Fast‐growing phototrophic microorganisms and the productivity of phototrophic cultures

Abstract

Fast‐growing cyanobacterial and microalgal strains are considered to be a promising resource to overcome current productivity barriers of phototrophic cultivation. The purpose of this communication, however, is to argue that a high maximal growth rate itself is not a sufficient or necessary property for high phototrophic productivity. Rather, the light‐limited specific growth rate of a phototrophic microorganism is a product of several factors, including the rate of light absorption, the photosynthetic efficiency, and the maximal biomass yield per mol photons. It is suggested that, in addition to the maximal growth rate, reports on fast‐growing strains should also assess photosynthetic efficiency and maximal biomass yield as predictors of culture productivity. The arguments within the communication are underpinned by a theoretical analysis of a light‐limited chemostat, compared to its heterotrophic counterpart. It is shown that for the light‐limited chemostat maximal productivity occurs at low dilution rates.

A quantitative description of light-limited cyanobacterial growth using flux balance analysis

“…As shown in Figure 2, and characteristic for phototrophic microorganisms [31, 33, 34], the light-limited growth rate as a function of the light intensity I (measured in mol photons per area per time) can be described by a Haldane or Aiba equation, The phenomenological Haldane/Aiba equation is specified by three parameters, µ ∗ , K A , and γ .…”

“…In the following, we therefore propose a novel approach to incorporate light uptake and utilization into constraint-based models of phototrophic growth–with the aim to better capture the growth properties of cyanobacteria and other phototrophic microorganisms. Our approach is motivated by mechanistic models of phototrophic growth [31]. Specifically, we consider a two step process in which photons are first absorbed by the cell and are then utilized with a light-dependent photosynthetic efficiency (also denoted as light-dependent quantum yield ).…”

Cyanobacteria newly isolated from marine volcanic seeps display rapid sinking and robust, high density growth

“…Growth rate measurement in cyanobacteria is also difficult to reproduce between labs, varying as much as 36% even when the same strain and methods are used, likely due to the intrinsic sensitivity to light quality and air composition 54 . Ultimately we focused on high-density growth, where UTEX 3222 out-performed the comparison strain UTEX 3154 by more than 2-fold greater biomass titer after 12 days, which is a potentially more biotechnologically relevant trait than exponential growth rate 44,45 . Marine phytoplankton accounts for about half the photosynthetic primary production on earth (165-183Gt CO2/yr) 72,73 , fixing approximately 3-fold as much carbon as total anthropogenic greenhouse gas emissions(59±6.6 CO2e/yr) 74 .…”

“…While fast growth on solid medium (Fig 1B) and reasonable growth rate at low density (Fig 2A -D) are good predictors of an organism's facility in the lab and preferences among growth conditions, light-limited growth at high density is predicted to be more relevant for industrial applications, where high culture density is needed for high volumetric or areal productivity 44,45 . Following an initial observation of planktonic liquid growth of UTEX 3222 to high-density, we explored high density batch growth as a relevant industrial behavior.…”

Development of a Biotechnology Platform for the Fast-Growing Cyanobacterium Synechococcus sp. PCC 11901

“…This knowledge is required to perform metabolic modeling and flux analysis and may also provide insight into the physiological features underlying the fast, sustained growth phenotype of PCC 11901 [ 10 ]. Moreover, a recent analysis suggests that factors other than fast growth are also critical for high phototrophic productivity, including the rate of light absorption, photosynthetic efficiency, and the conversion rate of photons to biomass [ 11 ]. Finally, although genetic manipulation of PCC 11901 has been demonstrated, a system for generating unmarked mutants at different chromosomal locations in this species has not been developed.…”