Bacteria are the workhorses for a large number of biotechnological processes. From different fermentation processes to insulin production, they are widely used in industry due to their efficiency, fast duplication times and ease of maintenance. But often their behaviour it´s much more complex than one would expect from a unicellular organism. This is where the beauty of bacteria resides, but this also drives researchers crazy: they have a life of their own.
For decades, genetics has been considered the only basis of natural diversity: mutations in genes that result in phenotypic (observable) changes. The surprise came when identical bacteria that live in the same environment showed big phenotypic differences that cannot be explained by genetic variations.
The expression of genes has some degree of randomness, which is called “phenotypic noise”. This effect changes the physiology of single bacterium and is the origin of individuality. Despite the term noise intuitively suggests a negative process, it might be positive instead. If a population has different bacteria with diverse functionalities, some of them might be able to respond to environmental changes faster. This is a simple concept: the bigger the functional diversity, the higher the probability that some individuals adapt to changes in their living conditions and, thus, survive.
Bacterial individuality is far from being a matter of academic curiosity: it is an important drawback in the efficiency of antibiotics. A large percentage of a bacterial population is killed when treated with high doses of antimicrobials, but it´s normally the case that a small fraction of individuals survive. However counterintuitive, these bacteria are not genetically resistant to the antibiotic, but they have a different phenotype that has somehow allowed them to survive. The persistence of bacteria that are never completely eliminated complicates the treatment of infectious diseases such as turberculosis.
For similar reasons, microorganisms used in bioreactors as catalysts for specific industrial transformations, often divert into inefficient types. In a population of bacteria that are engineered to synthesise, for example, human insulin, a group of individuals simply stops the production. Since this decreases the efficiency of biotechnological processes, an increasing attention has been drawn to studying bacterial metabolism at a single-cell level.
Under the assumption that a bacterial population is the sum of different individualities, and not a homogeneous entity, the social behaviour of these organisms is studied under a whole new light. And recent conclusions suggest that bacterial societies might be much more complex than initially expected. In fact, it is possible that bacteria were already performing societal roles when humans were still not around.
Researchers have studied 1 the social behaviour of the soil bacteria Pseudomonas putida focusing on their ability for the degradation of organic pollutants. Vicious contaminants such as toluene or xylene, generated by different human activities, can be detoxified by certain strains of Pseudomonas through a complex metabolic route comprising different sequential steps. Surprisingly, in a genetically identical bacterial population, different groups were found to perform different parts of the process. This finding might be the first hint of a bacterial community performing labour division, a behaviour usually associated with multicellular organisms or complex societies.
This might also be the basis for cooperative behaviour, something that cannot be completely explained through the Natural Selection theory from Darwin. If we inspect the different groups of bacteria that carry out each part of the detoxification route, most of them are not individually benefited from their particular role, for which they use energy and resources without any positive physiological outcome. Only if we look at the process as a whole (toxic chemical turned into innocuous substance), can we understand the individual contributions in evolutionary terms.
The division of tasks to perform a complex function has not only been observed between different bacteria from the same species, but also among different species. Examples of the latter have been found in the tanks that are used for the treatment of waste water, where several different microorganisms form a consortium to transform complex substrates into biodegradable molecules.
Understanding how bacterial individualities are integrated in a social structure is generating a paradigm shift in the study of evolution and in the application to biotechnology. As a result, researchers might start using analytic tools from seemingly distant areas such as sociology and economy. One may wonder whether these disciplines could also learn something from bacteria and reconsider the consequences of cooperative behaviour, as a strategy that is adopted by one the most ancestral forms of life.