Structure, morphogenesis of calyptra and nomenclatural identity of Trichodesmium erythraeum Ehr. (Cyanobacteria) newly recorded off the Southwest coast of Bangladesh

Trichodesmium erythraeum Ehrenberg 1830 (Cyanobacteria) has been described and newly recorded from three km off the west coast of the St. Martin’s Island (SMI), Cox’s Bazar, Bangladesh. The Red Sea algal bloom was narrowly elliptical raft-like loose aggregates 20-40 cm long, 4-8 cm wide and 2-3 cm thick. Volume of small and large Sea sawdust were 160×10-6 to 960×10-6 m3 consisting of 25-153 millions flat tuft or spindlelike colonies measured 830-1500 μm long and 155-260 μm wide with 13-16 filaments laterally in the median region. Sheath was present around each trichome even covering the tip cell wall the feature has so far not been reported for the Trichodesmium spp. Because of most likely sticky nature of the sheath 300-600 μm long filaments of 195-450 formed compact colonies without colonial sheath around. In interior filaments cells were rectangular 7-10 μm long and 6.3-10 μm wide with abundant gas vacuoles, bluish-green red, no diazocytes developed and without calyptrae. Cells of peripheral filaments were without gas vacuoles, cytoplasm disorganized, appearing necrotic with glycogen granules, and produced convex to sickle-shaped four-layered calyptra consisting of outermost sheath followed by outer extra thick wall, tip cell wall and inner extra thick wall on the tip cell. Calyptra was also produced on tip cells of tapered filaments. Presence of sheath around each trichome binding all filaments into a colony without colonial sheath described here, and presence of nitrogenase containing diazocytes in interior filaments, both temporal and spatial segregation of N2 fixation and photosynthesis within the photoperiod described and discussed in literature made the authors to consider T. erythraeum Ehr. a distinct taxon under family Microcoleacece. Bangladesh J. Plant Taxon. 27(2): 273-282, 2020 (December)

An alternative method to improve the settleability of gas-vacuolated cyanobacteria by collapsing gas vesicles

This study estimated the ability of pressurization to collapse gas vesicles and thereby enhance the settleability of fresh water cyanobacteria. Settling velocities of Pseudanabaena galeata and Microcystis aeruginosa were measured at 11 different pressure values from 0 to 0.5 MPa. The morphological variations that occurred in the gas vacuoles according to the applied pressure were investigated using transmission electron microscopy images. The settleability of both cyanobacteria species increased statistically significantly (P = 0.000) with increasing pressure, whereas the gas-vacuolated area of both species decreased significantly (P = 0.000) with the magnitude of the applied pressure. The removal ability of cyanobacterial cells from the water layer increased with high pressure treatment. The maximum removal efficiency observed of P. galeata and M. aeruginosa cells relative to the control culture were 82% and 95%, respectively, at the maximum tested pressure value of 0.5 MPa.

Using a two-layered sphere model to investigate the impact of gas vacuoles on the inherent optical properties of <i>Microcystis aeruginosa</i>

A two-layered sphere model is used to investigate the impact of gas vacuoles on the inherent optical properties (IOPs) of the cyanophyte Microcystis aeruginosa. Enclosing a vacuole-like particle within a chromatoplasm shell layer significantly altered spectral scattering and increased backscattering. The two-layered sphere model reproduced features in the spectral attenuation and volume scattering function (VSF) that have previously been attributed to gas vacuoles. This suggests the model is good at least as a first approximation for investigating how gas vacuoles alter the IOPs. Measured Rrs was used to provide a range of values for the central value of the real refractive index, 1 + ε, for the shell layer using measured IOPs and a radiative transfer model. Sufficient optical closure was obtained for 1 + ε between 1.1 and 1.14, which had corresponding Chl a-specific phytoplankton backscattering, bbφ*, between 3.9 and 7.2 × 10−3 m2 mg−1 at 510 nm. The bbφ* values are in close agreement with the literature and in situ particulate backscattering measurements. Rrs simulated for a population of vacuolate cells was greatly enlarged relative to a homogeneous population. A sensitivity analysis of empirical algorithms for estimating Chl a in eutrophic/hypertrophic waters suggests these are robust under variable constituent concentrations and likely to be species-sensitive. The study confirms that gas vacuoles cause significant increase in backscattering and are responsible for the high Rrs values observed in buoyant cyanobacterial blooms. Gas vacuoles are therefore one of the most important bio-optical substructures influencing the IOPs in phytoplankton.

Using a two-layered sphere model to investigate the impact of gas vacuoles on the inherent optical properties of <i>M. aeruginosa</i>

A two-layered sphere model is used to investigate the impact of gas vacuoles on the inherent optical properties (IOPs) of the cyanophyte Microcystis aeruginosa. Enclosing a vacuole–like particle within a chromatoplasm shell layer significantly altered spectral scattering and increased backscattering. The two-layered sphere model reproduced features in the spectral attenuation and volume scattering function (VSF) that have previously been attributed to gas vacuoles. This suggests the model is good at least as a first approximation for investigating how gas vacuoles alter the IOPs. The central value of the real refractive index, 1+ ε, for the shell layer was determined using a radiative transfer model and measured remote sensing reflectance, Rrs, and IOP data. For a cell with 50% vacuole volume, the mean 1+ ε value for the shell layer was 1.12. The corresponding chl a specific phytoplankton backscattering coefficient, bbφ&amp;ast;, ranged between 3.9 × 10−3 and 7.2 × 10−3 m2 mg−1 at 510 nm. This agrees closely with in situ particulate backscattering measurements and values reported elsewhere. Rrs simulated for a population of vacuolate cells was greatly enlarged relative to a homogeneous population. Empirical algorithms based on Rrs were derived for estimating chl a in eutrophic/hypertrophic waters dominated by M. aeruginosa. The study confirms that gas vacuoles cause significant increase in backscattering and are responsible for the high Rrs values observed in buoyant cyanobacterial blooms. Gas vacuoles are therefore one of the most important bio-optical substructures influencing the IOPs in phytoplankton.

Benthic cyanobacteria of the genus Nodularia are non-toxic, without gas vacuoles, able to glide and genetically more diverse than planktonic Nodularia

Diversity and ecological features of cyanobacteria of the genus Nodularia from benthic, periphytic and soil habitats are less well known than those of Nodularia from planktonic habitats. Novel benthic Nodularia strains were isolated from the Baltic Sea and their morphology, the presence of gas vacuoles, nodularin production, gliding, 16S rRNA gene sequences, rpoB, rbcLX and ndaF genes, and gvpA-IGS regions were examined, as well as short tandemly repeated repetitive sequence fingerprints. Strains were identified as Nodularia spumigena, Nodularia sphaerocarpa or Nodularia harveyana on the basis of the size and shape of the different types of cells and the presence or absence of gas vacuoles. The planktonic strains of N. spumigena mostly had gas vacuoles and produced nodularin, whereas the benthic strains of N. sphaerocarpa and N. harveyana lacked gas vacuoles and did not produce nodularin (except for strain PCC 7804). The benthic strains were also able to glide on surfaces. In the genetic analyses, the planktonic N. spumigena and benthic N. sphaerocarpa formed monophyletic clusters, but the clusters were very closely related. Benthic strains determined as N. harveyana formed the most diverse and distant group of strains. In addition to phylogenetic analyses, the lack of the gvpA-IGS region and ndaF in N. sphaerocarpa and N. harveyana distinguished these species from the planktonic N. spumigena. Therefore, ndaF can be considered as a potential diagnostic tool for detecting and quantifying Baltic Sea bloom-forming, nodularin-producing N. spumigena strains. The data confirm that only one morphologically and genetically distinct planktonic species of Nodularia, N. spumigena, and at least two benthic species, N. sphaerocarpa and N. harveyana, exist in the Baltic Sea.