Abstract
The genus Gracilaria, largest biomass producer in coastal regions, encompasses a wide range of species including
Gracilaria gracilis
. Nowadays, there is a spate of interest in its culture ...in lagoon where the water sulfate concentration is variable. A laboratory culture was carried out to determine the sulfate concentration effect on their growth as well as their biochemical composition, which were 2.5, 27 or 50 mM, referred to as SSS (sulfur starved seawater), SW (seawater) and SES (sulfur enriched seawater).We found that the sulfate content of the surrounding medium is a key parameter influencing both the alga growth and its composition. However, seawater proved to be the most suitable environment to sustain alga growth, proteins, R-phycoerythrin and agar yields, but sulfur enrichment and starvation affects them. The sulfate degree of agar and therefore its quality is related to the medium sulfate concentration. We conclude that sulfur starvation (2.5 mM) for three weeks, led to severe growth retardation, lower agar yield and quality and indicated the limit potential of
G. gracilis
for mariculture under these conditions. These results demonstrated that the success of
G. gracilis
culture in the lagoon is feasible if sulfate concentration is closer to that of seawater.
This study evaluated the growth and biochemical composition of farming Gracilaria gracilis (Stackhouse) M. Steentoft, L. M. Irvine & W. F. Farnham in the Bizerte Lagoon (BL) and Bizerte Bay (BB) in ...the North Coast of Tunisia, using lantern nets. Effects of site and depth on alga daily growth rate (DGR) and biochemical composition were investigated. The DGR was affected by culture site (1.42 ± 0.65% day
and 1.19 ± 0.34% day
for the BL and the BB respectively). Agar yield, was higher (p < 0.05) in the BB than the BL (23.31 ± 2.64% vs. 19.19 ± 2.32%) with a higher (p < 0.05) 3,6-anhydrogalactose (3,6-AG) contents (41.37 ± 3.68% vs 23.30 ± 5.40%) and a lower (p < 0.05) sulphate degree (6 ± 2.00% vs 8.80 ± 0.86%). The proteins contents were independent of the site and depth of culture (20.74 ± 7.22% and 22.02 ± 6.34% for the BL and the BB respectively). R-phycoerythrin (R-PE) contents were significantly higher (p < 0.05) in the BB (0.86 ± 0.31 mg g
) than those obtained in the BL (0.33 ± 0.12 mg g
). The salinity, transparency, nitrate and ammonium were monitored in both sites, and their influences were discussed. Our results suggest that G. gracilis cultured in Bizerte Bay can be used in a cascading biorefinery approach.
Laboratory culture of the rhodophyte
Gracilaria gracilis
(Stackhouse) M. Steentoft, L.M.Irvine & W.F.Farnham which often grows in many stressed Mediterranean coasts, mainly lagoons, was carried out ...to ascertain the optimum range and interaction of environmental factors on growth and composition with a view to potential mariculture. The methodology adopted was based on the synergy between mathematical modeling and laboratory experiments. An experimental design and a response surface methodology (RSM) were used to simulate field conditions. Experiments were done at 20 °C. The studied responses were daily growth rate (DGR), agar yields, and protein and R-phycoerythrin (RPE) contents. Second-order quadratic polynomial models for all studied responses were deduced and ANOVA showed them to be significant (
p
< 0.05). The RSM was successfully applied to assess the effects of abiotic factors (light, salinity, ammonium, and nitrate) and their interaction on the DGR, agar yields, and protein content.
Gracilaria gracilis
grew well (> 3% day
−1
) under all the combined abiotic factor conditions that were simulated. Hence, the optimum (5% day
−1
) was obtained around seawater salinity (36 psu), 198 μmol photons m
−2
s
−1
irradiance and nitrogen concentration of 80 μmol ammonium g
−1
fw L
−1
, and 210 μmol nitrate g
−1
fw L
−1
. Optimum agar yields (15%) were obtained at a lower irradiance (70 μmol photons m
−2
s
−1
) and a salinity of 24 psu combined with similar ammonium (80 μmol g
−1
fw L
−1
) and nitrate (100 μmol g
−1
fw L
−1
) concentrations. Optimum protein contents (23%) and RPE contents (1.2 mg g
−1
fw) were obtained at lower irradiance (70 μmol photons m
−2
s
−1
), a salinity of 24 psu, an ammonium concentration of 80 μmol g
−1
fw L
−1
, and lower nitrate concentration (10 μmol g
−1
fw L
−1
). In addition, abiotic factor interaction effects occurred when one of them significantly contributes to response reduction. In conclusion, potential mariculture of
G. gracilis
in the lagoon is possible but related to their proteins and pigments (essentially RPE) contents in addition to agar yields.
Different light qualities, i.e. ultraviolet (280–400 nm), blue (400–450 nm), green (500–550 nm) and red (620–670 nm) were combined with the actinic yellow light (SOX) (590 nm) under saturation of ...photosynthetic activity conditions, in order to consider the specific effects of each waveband on the red macroalga
Gracilaria gracilis
physiology
.
In this context, the fluctuation of biomass production, photosynthetic activity estimated as in vivo chlorophyll
a
fluorescence, protein and pigment contents, polyphenol concentration, antioxidant activity and the content and composition of the mycosporine-like amino acids (MAAs)-UV-absorbing compounds were studied. After 3 days of culture, the supplemented light had not induced any variation in photosynthetic pattern compared to the control (only SOX light). However, after 2 weeks of culture, supplemented blue light stimulated the accumulation of phenolic compounds which reached a value of 2.92 ± 0.22 mg g
−1
DW, 68% higher than the control. Moreover, supplemented green light induced the accumulation of proteins and R-phycoerythrin (R-PE), i.e. 29 ± 4.32 mg g
−1
DW and 0.91 ± 0.34 mg g
−1
DW, respectively, being an increase of 56% and 78%, respectively, compared to the control. Red light boosted the growth rate, i.e. 7.24% ± 1.06 compared to the control which was 2.17% ± 0.2. Finally, UV radiation induced a marked increase of MAAs reaching 133.03 ± 41.54 mg g
−1
DW, 162% higher content than the one in the control. The use of supplemented light of specific wavelengths to a saturated light irradiance for photosynthesis as an effective approach to increase the content of bioactive compound for biotechnology application is concretely discussed.
The diversity of marine biomasses is a set of exploitable and renewable resources with application in several sectors. In this context, a co-culture based on three protease-producing bacterial ...isolates, namely
Aeribacillus pallidus
VP3,
Lysinibacillus fusiformis
C250R
,
and
Anoxybacillus kamchatkensis
M1V strains, was carried out in a medium based on the blue swimming crab
Portunus segnis
bio-waste. Proteases production was optimized using a central composite design (CCD). The highest level of proteases production obtained was 8,809 U/mL in a medium comprising 75 g/L of
Portunus segnis
by-product powder (P
spp
). The biological value of P
spp
and its obtained derivatives were evidenced via accredited protocols. The recovered protein hydrolysate (P
Hyd
) was found to be active towards radical scavenging power and against angiotensin I-converting enzyme (ACE). The blue crab chitin (BC) extraction efficiency was achieved with a yield of 32%. Afterwards, chitosan was prepared through chitin
N
-deacetylation with a yield of 52%, leading to an acetylation degree (AD) of 19% and solubility of 90%. In addition, chitosan is found to be active against the growth of all pathogenic bacteria tested.
Graphical abstract
R-phycoerythrin (RPE) extracted from the red alga
Gracilaria verrucosa
by enzymatic hydrolysis generates a large amount of coproduct containing agar. We developed a process for the sequential ...extraction of RPE and agar. A Box–Behnken design with three factors–three levels and response surface methodology were applied to study the influence of different extraction parameters (incubation temperature, incubation time, and algae-to-water ratio) on the yield, 3,6-anhydrogalatose (3,6-AG) content, and sulfated degree of agar from RPE coproduct. The extraction efficiency was maximized (28%) when the extraction process was carried out with these conditions: incubation temperature of 100 °C, time of 2.6 h, and algae-to-water ratio equal to 3 (%
w
/
v
). Optimum 3,6-AG content (30%) was maximized at 85 °C, 1.85 h, and 2.35 (%
w
/
v
). Sulfated degree varied between 6 and 12%. The results of this study indicate that fresh
G. verrucosa
can be subjected to a process of simultaneous extraction of R-phycoerythrin and agar.
In accordance with the framework of the Circular Blue Bioeconomy in the Mediterranean region, the objective of this study was to evaluate the biotransformation of blue swimming crab (
Portunus segnis
...) residues obtained from the port of Sfax by an extracellular chitinase produced by
Nocardiopsis halophila
strain TN-X8 isolated from Chott El Jerid (Tozeur, Tunisia). From the analysis of multiple extremophilic
Actinomycetota
, it was determined that strain TN-X8 exclusively utilized 60 g/L of raw blue swimming crab as its carbon and energy source, achieving a chitinase activity of approximately 950 U/mL following a 6-day incubation period at 40 °C. Pure chitinase, designated as ChiA-Nh30, was obtained after heat treatment, followed by ammonium sulfate fractionation and Sephacryl® S-200 column chromatography. The maximum ChiA-Nh30 activity was observed at pH 3 and 75 °C. Interestingly, compared with cyclohexamidine, ChiA-Nh30 showed a good antifungal effect against four pathogenic fungi. Furthermore, when using colloidal chitin as substrate, ChiA-Nh30 demonstrated a higher degree of catalytic efficiency than the commercially available Chitodextrinase®. In addition, ChiA-Nh30 could be immobilized by applying encapsulation and encapsulation-adsorption techniques. The kaolin and charcoal used acted as excellent binders, resulting in improved ChiA-Nh30 stability. For the immobilized ChiA-Nh30, the yield of
N
-acetyl-
d
-glucosamine monomers released from 20% (
w
/
v
) blue swimming crab residues increased by 3.1 (kaolin) and 2.65 (charcoal) times, respectively.
Gracilaria gracilis
farming was conducted in the Bizerte lagoon (North of Tunisia) at two depths (0.5 and 2.5 m) using various initial fragment weights (5, 20, and 40 g) in order to investigate the ...alga growth, agar yield, and quality. IR spectra of agar were performed in comparison to the commercial one. Moreover, the proximate biochemical composition of seaweeds was investigated. The results showed that the highest daily growth rate and agar yield were recorded at 0.5 m, using 5 g as initial fragment weight (5.98 ± 1.98% day
−1
, 14.87 ± 1.91% dw, respectively). Maximum gel strength was 356.67 ± 15.25 g cm
−2
at 2.5 m using an initial weight of 20 g. Gelling and melting temperatures varied from 34.33 ± 0.57 to 35.50 ± 0.57 °C and from 77.00 ± 1.00 to 85.00 ± 0.50 °C, respectively. IR analysis revealed that some spectra were similar, while others were different. The highest dry matter (22.68 ± 1.77%) and ash content (35.25 ± 0.02% of dw) were recorded at 2.5 m, using initial weights of 20 and 5 g, respectively. The maximum carbohydrate and the crude protein contents were obtained at 0.5 m, using 5 g as initial weight (9.52 ± 0.36 and 5.83 ± 0.7% dw, respectively). The highest R-phycoerythrin content was recorded at 0.5 m (0.050 ± 0.007 mg g
−1
dw), while the maximum of total lipid content was recorded at 2.5 m with initial weight of 5 g (3.58 ± 0.63% dw). Our findings indicated that growth and biochemical composition of
G. gracilis
depend on the depth and initial fragment weights.
The aim of this research is to statistically optimize enzymatic hydrolysis parameters for the production of R-phycoerythrin (RPE) from red algae Gracilaria verrucosa. Six independent variables, ...incubation temperature, incubation time, ratio of buffer to raw material, cellulase loading, xylanase loading, and pH, were selected for response surface methodology studies. A central composite design was employed to maximize RPE production. A mathematical model with high determination coefficient (R 2 = 0.86) was developed and could be employed to optimize RPE extraction. The optimal extraction conditions of RPE were determined as follows: incubation temperature (48°C), incubation time (6 h), ratio of buffer to raw material (20 w/v), cellulase loading (15%), xylanase loading (5%), and pH (6.5). Under this optimal condition, the experimental yield of RPE was 6.25 mg g−1. Based on the result of response surface methodology and desirability function approach study, total sugar, the main by-product in RPE extraction was considered as another response. A new optimal condition was predicted as follows: incubation temperature (30°C), incubation time (12 h), ratio of buffer to raw material (20, w/v), cellulase loading (15%), xylanase loading (5%), and pH (6). Under this condition, similar RPE levels were obtained while the concentration of total sugar decreased by 40%.
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