DNA ATP RATIOS IN MARINE MICROALGAE AND BACTERIA - IMPLICATIONS FOR GROWTH-RATE ESTIMATES BASED ON RATES OF DNA-SYNTHESIS/

DNA:ATP and carbon:DNA (C:DNA) ratios were measured in a total of 14 s pecies of marine microalgae and bacteria. Comparison of several DIVA a ssay methods with results obtained with cultures uniformly labeled wit h P-33 indicated that by far the most accurate results were obtained u sing diaminobenzoic acid (DABA) or diphenylamine, with DABA having the highest precision. Both the Hoechst and DAPI methods seriously undere stimated DNA concentrations in algal cultures. Average DNA:ATP ratios in the algal and bacterial cultures were 17 and 34 by weight, respecti vely, with almost all values lying in the range of 10-40. DNA:ATP rati os in the microalgae showed no correlation with growth conditions but varied by about a factor of 3 among species. C:DNA ratios for individu al species of microalgae and bacteria ranged from 21 to 155 by weight and averaged 50 for the microalgae and bacteria taken together. Growth rates of microalgal species grown in cyclostats were estimated to wit hin 8% of dilution rates when calculated from the uptake of H-3-adenin e and the DNA:ATP ratio of the species. Use of the H-3-adenine method for estimating microalgal growth rates in the field may thus be a usef ul tool for investigating the physiology of microalgae in nature.