Installing extra bicarbonate transporters in the cyanobacterium Synechocystis sp. PCC6803 enhances biomass production

Abstract

As a means to improve carbon uptake in the cyanobacterium Synechocystis sp. strain PCC6803, we engineered strains to contain additional inducible copies of the endogenous bicarbonate transporter BicA, an essential component of the CO2-concentrating mechanism in cyanobacteria. When cultured under atmospheric CO2 pressure, the strain expressing extra BicA transporters (BicA(+) strain) grew almost twice as fast and accumulated almost twice as much biomass as the control strain. When enriched with 0.5% or 5% CO2, the BicA(+) strain grew slower than the control but still showed a superior biomass production. Introducing a point mutation in the large C-terminal cytosolic domain of the inserted BicA, at a site implicated in allosteric regulation of transport activity, resulted in a strain (BicA(+)(T485G) strain) that exhibited pronounced cell aggregation and failed to grow at 5% CO2. However, the bicarbonate uptake capacity of the induced BicA(+)(T485G) was twice higher than for the wild-type strain. Metabolic analyses, including phenotyping by synchrotron-radiation Fourier transform Infrared spectromicroscopy, scanning electron microscopy, and lectin staining, suggest that the excess assimilated carbon in BicA(+) and BicA(+)(T485G) cells was directed into production of saccharide-rich exopolymeric substances. We propose that the increased capacity for CO2 uptake in the BicA(+) strain can be capitalized on by re-directing carbon flux from exopolymeric substances to other end products such as fuels or high-value chemicals.

A warm welcome for alternative CO2 fixation pathways in microbial biotechnology

“…Shih et al ., 2014) and introducing CO 2 concentrating mechanisms to increase the carboxylating activity of RubisCO (e.g. Bonacci et al ., 2012; Kamennaya et al ., 2015). Some of these attempts have slightly improved the performance of autotrophs employing the Calvin cycle.…”

Sedimentation of ballasted cells‐free EPS in meromictic Fayetteville Green Lake

“…In aquatic systems with low availability of organic carbon, EPS are products mainly of photosynthetic fixation of inorganic carbon (C i ) and their synthesis can be affected by the substrate concentration (DIC) and availability relative to the availability of other essential nutrients (Crosbie, Tuebner, and Weisse, (); Gordillo, Jiménez, Figueroa, & Niell, ; Otero & Vincenzini, ; De Philippis, Sili, & Vincenzini, ; Kamennaya et al, ; Kamennaya et al, ). The ambient DIC concentrations in FGL are relatively high (Table ) owing to an input of DIC‐rich groundwater (Havig et al, ; Takahashi et al, ).…”

“…Cations interact with negatively charged groups, for example carboxyl residues, which are particularly abundant in cyanobacterial EPS (De Philippis, Sili, Paperi, & Vincenzini, ; Kamennaya et al, ) and which serve as nucleation sites for mineral formation (Kamennaya et al, ; Obst et al, ). In situ formation of calcite, magnesite, and gypsum in FGL was linked to Synechococci but was explained by mineral‐nucleating capacity of their S‐layer (Thompson & Ferris, ; Thompson et al, ).…”

“…In some case, EPS was associated with non-conductive presumably mineral material (h). Scale bar = 2 μm (a-c); 25 μm (c); 1 μm (d-f); 0.5 μm (g, h) nutrients (Crosbie, Tuebner, and Weisse, (2003); Gordillo, Jiménez, Figueroa, & Niell, 1998;Otero & Vincenzini, 2004;De Philippis, Sili, & Vincenzini, 1996;Kamennaya et al, 2015;Kamennaya et al, 2018). The ambient DIC concentrations in FGL are relatively high (Table 1) owing to an input of DIC-rich groundwater (Havig et al, 2018;Takahashi et al, 1968).…”

Cyanobacterial photo-driven mixotrophic metabolism and its advantages for biosynthesis

“…CO 2 uptake involves several different bicarbonate transporters, some of which consume cellular energy (e.g., ATP or NADPH). Overexpression of Na(+)-dependent bicarbonate transporters doubles cyanobacterial biomass production under aerated atmospheric CO 2 conditions, but the mutant grows slower in enriched CO 2 conditions due to metabolic burdens [19]. Moreover, the RuBisCO is an inefficient enzyme for CO 2 fixation.…”