A rarely frequented salty lagoon in Jeddah is hosting quadrillions of unusual summer visitors. They will only be here for a short time, until the temperature of their salty lagoon on the Corniche falls below 21 Celsius. They have been dropping in and out of comfortable salt ponds for the last 3.5 billion years or so. And when they come, they paint the town pink.
Halophilic archaebacteria (HA, for short) are one of the oldest life forms on the planet and apparently are easily satisfied judging by their idea of holiday fun. Their fun consists mainly of lying about in hot salty water and going pink. They are incredibly tough for they exist in conditions that would kill off more complicated creatures.
A single drop of the brine they thrive in contains millions of rod-shaped bacterial cells. The bacteria produce a red carotenoid pigment that is similar to that found in tomatoes, red peppers and pink flamingos. Carotenoid pigments are also the source of Beta-carotene, an important antioxidant and the precursor of vitamin A. The red pigment probably protects the cells from the ravages of direct sunlight.
Halophilic (salt-loving) bacteria thrive in saline lakes with salt concentrations of 15 to 30 percent, about four to nine times the salinity of seawater (3.5 percent). They can even live in saturated salt and remain alive in salt crystals for years. They cannot, however, survive if the salt concentration drops much below 12 percent. Very few life forms on earth have adapted to that extreme salinity.
All living things are classified into six ‘kingdoms’. Archaebacteria are the oldest organisms living on the earth. They are prokaryocytes and unicellular and belong to the kingdom, Archae. They were first discovered in 1977 and were classified as bacteria.
There are three phyla — or groups — of archaebacteria: methanogens, halophiles and thermoacidophiles.
Methanogens harvest energy by converting hydrogen and carbon dioxide into methane gas. They are found in the intestinal tracts of humans and some animals such as cows and in marshes.
Thermoacidophiles, which are perhaps the hardiest of the three phyla, live in areas with very high temperatures and extremely acidic conditions. They can be found in hydrothermal and volcanic vents at temperatures well above 100 Celsius.
The halophile (salt loving) group, and our Jeddah guests, survive in a high-salt environment such as the Great Salt Lake, the Dead Sea and as long as the right conditions obtain, the lagoon by the Corniche. They are very modest in their dietary habits, simply requiring some oxygen, strong sunshine and salty water. If you need to though, you can hold the oxygen, because halophiles can produce energy without oxygen (anaerobic) in two ways: from the degradation of arginine (an amino acid) and by using the photosynthetic molecule bacteriorhodopsin.
Professor Shiladitya Das Sarma of the University of Maryland Biotechnology Institute, who has studied the evolution of these red salt-loving bacteria, has suggested that these two methods of anaerobic energy production are the last remnants of the halophile’s anaerobic ancestry from more than 2 billion years ago, a time when the earth’s atmosphere lacked free oxygen gas.
An article in Nature magazine in 2000 reported a remarkable discovery made in a deep mine shaft near Carlsbad, New Mexico. Scientists extracted some bacterial spores from cavities in salt crystals taken from an underground salt bed 600 meters below the surface. The salt deposits were formed from an ancient sea in a geologic formation that dated back about 250 million years. The spores had survived in a state of suspended animation for millions of years, from a time before dinosaurs roamed the earth. After extraction, they were grown into a living mass in a laboratory. Another microbe extracted directly from dissolved salt crystals appears to be related to the archaebacteria that thrive in the brine of present-day salt lakes and are now holidaying with friends in Jeddah.
NASA is interested in ancient salt deposits (and the life that might be there) because the planet Mars and Jupiter’s moon Europa once had oceans and may have similar subterranean salt formations. Space missions in search of extraterrestrial life may eventually explore these ancient salt beds.
Although the deep pink and murky liquid of the lagoon looks venomously poisonous, the HA family does not produce toxic waste. Neither does it smell but it does taste awful! I tried a drop.
While it is still on public display, the lagoon provides a fascinating example of the tenacity of life in its wonderful various forms and also a moment of humble contemplation.
It is quite likely that by looking at the odd pink water, you are looking across billions of years of natural history and even light years of space and time at some of the earliest life forms in creation.