Cyanobacterial biomass as carbohydrate and nutrient feedstock for bioethanol production by yeast fermentation

Abstract

BackgroundMicrobial bioconversion of photosynthetic biomass is a promising approach to the generation of biofuels and other bioproducts. However, rapid, high-yield, and simple processes are essential for successful applications. Here, biomass from the rapidly growing photosynthetic marine cyanobacterium Synechococcus sp. PCC 7002 was fermented using yeast into bioethanol.ResultsThe cyanobacterium accumulated a total carbohydrate content of about 60% of cell dry weight when cultivated under nitrate limitation. The cyanobacterial cells were harvested by centrifugation and subjected to enzymatic hydrolysis using lysozyme and two alpha-glucanases. This enzymatic hydrolysate was fermented into ethanol by Saccharomyces cerevisiae without further treatment. All enzyme treatments and fermentations were carried out in the residual growth medium of the cyanobacteria with the only modification being that pH was adjusted to the optimal value. The highest ethanol yield and concentration obtained was 0.27 g ethanol per g cell dry weight and 30 g ethanol L-1, respectively. About 90% of the glucose in the biomass was converted to ethanol. The cyanobacterial hydrolysate was rapidly fermented (up to 20 g ethanol L-1 day-1) even in the absence of any other nutrient additions to the fermentation medium.ConclusionsCyanobacterial biomass was hydrolyzed using a simple enzymatic treatment and fermented into ethanol more rapidly and to higher concentrations than previously reported for similar approaches using cyanobacteria or microalgae. Importantly, as well as fermentable carbohydrates, the cyanobacterial hydrolysate contained additional nutrients that promoted fermentation. This hydrolysate is therefore a promising substitute for the relatively expensive nutrient additives (such as yeast extract) commonly used for Saccharomyces fermentations.

Recovery of Protein Concentrates From Microalgal Biomass Grown in Manure for Fish Feed and Valorization of the By-Products Through Anaerobic Digestion

“…Cell disruption must be carried out by a pretreatment able to release intracellular proteins. Several mechanical, chemical, and biological (i.e., enzymatic) methods have been studied for cell disruption (Möllers et al, 2014;Hernández et al, 2015). Despite of high temperatures may degrade proteins, chemical methods have previously shown to be optimal to break down microalgal cell wall as a previous step for saccharification (Hernández et al, 2015), but they also can lead to the formation of amino acid complexes (Maillard reactions), which limit the availability of amino acids (Boisen et al, 2000).…”

Highly Potent Saccharification of Arthrospira maxima Glycogen by Fungal Amylolytic Enzyme from Trichoderma Species J113

“…Photosynthetic microorganisms have garnered increased interest as the biomass of choice for renewable energy production [7][8][9][10][11]. These organisms, namely microalgae and cyanobacteria, have advantageous characteristics for biofuel production when compared to conventional agricultural crops.…”

Sustainable life support on Mars – the potential roles of cyanobacteria

“…They could also provide organic substrates for production of biofuel precursors by other organisms, particularly relevant on Mars where importing substrates from Earth would be impractical. For instance, as mentioned above, lysed cyanobacterial biomass has been used as a fermentation substrate for ethanol production in yeasts (Aikawa et al 2013;Möllers et al 2014). However, genetic engineering could remove the need for other organisms even for production of biofuel precursors which are not naturally produced by cyanobacteria in adequately large amounts -if at all.…”

“…Note that these results are preliminary and that no optimization step (e.g., choice of a strain that can metabolize sucrose, alteration of culture conditions to modify cyanobacterial biomass's composition and/or more efficient extraction method) has yet been performed. Lysed cyanobacterial biomass has also been shown to be a suitable substrate for ethanol production in yeasts (Aikawa et al 2013;Möllers et al 2014). In lysogeny broth (LB), the most common growth medium for heterotrophic bacteria in laboratories, the concentration of fermentable sugars and sugar equivalents (sugar phosphates, oligosaccharides, nucleotides, etc.)…”