Potential role of -acetyl glucosamine in assisted harvesting.

BACKGROUND

Algal harvesting is a major cost which increases biofuel production cost. Algal biofuels are widely studied as third-generation biofuel. However, they are yet not viable because of its high production cost which is majorly contributed by energy-intensive biomass harvesting techniques. Biological harvesting method like fungal-assisted harvesting of microalgae is highly efficient but poses a challenge due to its slow kinetics and poorly understood mechanism.

RESULTS

In this study, we investigate - attachment resulting in a harvesting efficiency of 90% within 4 h. To pinpoint the role of extracellular metabolite, several experiments were performed by eliminating the or spent medium from the - mixture. In the absence of spent medium, the harvesting efficiency dropped to 20% compared to > 90% in the control, which was regained after addition of spent medium. Different treatments of spent medium showed drop in harvesting efficiency after periodate treatment (≤ 20%) and methanol-chloroform extraction (≤ 20%), indicating the role of sugar-like moiety. HR-LC-MS (high-resolution liquid chromatography-mass spectrometry) results confirmed the presence of -acetyl-d-glucosamine (GlcNAc) and glucose in the spent medium. When GlcNAc was used as a replacement of spent medium for harvesting studies, the harvesting process was significantly faster ( < 0.05) till 4 h compared to that with glucose. Further experiments indicated that metabolically active produced GlcNAc from glucose. Concanavalin A staining and FTIR (Fourier transform infrared spectroscopy) analysis of spent medium- as well as GlcNAc-incubated cells suggested the presence of GlcNAc on its cell surface indicated by dark red dots and GlcNAc-specific peaks, while no such characteristic dots or peaks were observed in normal cells. HR-TEM (High-resolution Transmission electron microscopy) showed the formation of serrated edges on the cell surface after treatment with spent medium or GlcNAc, while Atomic force microscopy (AFM) showed an increase in roughness of the cells surface upon incubation with spent medium.

CONCLUSIONS

Results strongly suggest that GlcNAc present in spent medium induces surface changes in cells that mediate the attachment to hyphae. Thus, this study provides a better understanding of the -assisted harvesting process.