Comparative Assessment of Zarrouk and BG-11 Media Effects on the Growth and Biomass Accumulation of Cyanobacterial Strains

Abstract

Cyanobacteria represent a highly versatile group of photosynthetic prokaryotes with substantial potential for bioenergy production, high-value nutraceuticals, bioactive pharmaceuticals, and sustainable agricultural biostimulants. However, industrial scalability remains constrained by the optimization of strain-specific nutritional regimes. This study presents an exhaustive comparative evaluation of two benchmark cultivation media—Zarrouk medium and BG-11 medium—on the growth kinetics, biomass productivity, and pigment accumulation of four morphologically and ecologically diverse cyanobacterial strains: Arthrospira platensis SAG 21.99, Synechocystis sp. PCC 6803, Anabaena cylindrical SAG 1403-1b, and Nostoc muscorum Kazakh-102.

Cultivation was performed over a 21-day photoautotrophic period under controlled laboratory conditions (28 \pm 1^\circ\text{C}, 65\,\mu\text{mol}\cdot\text{m}^{-2}\cdot\text{s}^{-1} photosynthetic photon flux density, 16:8 light-dark photoperiod, continuous aeration with 0.04\% \text{CO}_2). Growth dynamics were monitored via optical density (\text{OD}_{680} and \text{OD}_{750}), dry cell weight (DCW) gravimetry, specific growth rate (\mu), doubling time (dt), and volumetric biomass productivity (P_{\text{biomass}}). In addition, spectrophotometric profiling of photosynthetic pigments—chlorophyll-a, total carotenoids, and phycobiliproteins (phycocyanin, allophycocyanin, phycoerythrin)—was performed across distinct growth phases.

Empirical results demonstrated profound strain-dependent variations driven by media composition and ionic strength. Arthrospira platensis exhibited superior physiological performance in Zarrouk medium, achieving a peak DCW concentration of 3.84 \pm 0.12\,\text{g}\cdot\text{L}^{-1}, a maximum specific growth rate (\mu_{\max}) of 0.312 \pm 0.011\,\text{day}^{-1}, and a volumetric biomass productivity of 0.218 \pm 0.008\,\text{g}\cdot\text{L}^{-1}\cdot\text{day}^{-1}. Conversely, A. platensis cultured in BG-11 medium experienced severe osmotic shock and chlorosis, resulting in negligible biomass accumulation (0.42 \pm 0.03\,\text{g}\cdot\text{L}^{-1}). In contrast, unicellular Synechocystis sp. PCC 6803 and diazotrophic filamentous Anabaena cylindrical performed optimally in BG-11 medium, generating maximum DCW values of 1.96 \pm 0.07\,\text{g}\cdot\text{L}^{-1} (\mu_{\max} = 0.415 \pm 0.014\,\text{day}^{-1}) and 1.68 \pm 0.05\,\text{g}\cdot\text{L}^{-1} (\mu_{\max} = 0.288 \pm 0.009\,\text{day}^{-1}), respectively. When subjected to Zarrouk medium, Synechocystis sp. PCC 6803 showed reduced growth (\text{DCW} = 0.81 \pm 0.04\,\text{g}\cdot\text{L}^{-1}) due to hyperosmotic stress, whereas A. cylindrica underwent rapid filament fragmentation and cell lysis. Nostoc muscorum Kazakh-102 exhibited broad physiological tolerance, achieving moderate growth in both BG-11 (\text{DCW} = 1.54 \pm 0.06\,\text{g}\cdot\text{L}^{-1}) and Zarrouk (\text{DCW} = 1.12 \pm 0.04\,\text{g}\cdot\text{L}^{-1}) media. Pigment analyses confirmed that high bicarbonate buffer capacity in Zarrouk medium enhanced phycocyanin accumulation in A. platensis (142.6 \pm 4.2\,\text{mg}\cdot\text{g}^{-1}\text{ DCW}), whereas BG-11 supported higher chlorophyll-a and carotenoid levels in Synechocystis sp. PCC 6803. This study provides crucial empirical benchmarks for media selection, bioprocess design, and metabolic optimization in scalable cyanobacterial biotechnology.