Planctomycetota

The Planctomycetota are a phylum of widely distributed bacteria, occurring in both aquatic and terrestrial habitats. They play a considerable role in global carbon and nitrogen cycles, with many species of this phylum capable of anaerobic ammonium oxidation, also known as anammox. Many Planctomycetota occur in relatively high abundance as biofilms,

Planctomycetota are included in the PVC superphylum along with Verrucomicrobiota, Chlamydiota, Lentisphaerota, Kiritimatiellaeota, and Candidatus Omnitrophica. The phylum Planctomycetota is composed of the classes Planctomycetia and Phycisphaerae. First described in 1924, members of the Planctomycetota were identified as eukaryotes and were only later described as bacteria in 1972. Members of the Planctomycetota also display distinct reproductive habits, with many species dividing by budding, in contrast to most other free-living bacteria, which divide by binary fission.

Interest is growing in the Planctomycetota regarding biotechnology and human applications, mainly as a source of bioactive molecules. In addition, some Planctomycetota were recently described as human pathogens. such as their ability to synthesize sterols. Many Planctomycetota also have a holdfast, or stalk, which attaches the cell to a surface or substrate.

In marine environments, Planctomycetota are often suspended in the water column or present as biofilms on the surface of macroalgae, and are often exposed to harmful ultraviolet radiation. More highly pigmented species of the Planctomycetota are more resistant to ultraviolet radiation, although this is not yet well understood. It has since been shown that Planctomycetota synthesize C30 carotenoids from squalene and that this squalene route to C30 carotenoids is the most widespread in prokaryotes.

Unique characteristics of anammox cells

Bacteria in the Planctomycetota that are anammox-capable form the order Brocadiales.

Life history and reproduction

Growth

Planctomycetota species grow slowly, when compared to other bacteria, often forming rosette structures of 3-5 cells. with a doubling time of roughly 6–14 days. In contrast, some other Planctomycetota have doubling times of around 30 days. In contrast, many bacteria in the Planctomycetota divide by budding. and is essential for septal formation during cell division. The species Kolteria novifilia forms a distinct clade of Planctomycetota, and is the only known species to divide by lateral budding at the middle of the cell. Lastly, members of the clade Saltatorellus are capable of switching between both binary fission and budding. These CSIs demarcate the group from neighboring phyla within the PVC group. An additional CSI has been found that is shared by all Planctomycetota species, with the exception of Kuenenia stuttgartiensis. This supports the idea that K. stuttgartiensis forms a deep branch within the Planctomycetota phylum.

A CSI has also been found to be shared by the entire PVC superphylum, including the Planctomycetota.

General characteristics

The genome size of Rhodopirellula baltica has been estimated to be over 7 million bases, making it one of the largest prokaryotic genomes sequenced. Extensive genome duplication takes up about 25% of the genome sequence.

When comparing under a microscope, a defining characteristic for some Planctomycetota is that a single unlinked rRNA operon can be identified near the origin. The changes of genetic material is through internal chromosomal inversion, and not through lateral gene transfer. This creates a way of diversification in the Planctomycetota variants as multiple transposon genes in these regions have reverse orientation that transfers to rearrangements.

Some Planctomycetota thrive in regions containing highly concentrated nitrate,

There is massive emergence of novel protein families within the Gemmataceae. More than one thousand protein families were acquired by duplications and domain rearrangements. The new paralogs function in signal transduction, regulatory systems, and protein interaction pathways. They are related to the functional organisation of the cell, which can be interpreted as an adaptation to a more complex lifestyle. the existence of eukaryotic traits and genes is more likely explained through lateral gene transfer, and not a more recent eukaryotic ancestor.

! colspan=1 | 120 marker proteins based GTDB 10-RS226

|-

| style="vertical-align:top|

|

|}

Ecology

Distribution and abundance

Members of the Planctomycetota are found in a diverse range of environments, both geographically and ecologically, Planctomycetota were originally believed to exist exclusively in aquatic environments, but they are now known to be also abundant in soils and hypersaline environments. They are widespread on five continents, including Antarctica and Australia. As both obligate and facultative aerobic chemoheterotrophs, the primary source of carbon used by Planctomycetota is from carbohydrates. Many Planctomycetota have the ability to breakdown extremely complex carbohydrates, making these nutrients available to other organisms. This ability to recycle carbon has been linked to specific C1 metabolism genes observed in many Planctomycetota and are suggested to play a significant role, but this area of research is still poorly understood.

Planctomycetota also display many sulfatase enzymes, which are capable of breaking down sulfated heteropolysaccharides, which are produced by many groups of macroalgae. The breakdown of these sulfated heteropolysaccharides by Planctomycetota are then used as an energy source. Some Planctomycetota are suggested to be capable of breaking down carrageenan. Roughly 70% of the bacterial community on Ecklonia radiata were Planctomycetota. Planctomycetota also play an important role as components of detritus in the water column, also known as marine snow,

As the climate continues to warm, the abundance of Planctomycetota associated with macroalgae might increase. The seaweed Caulerpa taxifolia was incubated under higher CO₂ conditions, and the abundance of Planctomycetota increased substantially, as much as 10 times in some species. In 2024, another species, Ca. Uabimicrobium helgolandensis, was reported that showed similar cellular faetures including phagocytosis.

Osmotic regulation

thumb|250x250px|Labeled diagram of an anammox cell.

Almost all bacteria have a cytosol following the outer shape of their peptidoglycan cell wall. Eukaryotes are different in that they have their cytosol divided into multiple compartments to create organelles such as a nucleus. Planctomycetota are unique in that they have large invaginations of their cytoplasmic membrane, pulling away from the peptidoglycan cell wall and leaving room for the periplasm. Traditionally, the cytoplasmic membrane has been thought to be responsible for controlling the osmotic pressure of bacterial cells. Yet due to the folds in the cytoplasmic membrane, and the existence of large spaces of periplasm within Planctomycetota, their peptidoglycan acts as an osmotic barrier with the periplasm being isotonic to the cytosol. In a marine environment, this ultimately removes nitrogen from the water, as N₂ gas cannot be used by phytoplankton and is released into the atmosphere. Up to 67% of dinitrogen gas production in the ocean can be attributed to anammox and about 50% of the nitrogen gas in the atmosphere is thought to be produced from anammox. Planctomycetota are the most dominant phylum of bacteria capable of performing anammox, thus the Planctomycetota capable of performing anammox play an important role in the global cycling of nitrogen. Many researchers have designed wastewater treatment bioreactor systems using Planctomycetota as the biological chassis.

Sterol synthesis

The synthesis of sterols, often observed in eukaryotes and uncommon among bacteria, has been observed very rarely in Planctomycetota.

Biotechnology and human applications

Recently, interest has arisen in examining the Planctomycetota regarding their potential roles in biotechnology, mainly as a source of bioactive molecules, This is unexpected, as the Planctomycetota have several key features as other known producers of bioactive molecules, such as the Myxobacteria.