Effects of sudden temperature shifts on pure cultures of four strains of freshwater bacteria.

Three psychrotrophic and one mesophilic strains were isolated from winter water samples of different freshwater biotopes and identified asCytophaga johnsonae (C-21),Cytophaga sp. (M-17),Pseudomonas fluorescens (KD), andEnterobacter cloacae (BS-2). Temperature shift-up experiments with emphasis on low temperatures were carried out with aerated pure batch cultures in glucose mineral medium. The effects of sudden temperature increases on growth rates and substrate conversion were investigated. All three psychrotrophic strains in the temperature increase experiments at low temperatures showed differing reactions within the linear zone of the Arrhenius plot. TheC. johnsonae (C-21) shift-up cultures adjusted the growth rate immediately to the rate of the temperature adapted cultures, whereasCytophaga sp. (M-17) shift-up cultures showed a lower andP. fluorescens (KD) a higher growth rate. The mesophilicE. cloacae (BS-2), likeC. johnsonae (C-21), adjusted immediately to the new growth rate. Substrate conversion increased in all experiments immediately after the shift-up. The extracellular substrate conversion byP. fluorescens (KD) of glucose to gluconate and 2-ketogluconate was particularly affected by the sudden temperature increase.