THE ADENYLATE ENERGY CHARGE AND ADENOSINE PHOSPHATES AS BIOCHEMICAL INDICATORS OF PHYSIOLOGICAL STATE IN FLUCTUATING ENVIRONMENTS (ATP, BIOMASS, STRESS)

The adenylate energy charge and other adenylate ratios are often considered to reflect "growth state" and stress in bacterial and algal cultures. In an attempt to determine the advantages and limitations of using the phosphoadenylate system as an ecological tool, I examined a series of batch cultures of the bacterium Enterobacter aerogenes and the green alga Chlorella pyrenoidosa. These cultures were monitored to test the effects of changing environments on the short and long term responses of the adenylate system. The bacterial cultures were the simplest systems and underwent the least environmental fluctuations. The adenylate values for the bacterial growth curves corresponded, in general, to literature values but there was a transient decline in the adenylate energy charge during the transition from aerobic to anaerobic metabolism. Adenylates were followed in autotrophic systems during the course of growth under a 12:12 L:D cycle and also under conditions of long term stress due to lead toxicity. Under normal growth conditions adenylate ratios showed large diurnal variations, and also large variations during light-dark transitions over the entire growth curve. Chlorella cultures exposed to high concentrations of free lead ion had a reduced rate of growth as measured by cell counts and chlorophyll a determinations. This reduction of growth was not evident from adenylate concentrations or ratios, other than a transient decline in ATP during the first day, and the lack of an increase in ATP and the adenylate ratios during the light transitions relative to the unstressed cultures. The stressed cultures also had much higher ATP:chlorophyll a ratios indicating the possibility of a relatively large contribution of heterotrophic biomass in the stressed cultures.; The results indicate that point estimates of the adenylate ratios are not useful as a single ecological indicator for microbial communities subject to rapid metabolic, organismic and environmental fluctuations.