Bhattacharya Arghya, Mathur Megha, Kumar Pushpendar, Malik Anushree
Applied Microbiology Laboratory, Centre for Rural Development and Technology, Indian Institute of Technology, Delhi, Hauz Khas, New Delhi 110016 India.
Biotechnol Biofuels. 2019 Jul 10;12:178. doi: 10.1186/s13068-019-1519-3. eCollection 2019.
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.
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.
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.
藻类收获是一项主要成本，会增加生物燃料的生产成本。藻类生物燃料作为第三代生物燃料受到广泛研究。然而，由于其高昂的生产成本，它们尚不具备可行性，而这主要是由能源密集型生物质收获技术造成的。像真菌辅助收获微藻这样的生物收获方法效率很高，但由于其动力学缓慢且机制尚不清楚，也带来了挑战。
在本研究中，我们研究了附着情况，4小时内收获效率达到90%。为了确定细胞外代谢物的作用，通过从混合物中去除或废弃培养基进行了多项实验。在没有废弃培养基的情况下，收获效率降至20%，而对照组中则大于90%，添加废弃培养基后收获效率得以恢复。对废弃培养基的不同处理显示，高碘酸盐处理（≤20%）和甲醇 - 氯仿萃取（≤20%）后收获效率下降，表明存在类似糖的部分起作用。高分辨率液相色谱 - 质谱（HR - LC - MS）结果证实废弃培养基中存在N - 乙酰 - d - 葡萄糖胺（GlcNAc）和葡萄糖。当使用GlcNAc替代废弃培养基进行收获研究时，与使用葡萄糖相比，收获过程在4小时内明显更快（P < 0.05）。进一步的实验表明，代谢活跃的产生了从葡萄糖生成的GlcNAc。对废弃培养基以及用GlcNAc孵育的细胞进行伴刀豆球蛋白A染色和傅里叶变换红外光谱（FTIR）分析，结果表明其细胞表面存在GlcNAc，表现为深红色斑点和GlcNAc特异性峰，而在正常细胞中未观察到此类特征性斑点或峰。高分辨率透射电子显微镜（HR - TEM）显示，用废弃培养基或GlcNAc处理后，细胞表面形成了锯齿状边缘，而原子力显微镜（AFM）显示，与废弃培养基孵育后，细胞表面粗糙度增加。
结果有力地表明，废弃培养基中存在的GlcNAc会诱导细胞表面变化，从而介导其与菌丝的附着。因此，本研究有助于更好地理解辅助收获过程。
