EFFECT OF SUBSTRATE AND CELL-SURFACE HYDROPHOBICITY ON PHOSPHATE UTILIZATION IN BACTERIA

We measured the rates of utilization of hydrophobic and hydrophilic ph osphate compounds in gram-negative bacteria with different surface hyd rophobicities, isolated from wetland habitats, Three hydrophobic and t wo hydrophilic bacterial species, were selected for study by measuring cell adherence to hydrocarbons. The bacteria were grown. under phosph orus-limited conditions with P-i, hydrophilic beta-glycerophosphate, o r hydrophobic phosphatidic acid as the phosphate source. Hydrophilic b acteria grew most rapidly on P-i, followed by beta-glycerophosphate. P hosphatidic acid did not support growth or did so at a much later time (40 h) than did the other phosphate treatments. Although all hydropho bic species grew well on these substrates, the rate of growth of two A cinetobacter baumannii isolates on phosphatidic acid exceeded the rate of growth on phosphate or beta-glycerophosphate. A membrane phospholi pid and lipopolysaccharide were used as a source of phosphorus by hydr ophobic species, whereas hydrophilic species could not use the membran e phospholipids and used lipopolysaccharide to a lesser extent, Beside s hydrophobic interaction between cells and substrate, phosphatase act ivity, which was cell bound in hydrophilic species but 30 to 50% unbou nd in hydrophobic species, affected cell growth. Dialyzed culture supe rnatant containing phosphatase from hydrophobic species increased the phosphate availability to hydrophilic species. Additionally, cellular extracts from a hydrophilic species, when added to hydrophilic cells, permitted growth on hydrophobic phosphate sources. Naturally occurring amphiphilic humic acids affected the utilization of P-i and beta-glyc erophosphate in bacteria with hydrophilic surfaces but did not affect hydrophobic bacteria. Our results indicate that hydrophobic phosphate sources can be used by bacteria isolated from aquatic environments as the sole phosphorus source for growth. This utilization, in part, appe ars to be related to cell surface hydrophobicity and extracellular enz yme production.