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（EPSs）的广泛应用、独特性和高质量吸引了许多生物技术人员。尽管如此，蓝藻中EPS生物合成的诱导剂和分子决定因素鲜为人知。尽管研究表明环境因素，尤其是 C/N 比作为主要调节剂，但光、温度、湿度和养分利用率等因素却被忽视了。因此，通过修改生长培养基或代谢工程来修改蓝藻系统以实现更高数量的 EPS 的可能性仅限于少数优化。因此，目前的工作描述了硫酸盐限制对蓝藻鱼腥藻中EPS 生产和组成的影响sp. PCC 7120。在较低的硫酸盐补充剂中观察到EPS 产量增加，alr 2882表达增强；然而，FTIR 分析显示超分子的组成发生了变化。此外，Alr2882 的计算机分析描述了 ExoD 结构域和三个跨膜区域的存在，从而表明其膜定位和在 EPS 生产中的作用。此外，系统发育和多序列比对显示了蓝藻之间exoD 的垂直遗传和保守性。基于元线程模板的建模和从头开始LOMET 和 ModRefiner 服务器的完全原子弛豫也分别展示了 Alr2882 的螺旋拓扑结构，其中 9 个 α 螺旋与前一个螺旋反平行排列。此外，Alr2882 中预测的翻译后修饰表明鱼腥藻中EPS 生产的高阶分子调控。PCC 7120。这项研究为了解硫限制下的 EPS 生物合成机制和 ExoD 在蓝藻中的可能作用提供了基础。