Chlamydomonas reinhardtii

It combines photosynthesis with active swimming, making it a useful organism for asking how a cell obtains energy and responds to its surroundings.

Its two flagella can beat in a breaststroke-like pattern that propels the cell through water.

A light-sensitive system links the direction of illumination to changes in movement.

Photosynthesis allows the alga to grow using light and inorganic nutrients; laboratory cells can also grow in darkness when acetate supplies an alternative carbon source.

Light also acts as a signal: cells can orient toward or away from a light source, a behaviour called phototaxis.

Channelrhodopsins are light-gated ion channels involved in this response.

Experiments with altered channelrhodopsins changed or abolished photoresponses in the tested strains, connecting particular proteins to whole-cell behaviour.

Vegetative growth uses a multiple-fission cell cycle: a cell grows, then performs successive rounds of DNA replication and division before daughter cells emerge.

Larger mother cells can complete more division rounds than smaller ones.

The result is not simply one large cell splitting once into two equally large cells.

This organisation makes C. reinhardtii useful for studying how growth and cell division are coordinated.

In a 2024 study, loss of the regulator TNY1 allowed extra divisions and produced smaller daughter cells.

Vegetative cells are haploid, meaning that their nuclei normally contain one chromosome set.

Under suitable conditions, nitrogen deprivation and light promote differentiation into gametes of plus or minus mating type.

Compatible gametes fuse to form a diploid zygospore with a protective wall.

When conditions again support growth, meiosis can yield four haploid cells that return to the vegetative cycle.

Plus and minus are mating-type labels, not pollen and ovule.

Research on field isolates places C. reinhardtii in freshwater and moist-soil settings, including sampled material from North America and Japan.

A 2015 genomic study compared field isolates with laboratory strains and found substantial genetic variation.

It also found genes in field isolates that were missing from the reference assembly used for comparison.

A familiar laboratory strain is therefore a starting point for understanding the species, not a substitute for all its natural diversity.

The version 6 genome project shifted its principal reference from the cell-wall-deficient strain CC-503 to the minus mating-type strain CC-4532.

That change matters because laboratory strains can accumulate structural changes and because a reference must account for mating-type-specific sequence.

A genome is most useful when its strain and version stay attached to the biological question.

Compare photosynthetic growth with a phototactic response: the first concerns how the cell supports growth, while the second concerns how it responds to a light signal.

Scope and reading guidance

A cell that moves toward light is not, for that reason alone, a measurement of photosynthetic efficiency.

The checked NCBI record identifies Chlamydomonas reinhardtii as Taxonomy ID 3055 at species rank.

The field-versus-laboratory comparison in Flowers et al. used 12 field isolates and eight laboratory strains.

Those sample counts describe that study, not the number of strains or populations in the species.

The channelrhodopsin study measured photoorientation using a population light-scattering assay and also tracked individual cells.

The cell-cycle study addressed division control and daughter-cell size through TNY1.

Scope and reading guidance

Neither measurement is interchangeable with biomass production, carbon fixation or a natural-population abundance estimate.

Craig et al. distinguish the CC-4532 v6 assembly from the CC-4532 v6.1 structural annotation.

They added strain-specific suffixes such as _4532 and _0503 to distinguish gene models in different assemblies.

Their PSY1 example retains the primary identifier Cre02.g095092_4532 but has the associated locus identifier 4532_11_52343, which gives its corrected chromosome context.

Do not infer the chromosome from an old Cre identifier prefix without checking the mapped assembly coordinates.

The Resource Center’s general introduction describes the historical CC-503 sequencing strain, whereas its dated version 6 notice explicitly names CC-4532 as the new reference.

An older CC-503 result still belongs to CC-503.

Scope and reading guidance

Retain strain, mating type, assembly, annotation and assay conditions when comparing experiments.

A mutant produces smaller daughters after extra divisions; the immediate conclusion concerns its division-control phenotype, not a universal reduction in the size of this species.

Scope and reading guidance

A useful follow-up comparison keeps growth conditions and the parental strain matched before attributing the phenotype to a mechanism.