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Biologists estimate that there are about 5 to 100 million species of organisms living on Earth today. Evidence from morphological, biochemical, and gene sequence data suggests that all organisms on Earth are genetically related, and the genealogical relationships of living things can be represented by a vast evolutionary tree, the Tree of Life. The Tree of Life then represents the phylogeny of organisms, i. e., the history of organismal lineages as they change through time. It implies that different species arise from previous forms via descent, and that all organisms, from the smallest microbe to the largest plants and vertebrates, are connected by the passage of genes along the branches of the phylogenetic tree that links all of Life (Figure 1).

When watermen find wounded fish along a lonely river in Maryland, they kick off a scientific debate and an environmental crisis focused on a mysterious microbe that may -- or may not -- cause sick fish and sick people. Watch the title sequence from this award-winning, hour-long film.

Life on Earth is intimately connected to the natural cycles of light and dark that make up a 24-hour day. For plants, animals, and even bacteria, these circadian rhythms control many biological functions. Humans can overrule their body clocks, but at a price: People whose circadian rhythms are regularly disrupted-by frequent jet lag or shift work, for example-are more vulnerable to diabetes, obesity, cardiovascular disease, and cancer. There are various theories to explain these associations, and researchers now have a new player to consider: the bacteria that live in the digestive tract. According to a study in mice and a small group of human volunteers, the internal clocks of these gut microbes sync up with the clocks of their hosts. When our circadian rhythms get out of whack, so do those of our bacteria.

2014 was a banner year for making automotive fuel from nonfood crops, with a series of major new production plants opening in the United States. However, producing this so-called cellulosic ethanol remains considerably more expensive than gasoline. So researchers are always on the lookout for new ways to trim costs. Now they have a new lead, a microbe that can use abundant nitrogen gas as the fertilizer it needs to produce ethanol from plants.

When life emerged on Earth about 4 billion years ago, the earliest microbes had a set of basic genes that succeeded in keeping them alive. In the age of humans and other large organisms, there are a lot more genes to go around. Where did all of those new genes come from? Carl Zimmer examines the mutation and multiplication of genes.

When scientists first made contact with an isolated village of Yanomami hunter-gatherers in the remote mountains of the Amazon jungle of Venezuela in 2009, they marveled at the chance to study the health of people who had never been exposed to Western medicine or diets. But much to their surprise, these Yanomami's gut bacteria have already evolved a diverse array of antibiotic-resistance genes, according to a new study, even though these mountain people had never ingested antibiotics or animals raised with drugs. The find suggests that microbes have long evolved the capability to fight toxins, including antibiotics, and that preventing drug resistance may be harder than scientists thought.

But now, a century and a half later, scientists from 11 different institutions have joined forces to amass all of that information, plus new data, to create the most comprehensive version of the tree so far. As detailed in a recent article in Proceedings of the National Academy of Sciences, the new Tree of Life shows how 2.3 million different types of animals, plants, fungi and microbes are interconnected, and how those relationships have diverged since life began on Earth more than 3.5 billion years ago.

Most colon cancers may be caused by infections with bacteria that are normally found in cows. For decades we have known that Streptococcus gallolyticus gallolyticus (SGG) is sometimes found in colon tumours, but now the microbes have been found to directly cause tumour growth in mice.

The bacteria in our guts can break down food the body can't digest, produce important nutrients, regulate the immune system, and protect against harmful germs. And while we can't control all the factors that go into maintaining a healthy gut microbiome, we can manipulate the balance of our microbes by paying attention to what we eat. Shilpa Ravella shares the best foods for a healthy gut.

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This interrupted case study introduces the topic of bacterial sporulation and cannibalism in Bacillus subtilis. The storyline follows Susan and her lab mates who are presenting research at a lab meeting when Susan falls asleep and dreams they are stranded on a deserted island. She makes connections between their fight for survival in the dream and the survival mechanisms of the bacteria they study in the lab. The benefits of sporulation under conditions of sustained stress are fairly obvious, but Susan's dream is used to examine the idea that sporulation may not always be beneficial and that bacteria would not want to commit to entering such a state in response to temporary stresses. Through the analysis of actual data from the scientific literature, students uncover a mechanism by which B. subtilis delays its commitment to sporulation by killing members of its own species to release nutrients (i.e., cannibalism). Originally developed for a general undergraduate microbiology course when discussing the structure and growth of prokaryotic cells, the case could also be used in an introductory biology course that emphasizes bacteria and data literacy.

If you think you can rid your body of bacteria with a quick squirt of hand sanitizer, you'd be oh so wrong. Turns out we have an incredible array of microorganisms living on us AND inside us. But as Anthony tells you, these little guys do some very important work.

10:04 video, Don't panic! But you should really know about antibiotic-resistant bacteria, aka super bugs. They're here, and they're doing very well, thank you. SciShow explains what they are, how they're getting around our best drugs, and what science (and you) can do to help.

This case study presents the story of Phil, an undergraduate majoring in biology, whose Russian cousin Dimitri has contracted tuberculosis (TB) from inmates at the prison where he works.  Phil learns that his cousin's failure to complete his antibiotic regimen likely contributed to the evolution of antibiotic-resistant TB in his body.  Phil consults with his friend Stacy, and together they try to understand Dimitri's condition by applying what they are learning in their genetics lab experiment about the role of random mutation in bacterial evolution (including the development of antibiotic resistance) through Luria- Delbrück fluctuation analysis. The same analysis includes calculation of the mutation rate, which Phil realizes is sufficient to cause MRSA and other antibiotic-resistant infections. This case study was originally developed for concurrent use in freshman/sophomore-level genetics, elementary statistics, and precalculus. However, it is also very appropriate for courses in introductory biology, evolutionary biology, and biostatistics. The teaching notes discuss various ways to run the case depending on the mathematics and biology background of students.

4:34 video Right now, you are inhabited by trillions of microorganisms. Many of these bacteria are harmless (or even helpful!), but there are a few strains of 'super bacteria' that are pretty nasty -- and they're growing resistant to our antibiotics. Why is this happening? Kevin Wu details the evolution of this problem that presents a big challenge for the future of medicine.

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