Otero Ana, Vincenzini Massimo
Dipartimento di Biotecnologie Agrarie, Universitá degli Studi di Firenze, Piazzale delle Cascine 27, I-50144, Florence, Italy.
J Biotechnol. 2003 Apr 24;102(2):143-52. doi: 10.1016/s0168-1656(03)00022-1.
A study on the effect of two of the main factors affecting energy flux in N(2)-fixing cyanobacteria, i.e. light intensity and availability of combined nitrogen, on the synthesis of soluble exopolysaccharides was carried out with three strains of the genus Nostoc (PCC 7413, PCC 7936, and PCC 8113) presenting different capsular polysaccharidic morphologies and released polysaccharide productions. Strains acclimated to diazotrophic and non-diazotrophic conditions were cultured at high and low light intensities in aerated batch cultures. High light intensities enhanced total carbohydrate synthesis in all the strains but growth measured as pigment and protein concentration, total and soluble carbohydrate concentrations presented a strain-dependent response to nitrate availability. When adequately acclimated to the presence of nitrate all the capsulated strains tested became non-capsulated, with no extracellular polysaccharide being produced. Carbon availability can be on the basis of the observed correlation between the synthesis of capsular polysaccharides and diazotrophy. The slime-forming strain Nostoc PCC 7413 was the only one releasing polysaccharides into the surrounding medium under both, diazotrophic and non-diazotrophic conditions, with the highest values being obtained in the presence of nitrate. This strain presented the highest total carbohydrate (3.5 gl(-1)), soluble carbohydrate (1.8 gl(-1)) concentrations and viscosity values of all the tested strains. Different mechanisms of nitrogen-control of the synthesis of exocellular polysaccharides are reported for each strain, which results in the requirement of a species-specific optimisation of the cultivation conditions for the development of an efficient technology for the production of cyanobacterial exopolysaccharides.
利用三种具有不同荚膜多糖形态和胞外多糖产量的念珠藻属菌株（PCC 7413、PCC 7936和PCC 8113），开展了一项关于影响固氮蓝细菌能量通量的两个主要因素，即光照强度和化合态氮的可利用性，对可溶性胞外多糖合成影响的研究。将适应于固氮和非固氮条件的菌株在通气分批培养中于高光强和低光强下培养。高光强增强了所有菌株的总碳水化合物合成，但以色素和蛋白质浓度、总碳水化合物和可溶性碳水化合物浓度衡量的生长对硝酸盐的可利用性呈现出菌株依赖性反应。当充分适应硝酸盐的存在时，所有测试的有荚膜菌株都变成无荚膜的，且不产生胞外多糖。基于观察到的荚膜多糖合成与固氮之间的相关性，碳的可利用性可能存在。形成黏液的菌株念珠藻PCC 7413是唯一在固氮和非固氮条件下都向周围培养基中释放多糖的菌株，在有硝酸盐存在时获得的值最高。该菌株在所有测试菌株中呈现出最高的总碳水化合物（3.5 g L-1）、可溶性碳水化合物（1.8 g L-1）浓度和黏度值。报道了每种菌株控制胞外多糖合成的不同氮调控机制，这导致需要针对特定物种优化培养条件，以开发一种高效的蓝细菌胞外多糖生产技术。
