Flocculation and pentadecane production of a novel filamentous cyanobacterium Limnothrix sp. strain SK1-2-1.

OBJECTIVE: A novel filamentous cyanobacterium, a photosynthesizing microorganism, was isolated from a river, and its unique features of flocculation and pentadecane production were characterized. RESULTS: Microscopic observations and a phylogenetic analysis with 16S rDNA revealed that this strain was a Limnothrix species denoted as the SK1-2-1 strain. Auto cell-flocculation was observed when this strain was exposed to a two-step incubation involving a standing cultivation following a shaking preincubation. Flocculation was enhanced by blue light at a wavelength at 470 nm and irradiation for several hours to 1 day. Moreover, the strain exhibiting exponential cell growth may preferentially accumulate alkanes as pentadecane C15H32 alkane, which may be used as jet fuel, at a range of approximately 1% in the dry cell weight of flocculated cells. CONCLUSION: This is the first study on biofuel production using flocculated cells in which the specific manner of production may be regulated by cultivation conditions.

Overproduction and easy recovery of biofuels from engineered cyanobacteria, autolyzing multicellular cells.

The semi-filamentous multicellular cyanobacterium Limnothrix/Pseudanabaena sp. strain ABRG5-3 undergoes autolysis, which involves the accumulation of polyphosphate compounds and disintegration of thylakoid membranes in cells, as a unique feature that occurs due to growth conditions. In this study, the overexpression and easy recovery of alkane (a saturated hydrocarbon, C17H36) as a biofuel were examined in recombinants of the cyanobacteria ABRG5-3 and Synechocystis sp. strain PCC6803. The results obtained indicated that the accumulated mass of alkane accounted for ∼50 or 60% of the dry weight of ABRG5-3 or PCC6803 recombinant cells, respectively. Furthermore, cultivating cells in liquid medium BG11 in which the nitrogen resource had been depleted promoted the production of alkane and cell lysis, resulting in the easy recovery of target products from the supernatant.

Characterization of lysis of the multicellular Cyanobacterium Limnothrix/Pseudanabaena sp. strain ABRG5-3.

The cyanobacterium semi-filamentous multicellular strain ABRG5-3 undergoes cell lysis as a unique feature that occurs due to growth condition changes from normal cultivation with shaking to static cultivation without shaking in liquid culture (Nishizawa et al., 2010). Microscopic observation and energy dispersive X-ray spectrometer (EDX) analysis have revealed that lysis is involved in the accumulation of polyphosphate compounds and the disintegration of thylakoid membranes in cells. Static cultivation, dark or red light exposure, and temperature (22 to 42 °C) conditions were found to be effective factors for the induction of lysis. Moreover, stress induced by salts, osmotic pressure with sucrose, and the depletion of nitrogen or phosphate in cultures also induced ABRG5-3 cell lysis. Based on these results, we discuss lysis and its utilization in the biotechnology industry.