Researchers Discover New Bacterial Species with Reversed Lifecycle Complexity

Researchers at Stockholm University have made unexpected discoveries regarding a significant, previously unexamined group of bacteria, with some sourced from Swedish lakes. The results illustrate the evolution of bacterial lifecycles and how their complexity has even regressed over time. The study is published in Nature Communications.

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Bacteria represent some of the most varied and ancient life forms on the planet. However, a significant portion of the knowledge about them is derived from a limited number of species, primarily examined for their contributions to human health.

The vast majority of bacterial species remain unexplored, and this really limits our understanding of how bacteria shape ecosystems and have evolved to thrive in different environments.

Joel Hallgren, Study Lead Author, Stockholm University

Complex Lifecycle

Most bacteria reproduce via straightforward, symmetrical cell division. Nevertheless, a unique group known as the Caulobacterales, recognized for their "stalked" morphology, diverges from this norm. They exhibit a more intricate lifecycle characterized by asymmetric cell division, leading to the formation of two distinct cell types: one that is mobile and exploratory, and another that is sessile and reproductive.

The evolutionary motivations for this complex lifecycle have long intrigued researchers. Caulobacterales bacteria are also recognized for their widespread presence in various environments and are believed to play a significant role in the degradation of plant matter in nature; however, their ecological and evolutionary aspects have not been extensively investigated.

Researchers at Stockholm University conducted an analysis of the DNA from all known Caulobacterales species, including newly obtained samples from forest lakes in Sweden and Finland. The team found that several freshwater species were missing over a hundred genes typically associated with the group’s complex lifecycle. These bacteria represent three new species within a previously unidentified genus, which the research team has designated as Acaudatibacter, meaning "bacterium without a tail" in Latin.

Genetic Signature of How Complexity Arises and Disappears

Another member of the Caulobacterales found in Ecuador also exhibited a deficiency in the same group of lifecycle genes and, as noted by the researchers through microscopy, reproduces via straightforward, symmetric cell division. This independent reduction in complexity across different lineages offers valuable insight into the genes that are crucial for the intricate lifecycles of bacteria.

“It’s fascinating to see that evolution has reversed lifecycle complexity multiple times in the same way. It gives us a unique genetic signature of how complexity arises and disappears during the evolution of bacterial lifecycles,” said Joel Hallgren.

Unexpected Discovery: Genes for Photosynthesis

The researchers uncovered another surprising finding: the bacteria from the Swedish lake contained all the necessary genes for photosynthesis, a trait that had not been recognized in Caulobacterales before, underscoring that the ability to perform photosynthesis is more prevalent among bacteria than was previously believed. In fact, additional analysis indicated that approximately 10 % of species within this group possess genes for capturing light energy.

It’s exciting that novel bacterial species from my own country are giving us new perspectives on fundamental concepts in microbiology.

Joel Hallgren, Study Lead Author, Stockholm University