Raphidiopsis raciborskii is a widely distributed, potentially toxic cyanobacterium described as a tropical-subtropical species. However, its occurrence in temperate regions has been expanding. Understanding the environmental factors underlying the expansion and colonization success of Raphidiopsis has been the object of numerous studies. However, less is known regarding its responses to pH and inorganic carbon in water. Thus, the aim of the present study was to investigate the effects of changes in pH and dissolved inorganic carbon on growth and saxitoxins production in the strain R. raciborskii ITEP-A1. We incubated batch cultures with different unbuffered and buffered pH (neutral-acid and alkaline) and inorganic carbon availability (CO₂-rich air bubbling and the addition of NaHCO₃) to assess the effect of these factors on the growth, toxin production as well as saxitoxins composition of the cyanobacterium. The carbon concentrating mechanism (CCM) system of ITEP-A1 was also characterized by an in silico analysis of its previously sequenced genome. The growth and saxitoxins production of R. raciborskii were affected. The addition of sodium bicarbonate and air bubbling enhanced the growth of the cyanobacterium in alkaline pH. In contrast, saxitoxins production and relative toxicity were decreased. Moreover, significant changes in the cellular composition of saxitoxins were strongly related to pH changes. ITEP-A1 potentially expresses the low-flux bicarbonate transporter BicA, an efficient CCM which uptakes most of its carbon from HCO₃⁻. Hence, increasing the diffusion of CO₂ in alkaline eutrophic lakes is likely to increase R. raciborskii dominance, but produce less toxic blooms.

Raphidiopsis raciborskii是一种分布广泛，潜在有毒的蓝细菌，被描述为热带亚热带物种。但是，它在温带地区的发生率正在扩大。理解立楠属植物的扩张和定殖成功的环境因素已经成为众多研究的对象。但是，关于其对水中pH和无机碳的响应知之甚少。因此，本研究的目的是研究pH值和溶解的无机碳的变化对R. raciborskii ITEP-A1菌株生长和毒素毒素产生的影响。我们用不同的非缓冲和缓冲pH（中性酸和碱性）和无机碳利用率（CO ₂）孵育分批培养物空气鼓泡和添加NaHCO ₃）以评估这些因素对蓝细菌的生长，毒素产生以及毒素的组成的影响。ITEP-A1的碳浓缩机制（CCM）系统的特征还在于对其先前测序的基因组进行了计算机分析。R.raciborskii的生长和毒毒素的产生受了影响。碳酸氢钠的添加和鼓泡增强了碱性pH下蓝细菌的生长。相反，毒毒素的产生和相对毒性降低了。此外，赛毒素的细胞组成的显着变化与pH值变化密切相关。ITEP-A1潜在表达低通量碳酸氢根转运BICA，一个高效的CCM，其摄取量的大部分碳从HCO ₃ ^- 。因此，增加CO ₂在碱性富营养化湖泊中的扩散可能会增加R. raciborskii的优势，但产生的毒性较小。