In SituMicrobial Detection in Mojave Desert Soil Using Native Fluorescence

Abstract

We report on the use of a portable instrument for microbial detection in the Mojave Desert soil and the potential for its use on Mars. The instrument is based on native fluorescence and employs four excitation wavelengths combined with four emission wavelengths. A soil dilution series in which known numbers of Bacillus subtilis spores were added to soil was used to determine the sensitivity of the instrument. We found that the fluorescence of the biological and organic components of the desert soil samples studied can be as strong as the fluorescence of the mineral component of these soils. Using the calibration derived from B. subtilis spores, we estimated that microbial content at our primary sampling site was 10(7) bacteria per gram of soil, a level confirmed by phospholipid fatty acid analysis. At a nearby site, but in a slightly different geological setting, we tested the instrument's ability to map out microbial concentrations in situ. Over a ∼50 m diameter circle, soil microbial concentrations determined with the B. subtilis calibration indicate that the concentrations of microorganisms detected varies from 10(4) to 10(7) cells per gram of soil. We conclude that fluorescence is a promising method for detecting soil microbes in noncontact applications in extreme environments on Earth and may have applications on future missions to Mars.

Stress-Tolerance and Taxonomy of Culturable Bacterial Communities Isolated from a Central Mojave Desert Soil Sample

“…The total number of prokaryotes and numbers of culturable bacteria revealed in soil studied are in accordance with the previously obtained data for the soils of other regions of the Mojave Desert [32,36,37]. Different cell numbers observed in different regions of the desert could be caused by the high heterogeneity of soil composition and the high heterogeneity of soil resources in this desert, as well as past and current climatic conditions or plant associations which influence bacterial Strains of the community isolated on CM medium at 25 • C (33% of strains) were resistant to the presence of 10% magnesium perchlorate.…”

“…Using the methods of native fluorescence and fatty acid analysis of phospholipids, the number of bacterial cells was found to be 10 7 bacteria per gram of soil [35,36]. Studies of culturable bacteria of this desert are less common, compared to culture-independent methods.…”

Racemization in Reverse: Evidence that D-Amino Acid Toxicity on Earth Is Controlled by Bacteria with Racemases

“…The contribution of DAAOs cannot be ruled out, but is likely minor, for two reasons. First, yeasts and fungi are present in these soils in minor numbers [34]–[36]. Second, DAAOs are induced by D-enantiomers, not L-enantiomers [21], [24], [37]–[40].…”

An instrument design for non-contact detection of biomolecules and minerals on Mars using fluorescence

“…These instruments are aimed at detecting microbes by adding a fluorescing reagent [17] or within a fairly uniform, low fluorescence material such as ice [18,19] and in the ocean [20]. Work has begun to look at native fluorescence in soil as well [21]. These instruments provide a fluorescent method for detecting biomolecules and chemical organics.…”

“…In addition other biomolecules can be detected and identified using fluorescence as shown for ATP and NADH in Table 1 . For a more detailed list of fluorescence of common biomolecules and detection of biomolecules by fluorescence refer to the Additional file 1 which is based on Smith et al [ 29 ].…”