Department of Environmental Engineering, METU, Ankara, Turkey.
J Ind Microbiol Biotechnol. 2012 Mar;39(3):513-9. doi: 10.1007/s10295-011-1043-3. Epub 2011 Oct 19.
Alginate is a copolymer of β-D: -mannuronic and α-L: -guluronic acids. Distribution of these monomers in the alginate structure is one of the important characteristics that affect the commercial value of the polymer. In the present work, the effect of agitation speed in the range of 200-700 rpm on alginate production by Azotobacter vinelandii ATCC(®) 9046 was investigated at a dissolved oxygen tension of 5% of air saturation. Experiments were conducted in a fermentor operated in batch mode for 72 h while the production of biomass and alginate, the consumption of substrate and the change in culture broth viscosity and monomer distribution of the polymer were monitored. Results showed that the growth rate of the bacteria increased from 0.165 to 0.239 h(-1) by the increase of mixing speed from 200 to 400 rpm. On the other hand, alginate production was found to be the most efficient at 400 rpm with the highest value of 4.51 g/l achieved at the end of fermentation. The viscosity of culture broth showed similar trends to alginate production. Viscosity was recorded as 24.61 cP at 400 rpm while it was only 4.26 cP at 700 rpm. The MM- and GG-block contents were almost equal in most of the culture times at 400 rpm. On the other hand, GG-blocks dominated at both low and high mixing speeds. Knowing that GG-blocks make rigid and protective gels with divalent cations, due to the higher GG-block content, the gel formation potential is higher at 200 rpm as well at 700 rpm, which might originate from the unfavorable environmental conditions that the bacteria were exposed to.
海藻酸盐是β-D: -甘露糖醛酸和α-L: -古洛糖醛酸的共聚物。这些单体在海藻酸盐结构中的分布是影响聚合物商业价值的重要特征之一。在本工作中，在溶解氧张力为空气饱和 5%的条件下，研究了搅拌速度在 200-700rpm 范围内对固氮菌 ATCC(®)9046 生产海藻酸盐的影响。实验在分批模式下的发酵罐中进行了 72 小时，同时监测了生物量和海藻酸盐的生产、底物的消耗以及培养液粘度和聚合物单体分布的变化。结果表明，通过将混合速度从 200rpm 增加到 400rpm，细菌的生长速率从 0.165 增加到 0.239h(-1)。另一方面，发现海藻酸盐的生产在 400rpm 时效率最高，在发酵结束时达到了 4.51g/l 的最高值。培养液的粘度与海藻酸盐的生产呈现出相似的趋势。在 400rpm 时，粘度记录为 24.61cP，而在 700rpm 时仅为 4.26cP。在 400rpm 时，在大多数培养时间内 MM-和 GG-块的含量几乎相等。另一方面，在低和高混合速度下，GG-块都占主导地位。由于 GG-块与二价阳离子形成刚性和保护性凝胶，因此在 200rpm 和 700rpm 时，由于细菌所处的环境条件不利，凝胶形成潜力更高。
