Extreme Environment Bacteria Reveal New Insights into Their Symbiotic Life

Jenn Hoskins
10th April, 2025

Extreme Environment Bacteria Reveal New Insights into Their Symbiotic Life

Microbial community analysis of a hyperalkaline environment formed by weathering steel slag deposits (a, b) reveals that symbiotic Candidate Phyla Radiation (CPR) bacteria are highly abundant, comprising up to 34.8% of the total population (c).

Image adapted from: He et al. / CC BY (Source)

Key Findings

  • *Researchers in Wuhan explored ultra-alkaline environments and found that CPR bacteria make up up to 35% of the microbial communities there.*
  • *These tiny bacteria rely on partner organisms for essential nutrients because they can't produce them on their own.*
  • *CPR bacteria supply vital folate compounds to their hosts, highlighting a mutualistic relationship that supports ecosystem stability.*
Candidate Phyla Radiation (CPR) bacteria represent one of the most intriguing and diverse groups within the microbial world. These ultra-small bacteria are known for their symbiotic lifestyles, often relying on host organisms to survive. Despite their abundance in various environments, many aspects of their distribution, host associations, and ecological roles remain poorly understood. A recent study conducted by researchers at the China University of Geosciences (Wuhan)[1] sheds new light on these enigmatic microorganisms by exploring their presence and interactions in a highly alkaline, serpentinite-like environment. CPR bacteria are part of a vast superphylum that includes more than 35 phyla, accounting for over 15% of the bacterial domain[2][3]. These bacteria are typically characterized by their small cell sizes and dependence on other microorganisms for essential nutrients. Previous research has revealed that CPR bacteria play significant roles in carbon and hydrogen cycles across diverse ecosystems[2]. However, their metabolic limitations have made it challenging to cultivate them in laboratory settings, hindering comprehensive studies of their biology and interactions[3]. In the newly conducted study, scientists focused on a serpentinite-like ecosystem with extremely high alkalinity (pH = 10.9–12.4). Such environments are considered extreme due to their high pH levels, which can be hostile to many forms of life. By analyzing water and sediment samples from this habitat, the researchers used metagenomic techniques to investigate the CPR communities present. Metagenomics involves sequencing the genetic material directly from environmental samples, allowing scientists to study organisms that are otherwise difficult to culture. The findings were remarkable. CPR bacteria constituted between 1.93% and 34.8% of the microbial communities in the sampled environments. The researchers reconstructed 12 high-quality CPR genomes, affiliated with novel taxa from the orders UBA6257, UBA9973, and Paceibacterales. These genomes revealed that CPR bacteria in this environment lack complete biosynthetic pathways for producing essential molecules like amino acids, lipids, and nucleotides. This deficiency underscores their reliance on symbiotic relationships with host organisms to obtain these vital nutrients. One of the most significant discoveries of the study was the presence of genes involved in the biosynthesis and metabolism of folate, an essential cofactor necessary for various cellular processes. Specifically, the CPR bacteria possessed genes such as dihydrofolate reductase (folA), serine hydroxymethyltransferase (glyA), and methylenetetrahydrofolate reductase (folD). These genes are crucial for the production of tetrahydrofolate (THF), a molecule that plays a key role in the synthesis of nucleic acids and amino acids. Interestingly, the researchers identified potential host organisms that lacked the folA gene, making them unable to produce THF on their own. These auxotrophic hosts could rely on the CPR bacteria to supply the necessary folate derivatives, illustrating a clear example of mutualistic symbiosis. To confirm the functionality of the CPR-derived folA genes, the team performed experiments where they expressed these genes in a folA-deletion mutant of Escherichia coli. The successful restoration of THF production demonstrated that the CPR genes were indeed functional and capable of complementing the host's metabolic deficiencies. Further analysis of a broader dataset comprising 4,581 CPR genomes revealed that approximately 90.8% contained genes for bioactive folate derivative synthesis. This widespread presence suggests that metabolic complementarity, particularly in folate biosynthesis, is a common feature among CPR bacteria and their hosts. Such interactions likely play a crucial role in maintaining the balance of microbial communities and influencing biogeochemical processes in various environments. Previous studies have highlighted the unique biological features of CPR bacteria, such as their unusual ribosome compositions and the presence of self-splicing introns and proteins within their rRNA genes[3]. Additionally, CPR bacteria have been found to be rare in soil environments but can become enriched under specific conditions, such as in the presence of small soil particles[4]. The current study builds on these findings by demonstrating that CPR bacteria can adapt to extreme, oxic conditions by acquiring genes that enhance their metabolic capabilities, such as those for aerobic respiration. Moreover, the study aligns with earlier research indicating that CPR and related archaea (DPANN) often engage in symbiotic relationships[5]. By uncovering the specific metabolic dependencies between CPR bacteria and their hosts, the researchers provide deeper insights into the mechanisms that drive these mutualistic interactions. This understanding is essential for elucidating the roles of CPR bacteria in various ecosystems, particularly in environments with extreme conditions like high alkalinity. The implications of this research are significant. By revealing the metabolic interdependencies between CPR bacteria and their hosts, the study enhances our understanding of microbial ecology and the intricate web of interactions that sustain life in diverse habitats. Furthermore, the discovery of widespread folate biosynthesis genes among CPR bacteria opens new avenues for exploring how these microorganisms contribute to nutrient cycling and ecosystem stability. In conclusion, the study conducted by the China University of Geosciences (Wuhan) advances our knowledge of CPR bacteria by highlighting their prevalence in extreme alkaline environments and their essential role in supporting host organisms through metabolic complementarity. This work not only builds on previous studies but also paves the way for future research aimed at unraveling the complex interactions and ecological functions of CPR bacteria in various ecosystems.

EnvironmentEcology

References

Main Study

1) Candidate Phyla Radiation (CPR) bacteria from hyperalkaline ecosystems provide novel insight into their symbiotic lifestyle and ecological implications

Published 7th April, 2025

https://doi.org/10.1186/s40168-025-02077-y

Related Studies

2) Beyond genomics in Patescibacteria: A trove of unexplored biology packed into ultrasmall bacteria.

https://doi.org/10.1073/pnas.2419369121

3) Unusual biology across a group comprising more than 15% of domain Bacteria.

https://doi.org/10.1038/nature14486

4) Soil Candidate Phyla Radiation Bacteria Encode Components of Aerobic Metabolism and Co-occur with Nanoarchaea in the Rare Biosphere of Rhizosphere Grassland Communities.

https://doi.org/10.1128/mSystems.01205-20

5) Major New Microbial Groups Expand Diversity and Alter our Understanding of the Tree of Life.

https://doi.org/10.1016/j.cell.2018.02.016


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