Life on Earth can grow on extraterrestrial organic carbon

Abstract

The universe is a vast store of organic abiotic carbon that could potentially drive heterotrophy on habitable planets. Meteorites are one of the transporters of this carbon to planetary surfaces. Meteoritic material was accumulating on early Earth when life emerged and proliferated. Yet it is not known if this organic carbon from space was accessible to life. In this research, an anaerobic microbial community was grown with the CM2 carbonaceous chondrite Aguas Zarcas as the sole carbon, energy and nutrient source. Using a reversed ¹³C-stable isotope labelling experiment in combination with optical photothermal infrared (O-PTIR) spectroscopy of single cells, this paper demonstrates the direct transfer of carbon from meteorite into microbial biomass. This implies that meteoritic organics could have been used as a carbon source on early Earth and other habitable planets, and supports the potential for a heterotrophic metabolism in early living systems.

Figure 1

Microbial uptake of organic material from the carbonaceous chondrite Aguas Zarcas. Optical photothermal infrared (O-PTIR) spectroscopy spectra of biological samples with the amide I peaks indicated by dashed lines. The bacteria in the starting culture, Control A (containing ¹³C-labelled sodium acetate) and C (containing no carbon source) have an amide I peak associated with ¹³C (the carbonyl vibrations are at 1616 cm⁻¹). Bacteria on Aguas Zarcas and in Control B (non-labelled sodium acetate) have an amide I peak associated with ¹²C (carbonyl vibrations are at 1657 cm⁻¹).

Figure 2

Bacterial differentiation based on the stable isotope of the carbon source. Principal component analysis (PCA) of optical photothermal infrared (O-PTIR) spectroscopy spectra from 1500 to 1760 cm⁻¹ of biological samples. Principal component 1 (PC1) separates bacteria grown on a ¹²C carbon source (Bacteria on Aguas Zarcas and Control B) from bacteria grown on a ¹³C carbon source or without an external carbon source (Starting culture, Control A and Control C). See PCA loading plots in Supplementary Fig. S1.

Figure 3

Bacteria growing on the carbonaceous chondrite Aguas Zarcas. Stacked barplot of the abundance of bacterial families present in the starting culture (SC), Aguas Zarcas containing microcosms 14 days after inoculation (Aguas Zarcas), Control A (containing ¹³C-labelled sodium acetate), Control B (non-labelled sodium acetate) and Control C (containing no carbon source). Samples 1, 2 and 3 are biological replicates.