Low-substrate regulated microaerophilic behavior as a stress response of aquatic and soil bacteria

Low-substrate regulated microaerophilic behavior (LSRMB) was observed in 10 -54% of the bacteria isolated from several fresh-water lakes or ponds, subs urface soils, activated sludge, and Antarctic dry valley soils. Five Pseudo monas and two Bacillus type species showed LSRMB. A subsurface Pseudomonas jessenii strain was used as a model to show the metabolic interaction betwe en substrate and oxygen concentrations, cell band movement, and the appeara nce of unique stress lipids and proteins When the oxygen in the P, jessenii culture medium was increased from 11% to 100% saturation under atmospheric condition, the concentration of 17:0 cyclopropane fatty acid, a stress ind icator, increased five-fold, and four unique proteins were also detected. T his stress response occurred only in low-substrate media. It is our hypothe sis that LSRMB is a common but under-appreciated trait of many aquatic and soil bacteria.