Effect of temperature on growth and protein turnover in Bacillus megaterium

Abstract

The ARRHENIUS plot of the specific growth rate p of an asporogenic mutant of Bacillus nlegaterium, growing in the range of 17-37 "C followed a straight line, whose slope was affected by the composition of the medium. The maximal p was found a t 40 "C in all media tested and decreased rapidly above 42 "C. The portion of protein degraded also followed a straight line but reached its maximal value a t 45-47 "C. I t s slope was affected substantially by the composition of the medium; the mixture of amino acids suppressed protein degradation a t temperature lower than 37 "C. The extent of the short-lived protein fraction, degraded with the half-time of about 1 h, was mostly affected by both -the temperature and the medium. The amount of proteins degraded per one biomass doubling was almost constant up to 37 "C but was affected by the composition of the medium. At higher temperatures it increased rapidly and reached values of 20-40% of pulselabelled proteins degraded per one cell cycle. The degradation of ethionine-containing proteins was similarly dependent on the temperature but the extent of proteins degraded was increased.The effect of temperature on protein synthesis and growth is inteiisively studied a t present, because temperature is considered to be an important factor regulating various biological processes (SCHLESINGER et al. 1982 (RATKOWSKY et al. 1982 and1983) tried to overcome this problem by using the square root plot.Within a narrow range around the optimal temperature (Topt, i. e. the temperature of the maximal value of p), the ARRHENIUS plot of p usually deviates from the straight line. One of the factors responsible for this deviation could be an increased protein turnover, which could result in a disharmony between protein synthesis and degradation.The effect of temperature on protein turnover in Escherichia coli was first studied by PINE (1967, 1973). He found that an increased temperature stimulated protein turnover and that the estent of protein degradation in growing and starving populations was similar a t supraoptimal temperatures. The extensive protein turnover at high temperatures might be explained by a recent observation that one of the intracellular proteinases is a heat-shock protein (PHILLIPS et al. 1984). Also in Bacillus megaterium, an increased temperature stimulated the initial rate of protein degradation during growth and sporogenesis. However, a slightly supraoptimal temperature may I ) Participant of the UNESCO Course on Modern Problems in Biology and Biotechnology.

Protein catabolism in growingBacillus megateriumduring adaptation to salt stress

“…3 were characterized by degradation constant k approximately equal to the relative degradation rate: k ∼∂ d r /∂τ ( k =−ln(1− d r )/τ∼ d r /τ; for d r <0.2). The degradation constant k 2 , which describes the degradation of long‐lived intracellular proteins (LLP) [13], was decreased by 1 M NaCl from k [0] 2 =0.032 in the control culture to k [1] 2 =0.018 in the stressed culture. This decrease represents 43% reduction in the degradation rate of long‐lived proteins.…”

“…Intracellular protein was labeled by a 10‐min pulse of L ‐[ 14 C]leucine (3.7 kBq ml −1 , 5 μM) during exponential growth in SG medium. The labeled culture was centrifuged (5 min, 10 000× g , 4°C), resuspended in fresh ice‐cold SG medium supplemented with L ‐leucine (final concentration: 2 mM) [13], divided in two equal portions, and placed on a water bath shaker (35°C). After a 1‐min temperature equilibration of the resuspended culture, the salt stress was applied in one half of the population.…”

Protein catabolism in growing Bacillus megaterium during adaptation to salt stress

“…The labeled culture was centrifuged (5 min, 10 000Ug, 4³C), resuspended in fresh icecold SG medium supplemented with L-leucine (¢nal concentration : 2 mM) [13], divided in two equal portions, and placed on a water bath shaker (35³C). After a 1-min temperature equilibration of the resuspended culture, the salt stress was applied in one half of the population.…”

“…3 were characterized by degradation constant k approximately equal to the relative degradation rate : kWDd r /Dd (k = 3ln(13d r )/dWd r /d; for d r 6 0.2). The degradation constant k 2 , which describes the degradation of long-lived intracellular proteins (LLP) [13], was decreased by 1 M NaCl from k[0] 2 = 0.032 in the control culture to k[1] 2 = 0.018 in the stressed culture. This decrease represents 43% reduction in the degradation rate of long-lived proteins.…”

“…Furthermore, degradation kinetics of the LLP was the only ¢rst-order degradation kinetics noticed in the control culture. Proteins with half-life shorter than 1 h are called short-lived proteins (SLP) [13]. The relative size of the ostensible`fraction' they form can be read from the intercept of the LLP degradation line with the zero time ordinate in Fig.…”