As shown in Figure 4, the highest heat output by the bacterial isolates was 0.8 mW/mg protein when cultures were incubated at 30°C. The temperature of this extraordinary, microcalorimetrically determined thermogenesis corresponded with the thermographically observed increase in bacterial colony temperature. These data suggested that the increase in colony temperature at 30°C was caused by increased thermogenesis by these bacterial cells. The growth rate of this strain on LB agar was also determined from the time-dependent changes in heat output. The optimal growth temperature of this bacterium in the microcalorimeter was 33°C. These ICG-001 data indicated
that the extraordinary thermogenesis of P. putida TK1401 occurred at a suboptimal growth temperature. Figure 4 Temperature dependence of the heat output and growth rate of P. putida TK1401. Heat BMS-777607 output and growth rate were determined using a microcalorimeter. Open circles: heat output from bacterial cells; closed circles: growth rates. Results are means ± standard deviations determined from three replicates. To compare the heat production by P. putida TK1401 with the heat production by other bacteria, the heat output of P. putida KT2440 was measured. P. putida KT2440 is phylogenetically
close to P. putida TK1401; however, it did not exhibit any increase in colony temperature. The heat production by this bacterium remained nearly constant when incubated at varying temperatures (Figure 5), which indicated that the heat output of P. putida KT2440 was independent of the growth temperature. Figure 5 Temperature dependence of the heat output and growth rate of
P. putida TK2440. Heat output and growth rate were determined using a microcalorimeter. Open circles: heat output from bacterial cells; closed circles: growth rates. Results are means ± standard deviations determined from three replicates. SB-3CT In order to produce excess heat, bacteria utilize more energy than that required for their growth. To investigate the effects of varying concentrations of an energy source on thermal behavior, the colony temperature and heat production of P. putida TK1401 were measured using varying concentrations of an energy source (Table 1). Colony temperature did not increase when this bacterium was grown on 0.25× and 0.5× LB media, but it did increase when this bacterium was cultured on 1×, 2×, and 5× LB agar plates. The highest colony temperature was observed when P. putida TK1401 was grown on 5× LB medium. These data indicated that the colony temperature of P. putida TK1401 increased under energy-rich conditions. Table 1 Effects of energy source on P. putida TK1401 colony temperature Medium ΔTemperaturea Heat outputb Specific growth rateb (°C) (mW mg protein−1) (h−1) 0.25× LB medium 0.00 ± 0.00 0.62 ± 0.00 1.3 ± 0.1 0.5× LB medium 0.00 ± 0.00 0.70 ± 0.10 1.4 ± 0.1 1× LB medium 0.24 ± 0.17 0.82 ± 0.03 1.2 ± 0.0 2× LB medium 0.22 ± 0.15 0.88 ± 0.03 1.4 ± 0.