A study of the influence of different laboratory growth conditions on the biomass and EPS production by Nostoc minutum, a diazothophic cyanobacterium locally isolated, was carried out. Two culture media were tested, with or without NaNO3 addition, and three luminous intensities: low (4530 lux), intermediate (7300 lux) and high (9860 lux). BW3 medium was better than BG11 for N. minutum growth, with maximal values of biomass concentration (4.98 DO) and the highest growth rate (0.019 h -1) at 9860 lux of light intensity. A progressive increase in culture viscosity of N. minutum cultures was observed, for stirred condition and non-diazotrophic growth in BG11 medium, together with the production of maximal EPS concentration (2.485 g/L). On the other hand, the EPS production in BW3 medium was maximal in diazotrophic conditions, both for still (1.66 g/L) and stirred (2.56 g/L) cultures. The different yields of EPS reported for each condition, results in the requirement of a species-specific optimization of the cultivation conditions for the exploitation of an efficient technology for the production of N. minutum EPS.
Cyanobacteria are photosynthetic microorganisms with morphological diversity and metabolic versatility. They are included in a wide range of microorganisms that are able to synthesize and secrete extracellular polymeric substances (EPS) mainly of polysaccharidic nature, which can remain covalently linked or loosely bound to the cell surface, or be liberated to the surrounding medium [
Due to their interesting physicochemical properties, the EPS have found applications in many industries like textiles, adhesives, paint, food, and beverage, among others [
The cyanobacterium Nostoc minutum [
All culturing procedures were performed aseptically. Stockcultures, 10 mL (0.15 g/L), were used to inoculate either erlenmeyers flasks (still cultures) or glass columns (stirred cultures). Cultivation was carried out in sterilised photobiorectors consisting of 250 mL Erlenmeyer flasks equipped with a device for aseptic removal of samples (still cultures) or 250 ml glass columns 37 mm i.d., containing 200 ml of BW3 or BG11 medium with or without the addition of NaNO3 and mixed through air injection with an aeration flow of 6.13 mL/seg (stirred cultures). The aeration was performed with filter-sterilized air. The cultures were run for 2 weeks (14 days) at 30˚C under permanent lighting of 4530 (low intensity), 7300 luxes (intermediate intensity) and 9860 luxes (high intensity).
Cyanobacterial growth was estimated by optical density (OD) at 580 nm every 48 h. EPS production was determinated after cultures reached the stationary phase, qualitatively by Alcian blue tintion and India ink, and quantitatively by dry weight determinations. The experiment was conducted in triplicates and values were expressed as their mean.
EPS was quantified by the method of Mondal et al. modified [
For physical characterization of the EPS, it was determined the electric charge by precipitation with cetylpe- ridium chloride (CPC) [
An increase in biomass production and specific growth rate with the increment of light intensity were observed. However, for still cultures the light intensity showed a slight incidence. Different authors reported the impor- tance to consider this parameter because it is often found as a limiting factor in culture systems [
N. minutum cells are enclosed in a fibrous matrix at the cell wall surface that has a structural coherence suffi- cient to exclude particles (e.g. India ink, see
Biomass (DO) | Growth rate (h−1) | ||||
---|---|---|---|---|---|
Culture Medium | Light Intensity (lux) | Still Cultures | Stirred Cultures | Still Cultures | Stirred Cultures |
BG11 | 4530 | 0.64 ± 0.02 | 3.13 ± 1.53 | nd | 0.011 ± 0.03 |
BG110 | 4530 | 0.56 ± 0.06 | 0.69 ± 0.23 | nd | 0.001 ± 0.08 |
BW3 | 4530 | 0.72 ± 1.03 | 3.73 ± 0.06 | 0.011 ± 2.55 | 0.013 ± 0.07 |
BW30 | 4530 | 0.70 ± 0.02 | 3.02 ± 0.07 | nd | 0.010 ± 0.01 |
BG11 | 7300 | 0.86 ± 0.07 | 3.09 ± 0.02 | nd | 0.009 ± 0.11 |
BG110 | 7300 | 0.67 ± 0.01 | 1.07 ± 0.01 | nd | 0.004 ± 0.40 |
BW3 | 7300 | 0.85 ± 0.05 | 4.02 ± 2.03 | 0.012 ± 0.12 | 0.014 ± 0.06 |
BW30 | 7300 | 0.80 ± 0.02 | 3.54 ± 0.07 | nd | 0.010 ± 0.06 |
BG11 | 9860 | 1.18 ± 0.02 | 3.04 ± 0.05 | nd | 0.012 ± 0.11 |
BG110 | 9860 | 0.85 ± 0.04 | 1.89 ± 0.04 | nd | 0.006 ± 0.07 |
BW3 | 9860 | 1.30 ± 0.02 | 4.98 ± 0.02 | 0.016 ± 0.10 | 0.019 ± 0.03 |
BW30 | 9860 | 1.22 ± 0.03 | 3.99 ± 0.09 | nd | 0.015 ± 0.02 |
BG110, BW30: culture media without NaNO3 added. Mean values ±SD are shown. Máximum values are in bold letter. nd = not determined.
specific to acid mucopolysaccharide [
There is a marked difference between the main components of the two culture media used. While, both BG110 and BW30 have no NaNO3 added, BG11 have three times NaNO3 concentration than BW3. The absence of NaNO3 could be a stress factor favourable for EPS synthesis. In fact, a number of diazotrophic strains of Nostoc have shown to produce EPS under N2-fixing conditions, with reduce production when grown on an exogenous N source [
This work was supported by the Secretaría de Ciencia y Técnica, UNSL, Argentina.
Dante S. Videla Pereyra,Susana G. Ferrari, (2016) Extracellular Polymeric Substance (EPS) Production by Nostoc minutum under Different Laboratory Conditions. Advances in Microbiology,06,374-380. doi: 10.4236/aim.2016.65036