Identification of a Halotolerant Mutant via In Vitro Mutagenesis in the Cyanobacterium Fremyella diplosiphon

Nanoparticle-mediated Impact on Growth and Fatty Acid Methyl Ester Composition in the Cyanobacterium Fremyella diplosiphon

Insufficient light supply is a major limitation in cultivation of cyanobacteria for scaled up biofuel production and other biotechnological applications, which has driven interest in nanoparticle-mediated enhancement of cellular light capture. In the present study, Fremyella diplosiphon wild type (Fd33) and halotolerant (HSF33-2) strains were grown in solution with 20, 100, and 200 nm-diameter gold nanoparticles (AuNPs) to determine their impact on biomass accumulation, pigmentation, and fatty acid methyl ester (FAME) production. Results revealed a significant increase in growth of Fd33 (0.244 ± 0.006) and HSF33-2 (0.112 ± 0.003) when treated with 200 nm AuNPs. In addition, we observed a significant increase in chlorophyll a accumulation in 200 nm AuNP-treated Fd33 (25.7%) and HSF33-2 (36.3%) indicating that NPs enhanced photosynthetic pigmentation. We did not observe any alteration in FAME composition and biodiesel properties of transesterified F. diplosiphon lipids among all AuNP treatments. Interactions between F. diplosiphon and AuNPs were visualized using scanning electron microscopy. Energy dispersive X-ray spectroscopy confirmed the presence of AuNPs outside cells with aggregation in high cell density locales. Our findings indicate that nanotechnological approaches could significantly enhance growth of the organism with no negative effect on FAME-derived biodiesel properties, thus augmenting F. diplosiphon as a potential biofuel agent.

Fremyella diplosiphon as a biodiesel agent: Identification of fatty acid methyl esters via microwave-assisted direct in situ transesterification

Increasing concerns on environmental and economic issues linked to fossil fuel use has driven great interest in cyanobacteria as third generation biofuel agents. In this study, the biodiesel potential of a model photosynthetic cyanobacterium, Fremyella diplosiphon, was identified by fatty acid methyl esters (FAME) via direct transesterification. Total lipids in wild type (Fd33) and halotolerant (HSF33-1 and HSF33-2) strains determined by gravimetric analysis yielded 19% cellular dry weight (CDW) for HSF33-1 and 20% CDW for HSF33-2, which were comparable to Fd33 (18% CDW). Gas chromatography-mass spectrometry detected a high ratio of saturated to unsaturated FAMEs (2.48-2.61) in transesterified lipids, with methyl palmitate being the most abundant (C16:0). While theoretical biodiesel properties revealed high cetane number and oxidative stability, high cloud and pour point values indicated that fuel blending could be a viable approach. Significantly high FAME abundance in total transesterified lipids of HSF33-1 (40.2%) and HSF33-2 (69.9%) relative to Fd33 (25.4%) was identified using comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometry, indicating that robust salt stress response corresponds to higher levels of extractable FAME. Alkanes, a key component in conventional fuels, were present in F. diplosiphon transesterified lipids across all strains confirming that natural synthesis of these hydrocarbons is not inhibited during biodiesel production. While analysis of photosynthetic pigments and phycobiliproteins did not reveal significant differences, FAME abundance varied significantly in wild type and halotolerant strains indicating that photosynthetic pathways are not the sole factors that determine fatty acid production. We characterize the potential of F. diplosiphon for biofuel production with FAME yields in halotolerant strains higher than the wild type with no loss in photosynthetic pigmentation.