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Bacillus Subtilis Ncim2063 Batch Cultivation: The Advanced technologies 9(1) (2020) 44-49 BACILLUS SUBTILIS NCIM2063 BATCH CULTIVATION: THE INFLUENCE OF THE SUBSTRATE CONCENTRATION AND OXYGEN TRANSFER RATE ON THE BIOMASS YIELD Sandra Stamenković Stojanović1*, Ivana Karabegović1, Vladimir Beškoski2, 1 1 Nada Nikolić , Miodrag Lazić (ORIGINAL SCIENTIFIC PAPER) UDC 602.3:579.6 1Faculty of Technology, Leskovac, University of Niš, Serbia 2Faculty of Chemistry, Belgrade, University of Belgrade, Serbia The objective of this study was to investigate the growth kinetics of Bacillus subti- lis NCIM 2063 under different cultivation conditions. For that purpose, the growth medium was supplemented with different glucose concentrations and exposed to different values of the oxygen transfer rate (OTR). As a result, it was found that the Keywords: microbial biomass, Bacillus biomass yield, the specific growth rate and generation time were affected by the subtilis, growth kinetics change of cultivation conditions and the composition of the nutrient medium. It was confirmed that glucose is readily available substrate that enhances the cultivation in the concentration range of 5-15 g/L. Also, it was proved that the restriction of avail- able oxygen lowers the biomass yield and slows down the replication of bacteria. The maximum biomass concentration was achieved in the medium with 10 g/L of glucose and the OTR value of 10 mol/m3 h, when the specific growth rate and gen- eration time were 0.273 h-1 and 2.54 h, respectively. Such biomass yield can be achieved in only 24 h, which is also economically acceptable. Therefore, the growth conditions optimized in this experiment are recommended as optimized values for further research, and can be used for economically sustainable and efficient cultiva- tion of B. subtilis NCIM 2063. Introduction Bacillus subtilis is aerobic, rod-shaped endospore- dependent on different factors that affect the growth. In forming bacteria usually found in soil or water [1,2]. It has order for a microorganism to grow rapidly, it is necessary the ability to form endospores which is why it is resistant to obtain the optimum growth conditions in terms of the to different environmental stresses [3]. The species is also adequate temperature, pH, stirring speed, the oxygen con- confirmed to have probiotic properties and the ability to centration and the presence of required nutrients [14,19]. produce various industrially important metabolites such as Oxygen concentration is an especially important parame- enzymes, antibiotics, polysaccharides and proteins [4–10]. ter when it comes to aerobic cultures. It depends on the spe- Thanks to those abilities, the genus Bacillus is suitable cific growth rate and biomass concentration [20,21] and it is for biocontrol of pathogens and has the application in many limited by oxygen solubility and oxygen transfer rate (OTR) fields such as agriculture, pharmacy, medicine and many [22]. Sufficient aeration is a primary precondition to success- others [8,11–15]. ful cultivation which is why OTR needs to be monitored and Before starting the industrial production of B. subtilis adjusted during the cultivation [23]. It is also essential to opti- and its metabolites, it is important to optimize the growth mize the growth medium, taking into account all the nutrients conditions and describe the bacterial growth, taking into ac- necessary for rapid replication of microorganisms. Glucose, count the influence of the important factors such as oxygen which acts as a carbon source, is one of the most common- availability and substrate utilization [15]. The first step in ly used substrates in various cultivations. Knowing that at the course of observation and description of the bacterial some concentrations the substrate inhibition could occur, it is growth is measuring a growth curve. The increase in bac- fundamental to determine the optimum medium composition terial biomass is usually measured as a function of time, that will enhance the growth of a particular bacterium [18]. forming a growth curve of a certain shape from which spe- The aim of this work is to investigate the influence of dif- cific parameters can be calculated [16,17]. The usual goal ferent glucose quantities in the growth medium and OTR is to lower the duration of the lag phase, and to increase values on the growth of B. subtilis NCIM 2063 in terms of the specific growth rate which will reduce the production achieving the highest biomass yield, as well as to calculate time and eventually the costs [18]. The value of those pa- the most important parameters that are suitable for describ- rameters, and therefore the shape of the growth curve, is ing the growth kinetics. *Author address: Sandra Stamenković Stojanović, University of Nić, Faculty of Technology, Bulevar oslobođenja 124, 16000 Leskovac, Serbia E-mail: [email protected] The manuscript received: March,05, 2020. Paper accepted: April, 24, 2020. 44 Advanced technologies 9(1) (2020) 44-49 Experimental was determined based on a standard curve in the range of up to 15 g/L glucose. Bacterial strain and growth conditions B. subtilis NCIM 2063 strain from National collection of Determination of kinetic parameters Industrial Microorganisms (NCIM) was used to study the ef- For each growth curve, the specific growth rateμ m and fect of different glucose concentrations and OTR values on generation time td were calculated using the following equa- the biomass yield and kinetic parameters. A bacterial strain tions [26]. was stored at -80 °C in vials and at 4 °C in agar plates. To form an inoculum, Erlenmeyer flask containing 300 ml of ......................................................................(2) Nutrient Broth (NB) was inoculated with a single colony and grown for 24 h in a rotary shaker at 37 °C and 150 rpm. ..............................................................................(3) This culture was then used for inoculation of 500 mL Er- lenmeyer flask containing the sterilized cultivation medium where, x is the biomass concentration in the moment t and which consisted of: Nutrient Broth, 10% (w/v) KCl, 1.2% x0 is the starting biomass concentration. (w/v) MgSO4∙7H2O, 1M NaOH, 1M Ca(NO3)2, 0.01M MnCl2 and 1 mM FeSO4. In the first part of the experiment, four Results and discussion glucose concentrations and OTR values were tested (0 g/L, 5 g/L, 10 g/L, 15 g/L). After that, the effect of different OTR The regulation of growth parameters is the first step values was evaluated (10 mol/m3 h, 5 mol/m3 h, 4 mol/m3 h, in the process of obtaining the quality microbial biomass 2 mol/m3 h) at the constant glucose concentration (10 g/L). with the desired cell density. To fully understand the nutri- The shake flask cultures were grown at 150 rpm and 37 °C, ent requirements and microorganism behavior, it is very for 48 h. The samples were taken at regular intervals for important to analyze the growth curve and be aware of the biomass and glucose determination. kinetic parameters values [27,28]. The aim of this work was to study the microbial growth of B. subtilis under different Biomass determination cultivation conditions, particularly the glucose concentra- For dry biomass determination, 10 mL of the sample tion and OTR. was centrifuged at 4000 rpm, the pellet was decanted, A recent study showed that among various carbon resuspended in 5 ml of water, transferred to a previously sources, glucose was the most suitable carbon source for measured empty glass Petri dish and dried at 105 °C until B. subtilis growth [29]. For that reason, glucose was chosen the constant mass was achieved. Dry biomass was meas- as the main substrate for further examination in our study. ured from the weight difference. The experiments were The addition of glucose at four different concentrations done in duplicate and the results are expressed as mean was performed to increase the overall biomass, which is values. presented in Figure 1. After 48 h of cultivation, the maxi- mum biomass yield (6.2 g/L) was noticed in the medium OTR determination containing 10 g/L glucose, while the fastest growth was OTR was calculated from the empirical equation for noticed in the one containing 5 g/L glucose. The fact that flasks shaken on orbital shakers (Equation 1) [24]: glucose enhances the bacteria growth is also confirmed by the values of basic kinetics parameters given in Table 1. It ................................(1) can be seen that a microorganism achieved the lowest spe- cific growth rate and the highest generation time in the me- where VL is the liquid volume, VF is the flask volume, C is dium without glucose. On the contrary, the highest specific the dissolved oxygen concentration and N is the shaking growth rate and the lowest generation time (0.329 h-1 and speed. Since the experiments were conducted under the 2.1 h, respectively) were noticed in the medium containing same conditions and the shaking speed remained constant 5 g/L glucose. The consumption of glucose, on the other at 150 rpm, OTR was controlled by adjusting the volume of hand, was a relatively slow process (Figure 2). At 5 g/L, the medium and the volume of the actual flask itself. all the glucose which had been initially added to the me- dium was consumed after the end of the stationary phase. Consumption of glucose For higher initial concentrations there was still glucose left, In order to determine the consumption of glucose over even after the stationary phase. time, the samples were taken at regular intervals in aseptic conditions for the measurement of the remaining glucose Table 1. Kinetic parameters for the bacterial growth in the me- concentration. The concentration of glucose was deter- dia with different glucose concentrations mined spectrophotometrically, using a modified picric acid method [25]. Shortly, the samples were first centrifuged for 10 min at 3000 rpm, the supernatant was diluted and mixed with the picric acid solution.
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