Effect of microbial growth rate on temperature and metabolic water recorded in 18O/16O ratios of PO4 in DNA

Abstract

It has been recently demonstrated that both temperature and intracellular/metabolic water are recorded by the PO4 moieties comprising the backbone of DNA in microbial cells as well as in total microbial biomass PO4 (Blake et al., 2016; Li et al., 2016). Temperature and intracellular water composition are reflected in the 18O/16O ratio of PO4 (δ18OP) in DNA (Blake et al., 2016). To determine whether the reported temperature recording by microbial DNA-PO4 could be an artifact of variable microbial growth rate, which may also vary as a function of temperature, three strains of microorganisms having distinct and different growth rate patterns between 23 and 42 °C—Pseudomonas fluorescens, Acinetobacter ADP1 and Marinobacter aquaeolei were cultured over a range of temperatures and growth rate patterns. Growth curve patterns for the different strains were distinct and growth rates increased with temperature. However, as we show here, variations in δ18OP values of DNA-PO4 did not correlate with changes in bacterial growth rates at a given temperature, and O isotope fractionations (i.e., partitioning of O isotopes) between PO4 in DNA and O in water were not significantly different between strains (<1‰). Results suggest that for some microbial strains, strain-specific growth rates could cause minor variation in δ18OP values of microbial DNA independent of temperature effects. Thus, we interpret observed trends as strain-specific, intrinsic differences in growth patterns that do not significantly overprint the recording of temperature and intracellular water O isotopic composition by PO4 comprising the backbone of DNA.