Aging and Respiration in the Marine Bacteria, Pseudomonas nautica

Abstract

The effect of aging and substrate limitation on respiratory metabolism was comparedd during two different physiological states of acetate-grown Pseudomonas nautica cultures. In this study, we analyze 30 h and 170 h time-course experiments in which cell-protein, acetate, respiratory CO2 production (RCCO2) and respiratory O2 consumption (RO2) were measured and respiratory quotients (RQs= RCO2/RO2) were calculated. RQs are commonly used as a constant, over a range of 0.8 to 1, in ocean studies, to evaluate many factors such as the autotrophic-heterotrophic nature of the ocean and the vertical carbon flux. In the laboratorry we observed that RQ can rise an order of magnitude above this constant. In the early well-fed growth sttage of our short term experiment RO2 rates were higher than RCO2 rates (RQ=0,4), nevertheless in senescence and under limited carbon-substrate conditions this ratio shifted up to 9,6. We conclude that the culture aging and substrate limitations affected the RQ of P. nautica culture, in a way that the use of a constant RQ for biological calculations is inadvisable. Therefore, these results argue that oceanic measurements which are influenced by bacterial metabolism and nutrient limitation need to be reconsidered in face of this strong RQ variability. Lastly, because our microbial biomass remained relatively constant in face of nutrient-limitation, our results suggest a link between substrate deprivation, senescence and possibly, longevity.