Australasian Science Magazine

By Magdeline Lum

Traces of DNA sampled across New York’s subway have revealed a trail of anthrax, bubonic plague and drug-resistant microbes.

An extensive survey of the traces of DNA left behind by New Yorkers include a trail of anthrax, drug-resistant microbes, cheese and sausage throughout the network of the New York City subway.

Humans are home to a diverse variety of bacteria. The average person is home to approximately 100 trillion microbial cells. This outnumbers human cells by a ratio of 10:1. They make up 36% of active molecules in the human bloodstream, and some life processes we take for granted would not happen without them. We need the bacteria as much as they need us to live.

As people move throughout a city, 1.5 million microscopic skin cells are left behind each hour. Each city contains a rich collection of microbial population that is as unique as its population. Like a rainforest or reef system made of smaller unique areas of life, so are the collections of bacteria in smaller unique areas of the cities like train stations.

Very little is known about the ecology of microbes in urban environments. However, the PathoMap Project led by geneticist Christopher Mason of Weill Cornell Medical College has now sampled surfaces across 466 open stations throughout New York. Surfaces swabbed included kiosks, benches, tunstiles, garbage cans and railings over an 18-month period. More than 10 billion fragments of DNA was collected, and the data was analysed by a supercomputer containing a genetic database of all known plants, animals, microbes and viruses.

A total of 15,152 different types of organisms were identified, of which 46.9% came from bacteria (most of it was harmless) while 48% of all DNA analysed did not match any known organism. Although much work has been done in the sequencing of genomes there are few organisms that have had their entire genome sequenced.

Unexpected traces of anthrax and bubonic plague were detected but at levels too low to pose a health risk to people. Bacteria whose diet includes hazardous chemicals and toxic waste were also found. These bacteria was found more often and in a number of locations. Additionally, bacteria associated with cheese and sausage were found at numerous subway stops and stations, seemingly confirming New Yorkers’ love of pizza.

Apart from following the trail of people throughout a public transport system, this particular work can be adapted to predict the nature of an outbreak. Populations of microbes could be monitored for changes, especially at the beginning of an outbreak, leading to better control measures and reducing its impact.

Mantis Males Prefer Anorexic Mates

The reproductive stage of the mantis is often discussed with the female cast in the role of femme fatale and the male as the mate who becomes a meal. While pheromones released by the female attract hopeful males, not all of these signals are advertising the opportunity to fertilise eggs. Some malnourished females are luring a male so they can eat in order to gain the energy to reproduce.

A male mantis is a relatively large prey. For decades it has been thought that hungry females could use pheromones to attract males to cannibalise them for food. However, no study has been able to provide data to support this hypothesis.

Evolutionary biologist Dr Kate Barry of Macquarie University has recently collected information that supports this hypothesis. She used three groups of eight female false garden mantids (Pseudomantis albofimbriata) in cages that hid them from view. The mantids were grouped by their nourishment status of very poor, poor, medium and good, and male mantids were then released around the caged females.

The poor, medium and good groups attracted 5, 10 and 15 males, respectively, while the very poorly nourished females with attracted 25 males: the most of any group.

Barry surmises that a hungry female is willing to spend more energy on producing and releasing pheromones because the benefits of a meal outweigh this expense. However, a female mantis needs to have at least one egg to produce sex pheromones. Previous studies had not considered this aspect.

In this particular species, cannibalism begins before copulation. The female disables the male by biting off its head and forelegs, but there is still a chance for copulation because the male has two brains: one in the head and the other in the abdomen. Although headless, the male is still able to bend the rest of his body to copulate, as the majority of his body is free from the female’s grasp.

The male fertilises only one or two eggs of a malnourished female compared with hundreds of eggs for a well-fed female.