Soil protozoa are critical components of the soil food web and represent the most diverse group of eukaryotes in terrestrial ecosystems. Their actively shape soil microbial community structures, regulate soil fertility, and help plant roots resist pathogenic bacteria. Despite advances in high-throughput sequencing shows their diversity rivals that of aquatic systems, research on soil protozoa remains significantly lagging.

Colpoda, a genus of kidney-shaped ciliates widely distributed in soils, is known for its ease of collection and remarkable resilience through cyst formation under unfavorable conditions. While most studies have focused on resting cysts, reproductive cysts—essential for cell division and proliferation—have received limited attention, with molecular mechanisms remaining unclear.

Recently, a research group led by Prof. Miao Wei from the Institute of Hydrobiology (IHB) of the Chinese Academy of Sciences revealed alpha-amylase that promote the proliferation of Colpoda, a major soil protozoan. This study was published in SCIENCE CHINA Life Sciences.

In this study, the team systematically depicted the complete life cycle of Colpoda inflata, and discovered that during the formation of reproductive cysts, by high-resolution microscopy. They discovered unique sugar-coated granules containing bacterial DNA that accumulate during reproduction. These granules constitute a "nutrient reservoir," providing essential material for subsequent cell division and offspring development.

Through genome sequencing and protein analysis, researchers found that old culture medium containing secreted proteins could induce reproductive cyst formation. Mass spectrometry pinpointed an alpha-amylase as the key inducing protein.

Lab experiments showed that purified alpha-amylase alone drives reproduction, achieving cell densities 4.6 times higher than standard methods and cutting generation time nearly in half—from 9 to 5 hours.

The enzyme also induced reproduction in different Colpoda species, with effectiveness linked to evolutionary distance—suggesting a novel mechanism for microbial communication in soil ecosystems. Correspondingly, analysis of rice root nematodes also shows that about 90% of soil samples contain multiple Colpoda species coexisting.

This study reveals the reproductive mechanism of Colpoda, discovers a method that greatly increases their culture density, and identifies alpha-amylase as a key regulator of cyst formation and population growth. The findings not only provide new insights into microbial life cycle regulation, but also reveals a previously unknown form of chemical communication among soil protists, which may play an important role in soil remediation and sustainable agriculture in the future.

A tubulin staining image shows the morphology of C. inflate (Image by IHB)

The detailed process of the reproductive cyst formation (Video by IHB)

(Editor: MA Yun)