Laboratory of Microbial Genetics, Department of Botany, Banaras Hindu University, Varanasi, 221005, India.
Appl Biochem Biotechnol. 2021 May;193(5):1447-1468. doi: 10.1007/s12010-021-03501-3. Epub 2021 Jan 23.
The wide applications, uniqueness, and high quality of cyanobacterial exopolysaccharides (EPSs) have attracted many biotechnologists. Despite it, the inducers and molecular determinants of EPS biosynthesis in cyanobacteria are lesser known. Although, studies revealed that environmental cues especially C/N ratio as the prime modulator, the factors like light, temperature, moisture, and nutrient availability, etc. have been overlooked. Due to this, the possibilities to modify cyanobacterial system for achieving higher quantity of EPS either by modifying growth medium or metabolic engineering are restricted to few optimisations. Therefore, the present work describes the impact of sulfate limitations on the EPS production and compositions in the cyanobacterium Anabaena sp. PCC 7120. Increased EPS production with enhanced expression of alr2882 was observed in lower sulfate supplementations; however, FTIR analysis depicted an altered composition of supramolecule. Furthermore, in silico analysis of Alr2882 depicted the presence of ExoD domain and three transmembrane regions, thereby indicating its membrane localisation and role in the EPS production. Additionally, the phylogeny and multiple sequence alignment showed vertical inheritance of exoD and conservation among cyanobacteria. The meta-threading template-based modelling and ab initio full atomic relaxation by LOMET and ModRefiner servers, respectively, also exhibited helical topology of Alr2882, with nine α-helices arranged antiparallel to the preceding one. Moreover, post-translational modifications predicted in Alr2882 indicated high order of molecular regulation underlining EPS production in Anabaena sp. PCC 7120. This study provides a foundation for understanding the EPS biosynthesis mechanism under sulfur limitation and the possible role of ExoD in cyanobacteria.
蓝藻胞外多糖 (EPS) 的广泛应用、独特性和高质量引起了许多生物技术人员的关注。尽管如此，蓝藻 EPS 生物合成的诱导剂和分子决定因素知之甚少。然而，研究表明，环境线索，特别是 C/N 比作为主要调节剂，光照、温度、水分和养分供应等因素都被忽视了。由于这个原因，通过修改生长培养基或代谢工程来修改蓝藻系统以获得更高数量 EPS 的可能性仅限于少数优化。因此，本工作描述了硫酸盐限制对蓝藻 Anabaena sp. PCC 7120 中 EPS 生产和组成的影响。在较低的硫酸盐补充下，观察到 EPS 产量增加，alr2882 表达增强；然而，FTIR 分析表明超分子的组成发生了改变。此外，对 Alr2882 的计算机分析表明存在 ExoD 结构域和三个跨膜区，表明其在膜定位和 EPS 生产中的作用。此外，系统发育和多重序列比对显示 exoD 的垂直遗传和蓝藻之间的保守性。基于元线程模板的建模和由 LOMET 和 ModRefiner 服务器分别进行的从头全原子松弛的 ab initio，分别显示了 Alr2882 的螺旋拓扑结构，其中九个α-螺旋与前一个呈反平行排列。此外，在 Alr2882 中预测的翻译后修饰表明在 Anabaena sp. PCC 7120 中 EPS 生产存在高度的分子调控。本研究为了解在硫限制下 EPS 生物合成机制以及 ExoD 在蓝藻中的可能作用提供了基础。
