The polyphasic analysis of two native Raphidiopsis isolates supports the unification of the genera Raphidiopsis and Cylindrospermopsis (Nostocales, Cyanobacteria)

Abstract

Raphidiopsis and Cylindrospermopsis are planktic, freshwater bloom-forming cyanobacteria of great concern to human health due to the production of potent cyanotoxins. The presence (in Cylindrospermopsis) or absence (in Raphidiopsis) of heterocytes is the traditional character used to distinguish them. This has led to misidentifications and to questions about the validity of the genus Raphidiopsis. We studied two strains of R. mediterranea isolated from Argentinean shallow lakes using a polyphasic approach that included the morphological description of the natural populations and their ultrastructural, physiological and molecular characterisation. Heterocyte differentiation was not observed in the field or in cultures of R. mediterranea submitted to nitrogen deprivation. These results support the occurrence of stable native populations of R. mediterranea without heterocytes, which would not be a part of the Cylindrospermopsis complex life cycle. Based on 16S rRNA, 16S-23S ITS, and cpcBA-IGS sequences, these two genera are virtually identical. Thus, strains of Raphidiopsis and Cylindrospermopsis make up a monophyletic lineage in all phylogenetic reconstructions. Furthermore, the 16S-23S ITS secondary structure provided further evidence that these two genera cannot be separated. The intermixed position in the trees points to several losses of heterocytes during the evolution of these cyanobacteria. We conclude that these two genera should not be regarded as separate and distinct generic units and propose their unification under the name Raphidiopsis, respecting the principle of priority. Accordingly, we revisited and emended the description of Raphidiopsis.

Regulation of phosphate uptake reveals cyanobacterial bloom resilience to shifting N:P ratios

“…Filamentous cyanobacterial blooms are common in well‐mixed waters with different light intensity conditions (Aguilera et al., ; Havens, James, East, & Smith, ; Paerl et al., ). For instance, while some species such as Cylindrospermopsis raciborskii , a species phylogenetically related to R. mediterranea (Aguilera, Berrendero, Kaštovský, Echenique, & Salerno, in press; Moustaka‐Gouni, Kormas, Vardaka, Katsiapi, & Gkelis, ), succeed under high‐ Z eu / Z mix conditions (values ≥1) (Bonilla et al., ), P. agardhii blooms in highly turbid water columns ( Z eu / Z mix < 1; Bonilla et al., ) (Scheffer et al., ). Variable conditions in the Z eu / Z mix ratio during our study (range 0.37–1.42) may have favoured both cyanobacteria species in combination with changing nutrient conditions.…”

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

“…The bloom-forming freshwater filamentous cyanobacterium, Raphidiopsis raciborskii [previously named Cylindrospermopsis raciborskii (Aguilera et al, 2018)], is of increasing global environmental and social concerns because of its adverse effects on the quality of drinking water reservoirs and lakes as a result of the potential generation of toxic metabolites such as cylindrospermopsin (CYN) and saxitoxins (Hoff-Risseti et al, 2013;Lei et al, 2014;Botana, 2016;Martin et al, 2018). In recent decades, this diazotrophic cyanobacterium has spread from its native tropical region to subtropical and temperate zones (Burford et al, 2016;Burford et al, 2018).…”

Odorella benthonica gen. & sp. nov. (Pleurocapsales, Cyanobacteria): an odor and prolific toxin producer isolated from a California aqueduct

“…Both collected and original sequences were manually aligned in Microsoft Word (Microsoft Corp., Redmond, WA, USA) according to the secondary structure of the 16S molecule ( Reh akov a et al 2014). The jModel-test2 software was used for estimation of the best fit substitution model, found to be GTR+I+G (Darriba et al 2012) for both Bayesian Inference (BI) and Maximum Likelihood (ML) as demonstrated previously , Mare s 2017, Aguilera et al 2018. For ML analysis we used RaxML v.7.2.8 (Stamatakis et al 2008) with 1,000 bootstrap replicates.…”