Are bacteria conscious?

Consciousness, as a quality neither directly observable nor even able to be empirically proved, divides the scientific community with two overarching questions: which organisms apart from humans are conscious (if any), and when did consciousness originate?

Currently, many hypotheses exist regarding the origins of consciousness with differing degrees of scientific probability, stating a range of junctures when consciousness could have emerged. One hypothesis proposes that consciousness began with multicellular plants 850 million years ago; another suggests animals such as jellyfish were the first conscious organisms when they developed thousands of neurons 580 million years ago; Panpsychism is the theory that consciousness began when the universe formed around 13.7 billion years ago, while the most scientifically supported hypothesis is that consciousness began when animals such as birds and mammals developed much larger brains with hundreds of millions of neurons, around 200 million years ago.

However, there has been a recent movement supporting the theory that bacteria and other single-celled microorganisms possess high levels of intelligence or even consciousness. Although past efforts have been dedicated to studying intelligent processes in humans, other mammals, and birds, the topic of microbial intelligence has recently been gaining traction. Analysis of microbial models and comparative genomics studies confirm that microbes have evolved various means of memory, learning, and processing information, all classified as ‘intelligent behaviour’. The most studied manifestations of Intelligence in the microbial world include decision-making, problem-solving, associative learning, and quorum sensing.

Microbes can monitor their environment, process information, and intelligently decide. These decisions can be made through various mechanisms and networks, such as gene-expression regulation, signalling pathways, transport, metabolism, etc. There are ongoing studies involved in constructing genome-wide protein interaction networks to gain a better understanding of the molecules and interconnections required for microbes to make decisions. The most well-studied example of microbes’ decision-making capabilities is the chemotaxis of E. coli. These microbes decide by monitoring their environment through plasma membrane receptors. If these receptors bind to specific ligands, a signalling pathway involving phosphorylation and methylation is induced within the cells. In this example, it is the level of phosphorylated CheY, a downstream protein of the signalling pathway, that ultimately decides which of two movements the E. coli cells undertake.

When the amoeba Dictyostelium searches the surface of a Petri dish for food, it makes frequent turns. But it does not do so entirely randomly. If it has just turned right, it is twice as likely to turn left as right on its next turn, and vice versa. In some way, it “remembers” which direction it last turned. Human sperm also have the same ability. E. coli goes one better. This bacterium spends part of its life cycle travelling through the human digestive system, encountering different environments as it goes. During its journey, it meets the sugar lactose before it finds the related sugar, maltose. At its first taste of lactose, it switches on the biochemical machinery to digest it – but it also partially activates the machinery for maltose so that it will be ready to digest maltose as soon as it reaches the lactose. To show that this was not simply hard-wired, the researchers from Tel Aviv University grew E. coli for several months with lactose but without maltose. The bacteria gradually changed their behaviour, so they no longer bothered to switch on the maltose-digesting system. Remarkable though these behaviours are, we have only scratched the surface of what single-celled organisms can do. With so many microorganisms still unknown and their behaviour undiscovered, the emergence of consciousness will remain highly relevant, yet unsolved, in years to come.



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