Photo-autotrophic Production of Poly(hydroxyalkanoates) in Cyanobacteria

Abstract

In the last two decades, poly(hydroxyalkanoates) (PHA) were solely produced using heterotrophic bacteria in aerobic cultivation. With respect to the great potential (500 Mt yr -1 ) of raw industrial CO 2 streams and even greater potential of flue gases, the focus on photo-autotrophic biotechnological processes is increasing steadily. Primarily, PHA-gene transfer from heterotrophic bacteria into algae and plant cells was attempted, with the intention to combine the known biosynthesis pathway with autotrophic cultivation. The natural occurrence of PHA in cyanobacteria is known at least since 1966. However, cyanobacteria were never considered for commercial production because the PHA amount based on cell mass and based on volumetric productivity is generally very low. Therefore, strain improvements were suggested, either by gene amplification or by suppression of biochemical pathways competing for the cell's acetate pool. In the late 1990s, the success of genetic modification was confirmed experimentally, elevating the cyanobacteria cell's PHA content. With additional optimization, PHB amounts up to 50 % w/w of biomass dry matter or up to about 2.4 g L -1 bioreactor volume could be produced within 11 days. Considering the land use for agriculture and the competition for plant biomass between food, feed, fuel and energy production, the binding of CO 2 in a biotechnological process using photo-autotrophic microorganisms may become a promising option.

Co-production of bio-oil and propylene through the hydrothermal liquefaction of polyhydroxybutyrate producing cyanobacteria

“…Some strains of Synechocystis and Synechococcus in turn have been reported to accumulate high levels of PHB of up to 55 % (daf) when cultivated under nitrogen and phosphorus depleted conditions (Drosg et al, 2015;Miyake et al, 1996;Nishioka et al, 2001;Panda et al, 2006;Wu et al, 2002;Wu et al, 2001). …”

“…The PHA content in the biomass can range from below 1% to over 50% and depends on the strain, the carbon and nutrient source and composition as well as on the cultivation conditions (Drosg et al, 2015;Panda et al, 2006;Wu et al, 2002;Wu et al, 2001). …”

Evaluation of Growth Yield of Spirulina maxima in Photobioreactors

“…Each sample was diluted to make the absorbance less than 1.0 if the optical density was greater than 1.0. The concentration of Spirulina maxima was determined by equation (1) describing the relationship between the absorbance A 560 and the concentration of dry mass:…”

“…Human nutrition, animal feeding, biofuel production, and sustainable agriculture -these are the branches of industry that are interested in microalgae biomass 1,2 . The literature on the subject presents various studies on the productivity of different microalgal culture systems [3][4][5][6][7] .…”

“…The highest productivity was obtained for Chlorella and Spirulina: 7.70 g L -1 day and 51 g L -1 day -1 for Spirulina respectively 8 . Commercial production of Spirulina, that in the strict sense is not a microalga, but a cyanobacterium 1 , has gained worldwide attention for its use in human food supplements, animal feed, and pharmaceuticals. The production of Spirulina with reduced costs is necessary when considering a large-scale cultivation for industrial purposes.…”