No abstract

In order to use Synechocystis PCC 6803 as feedstock of nonpetroleum-based diesel fuel, pulsed electric field (PEF) technology was used for cell disruption prior to extraction of intracellular lipids. Severe cell disruption was evident after PEF treatment, especially with treatment intensity (TI) > 35 kWh/m(3). Temperature increase during the treatment brought about most of the destruction of autofluorescence compounds, as well as a fraction of inactivation and the destruction of the plasma and thylakoid membranes. However, the forces associated with the pulsing electric field caused significant damage to the plasma membrane, cell wall, and thylakoid membrane, and it even led to complete disruption of some cells into fragments, which resulted in biomass loss. Treatment by PEF enhanced the potential for the low-toxicity solvent isopropanol to access lipid molecules during subsequent solvent extraction, leading to lower usage of isopropanol for the same extraction efficiency. Thus, PEF shows promise for lowering the costs and environmental effects of the lipid-extraction step.

Microbial photosynthesis presents a valuable opportunity to capture abundant light energy to produce renewable bioenergy and biomaterials. To understand the factors that control the productivity of photosynthetic microorganisms, we conducted a series of semi-continuous experiments using bench-scale photobioreactor (PBR) systems, the cyanobacterium Synechocystis PCC6803 (PCC6803), and light conditions imitating actual day-night light irradiance (LI). Our results demonstrate that using normal BG-11 medium resulted in severe phosphate (P(i)) limitation for continuous operation. Mitigation of P(i)-limitation, by augmenting the P(i) content of BG-11, allowed higher biomass productivity; however, once P(i)-limitation was alleviated, limitation by inorganic carbon (C(i)) or LI occurred. C(i)-limitation was detected by a low total C(i) concentration (<5 mg C/L) and high and fluctuating pH. C(i)-limitation was relieved by delivering more CO(2), which led to a stable pH in the range of 7-9 and at least 5 mg/L of C(i) in HCO(3)(-). LI limitation, evidenced by an average LI <14 W/m(2) for PCC6803, was induced by a high biomass concentration of 1,300 mg/L. Thus, this work provides quantitative tools of stoichiometry and kinetics to evaluate limitation on PBRs.

No abstract