BIOLOGY, EVOLUTION, AND ENERGY

CCBE — Part 3: Bacteria and lateral gene transfer cont.

How the biology of energy shapes competition and cooperation among bacteria

Details about mechanisms of lateral gene transfer. Source: Wikimedia Commons

Recap

Last time we talked about four main points. (1) Bacteria spread their genes by replicating. (2) This process uses resources that bacteria scavenge or synthesise from constituents in their environment. (3) ATP acts as a universal source of energy in living organisms. (4) The pressure to be energetically efficient incentivises bacteria to purge genes they don’t need right now, resulting in the phenomenon of lateral (or horizontal) gene transfer. For the real keen beans, examples of specific gene transfer mechanisms are described by the figure above.

Today

So, what can this teach us about cooperation and competition? Bacteria don’t even have brains, so we need to be careful not to imply that they’re hatching schemes or working an angle when we think about cooperation and competition among bacteria.

But in a way that depends only on blind mechanism, the basics of cooperation and competition are present, as the bacteria compete individually for resources and cooperate as a population by sharing genes.

Lateral gene transfer as cooperation at the population level

To be fair, the act of purging genes isn’t cooperative on the part of the individual bacterium that attempts to replicate faster and outcompete its neighbours for vital resources. But at the group level, the gene sharing is a form of cooperation that provides greater robustness for the population as a whole. How does that work?

The key is that this gene trading means that different bacteria have different genes, which promotes genetic diversity among the population of bacteria. When environmental conditions change, which they eventually always do, many bacteria may be unable to cope.

DNA. Photo by Sangharsh Lohakare on Unsplash

But genetic diversity increases the chance that at least some of the population will have a few clever molecular tricks up their sleeve that allow them to survive and even thrive. A familiar example that’s also a growing issue in modern societies is the overuse of antibiotics leading to the emergence of drug-resistant bacteria.

The use of antibiotics saves lives and reduces suffering and disease, but it also puts evolutionary pressure on microorganisms to find strategies to beat the drugs. In turn, processes that increase genetic diversity, like lateral gene transfer, give microorganisms such as bacteria the tools to do just that.

In this way, the future of a bacterial population depends on cooperation, competition, and the state of their environment. Even in the total absence of brains, cooperation and competition are key drivers of bacterial life.

Bacteria and the evolution of multicellular life

Oddly enough, this isn’t where bacteria leave our story. Apart from how they colonise our bodies and constantly threaten us with invasion — so like us! — it turns out that bacteria are also at the heart of multicellular life.

This brings us back to ATP, the universal energy currency, and introduces a new character: mitochondria, often referred to as the powerhouses of our cells. Asking what mitochondria do and where they came from takes you to the birth of the family tree that we belong to, unhelpfully known as the eukaryotes — thanks, Science.

The word eukaryote translates to ‘true nucleus’ (or the more clunky ‘good nucleus’). The term distinguishes cells that contain two things, organelles (the cell’s equivalent of a body’s organs) and a nucleus packed with DNA, from organisms that have neither, known as the prokaryotes.

The union between a bacterium and an archaeon gave birth to the eukaryotes. Humans aren’t specifically mentioned, but we would occupy part of the animal branch of the eukaryotic tree. Some time later, the union between a eukaryote with a second bacterium, now known as chloroplasts, gave rise to plants and algae. Source: Wikimedia Commons

The prokaryote family has two types of members: the bacteria and the archaea, both of which are classes of single-celled organisms. Along with eukaryotes (or eukarya, because having just one term would be too simple and where’s the fun in that?), these groups define the three domains of life.

Next time

Okay, that’s probably pushing the envelope with too much obscure jargon for today, so we’ll leave it there. Next time we’ll find out how bacteria and archaea have an unexpected family history with mitochondria and eukaryotes like us, and what all that has to do with ATP, cooperation and competition. Until then!