The influence of temperature on the pathways of glucose catabolism in Pseudomonas fluorescens

Glucose Catabolism in Strains of Acidophilic, Heterotrophic Bacteria

Pathways of glucose catabolism, potentially operational in six strains of obligately aerobic, acidophilic bacteria, including Acidiphilium cryptum strain Lhet2, were investigated by short-term radiorespirometry and enzyme assays. Short-term radiorespirometry was conducted at pH 3.0 with specifically labeled [ 14 C]glucose. The high rate and yield of C-1 oxidized to CO 2 indicated that the Entner-Doudoroff, pentose phosphate, or both pathways were operational in all strains. Apparent nonequivalent yields of CO 2 from C-1 and estimated CO 2 from C-4 (C-1 > C-4) were suggestive of simultaneous glucose catabolism by both pathways in all strains tested. Variation in the relative contribution of the two pathways of glucose catabolism appears to account for observed strain differences. Calculation of the actual percent pathway participation was not feasible. Enzyme assays were completed with crude extracts of glucose-grown cells to substantiate the results obtained by radiorespirometry. The key enzymes of the pentose phosphate pathway (6-phosphogluconate dehydrogenase) and the Entner-Doudoroff pathway (2-keto-3-deoxy-6-phosphogluconate aldolase and 6-phosphogluconate dehydrase) were present in all strains examined (PW2, Lhet2, KLB, OP, and QBP). However, none of the strains exhibited detectable levels of the key enzyme of the Embden-Meyerhof-Parnas pathway, 6-phosphofructokinase. All strains contained glucose-6-phosphate dehydrogenase and fructose bisphosphate aldolase. The results of the enzyme study supported the contention that the pentose phosphate and Entner-Doudoroff pathways are operational for glucose catabolism in the acidophilic heterotrophs, and that the Embden-Meyerhof-Parnas pathway is apparently absent.

Influence of Temperature Adaptation on Glucose Metabolism in a Psychrotrophic Strain of Cytophaga johnsonae

Selective enrichment of yellow-orange-pigmented, gram-negative bacteria related to Cytophaga johnsonae from lake sediment was dependent on low temperatures (ca. 5°C). However, this temperature effect was abolished when excessive amounts of dissolved organic carbon (10 mM N -acetylglucosamine) were added. A psychrotrophic freshwater isolate of C. johnsonae was used to study the physiological versatility of this group. Exponential growth rates were found to be dependent on the temperature to which the cells used as the inocula were acclimated. Glucose incorporation and respiration were also dependent upon the acclimation temperature of the inocula. Patterns of 14 CO 2 evolution obtained from position-labeled [ 14 C]glucose indicated that glucose was predominantly metabolized via the Embden-Meyerhof-Parnas pathway, which, however, was greatly reduced at 25°C when the concentration of glucose was as low as 5 μM/liter. Transport, respiration, and incorporation of glucose (0.2- to 20,000-μM/liter concentrations) into macromolecular cellular compounds were characterized by multiple K m values which were a function of substrate concentration and temperature. It appeared possible that these multiple K m values reflected the changing participation of the Embden-Meyerhof-Parnas pathway in glucose metabolism. These results may provide a physiological explanation for the selective enrichment of psychrotrophic freshwater cytophagas. Moreover, they exhibit the limits of interpreting kinetic data based on conventional heterotrophic potential measurements, especially when some complications may arise from temperature and substrate adaptations of the more versatile members of the chemoorganotrophic microflora such as C. johnsonae.

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.