Largest bacterium, comet capture and growing deserts

The threadlike Thiomargarita magnifica Cells have a more complex internal organization than typical bacteria.Credit: Olivier Gros/Lawrence Berkeley National Laboratory

The largest bacterium ever found is surprisingly complex

Biologists have found filamentous bacteria that can grow to almost 1 centimeter in length – the largest ever found – with internal structures reminiscent of cells in more complex organisms. The results appeared in Science (J.-M. Volland et al. Science 376, 1453–1458; 2022).

Biologist Olivier Gros of the University of the Antilles in Pointe-à-Pitre on the French West Indian island of Guadeloupe discovered Thiomargarita magnifica on rotting mangrove leaves. He found that the bacteria live off the oxidation of sulfur.

“At first I thought it was something like a fungus or something — not bacteria, but maybe a eukaryote,” says Gros. Unlike bacteria and archaea, which are simple microorganisms, eukaryotes — which include animals and plants — have complex cells that contain a nucleus and organelles like mitochondria.

One of Gros’ collaborators, marine biologist Jean-Marie Volland of Lawrence Berkeley National Laboratory in California, used a series of imaging techniques to examine the bacterium more closely and helped confirm that it was a single cell.

The next largest Thiomargarita is only about 750 microns long. Other filamentous bacterial structures are also found in the mangroves, but they all consist of tens or hundreds of cells.

At the center of the bacterium is its vacuole – an inert, fluid-filled membrane. At its rim are thousands of membrane-bound structures called pepins. The authors describe these as being similar to the organelles found primarily in the cells of eukaryotes.

Pepins contain DNA and ribosomes, molecular machines that translate instructions from DNA to make proteins. In other bacteria, genetic material floats freely within the cell, usually in the form of just one circular chromosome. The pepins collectively harbor up to 700,000 copies of the genome, but it’s unclear whether each pepin contains just one copy of the genome or more than one.

Petra Levin of Washington University in St. Louis, Missouri, says the discovery challenges the conventional wisdom that bacteria have smaller size limits than eukaryotic cells. “Eventually there will probably be an upper limit to cell size, but I don’t think it will be typical of bacteria, archaea, or eukaryotes.”

An artist's illustration of the Comet Interceptor hitting its target comet

An artist’s rendering of the Comet Interceptor, which will launch in 2028 and wait up to six years to reach its destination.Credit: Geraint Jones, UCL Mullard Space Science Laboratory

European mission plans to raid a rare comet

The European Space Agency (ESA) last month approved the first mission to be launched without a preselected target. Instead, it will wait in space and be ready to fly at short notice.

The Comet Interceptor mission will launch in 2028 and travel to a point of gravitational stability 1.5 million kilometers from Earth. Once there, it can wait up to six years for a suitable comet to fly close enough to Earth’s orbit to visit it. In this case, the probe will take off on a flyby course. The main spacecraft will approach to a distance of about 1,000 kilometers – far enough away not to be damaged by nearby material – while two smaller probes will dive closer, to a distance of just 400 kilometers from the surface.

The goal is to find a pristine object, known as a long-period comet, approaching the Sun for the first time. The encounter would provide a glimpse of material that formed at the beginning of the solar system, 4.5 billion years ago. Other missions have visited comets that have been altered by the Sun because they have spent time in the inner Solar System.

Alternatively, the craft could intercept an object from another solar system, similar to the rock ‘Oumuamua that transited the solar system in 2017.

Two camels run through the desert in Uzbekistan

The spread of deserts in Uzbekistan and neighboring countries will change the composition of ecosystems.Credit: Matyas Rehak/Shutterstock

Climate change is expanding the deserts of Central Asia

As global temperatures have risen, the desert climate has spread north — by as much as 100 kilometers in parts of Central Asia since the 1980s, a climate assessment shows.

The study also found that temperatures have been rising across Central Asia, which includes parts of China, Uzbekistan, and Kyrgyzstan, over the past 35 years (Q. Hu and Z. Han Geophysics. Resolution Latvian. 49, e2022GL098895; 2022).

The research team used air temperature and precipitation data from 1960 to 2020 to divide Central Asia into 11 climate types. They found that the area classified as desert climate has spread eastward since the late 1980s, spreading up to 100 kilometers north in northern Uzbekistan and Kyrgyzstan, southern Kazakhstan and around the Junggar Basin in northwestern China.

Co-author Qi Hu, an earth and climate scientist at the University of Nebraska-Lincoln, says this is a significant expansion and has had a knock-on effect on neighboring climates, which have also become drier.

In some areas, the annual average temperature was at least 5 °C higher between 1990 and 2020 than between 1960 and 1979, with drier summers and winter precipitation occurring mainly.

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