating activity of the extracts was measured using the mung bean (Vigna radiata) rooting bioassay [44,45]. The beans were germinated in moist vermiculite at 26°C in a 16:8 h light:dark photoperiod and 120 µmol photons m − 2 s − 1 light intensity.…”