Littérature scientifique sur le sujet « Sodalinema »

Cyanobacteria mostly rely on the active uptake of hydrated CO2 (i.e., bicarbonate ions) from the surrounding media to fuel their inorganic carbon assimilation. The dehydration of bicarbonate in close vicinity of RuBisCO is achieved through the activity of carboxysomal carbonic anhydrase (CA) enzymes. Simultaneously, many cyanobacterial genomes encode extracellular α- and β-class CAs (EcaA, EcaB) whose exact physiological role remains largely unknown. To date, the CahB1 enzyme of Sodalinema gerasimenkoae (formerly Microcoleus/Coleofasciculus chthonoplastes) remains the sole described active extracellular β-CA in cyanobacteria, but its molecular features strongly suggest it to be a carboxysomal rather than a secreted protein. Upon expression of CahB1 in Synechocystis sp. PCC6803, we found that its expression complemented the loss of endogenous CcaA. Moreover, CahB1 was found to localize to a carboxysome-harboring and CA-active cell fraction. Our data suggest that CahB1 retains all crucial properties of a cellular carboxysomal CA and that the secretion mechanism and/or the machinations of the Sodalinema gerasimenkoae carboxysome are different from those of Synechocystis.

ABSTRACT Filamentous cyanobacteria belonging to the ‘marine Geitlerinema’ cluster are spread worldwide in saline environments and considered to play an important ecological role. However, the taxonomy of this group remains unclear. Here, we analyzed the phylogeny, ecology and biogeography of the ‘marine Geitlerinema’ cluster representatives and revealed two subclusters: 1) an ‘oceanic’ subcluster containing PCC7105 clade and BBD clade with free-living and pathogenic strains distributed in Atlantic, Indian and Pacific Ocean-related localities, and 2) a Sodalinema subcluster containing free-living strains from marine, hypersaline, saline-alkaline and soda lake habitats from the Eurasian and African continents. Polyphasic analysis using genetic and phenotypic criteria demonstrated that these two groups represent separate genera. Representatives of Sodalinema subcluster were phylogenetically attributed to the genus Sodalinema. Our data expand the ecological and geographical distribution of this genus. We emended the description of the genus Sodalinema and proposed three new species differing in phylogenetic, geographic and ecological criteria: Sodalinema orleanskyi sp. nov., Sodalinema gerasimenkoae sp. nov. and Sodalinema stali sp. nov. Additionally, a new genus and species Baaleninema simplex gen. et sp. nov. was discribed within the PCC7105 clade. By this, we put in order the current confusion of the ‘marine Geitlerinema’ group and highlight its ecological diversity.

AbstractCyanobacterial mats inhabit a variety of aquatic habitats, including the most extreme environments on Earth. They can thrive in a wide range of phosphorus (P) levels and are thus important players for ecosystem primary production and P cycling at the sediment-water interface. Polyphosphate (polyP), the major microbial P storage molecule, is assigned a critical role in compensating for phosphate fluctuations in planktonic cyanobacteria, but little is known about potentially analogous mechanisms of mat-forming cyanobacteria. To investigate acclimation strategies of cyanobacterial mats to fluctuating phosphate concentrations, laboratory batch experiments were conducted, in which the cosmopolitan mat-forming, marine cyanobacterium Sodalinema stali was exposed to low dissolved P concentrations, followed by a P pulse. Our results show that the cyanobacteria dynamically adjusted cellular P content to ambient phosphate concentrations and that they had accumulated polyP during periods of high phosphate availability, which was subsequently recycled to sustain growth during phosphate scarcity. However, following the depletion of dispensable cellular P sources, including polyP, we observed a reallocation of P contained in DNA into polyP, accompanied by increasing alkaline phosphatase activity. This suggests a change of the metabolic focus from growth towards maintenance and the attempt to acquire organic P, which would be naturally contained in the sediment. P overplus uptake following a simulated P pulse further suggests that Sodalinema-dominated mats exhibit elaborated mechanisms to cope with severe P fluctuations to overcome unfavourable environmental conditions, and potentially modulate critical P fluxes in the aquatic cycle.

AbstractCyanobacteria have many biotechnological applications. Increasing their cultivation pH can assist in capturing carbon dioxide and avoiding invasion by other organisms. However, alkaline media may have adverse effects on cyanobacteria, such as reducing the Carbon‐Concentrating Mechanism's efficiency. Here, we cultivated two halo‐alkaliphilic cyanobacteria consortia in chemostats at pH 10.2–11.4. One consortium was dominated by Ca. Sodalinema alkaliphilum, the other by a species of Nodosilinea. These two cyanobacteria dominate natural communities in Canadian and Asian alkaline soda lakes. We show that increasing the pH decreased biomass yield. This decrease was caused, in part, by a dramatic increase in carbon transfer to heterotrophs. At pH 11.4, cyanobacterial growth became limited by bicarbonate uptake, which was mainly ATP dependent. In parallel, the higher the pH, the more sensitive cyanobacteria became to light, resulting in photoinhibition and upregulation of DNA repair systems.

La spiruline est le nom commun de cyanobactéries comestibles cultivées dans des exploitations aquacoles généralement industrielles. Toutefois, en France, cette production est assurée par 180 fermes paysannes. La spiruline est consommée sous forme d’aliments ou de compléments alimentaires, pour sa valeur nutritionnelle et ses effets positifs sur la santé. Cependant, certaines cyanobactéries produisent des cyanotoxines et sont susceptibles de contaminer les cultures de spiruline. Ces toxines, notamment des microcystines (MCs), avaient été détectées dans des spirulines provenant de différents marchés étrangers. De plus, une espèce de spiruline, Limnospira fusiformis, était soupçonnée de toxicité suite à deux publications portant sur des souches kényanes. Enfin, une confusion taxonomique concernait les spirulines désignées par quatre noms d’espèces réparties sur deux genres. Au regard de ces éléments, il apparait nécessaire d’apporter des connaissances sur les contaminations, par des cyanotoxines et par des cyanobactéries, des cultures françaises de spiruline. En outre, il était indispensable de caractériser les différentes souches de spiruline cultivées afin d’identifier leur espèce et de vérifier si elles peuvent produire des cyanotoxines.Les résultats de 623 analyses de MCs sur des spirulines par la méthode enzymatique Adda-ELISA et de cinq résultats de contre-analyses par la méthode LC-MS/MS ont permis de conclure que les productions de spiruline de la filière paysanne française ne présentent pas de risque sanitaire lié aux MCs. Par ailleurs, des analyses métagénétique et métagénomique réalisées sur six échantillons de culture de spiruline ont montré que ces derniers ne contiennent que des cyanobactéries halo-alcalophiles non toxiques dont le genre Sodalinema qui est un contaminant dominant. A contrario, l’échantillon environnemental de la souche de spiruline camarguaise contenait des cyanobactéries potentiellement toxiques. Ces résultats, étayés par les dénombrements de cyanobactéries réalisés sur des échantillons issus de 95 fermes, ont révélé que la salinité et l’alcalinité des milieux de cultures utilisés en France ne sont pas propices au développement des cyanobactéries connues pour produire des MCs.La comparaison des génomes de 22 souches de spiruline, dont deux cultivars utilisés en France, ainsi que la souche camarguaise, a établi qu’il n’existe que deux espèces de spiruline, Limnospira maxima et L. platensis, et que les appellations L. fusiformis et L. indica sont des synonymes hétérotypes de L. maxima. La caractéristique morphologique permettant de distinguer ces deux espèces a également été trouvée. Enfin, l’analyse de 11 génomes de chaque espèce a démontré l’absence de séquences génétiques pouvant être associée aux cyanotoxines, prouvant par là leur innocuité
Spirulina is the common name for edible cyanobacteria cultivated in aquaculture facilities, which are generally industrial. In France, however, production is carried out by 180 small-scale farms. Spirulina is consumed as a food or dietary supplement for its nutritional value and health benefits. However, certain cyanobacteria produce cyanotoxins and can contaminate spirulina culture. These toxins, notably microcystins (MCs), have been found in spirulina samples from various foreign markets. In addition, one spirulina species, Limnospira fusiformis, was suspected of toxicity following two publications on Kenyan strains. Finally, a taxonomic confusion does exist for spirulina designated by four species names, spread among two genera. It therefore appears of interest to provide information on the cyanotoxin and cyanobacteria contamination of French spirulina cultures. Moreover, it was essential to characterize the different strains cultivated by the French spirulina farmers to assess the potential risk of cyanotoxins production.In that sense, the results of 623 analyses of spirulina for MCs using the enzymatic Adda-ELISA method complemented by five duplicate analyses using the LC-MS/MS method led to the conclusion that spirulina produced by French farmers does not present a health risk related to MCs. In addition, metagenomic and metagenetic analyses of six spirulina culture samples showed that they contained only non-toxic halo-alkalophilic cyanobacteria, including the genus Sodalinema, which is the most dominant and recurring contaminant. In contrast, the environmental sample of the Camargue spirulina strain contained potentially toxic cyanobacteria. These results, supported by cyanobacterial counts carried out on samples from 95 farms, revealed that the salinity and alkalinity of the growing media used in France are not promoting the development of cyanobacteria known to produce MCs.Finally, comparing the genomes of 22 spirulina strains, including two cultivars used in France as well as the Camargue strain, showed that there are only two species of spirulina, Limnospira maxima and L. platensis, and that the names L. fusiformis and L. indica are heterotypic synonyms for L. maxima. A morphological character was also found to distinguish the two species. Finally, the analysis of 11 genomes of each species demonstrated the absence of genetic sequences that could be associated with cyanotoxins, thus proving their safety