I Contain Multitudes: Chp. 6


  • Sodalis: A bacterium normally associated with insects that was discovered in a human wound, illustrating how a new relationship between a microbe and a host can begin.

  • Beewolves and Streptomyces: Mother beewolves pass protective bacteria to their offspring. The bacteria produce antimicrobial compounds that help protect the young from fungal infections.

  • Vertical transmission: Microbes pass from parent to offspring.

  • Horizontal transmission: Microbes pass between unrelated individuals or through the environment.

  • Host selection: Animals don't necessarily keep every microbe they encounter. Their bodies and environments help determine which microbes establish themselves.

  • Extended phenotype: An organism's genes can influence its environment, such as a beaver's genes enabling it to build a dam.

  • Hologenome: The idea of considering a host's genes and its associated microbes' genes together when thinking about evolution. Scientists debate how useful this idea is as an evolutionary framework.

  • How can we draw the line between a trait that comes from the host and a benefit that comes from its symbiotic relationship?

    The concept of holobionts makes this question complicated because a trait may result from the host and its microbes working together.

    For example:

    • The host provides a place for microbes to live and access to nutrients.

    • The microbes may help digest food, produce useful substances, or protect the host from harmful organisms.

    • The combined relationship can give the host abilities or benefits it would not have on its own.

    So, is that benefit a trait of the host, or is it a result of the entire holobiont? Sometimes, it's difficult to separate the two.

    Important terms to know

    Term

    Meaning

    Host

    The organism that houses or interacts with microbes.

    Symbiosis

    A close, ongoing relationship between different species.

    Holobiont

    A host plus its associated microbial community.

    Hologenome

    The combined genetic material of the host and its associated microbes.

    One important distinction for your quiz

    Scientists use the term holobiont to describe a host and its associated microbes, but that doesn't automatically mean they always evolve together as one unit of natural selection. That is part of the scientific debate surrounding the hologenome concept.

    Practice quiz question: If a caterpillar depends on bacteria to help it obtain nutrients from its food, why might a scientist study the caterpillar and its bacteria as a holobiont rather than studying the caterpillar alone?

    Try answering in your own words, and I'll help you make it quiz-ready.