Understanding Spiroplasma

When it comes to mycoplasma, everyone is familiar with it. It is one of the pathogens that doctors in pediatric clinics often talk about. For example, the pathogen that causes pneumonia in children is a mycoplasma.

However, when it comes to the protagonist of this article, Spiroplasma, people's reactions are a little unfamiliar. In fact, Spiroplasma is also a member of the mycoplasma family, belonging to the Spiroplasma family and the Spiroplasma genus under the order Mycoplasma.

Many characteristics of Spiroplasma are similar to those of other mycoplasmas. For example, they are all prokaryotic microorganisms without cell walls, are the smallest individual microorganisms that can grow and reproduce on culture media, and have diverse morphologies.

So, how big is Spiroplasma?

In fact, it is smaller than ordinary bacteria, smaller than chlamydia, and only slightly larger than viruses, only about 1/350 of a hair. Because they are usually spiral-shaped (as shown in the figure below) and have the ability to move in liquid culture media, they are named Spiroplasmas.

Figure: Transmission electron microscope photo of Spiroplasma taken by Yu Hanshou et al. (magnified 6000 times)

The morphology of Spiroplasma is not fixed and varies depending on different conditions. Even Spiroplasma of the same species can vary greatly.

Usually, the spiroplasma outside the cell is spiral-shaped, while the spiroplasma inside the cell can be oval or flask-shaped in addition to spiral. In addition, there are also tubular and round bottle shapes.

Most Spiroplasmas reproduce by fission and budding (below), and their genetic characteristics are all determined by their genome.

Figure: Spiroplasma budding morphology photographed by Pan Xiaoyi and others

The genome size of Spiroplasma is usually 760-2220 kilobase pairs, and the GC content of the genome is relatively low, about 24%-31%.

Some Spiroplasmas also carry plasmids, while others will lyse and die due to viral infection.

The name Spiroplasma was first proposed by Robert Davis, a well-known American plant pathologist in 1972, and the Spiroplasma classification unit was established the following year.

Spiroplasmas often interact with their hosts in three forms: mutualism, commensalism, and pathogenicity. They are mainly found in crustaceans, spiders, insects, and some plants.

In arthropods, Spiroplasmas mostly survive in the form of intestinal colonization, parasitism, and intracellular and extracellular symbiosis, while in plants, they are mostly found in flowers, epidermis, and phloem.

As one of the components of arthropod intestinal microorganisms, some spiroplasmas are non-pathogenic because of their small number and low content, which cannot reach the starting amount to infect intestinal cells.

However, other spiroplasmas can multiply rapidly in the intestines and cause infection.

How is Spiroplasma transmitted?

Taking arthropods as an example, they transmit Spiroplasma through feces and surface contact. For example, insects that feed on plant phloem (mainly leafhoppers) can transmit Spiroplasma to plants through saliva during feeding.

Of course, there are also some arthropods that pass Spiroplasma to their offspring through vertical transmission, that is, from parents to their children.

Are Spiroplasmas pathogenic like Mycoplasmas?

The answer is yes, but that doesn't mean all spiroplasmas are pathogenic. Common pathogenic spiroplasmas can cause diseases in some plants, crustaceans and insects.

Diseases such as "crawling bee disease" of bees and "trembling disease" of crabs are caused by Spiroplasma, and the losses caused by these diseases are very serious.

The earliest research and reporting on Spiroplasma in China can be traced back to the late 1980s, when Professor Chen Yongxuan of Nanjing Agricultural University first discovered and confirmed the existence of the pathogen Spiroplasma in honeybee "climbing bee disease" and completed its isolation.

After talking about bees, let's take a look at the "gutless man" that is rampant all over the world. When it comes to crabs, many people who love food will salivate. But who would have thought that the tiny snails would have a problem with this delicacy and cause their "trembling disease".

At the end of the 20th century, a large number of river crabs (Chinese mitten crabs) suffered from "trembling disease" in my country. After research by scientists, it was determined that the culprit was "crab snail plasmodium".

Figure: River crab infected with Spiroplasma

Because this spiroplasma can infect the crab's muscle and nervous system and reproduce in it, it causes damage to the crab's nerve and muscle connection system, causing spasms and then tremors.

As the research continued, scientists and aquaculture workers also found similar spiroplasmas in aquatic crustaceans such as shrimp, Macrobrachium rosenbergii (pictured below), Procambarus clarkii (crayfish), and Penaeus vannamei.

They are different and belong to different taxa (species or serotypes).

Figure: Ultra-thin sections of Macrobrachium rosenbergii tissue co-infected with bacteria and Spiroplasma

(The round object pointed by the arrow is Spiroplasma, and the one marked with △ is bacteria)

It is true that some Spiroplasmas can cause disease in animals and plants, but the relationship between most Spiroplasmas and animals and plants is still a relatively friendly mutualistic or symbiotic relationship. For food lovers, eating fully cooked ingredients is the safest and most recommended thing to do.

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