Strange diatom - Phaeodactylum tricornutum

Introduction

Phaeodactylum tricornutum is a diatom species. It is the only species in the genus Phaeodactylum. Unlike other diatoms P. tricornutum can exist in different morphotypes (fusiform, triradiate, and oval), and changes in cell shape can be stimulated by environmental conditions.

The genus Phaeodactylum contains a single species, Phaeodactylum tricornutum (Fig. 3.10). This is a very widely studied marine diatom, mainly because of the ease with which it can be cultured. However, it is also very unusual for a diatom as it can occur in several shapes (phenotypes)—oval, fusiform, and triradiate (with some intermediate forms known)—and cultures can change from one form to the other over time.

This feature can be used to explore the molecular basis of cell shape control and morphogenesis. Unlike most diatoms P. tricornutum can grow in the absence of silicon, and it can survive without making silicified frustules. This provides opportunities for experimental exploration of silicon-based nanofabrication in diatoms.

Another peculiarity is that during asexual reproduction the frustules do not appear to become smaller. This allows continuous culture without need for sexual reproduction. It is not known if P. tricornutum can reproduce sexually. To date no substantial evidence has been found to support sexual reproduction in a laboratory or other setting. Although P. tricornutum can be considered to be an atypical pennate diatom it is one of the main diatom model species. A transformation protocol has been established and RNAi vectors are available. This makes molecular genetic studies much easier.

History

Phaeodactylum tricornutum was first described in the triradiate morphotype by Bohlin in 1897. Recordings of the first cultures of P. tricornutum were published by Allen and Nelson in 1910, although it was misidentified as Nitzschia colsterium W. Sm., forma minutissima. The isolate was later correctly revised as P. tricorntum by J.C. Lewin in 1958. This strain among other later isolates are still maintained in culture collections around the world.

Genome sequencing

Phaeodactylum tricornutum is one of three diatoms whose genome has been sequenced (the others being Thalassiosira pseudonana and Fragilariopsis cylindrus). The genome contains approximately 10% prokaryote-like genes, an unusually large proportion. Over 30000 expressed sequence tags (ESTs) have been organized into the Diatom EST Database.

Phaeodactylum tricornutum has emerged as a potential microalgal energy source. It grows rapidly and storage lipids constitute about 20-30% of its dry cell weight under standard culture conditions. Nitrogen limitation can induce neutral lipid accumulation in P. tricornutum, indicating possible strategies for improving microalgal biodiesel production.

Source:

https://www.wikiwand.com/en/Phaeodactylum_tricornutum

https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/phaeodactylum-tricornutum

More info:

Diatoms are eukaryotic, photosynthetic microorganisms found throughout marine and freshwater ecosystems that are responsible for around 20% of global primary productivity. A defining feature of diatoms is their ornately patterned silicified cell wall (known as frustule), which display species-specific nanoscale-structures. These organisms therefore play major roles in global carbon and silicon cycles.

The marine pennate diatom Phaeodactylum tricornutum is the second diatom for which a whole genome sequence has been generated. It was chosen primarily because of the superior genetic resources available for this diatom (eg, genetic transformation, 100,000 ESTs), and because it has been used in laboratory-based studies of diatom physiology for several decades. Although not considered to be of great ecological significance, it has been found in several locations around the world, typically in coastal areas with wide fluctutations in salinity. Unlike other diatoms it can exist in different morphotypes, and changes in cell shape can be stimulated by environmental conditions. This feature can be used to explore the molecular basis of cell shape control and morphogenesis. Furthermore the species can grow in the absence of silicon, and the biogenesis of silicified frustules is facultative, thereby providing opportunities for experimental exploration of silicon-based nanofabrication in diatoms. The sequence is 30 mega base pairs and, together with the sequence from the centric diatom Thalassiosira pseudonana (34 Mbp; the first diatom whole genome sequence), it provides the basis for comparative genomics studies of diatoms with other eukaryotes and will provide a foundation for interpreting the ecological success of these organisms.

The clone of P. tricornutum that was sequenced is CCAP1055/1 and is available from CCAP. This clone represents a monoclonal culture derived from a fusiform cell in May 2003 from strain CCMP632, which was originally isolated in 1956 off Blackpool (U.K.). It has been maintained in culture continuously in F/2 medium.

Publication:

The Phaeodactylum genome reveals the evolutionary history of diatom genomes. Nature. 2008 Nov 13;456(7219):239-44.