Intercellular transfer along the trichomes of the invasive terminal heterocyst forming cyanobacterium Cylindrospermopsis raciborskii CS-505

Abstract

Cylindrospermopsis raciborskii CS-505 is an invasive freshwater filamentous cyanobacterium that when grown diazotrophically may develop trichomes of up to 100 vegetative cells while differentiating only two end heterocysts, the sole sites for their N2-fixation process. We examined the diazotrophic growth and intercellular transfer mechanisms in C. raciborskii CS-505. Subjecting cultures to a combined-nitrogen-free medium to elicit N2 fixation, the trichome length remained unaffected while growth rates decreased. The structures and proteins for intercellular communication showed that while a continuous periplasmic space was apparent along the trichomes, the putative septal junction sepJ gene is divided into two open reading frames and lacks several transmembrane domains unlike the situation in Anabaena, differentiating a 5-fold higher frequency of heterocysts. FRAP analyses also showed that the dyes calcein and 5-CFDA were taken up by heterocysts and vegetative cells, and that the transfer from heterocysts and 'terminal' vegetative cells showed considerably higher transfer rates than that from vegetative cells located in the middle of the trichomes. The data suggest that C. raciborskii CS-505 compensates its low-frequency heterocyst phenotype by a highly efficient transfer of the fixed nitrogen towards cells in distal parts of the trichomes (growing rapidly) while cells in central parts suffers (slow growth).

Physiological responses of the freshwater N2‐fixing cyanobacterium Raphidiopsis raciborskii to Fe and N availabilities

“…In accord with the higher 55 Fe uptake rates in Fig. Fe-limitation induces a decrease in the cell size of R. raciborskii with this change in size advantageous to energy and nutrient provision and ultimately favours Fe uptake under N-free conditions (Bothe et al, 2010;Plominsky et al, 2015;Burford et al, 2018). Moreover, the higher Fe uptake ability of R. raciborskii over the nondiazotroph M. aeruginosa may well contribute to the apparent dominant ecological advantage of diazotrophic phytoplankton over non-diazotrophic organisms under low nitrogen and high Fe conditions.…”

“…In contrast, the lower Chl a content of both strains under N-free conditions was stable for different Fe availabilities (50-1000 nM). Indeed, shorter R. raciborskii trichomes were expected in the N-free media, since strains with long trichomes have lower surface area to volume ratios and consequently are at a disadvantage with regard to supplying N (in the form of compounds such as glutamine) to neighbouring vegetative cells under Ndeficient conditions (Bothe et al, 2010;Plominsky et al, 2015;Willis et al, 2015;Burford et al, 2018). Moreover, the straight trichome of CS-509 in the medium with 200 and 1000 nM Fe was generally longer than the coiled trichome of CS-506.…”

Constitutive toxin production under various nitrogen and phosphorus regimes of three ecotypes of Cylindrospermopsis raciborskii ((Wołoszyńska) Seenayya et Subba Raju)

“…In N fixing conditions atmospheric N 2 is reduced to NH 4 + within heterocysts, which is then transferred to the vegetative cells (Plominsky et al, 2014). Asymmetric cell division leads to heterocyst formation (Komarek, 2013), and in C. raciborskii are only produced at the terminal ends of the trichomes and are thus limited to a maximum of two per trichome (Plominsky et al, 2013).…”

“…Asymmetric cell division leads to heterocyst formation (Komarek, 2013), and in C. raciborskii are only produced at the terminal ends of the trichomes and are thus limited to a maximum of two per trichome (Plominsky et al, 2013). Nitrogen limitation of vegetative cells can occur at a distance from the heterocyst leading to growth limitation or death of these vegetative cells (Komarek, 2013;Plominsky et al, 2014). N 2 fixation is energetically expensive (Ceuterick et al, 1978;Burgess and Lowe, 1996;Hoffman et al, 2014) and combined with constraints of N transfer may limit its availability as an N source.…”

“…European strains of C. raciborskii have been shown to have a high affinity and storage capacity for dissolved inorganic phosphorus (DIP) (Isvá novics et al, 2000). It can also fix atmospheric dinitrogen (N 2 ), but it has a 4-fold higher growth rate when dissolved inorganic nitrogen (DIN) is available (Plominsky et al, 2014). These combined features allow C. raciborskii to respond within minutes to nutrient inputs (Amaral et al, 2014), and may be key factors in its worldwide success and dominance in many ecosystems (Padisá k, 1997).…”