Researchers find phosphate in more soluble form on Mars

Synthetic crystals of the calcium phosphate mineral whitlockite similar to those used to produce the extraterrestrial mineral merrillite. 

If life ever arose on Mars, merrillite may have been a major source of biologically required phosphate. Largest crystal are ~1mm. 

Credit: C. T. Adcock / University of Nevada Las Vegas 

A trio of researchers at the University of Nevada has found that phosphate found in minerals on Mars, is far more soluble than it is in natural Earth minerals.

In their paper published in the journal Nature Geoscience, the researchers describe how they synthesized mineral types found on Mars and then tested how well they dissolved in water releasing phosphate as compared to samples from natural Earth minerals.

Most scientists agree that phosphate is a key ingredient for life. Put another way, they believe that life couldn't have evolved without it.

For that reason, scientists have been studying ways in which minerals that contain phosphate could have broken down to allow the phosphate to escape.

Such studies have thus far found that minerals that hold phosphate on Earth are not very soluble—they don't break down easily when soaked in sea water.

That has led to what Earth scientists call "the phosphate problem." How did life get started on Earth if there wasn't enough phosphate around when life was first beginning?

Some have suggested the answer is that it didn't, instead, it started on another planet, such as Mars, and made its way here via meteorites.

Prior research has already shown that Mars has much more phosphate than does Earth. In this new effort, the team in Nevada looked at minerals that exist on Mars to see if they might be more soluble in water as well.

Lacking samples from Mars to test, the researchers synthesized chlorapatite and merrillite in their lab—two common phosphate bearing minerals found on the Red Planet.

They then soaked samples in several tubs, each with a different pH level for varying amounts of time. As they did so, they measured how much phosphate made its way into the water and how long it took.

In analyzing their results, the researchers found that more phosphate made its way into the water with both types of minerals and they did so at a faster rate than minerals that contain phosphate found naturally on Earth.

In some cases, they report that the Mars rocks released phosphate up to 45 percent faster than Earth rocks.

The findings by the team don't prove that life began on Mars and migrated to Earth—after all, scientists have yet to prove life ever existed Mars. But it does add some credence to the argument that perhaps life did start somewhere other than our home planet, which if true, might mean it's still out there waiting for us to discover it.

More information: Readily available phosphate from minerals in early aqueous environments on Mars, Nature Geoscience (2013) DOI: 10.1038/ngeo1923

High dietary phosphate intake may promote skin cancer formation

A high dietary intake of phosphate promotes tumour formation in an animal model of skin cancer, researchers at Emory University School of Medicine have found.

The results, published in the journal Cancer Prevention Research, suggest that a high intake of phosphates may promote tumour development and contribute to tumour growth in skin cancer, while restricting phosphate intake may help prevent cancer.

The researchers applied dimethylbenzanthracene, a carcinogen found in cigarette smoke, to the skins of mice, followed by another chemical that stimulates cell growth.

Feeding these mice a high phosphate diet (1.2 percent by weight) increased skin papilloma number by 50 percent compared with a low phosphate diet (0.2 percent).

Skin papillomas are the initial stage of skin cancer development, which may progress to full carcinoma.

"This is a very well established model for the initiation and progression of cancer, and the effects of many physiological conditions on cancer initiation have been measured this way," says senior author George Beck, PhD, assistant professor of medicine (endocrinology). Beck is also a member of the Winship Cancer Institute, Emory University.

Phosphate is an essential nutrient forming both the physical support for bones, when complexed with calcium, and the chemical backbone of DNA. Phosphate chemical bonds provide the energy currency in the cell, in the form of ATP (adenosine triphosphate).

In addition, many oncogenes, the motors driving cancer cells to divide relentlessly, are regulatory enzymes that attach phosphate chemically to other proteins, turning their activity up or down depending on the protein target.

Altered levels of phosphate could be tipping the balance of these chemical reactions in complex ways, Beck says.

Public health researchers say that phosphate dietary intake has increased over the last 30 years and also may be underestimated because of the increasing contribution of food additives.

Phosphate is added to a variety of processed foods such as meats, baked goods and soft drinks to improve texture and durability.

The authors calculate that the human dietary equivalent of a mouse's high phosphate diet is 1,800 milligrams per day, an intake level that many humans match or exceed.

The high-phosphate diet did not have a corresponding increase in calcium, which would reflect the equivalent of a dairy-rich diet. A low-phosphate diet in the mice corresponds to 500 milligrams per day for humans.

"Another way to look at it is that a low-phosphate diet may help prevent cancer," Beck adds.