Patterns of asexual reproduction in Nannochloris bacillaris and Marvania geminata (Chlorophyta, Trebouxiophyceae)

Abstract

Non-flagellated vegetative green algae of the Trebouxiophyceae propagate mainly by autosporulation. In this manner, the mother cell wall is shed following division of the protoplast in each round of cell division. Binary fission type Nannochloris and budding type Marvania are also included in the Trebouxiophyceae. Phylogenetic trees based on the actin sequences of Trebouxiophyceae members revealed that the binary fission type Nannochloris bacillaris and the budding type Marvania geminata are closely related in a distal monophyletic group. Our results suggest that autosporulation is the ancestral mode of cell division in Trebouxiophyceae. To elucidate how non-autosporulative mechanisms such as binary fission and budding evolved, we focused on the cleavage of the mother cell wall. Cell wall development was analyzed using a cell wall-specific fluorescent dye, Fluostain I. Exfoliation of the mother cell wall was not observed in either N. bacillaris or M. geminata. We then compared the two algae by transmission electron microscopy with rapid freeze fixation and freeze substitution; in both algae, the mother cell wall was cleaved at the site of cell division, but remained adhered to the daughter cell wall. In N. bacillaris, the cleaved mother cell wall gradually degenerated and was not observed in the next cell cycle. In contrast, M. geminata daughter cells entered the growth phase of the next cell cycle bearing the mother and grandmother cell walls, causing the uncovered portion of the plane of division to bulge outward. Such a delay in the degeneration and shedding of the mother cell wall probably led to the development of binary fission and budding.

Isolation and Fatty Acid Profile of Selected Microalgae Strains from the Red Sea for Biofuel Production

“…However, the latter strains displayed distinct cell morphologies: Nannochloris sp. SBL1 cells were rod-shaped, showing some similarity to Nannochloris bacillaris [16], whereas Nannochloris sp. SBL4 presented rounded or slightly oval cells, as commonly found in this genus.…”

“…These values are in accordance with the European standard EN14214 [22], which states a maximum of 12% for α-linolenic acid and 1% for PUFA with ≥4 double bonds. Regarding the size of the carbon chain, isolates displayed a FAME profile ranging from C 15 to C 18 , dominated by C 16 and C 18 FAME. These main FAME are the same that compose soy biodiesel [23], proving the suitability of the FAME profile of these isolates for biodiesel production.…”

Pseudomarvania, gen. nov. (Chlorophyta, Trebouxiophyceae), a new genus for "budding" subaerial green algae Marvania aerophytica NEUSTUPA et ŠEJNOHOVÁ and Stichococcus ampulliformis HANDA.

“…In Marvania, by contrast, the "bud" that grows out through the break in the mother cell wall is just an expanding part of the cell residing in the remnant of the mother cell wall; the whole expanding protoplast is enclosed in a newly deposited cell wall and mitosis and subsequent cell division (by means of eleutheroschisis, i.e. deposition of yet another cell wall layer) occurs only when the "bud" is of about the size of the "mother cell" (hiNdák 1976, REymoNd et al 1986, sluimaN & REymoNd 1987, yamamoto et al 2007). Next, in Pseudomarvania, the daughter cell that "buds off" is much smaller than the mother cell (haNda et al 2003, NEustupa & šEjNohová 2003, whereas in Marvania the two cells are of approximately equal size when their separation takes place (hiNdák 1976, REymoNd et al 1986, sluimaN & REymoNd 1987.…”

“…The "bud" keeps expanding and when it reaches the dimensions of the part of the cell retained in the remnant of the mother cell wall, two separate cells are formed. Ultrastructural investigations of dividing M. geminata cells revealed that the "budding" is a highly modified form of autosporulation (REymoNd et al 1986, sluimaN & REymoNd 1987, yamamoto et al 2007) designated as semi-exogenous autosporogenesis (sluimaN & REymoNd 1987).…”

Diversity of Microscopic Green Algae (Chlorophyta) in Calcifying Biofilms of Two Karstic Streams in Germany

“…Using sequence comparisons most of our isolates were closely related to those of various other inland freshwaters (Supplementary Table 3). Within the Trebouxiophyceae, these were members of the Chlorellales clade, i.e., Chlorella (Bock et al 2010;Bock et al 2011), Muriella (Fawley et al 2004 and Marvania (Fawley et al 2004;Yamamoto et al 2007). Within the Chlorophyceae, at least the Scenedesmaceae, Selenastraceae and Mychonastes, which we also retrieved in our study, are well known from freshwaters Bock 2012).…”