The big science news last week was the announcement and publication in Science that a strain of bacteria that lives on arsenic instead of phosphorous was discovered. Arsenic, which appears below phosphorous in the periodic table, is toxic to most life forms mostly because it is chemically similar to phosphorous. It had thus been postulated that there could be life forms that utilize arsenic instead of phosphorous. In fact, astrophysicist Paul Davies had long suggested that a proof of principle of the possibility of alien life could be obtained by finding an alternative form of life on earth. The new bacterium comes from Mono Lake in California, which is very rich in arsenic. The authors put some samples from the lake into a medium rich in arsenic but devoid of phosphorous to see what would grow and found a strain that grew robustly. They then found that arsenic was actually incorporated into the proteins and DNA within the cells. In a post from five years ago, I speculated that we might find some new organism living on toxic waste some day although this cell is probably of ancient origin. However, there has been strong criticisms of the paper since the announcement. For example see here. Hence, the jury may still be out on arsenic loving microbes.