Imperfect Asymmetry of Life: Earth Microbial Communities Prefer D-Lactate but Can Use L-Lactate Also

Abstract

Asymmetrical utilization of chiral compounds has been sought on Mars as evidence for biological activity. This method was recently validated in glucose. Earth organisms utilize D-glucose, not L-glucose, a perfect asymmetry. In this study, we tested the method in lactate and found utilization of both enantiomers. Soil-, sediment-, and lake-borne microbial communities prefer D-lactate but can consume L-lactate if given extra time to acclimate. This situation is termed imperfect asymmetry. Future life-detection mission investigators need to be aware of imperfect asymmetry so as not to miss relatively subtle signs of life.

Multidisciplinary approach of the hyperarid desert of Pampas de La Joya in southern Peru as a new Mars-like soil analog

“…However, the same group also showed that this stereo selectivity is not applicable to all carbohydrates. So, in contrast to glucose, D-and L-lactate can be consumed after a short time to "bacteria acclimatization" (Moazeni et al, 2010). On other hand, Quinn et al (2007), conducted simulated LR experiments in Yungay soils and also found an achiral uptake of the nutrients.…”

The Ladder of Life Detection

“…Just like a repeating charge, chirality sets the geometry (conformation) of a polymer, helping preserve its structure even if another part of the molecule is affected. Most of life on Earth uses D-sugars and L-amino acids (Bada et al, 1998; Blackmond, 2011 ), although there are rare exceptions (Newton, 1970 ; Lam et al, 2009 ; Martinez-Rodriguez et al, 2010 ; Moazeni et al, 2010 ; Zhou et al, 2012 ; Zhang and Sun, 2014 ); these do not prevent the use of chirality as a possible biosignature. Abiotic enantiomeric excesses up to 20% have been measured in meteorite samples (Cronin and Pizzarello, 1997 ; Glavin and Dworkin, 2009 ).…”

Levorotatory carbohydrates and xylitol subdue Streptococcus mutans and Candida albicans adhesion and biofilm formation

“…As mentioned above, akin to adhesion experiments, a reversible mechanism of competitive inhibition of specific enzymes in the metabolic pathway of the dextrorotatory carbohydrates may explain the intermediate values for biofilm formation we noted in both species with the raceme solutions . Future studies are, nevertheless, needed to explore this hypothesis.…”

“…Levorotatory sugars led to the lowest levels of biofilm formation in both species, implying that the two tested microorganisms had difficulty in metabolizing these nutrients. In a previous study, Moazeni et al described the dissimilar ability of different microorganisms to selectively metabolize carbohydrates. It is intriguing in evolutionary terms, why some microorganisms, more than others are naturally selected to metabolize only certain enantiomeric forms of carbohydrates .…”

“…Interestingly, some carbohydrates are known to interfere with microbial adhesion and biofilm formation. In particular, levorotatory carbohydrates ( l ‐carbohydrates) are metabolized to a significantly lesser degree by microbial enzymatic systems than the corresponding dextrorotatory forms ( d ‐carbohydrates) . Moreover, some polyols cannot be metabolized by most of dental plaque microorganisms .…”