New Delhi: Scientists often focus on studying organisms that dominate their environments — the lion, the tiger, the killer whale. But recent research suggests that rare ocean bacteria, although small in number, plays an important role in maintaining the stability of marine microbial communities.
To arrive at this conclusion, researchers from the Indian Institute of Technology Madras (IIT Madras) analysed data from over 4,600 publicly available ocean samples across tropical, temperate, and polar regions to study how bacterial communities interact and support the marine ecosystem.
Their findings were published in mSystems in a study titled “Deciphering global patterns of marine microbial community assembly and network stability”.
“Marine microorganisms form the invisible foundation of ocean ecosystems. They regulate nutrient cycling, sustain marine food webs and play a vital role in controlling the Earth’s climate. However, despite their ecological importance, the scientific community has had only a limited understanding of the processes that govern the formation and resilience of these microbial communities on a global scale. Understanding these dynamics can help inform efforts to conserve ocean health,” said Karthik Raman, professor at the Wadhwani School of Data Science and AI.
When mathematicians study bacteria
According to the study, in recent years, sequencing data from large-scale ocean microbiome projects has made it easier to study the microbial community and its underlying mechanisms across global marine environments.
For this study, researchers looked at datasets including Tara Oceans, Malaspina, Global Ocean Sampling, and Australian microbiome and Earth Microbiome projects. Samples were collected between 2002 and 2023 and researchers analysed them using three analytical tools at hand at the Wadhwani School of Data Science and AI — neutral community modelling, iCAMP, and co-occurrence network analysis.
Neutral community modelling uses the mathematical concept of stochasticity or randomness to explore whether microbes in a particular area are there by chance rather than by differences in how well individual microbes are adapted to their environment. Neutral community models assume that microbes are all ecologically equal. Therefore, their presence in a region can change due to random events. These models allow researchers to study whether a particular community of bacteria are better suited to an environment or whether they might have collected because of random events.
iCAMP, or Infer Community Assembly Mechanisms by Phylogenetic-bin-based null model analysis, helps identify the ecological processes that may be responsible for the differences in microbial communities. A “null” model helps researchers estimate what a microbial community might look like in the absence of a particular ecological process.
Co-occurrence network analysis helps researchers turn the data into a network by reimagining every bacterial family as a dot. If the data shows that two bacterial groups are often found together they are shown to be connected by a line, allowing researchers to later calculate the mathematical properties of the network that eventually emerges from the data.
“While marine microbial communities are largely shaped by random ecological processes, the balance between randomness and environmental selection varies across different latitude zones. Polar microbial communities exhibited more modular interaction networks, whereas tropical and temperate communities were influenced by both environmental selection and stochastic ecological processes,” added Aarti Ravindran, postdoctoral researcher, WSAI.
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What the results hinted
The most significant finding was that rare ‘specialist’ bacteria contribute far more to the stability of marine microbial networks than previously recognised.
“Although these microbes occur in much lower abundance than widespread ‘generalist’ species, they serve as vital connectors within microbial interaction networks. Computational analyses showed that removing these specialist bacteria substantially weakened network stability, demonstrating their outsized role in preserving resilient marine ecosystems,” said Karthik Raman.
Researchers found that “randomness” plays a much larger role in the distribution of bacteria than they expected. However, the assembly of bacteria in different locations is determined by chance, geography, and climate too.
The study says that rare bacteria acts as a “connector” in marine ecosystems. This is a term used in mathematical network analysis to study what links separate groups. Think of friend groups in a classroom. If the common friends that bring these groups together disappear, the groups might still exist but they might not interact as much. A similar phenomenon can be observed in marine bacteria.
This makes rare bacteria interesting from a conservation perspective too. If these ecological bridges between microbial communities were to stop existing, it could impact the overall stability of the marine ecosystem in ways that are hard to predict at the moment. Their loss could potentially alter how these bacterial communities respond to environmental stress.
Exactly what this means for the wider ocean ecosystem remains an open question. The researchers’ findings are based on computational analyses of microbial communities and networks, rather than experiments showing what happens when these bacteria disappear from real-world ecosystems.