HKU Bulletin October 2012 (Vol. 14 No.1)

Cover Story and have no detectable metabolism. Some of these ‘living’ bacteria are hundreds and maybe even thousands of years old. Dr Pointing says that apart from informing microbiology, the findings also offer a route for understanding the impact of climate change on deserts. “Deserts are really fragile ecosystems. They’re almost the tipping point of what is sustainable. They’ve got very few plants, and the role of microbes becomes relatively more important, but they are living on the edge of extinction. In terms of biodiversity and functional role, they’re highly at risk from climate change. A 1º Celsius change in average temperature in the desert is far more dangerous than a similar change in, say, a temperate woodland,” he says. The findings were based on fossil records, genetic analysis, new pyrosequencing technology that vastly increased the resolution of the data, and old-fashioned microscopic investigations. They were published this year as a commissioned review in the prestigious Nature Reviews Microbiology journal. The water-desert link The research is now evolving to look at organisms in a seemingly opposite environment – fresh water – and this is also of interest to NASA. Freshwater corals are populated and supported exclusively by microbes, mainly cyanobacteria that share ancestry with desert cyanobacteria. (Unlike marine corals, no animal polyps contribute to freshwater coral building.) Many believe these organisms had a role to play in increasing oxygen levels on ancient Earth so more complex life forms could be supported. Microbialite cyanobacteria are also similar to desert cyanobacteria in that they are both intimately associated with minerals (such as carbonates, sulphates and porous minerals) during their growth. “NASA is very interested for the simple reason that about three or four million years ago, when water on Mars’ surface was disappearing, the water there was very carbonate rich. Microbialites on Earth are found in high carbonate lakes, so NASA felt these were quite good analogues for the lakes on Mars during its late wet phase and they’re interested in what sort of signatures these things leave as they grow and eventually die,” Dr Pointing says. Investigations into Earth’s tiniest inhabitants therefore are offering clues about Earth’s deep past and its closest neighbour. And hopefully, its future threats. M Several years ago, Dr Steve Pointing, Associate Professor in the School of Biological Sciences, travelled to the ends of the Earth in search of places that were similar to the environment on Mars. He was working with NASA, the space agency, but an interesting long-term outcome of that work has brought his focus straight back to Earth. During his field trips, Dr Pointing encountered cyanobacteria, a tiny photosynthetic bug, and collected vast amounts of data on it. His subsequent analysis of its dispersion around the world over time has turned conventional thinking about the evolution of certain life forms on Earth on its head. Using fossil records and present day samples from 21 deserts, including the polar regions, Dr Pointing and his colleagues have shown that against expectations, the bacteria were not globally dispersed. Instead they were very particular to places over periods stretching deep back into time, to before modern climates were formed. “We found that the cyanobacteria in every desert had a unique genetic signal. And the estimates of divergence were surprising, suggesting there was no gene flow between the deserts over these really long time scales.“ “The mantra on bacteria and distribution on Earth has been that everything is everywhere. But this study shows this is not always the case and I’m guessing we will find more exceptions to the rule,” he says. Implications for climate change, too So why don‘t cyanobacteria behave as expected? The best explanation is biofilms, which act like a glue, holding these bacteria in place even during dust storms. Just as importantly, the biofilms can support the bacteria in a near-dead state. In some of the deserts studied, the environment is so hostile that there are only 300 to 400 hours a year in which the cyanobacteria can be active. The rest of the time, they revert to a dessicated state in the cocoon of the biofilms Waking the Dead Near-dead cyanobacteria are providing insights into evolution and the possibility of life on Mars. w x l j m y r x v r w p k m y r v p m n p r l m j k m q m p r v k x j p r v k s ~ k y y m r ¦ r m w j r v r j o r j v v o k { ° x j p ± j k | s j k l p o r l m ~ r v r j p k q k y m v r y k p r j m ~ r v r j p v v x o v p o m v k y r m y { r v p r j y o m y j r q k y l m j k r v v x o v y k p r j m p k j j k x p r k v v p r l s x y p m k y v o r v r x y m ° x r s j r v o { p r j k j q v } q q r l m j k m q m p r v } l r k x j r v p n x r v v p q m s r k y j v x j m y n m p v q p r { r p o v r The mantra on bacteria and distribution on Earth has been that everything is everywhere. But this study shows this is not always the case. ² ³ ´ ¢ ² ´ ¢ µ 15 October 2012 The University of Hong Kong Bulletin