Microalgae are able to metabolize inorganic selenium (Se) to organic forms (e.g. Se-proteins); nevertheless at certain Se concentration culture growth is inhibited. The aim of this work was to ...confirm the hypothesis that the limit of Se tolerance in Chlorella cultures is related to photosynthetic performance, i.e. depends on light intensity. We studied the relation between the dose and irradiance to find the range of Se tolerance in laboratory and outdoor cultures. At low irradiance (250 mu mol photons m super(-2) s super(- 1)), the daily dose of Se below 8.5 mg per g of biomass (<20 mu M) partially stimulated the photosynthetic activity (relative electron transport rate) and growth of Chlorella cultures (biomass density of ~1.5 g DW L super(-1)) compared to the control (no Se added). It was accompanied by substantial Se incorporation to microalgae biomass (~0.5 mg Se g super(-1) DW). When the Se daily dose and level of irradiance were doubled (16 mg Se g super(-1) DW; 500 mu mol photons m super(-2) s super(- 1)), the photosynthetic activity and growth were stimulated for several days and ample incorporation of Se to biomass (7.1 mg g super(-1) DW) was observed. Yet, the same Se daily dose under increased irradiance (750 mu mol photons m super(-2) s super(- 1)) caused the synergistic effect manifested by significant inhibition of photosynthesis, growth and lowered Se incorporation to biomass. In the present experiments Chl fluorescence techniques were used to monitor photosynthetic activity for determination of optimal Se doses in order to achieve efficient incorporation without substantial inhibition of microalgae growth when producing Se-enriched biomass.
•TLC coupled to diode laser thermal vaporization ICP MS was used for Se speciation.•Selenomethionine and selenocysteine were quantified in microalgae Chlorella vulgaris.•TLC-DLTV ICP MS results were ...confirmed by standard HPLC-ICP MS.
In this work we present a simple and cost-effective approach for the determination of selenium species in algae and yeast biomass, based on a combination of thin-layer chromatography (TLC) with diode laser thermal vaporization inductively coupled plasma mass spectrometry (DLTV ICP MS). Extraction of freeze-dried biomass was performed in 4M methanesulphonic acid and the selenium species were vaporized from cellulose TLC plates employing a continuous-wave infrared diode laser with power up to 4 W using a simple laboratory-built apparatus. Selenomethionine and selenocysteine were quantified with limits of detection 3 μg L−1 in a Se-enriched microalgae Chlorella vulgaris and yeast certified reference material SELM-1. Results delivered by TLC-DLTV ICP MS were consistent with those obtained by a routine coupling of high-performance liquid chromatography (HPLC) to ICP MS. In addition, the TLC approach is capable of analyzing extract containing even undiluted crude hydrolysates that could damage HPLC columns.
Photoacclimation of two
Chlorella
cultures – strain g-120 characterised by a reduced size of light-harvesting antenna complex (LHC) and strain R-117 with full antenna size was studied during 5-day ...outdoor trials. The aim was to correlate the functional and structural changes in the photosynthetic apparatus to culture growth, photochemical activity and thylakoid composition of chlorophyll (Chl)-protein complexes and corresponding polypeptides.
Chlorella
g-120 was characterized by a low Chl/biomass ratio (< 0.5% of dry weight), about four times lower compared to
Chlorella
R-117. The important observation was that the high molecular mass Chl-binding protein supercomplexes, i.e. Photosystem II (PSII) and Photosystem I (PSI) cores associated with LHCs were physically missing or negligible in
Chlorella
g-120. However, there were no visible changes in Chl-protein composition in the g-120 strain during its acclimation to phototrophic conditions. Measurement of the effective absorption cross-section of PSII centres confirmed a markedly reduced functional antenna size in
Chlorella
g-120 as compared to R-117 which coincided with the absence of the PSII-LHC supercomplexes. We demonstrated that
Chlorella
g-120 represents a typical reduced antenna-size strain due to its Chl-protein composition. As compared to the full-antenna
Chlorella
R-117 strain, the outdoor cultures of
Chlorella
g-120 showed significantly lower oxygen production and electron transport rate measured
in-situ
. On the contrary,
Chlorella
g-120 revealed increased futile energy dissipation via non-photochemical quenching and higher respiration compared to
Chlorella
R-117. Consequently, the potential use of microalgae strains with reduced LHCII for outdoor mass cultivation may not be as straightforward as anticipated from laboratory experiments.
Nutrient and micropollutant removal, and bioactivity were studied in cultures of the green microalga
Tetradesmus obliquus
MACC-677 grown in centrate from municipal wastewater (WW). Two outdoor units, ...a thin-layer cascade (TLC) and a thin-layer raceway pond (TL-RWP), were tested for microalgal culturing in batch and semi-continuous regimes where their photosynthetic performance was monitored. The results revealed that the
T. obliquus
cultures grew well, showing a high specific growth rate
µ
of 0.31 day
−1
and 0.25 day
−1
when grown in WW in TLC and TL-RWP, respectively. The cultivation trials showed high nutrient removal efficiency for ammonium nitrogen (98.5%) as well as orthophosphate (89%), the most abundant forms of N and P occurring in municipal WW. The removal of selected pharmaceuticals and endocrine disruptors (e.g., ibuprofen, amitriptyline, bisphenol A, etc.) was also assessed. Ibuprofen was the most abundant micropollutant detected in the centrate, with concentrations up to 5000 ng L
−1
and fast removal during the cultivation. The biomass produced in the centrate revealed antimicrobial activity against plant pathogens, including fungi, oomycota, and bacteria. These findings have shown that the culturing of
T. obliquus
can be considered a suitable way to contribute to a circular economy, to remove nutrients and micropollutants from municipal WW from which biomass extracts can be further used for plant protection in agriculture.
Microalgae are able to metabolize inorganic selenium (Se) to organic forms (e.g. Se-proteins); nevertheless at certain Se concentration culture growth is inhibited. The aim of this work was to ...confirm the hypothesis that the limit of Se tolerance in
Chlorella
cultures is related to photosynthetic performance, i.e. depends on light intensity. We studied the relation between the dose and irradiance to find the range of Se tolerance in laboratory and outdoor cultures. At low irradiance (250 µmol photons m
−2
s
−1
), the daily dose of Se below 8.5 mg per g of biomass (<20 µM) partially stimulated the photosynthetic activity (relative electron transport rate) and growth of
Chlorella
cultures (biomass density of ~1.5 g DW L
−1
) compared to the control (no Se added). It was accompanied by substantial Se incorporation to microalgae biomass (~0.5 mg Se g
−1
DW). When the Se daily dose and level of irradiance were doubled (16 mg Se g
−1
DW; 500 µmol photons m
−2
s
−1
), the photosynthetic activity and growth were stimulated for several days and ample incorporation of Se to biomass (7.1 mg g
−1
DW) was observed. Yet, the same Se daily dose under increased irradiance (750 µmol photons m
−2
s
−1
) caused the synergistic effect manifested by significant inhibition of photosynthesis, growth and lowered Se incorporation to biomass. In the present experiments Chl fluorescence techniques were used to monitor photosynthetic activity for determination of optimal Se doses in order to achieve efficient incorporation without substantial inhibition of microalgae growth when producing Se-enriched biomass.
We have worked out a rapid 1-day test based on photosynthesis measurements to estimate suitable growth temperature of microalgae cultures. To verify the proposed procedure, several microalgae—
...Chlorella
,
Nostoc
,
Synechocystis
,
Scenedesmus
, and
Cylindrospermum—
were cultured under controlled laboratory conditions (irradiance, temperature, mixing, CO
2
, and nutrient supply) to find the optima of photosynthetic activity using the range between 15 and 35 °C. These activities were recorded at each temperature step after 2 h of acclimation which should be sufficient as oxygen production and the PQ cycle are regulated by fast processes. Photosynthetic activity was measured using three techniques—oxygen production/respiration, saturating pulse analysis of fluorescence quenching, and fast fluorescence induction kinetics—to estimate the temperature optima which should correspond to high growth rate. We measured all variables that might have been directly related to growth—photosynthetic oxygen evolution, maximum photochemical yield of PSII,
F
v
/
F
m
, relative electron transport rate rETR
max
, and the transients
V
j
and
V
i
determined by fast fluorescence induction curves. When the temperature optima for photosynthetic activity were verified in growth tests, we found good correlation. For most of tested microalgae strains, temperature around 30 °C was found to be the most suitable at this setting. We concluded that the developed test can be used as a rapid 1-day pre-screening to estimate a suitable growth temperature of microalgae strains before they are cultured in a pilot scale.
In this work, the key moments of the development of the so-called thin-layer cascades (TLC) for microalgae production are described. Development started at the end of the 1950s when the first ...generation of TLCs was set-up in former Czechoslovakia. Since, similar units for microalgae culturing, which are relatively simple, low-cost and highly productive, have been installed in a number of other countries worldwide. The TLCs are characterized by microalgae growth at a low depth (< 50 mm) and fast flow (0.4–0.5 m/s) of culture compared to mixed ponds or raceways. It guarantees a high ratio of exposed surface to total culture volume (> 100 1/m) and rapid light/dark cycling frequencies of cells which result in high biomass productivity (> 30 g/m
2
/day) and operating at high biomass density, > 10 g/L of dry mass (DW). In TLCs, microalgae culture is grown in the system of inclined platforms that combine the advantages of open systems—direct sun irradiance, easy heat derivation, simple cleaning and maintenance, and efficient degassing—with positive features of closed systems—operation at high biomass densities achieving high volumetric productivity. Among significant advantages of thin layer cascades compared to raceway ponds are the operation at much higher cell densities, very high daylight productivities, and the possibility to store the culture in retention tanks at night, or in unfavourable weather conditions. Concerning the limitations of TLCs, one has to consider contaminations by other microalgae that limit cultivation to robust, fast-growing strains, or those cultured in selective environments.
Diel changes in photosynthetic performance and biomass productivity were thoroughly examined in Arthrospira platensis cultures grown outdoors in an open circular pond (OCP) and a thin-layer cascade ...(TLC). The two cultures were grown at the same areal biomass density, but temperature maxima were adjusted to optimal (33°C) and suboptimal (25°C). At the optimal temperature, the cultures grown in TLC showed about 20% higher photosynthetic activity than those in OCP, while at the suboptimal one photosynthetic activity dropped by 20% and 35% in the TLC and OCP, respectively. Accordingly, the highest biomass productivity over 20gm−2d−1 was attained in the TLC at the optimal temperature, while at the suboptimal temperature the productivity decreased by 20%. In the OCP, the biomass productivity at both temperatures was about one third lower compared to those in the TLC.
The better culture performance in the TLC was mainly ascribed to the shorter light path that promoted much faster light/dark cycles favourable for photosynthesis, as well as the faster warming of the cultures in the morning as compared to the OCP cultures. Monitoring photosynthesis performance of a culture can indicate design improvements, which may capitalize this photochemical advantage, increasing biomass productivity further.
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•A first attempt to grow Arthrospira in thin-layer cultures is reported.•Productivity of Arthrospira attained with cascades was higher than in open ponds.•Higher yield attained with thin-layer culture was attributed to their short light path.•Phycocyanin content was 30% higher in the biomass grown in ponds
The objective of this work was to test the growth of the freshwater microalga
Chlamydopodium fusiforme
MACC-430 in diluted piggery wastewater (PWW) for biomass production which is a potential ...producer of biostimulating and antimicrobial compounds. The productivity and effectiveness in removing nitrogen and phosphorus by the cultures were tested outdoors in open ponds by comparing the mineral medium BG-11 medium (control) and piggery wastewater (PWW). Daily biomass yields were found 14.7 ± 4.6g m
-2
d
-1
in BG-11 and 17.6 ± 6.7g m
-2
d
-1
in 10-fold diluted wastewater (PWW10) with deionized water. Further increase in the biomass productivity yield (33.1 ± 5.6g m
-2
d
-1
) was achieved with more concentrated PWW (5-fold dilution – PWW5). Nitrogen removal rate (N-NH
4
+
) reached 21.4 ± 2.9mg L
-1
d
-1
in cultures grown in PWW10 and increased to 38.4±16.3mg L
-1
d
-1
using the PWW5. The use of undiluted PWW strongly increased the bacterial load, which caused the loss of the culture. The photosynthetic performance measured as the maximum fluorescence yield F
v
/F
m
ratio in both the PWW10 and BG-11 cultures showed a cyclic behavior, as it decreased during the day and recovered at night. However, in the cultures grown in diluted PWW the F
v
/F
m
ratio slightly increased throughout the cultivation. Between PWW10 and BG-11, no significant differences were observed in photosynthetic oxygen evolution; on the contrary, PWW5 showed a 30% reduction compared to PWW10 and BG-11. Significantly lower chlorophyll and carotenoid contents were found in the cultures grown in PWW compared to BG-11. Biochemical composition showed a slightly higher protein content in biomass grown in PWW10 (53.4%) compared to BG-11 (52.7%). The protein content further increased (61.3%) when the more concentrated PWW5 was used. The biomass, particularly that produced on PWW, revealed antimicrobial activity against plant pathogens, including fungi, and oomycete, while rather weak biostimulant activity was determined for the
C. fusiforme
biomass independently of the cultivation medium. Results demonstrated that
C. fusiforme
is a robust strain suitable to be grown in diluted PWW outdoors with a high nutrient removal rate.
Three cultivation regimes were tested in cold-adapted cultures of the green microalga Monoraphidium in an outdoor thin-layer raceway pond: cultivation under sunlight; its combination with continuous ...supplementary illumination; and nitrogen depletion using both light sources. The highest volumetric and areal productivity, 0.16 g L−1 d−1 and 3.22 g m−2 d−1, respectively corresponding to the specific growth rate μ of 0.191 d−1 were achieved when sunlight was combined with supplementary illumination. The maximum total fatty acid content, 20.29 % of DW, rich in oleic acid, 54 % of total fatty acid content, was achieved under nitrogen depletion stress. An outstanding amount of lutein, 26.39 mg lutein g−1 DW, was detected grown under sunlight in the first trial. From the harvested and fermented biomass in the second trial 236 mLN g−1oTS of methane was generated.
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•A high growth rate was obtained in low irradiance/temperature cultivation.•A close correlation was found between specific growth rates and photosynthetic activity.•The fatty acid profile was rich in monounsaturated and polyunsaturated fatty acids.•Biomass was enriched in lutein.•Significant methane production was found during fermentation.
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