Continuous Cultivation as a Method to Assess the Maximum Specific Growth Rate of Photosynthetic Organisms

Abstract

Modeling the growth of photosynthetic organisms is challenging, due to the complex role of light, which can be limiting because of self-shading, or photoinhibiting in the case of high intensities. A case of particular interest is represented by nitrogen-fixing cyanobacteria, whose growth is controlled not only by the light intensity, but also by the availability of atmospheric nitrogen in the liquid medium. The determination of the maximum specific growth rate is often affected by many variables that, in batch growth systems, may change significantly. On the other hand, in a continuous system, once the steady state is reached the values of all the process variables remain constant, including the biomass concentration and the specific light supply rate. In this work, the diazotrophic cyanobacterium Anabaena PCC 7122 was cultivated in continuous photobioreactors, to investigate the role of nitrogen, light and residence time on growth kinetics, and to retrieve the value of the maximum specific growth rate of this organism. In addition, the kinetic parameters for temperature and the half saturation constant for nitrogen (3 mg L−1) were measured by respirometric tests. Based on the results of continuous experiments, the specific maintenance rate was found to depend on the light intensity supplied to the reactor, ranging between 0.5 and 0.8 d−1. All these parameters were used to develop a kinetic model able to describe the biomass growth in autotrophic conditions. The maximum specific growth rate could hence be determined by applying the kinetic model in the material balances of the continuous photobioreactor, and resulted equal to 8.22 ± 0.69 d−1.

Fixing N2 into cyanophycin: continuous cultivation of Nostoc sp. PCC 7120

“…PCC 7120). The residence time ( τ ) and the incident light intensity ( I 0 ) were kept constant respectively at 2.3 d and 450 µmol photons m -2 s -1 , according to previous literature on cyanophycin production in continuous system (Trentin et al 2021 ) and on continuous cultivation of diazotrophic cyanobacteria (Barbera et al 2019 ). Inlet phosphorus concentration were varied from the one commonly present in standard BG11 medium (about 5 mg P L -1 ) to almost 1 mg P L -1 , modifying the concentration of potassium hydrogen phosphate (K 2 HPO 4 ) in the cultivation medium.…”

“…Concerning the possibility of continuously cultivating diazotrophic cyanobacteria, Barbera et al ( 2019 ) obtained remarkable productivities with Anabaena sp. in a continuous cultivation system, showing that the growth of diazotrophic organisms can be efficient is such operating conditions.…”

Differences in susceptibility to photoinhibition do not determinegrowth rate under moderate light in batch or turbidostat - a studywith five green algae

“…1). It has been proposed that even measurements of the maximum specific growth rate would be more reliable if done in a continuous culture (Barbera et al 2019). However, the conditions selected for our turbidostat cultivation would not reveal the maximum rate of cell division.…”

Yeasts from a traditional ferment Rabil: Molecular and physiological characterization

“…The maximum specific growth rate is inversely proportional to the generation time, and is one of the most important parameters in modelling microbial growth (Barbera et al, 2019).…”