Poly- β -Hydroxybutyrate Accumulation as a Measure of Unbalanced Growth of the Estuarine Detrital Microbiota

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Abstract
The procaryotic endogenous storage material poly- β -hydroxybutyrate (PHB) can be induced to accumulate in the estuarine detrital microbiota under conditions which suggest unbalanced growth, such as limitation of a critical factor(s) in the presence of carbon and energy sources. Changes in PHB-to-lipid phosphate ratios detected in field samples can be mimicked in the laboratory with common estuarine stresses. Acute anoxia or low pH induces conditions of no growth with depression of both the synthesis and catabolism of PHB without change in the lipid phosphate. Balanced growth induced by nutrients increases the lipid phosphate, depresses PHB synthesis, and stimulates PHB catabolism, resulting in a low ratio of PHB to lipid phosphate. Unbalanced growth induced to a small extent by high salinity or much more readily by dark upland runoff water results in rapid accumulation of PHB and slowing of PHB catabolism with little change in lipid phospate. Unbalanced growth conditions result in high PHB-to-lipid phosphate ratios in the detrital microbiota.