What happens after we die. What is the microbiome signature of a human being ?
Gut microbes are the main driver of tissue decay when animals die, and were probably important for preserving soft-tissue anatomy in fossil animals.
Philip Donoghue at the University of Bristol, UK, and his colleagues studied the brine shrimp and monitored its decay (pictured, middle and right) under various conditions. They found that soon after death, the shrimp’s gut wall breaks open and bacteria spill out into the body cavity. The bacteria form sticky aggregates, or biofilms, that gradually replace shrimp tissue and contain mineral deposits, as revealed by microscopy. This mineralization is a key step in tissue preservation in fossils. Evolution of the gut led to an explosion in both animal diversity and the abundance of fossils, the authors say. Royal Society Publishing Proceedings B. 13 May 2015. Open access.
Human lifestyles profoundly influence the communities of microorganisms that inhabit the body, that is, the microbiome; however, how the microbiomes of humans have diverged from those found within wild-living hominids is not clear. To establish how the gut microbiome has changed since the diversification of human and ape species, we characterized the microbial assemblages residing within hundreds of wild chimpanzees, bonobos, and gorillas. Changes in the composition of the microbiome accrued steadily as African apes diversified, but human microbiomes have diverged at an accelerated pace owing to a dramatic loss of ancestral microbial diversity. These results suggest that the human microbiome has undergone a substantial transformation since the human–chimpanzee split. PNAS 2014. Open Access.
According to the Human Microbiome Project, 90% of the cells in a healthy adult body are microorganisms. What happens to these cells after human host death, defined here as the thanatomicrobiome (i.e., thanatos-, Greek defn., death), is not clear. To fill the void, we examined the thanatomicrobiome of the spleen, liver, brain, heart and blood of human cadavers. These organs are thought to be devoid of microorganisms in a healthy adult host. We report that the thanatomicrobiome was highly similar among organ tissues from the same cadaver but very different among the cadavers possibly due to differences in the elapsed time since death and/or environmental factors.
Decomposition begins several minutes after death with a process called autolysis, or self-digestion. Soon after the heart stops beating, cells become deprived of oxygen, and their acidity increases as the toxic by-products of chemical reactions begin to accumulate inside them. Enzymes start to digest cell membranes and then leak out as the cells break down. BBC; Mosaic Science
Surprisingly, the previously unexplored microbiome of Amerindians contains antibiotic resistance genes. Clemente et al. characterized the fecal, oral, and skin bacterial microbiome of people in a Yanomami Amerindian village with no known previous contact with Western peoples for the past 11,000 years. Their microbiota are the most diverse yet reported for humans. These data offer a rare opportunity to understand what latent antibiotic resistance might have been present in the human holobiont before antibiotic use. Science Advances April 2015
North American coniferous forests harbor large amounts of the bacteria called bradyrhizobia. This genus made its name as obligatory symbionts of legumes, able to snatch atmospheric nitrogen via the nif gene product and supply it as nitrate to the plant and to fertilize soils. In return, the bacterium’s nod genes allow it to live within the safety of the plants’ roots. But legumes are rare in coniferous forests. Nevertheless, VanInsberghe et al. discovered that
diverse bradyrhizobia, all lacking nif and nod genes, occur abundantly in these forests’ soils. They are not symbionts, but they have other metabolic talents, depending on their environment. The symbionts are instead the minority in the
genus. ISME J. 10.1038/ismej.2015.54 (2015).