The mysterious soil bacteria that make up half of your garden's microbial life

Gardening · Published 3 October 2026 Swipe more like this →

In short: Acidobacteriota are ubiquitous, yet they remain one of microbiology's greatest enigmas. Despite representing up to 52 percent of the bacterial community in soil, they are notoriously difficult to cultivate in labs. Scientists are only just beginning to decode how these elusive organisms shape the ecosystems beneath our feet.

Discovered in 1991 with the identification of Acidobacterium capsulatum, this phylum was not formally recognized as a distinct clade until 1997, and only gained phylum status in 2012. Today, they are categorized into 26 accepted subdivisions. Despite their massive presence in diverse environments—ranging from caves and hot springs to metal-contaminated soils—our understanding of their metabolism remains limited. This knowledge gap is primarily due to the difficulty of replicating their natural habitats in a laboratory setting.

While genomic sequencing has provided a glimpse into their potential, there is often a disconnect between genetic predictions and observed behavior. For instance, while many strains possess genes for carbohydrate processing, experimental studies frequently show an inability to break down complex polysaccharides like cellulose. Only one species, Telmactobacter bradus, has been confirmed to process cellulose. Researchers currently suspect that xylan degradation may be their most universal carbon-processing ability, though they caution that current cultivation methods likely fail to capture the microbes' true natural activity.

The phylum is physiologically diverse, with most members being aerobic heterotrophs. However, some strains in subdivisions 8 and 23 are anaerobic, and others show a remarkable ability to thrive in extreme acidity, such as in acid mine drainage where pH levels drop to 2 or 3. Their role in nutrient cycling is equally complex; while there is no clear evidence they participate in standard nitrogen-cycle processes like fixation, they do possess genes for nitrate reduction and can directly uptake ammonium. As a developing field, the current count of 40 conclusive species across 22 genera is expected to shift drastically as new sequencing and cultivation techniques emerge.

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