^^^^^^^^^^^^ ЭКСПЕРИМЕНТАЛЬНЫЕ ^^^^^^^^^^^^
СТАТЬИ
581.1
PREDICTIVE MODELING OF p-CAROTENE ACCUMULATION BY Dunaliella salina AS A FUNCTION OF pH, NaCl, AND IRRADIANCE1
© 2014 A. Celekli*, H. Bozkurt**, G. Donmez***
*Department of Biology, Faculty of Art and Science, University of Gaziantep, Gaziantep, Turkey **Department of Food Engineering, Faculty of Engineering, University of Gaziantep, Gaziantep, Turkey ***Department of Biology, Faculty of Science and Engineering, University of Ankara, Tandogan, Ankara, Turkey
Received December 14, 2012
Predictive modeling of P-carotene accumulation by Dunaliella salina as a function of NaCl, pH, and irradi-ance was studied. Modified Logistic, Gompertz, Schnute, Richards, and Stannard models were fitted to describe P-carotene accumulation by the alga under various environmental conditions. Lag time (k, days), maximum accumulation (A, pg/cell), and the maximum production rate 1/day) for P-carotene accumulation were calculated by modified Logistic and Gompertz models. Values of k, A, and ^ for P-carotene accumulation varied between 0.26 and 20.14 days, 57.48 to 198.76 pg P-carotene/cell, and 1.80 to 3.68 1/day, respectively. Results revealed that Logistic and Gompertz models could be used to describe the accumulation of P-carotene by D. salina as a function of salt concentrations, pH, and irradiance. The highest asymptotic value was predicted from Logistic and Gompertz models at pH 9.0, 48 kerg/(cm2 s) light intensity, and 20% NaCl concentration.
Keywords: Dunaliella salina - fi-carotene - modeling - Logistic — Gompertz
ФИЗИОЛОГИЯ РАСТЕНИЙ, 2014, том 61, № 2, с. 235-243
УДК
DOI: 10.7868/S0015330314010035
INTRODUCTION
An increase in human population has stimulated the search for alternative food sources and new ecological technologies. One of them is the cultivation of microalgae, which offer significant commercial product in some industries, such as pharmaceuticals, alimentary or cosmetic products, and wastewater treatments [1, 2]. Moreover, some microalgae are used as nutrient supplements for human and animal consumptions due to their high content of protein, vitamins, and polysaccharides [1-3]. Some species contain high levels of lipids, which can be extracted and converted into biofuels [1, 2, 4, 5]. Microalgae have remarkable potential to curb emerging environmental problems, for example, the treatment of industrial water pollution, a source of renewable biodiesel, and greenhouse effect by reducing CO2 [6-8].
The unicellular green alga Dunaliella salina (Du-nal) Teodoresco (Dunaliellales, Chlorophyceae) is an extremely halotolerant organism, which has ovoid shape, contains one large cup-shaped chloroplast, is
1 This text was submitted by the authors in English.
Corresponding author. Abuzer Qelekli. Department of Biology, Faculty of Art and Science, University of Gaziantep, 27310 Gaziantep, Turkey. Fax. 009-034-2360-1032; e-mail. celekli.a@gmail.com
surrounded by a thin elastic membrane, and motile due to two equal long agella [9]. Main morphological characteristic is the absence of polysaccharide cell wall; this distinguishes this alga from the rest of the Volvocales [9, 10]. The species can grow and survive in media containing a wide range of salt concentrations, ranging from 0.05 M to saturation (5.0 M) [10-12].
D. salina is one of significant commercial microalgae; it can yield three major valuable products, P-car-otene, glycerol, and proteins [10, 12, 13]. Commercial production of D. salina, as a source of P-carotene, has become a major microalgal industry in Australia, Israel, and Mexico since 1980s [12, 14-16]. P-Carotene demand has been increased as a food coloring agent, a provitamin A in food supplement, animal food, anti-oxidant, an additive to cosmetics, and a multivitamin preparation [4].
Adverse environmental conditions, especially high irradiance, high salt concentration, stressful temperatures, and/or nutrient deficiency can stimulate the production and accumulation of P-carotene in oil globules within the algal chloroplast [10, 17-19]. The accumulation of P-carotene by this halotolerant green alga can be enhanced up to about 10-14% of algal dry weight [5, 13, 19-21]. Consequently, color of Dunaliella cells change from green to orange under ad-
verse cultivation conditions. This massive accumulation of P-carotene seems to be related to the protection mechanism against photoinhibition [21, 22].
Growth modeling of the organism provides knowledge of its behavior under environmental conditions, such as pH, salinity, irradiance, nutrients, etc. [23, 24]. Microbial development, optimization of growth conditions, biomass productions, and estimation of microbial safety and quality under various environmental conditions can be predicted by modeling. Within the last decades, several sigmoid mathematical models [6, 23, 24] have been used to predict growth as biomass and biovolume production by microalgae during their cultivation. Mathematical models, such as Gompertz, Logistic, Richards, Schnute, and Stan-nard models, have been developed to describe the microbial growth curve [23, 25]. Logistic and Gompertz equations consisting of three parameters are widely used models, which give biological parameters like lag time the specific growth rate and the maximum growth value (A).
Mathematical models contain some parameters (a, b, c, ...), which can be converted into biological information, such as lag time, the maximum rate, and asymptotic value for the accumulation of P-carotene by D. salina. These parameters provide for knowledge of the accumulation behavior, and they are used in the design of P-carotene production systems. Especially, the maximum accumulation rate and asymptotic value (maximum concentration) of P-carotene are important parameters in the design of culture systems.
Predictive modeling of P-carotene accumulation by D. salina at various environmental factors has not been previously investigated. Predictive modeling (lag time, maximum rate, and asymptotic value) for the accumulation of P-carotene by D. salina is the significant contribution of the present study. Thus, the aim of this study was (i) to predict P-carotene accumulation by D. salina by using modified equations of Logistic, Gompertz, Schnute, Richards, and Stannard models as a function of NaCl, pH, and irradiance; (ii) to determine the best model, which describes P-caro-tene accumulation per cell, and (iii) to predict biological parameters from the best fitted model(s). Moreover, the relationship between predict variable (accumulation of P-carotene and biological parameters) and response factors (pH, salt, and irradiance) was evaluated in the batch culture.
MATERIALS AND METHODS
The halophilic green microalgae used in the present study, Dunaliella salina obtained from Ankara University, was cultivated on Johnson medium [26] and incubated at 20 ± 2°C under continuous irradiance (cool-white fluorescent light, 32 kerg/(cm2 s)).
Batch cultivation was carried out in 250-mL flasks containing 100 mL of the medium, placed on an orbital shaker at 90 rpm for 39 days. Algal development was followed at three different salt concentrations (10, 15, and 20% NaCl) at four different pH values (pH 6.0, 7.0, 8.0, and 9.0) under 32 kerg/(cm2 s) light intensity at 20 ± 2°C. The P-carotene accumulation by the microalgae was also studied at pH 7.0 and 9.0 and at 48 kerg/(cm2 s) irradiance to compare with 32kerg/(cm2 s) irradiance at aforementioned three salt concentrations. Control medium was prepared without microalgae in Johnson medium. Experiments were carried out in triplicate.
Algal growth was determined by counting cells in a counting chamber (Thoma hemocytometer, 0.1 mm deep). During incubation, withdrawn algal culture was centrifuged to precipitate the suspended biomass at 4000 rpm for 12 min and then resuspended in 5 mL of 80% acetone. After centrifugation, the amount of P-carotene in the supernatant was determined with the spectrophotometer (Shimadzu UV 2001 model) at 455 nm using standard curves.
Effect of pH, light intensity, salt and nitrogen concentrations on growth and P-carotene accumulation was studied in batch systems [10]. In the present study, the accumulation of P-carotene by D. salina was predicted by using several nonlinear models to determine lag time, maximum rate, and asymptotic value.
Nonlinear modified equations of Logistic, Gompertz, Schnute, Richards, and Stannard (table 1) were fitted to experimental data to describe the accumulation of P-carotene by D. salina. The nonlinear fitting procedure was performed using the commercial computer software SigmaPlot v. 11 ("Systat Sofware Inc.", United States) via the Marquardt-Levenberg algorithm.
Determined biological parameters (^ is P-carotene production rate (1/day), X is lag time (days), and A is maximum accumulation (accumulation of P-carotene pg/cell)) among operating variables were compared by use of ANOVA with package program of SPSS v. 16.0 ("SPSS Inc.", United States). Tukey's Honestly Significant Difference (HSD) multiple range test was also carried out to distinguish examined groups.
In order to evaluate goodness of fitting, the predicted data were plotted against the experimental data and the coefficient (R2) and sum of square errors (SSE) values were calculated.
RESULTS AND DISCUSSION
Predictive modeling is an effective tool for assessing how combined environmental factors affect microbial growth during the system process [6]. Various models have been developed for describing biovolume, biom-
Table 1. Equations of models
Model
Modified equation
Reference
Logistic
Gompertz
Schnute
Richards
Stannard
y =
A
1 + exp
^ (X-1 ) + 2
y = A exp
y 4 ^
- exp {(a) (X-1) + 1
1 - b exp (AX + 1 - b - at) ~b
1/b
y = A{1 + v exp (1 + v) exp y = A <1 + v exp (1 + v) exp
H (1 + v)(1 -1) (X-1)
A (1+v)(1 - v) 1 )
-1/v)
(-1/v)
[23]
[23] [23] [23] [23]
y — P-carotene production, A — asymptote value,
Для дальнейшего прочтения статьи необходимо приобрести полный текст. Статьи высылаются в формате PDF на указанную при оплате почту. Время доставки составляет менее 10 минут. Стоимость одной статьи — 150 рублей.