Growth of Thiobacillus novellus on mixed substrates (mixotrophic growth)

Abstract

In a mixotrophic environment, Thiobacillus novellus concurrently utilized glucose and thiosulfate but showed no stimulation of growth rate or yield. In most mixotrophic environments examined, the growth rate was lower than the heterotrophic growth rate, the extent of tbe decrease depending on the concentration and relative proportion of thiosulfate and glucose in the medium. Both thiosulfate and glucose were degraded to their most oxidized products in mixotrophic medium, yet the biomass production in this medium was comparable to that found in heterotrophic medium containing glucose alone at the corresponding concentration. It was postulated that in mixotrophic medium the oxidation of thiosulfate, glucose, or partially that of both was uncoupled from energy generation. These results differ in many respects from those reported earlier by LeJohn et al. (J. Bacteriol. 94: 1484(J. Bacteriol. 94: -1491(J. Bacteriol. 94: , 1967; experiments designed to exactly duplicate some of the growth conditions employed by these workers did not resolve the discrepancy.Thiobacillus novellus, like other facultative chemolithotrophs, possesses the unique potential for autotrophic as well as heterotrophic growth. Since in nature these bacteria are likely to encounter the heterotrophic and autotrophic growth substrates simultaneously, it is of considerable interest to determine whether they are capable of mixotrophic growth, i.e., growth during which organic and inorganic substrates are concurrently utilized (4, 11). Mixotrophy in T. novellus has been previously studied by LeJohn et al. (2). These workers showed that the presence of glucose in the medium caused a complete inhibition of thiosulfate utilization by this bacterium and that the rates of growth and glucose utilization in thiosulfate-glucose medium were identical to those found in glucose medium. They also showed that in thiosulfate-glutamate medium, the organism used both substrates concomitantly, but they did not report on whether the growth rate, yield, or both were higher in the mixotrophic medium compared to heterotrophic glutamate medium.Our studies, however, revealed a very different picture, and in this paper we present our findings concerning the comparative growth patterns of T. novellus in autotrophic, heterotrophic, and mixotrophic environments. MATERIALS AND METHODSOrganism and growth procedures. The ATCC type strain of T. novellus (no. 8093) was used throughout; the experiment presented in Fig. 2 was also carried out by using our laboratory strain (6), with very similar results. The basal medium employed was similar to that previously described for T. novellus (6) except that FeCl3.6H20 was omitted, and a different trace elements solution (16), which contained a higher amount of iron, was used. There is no agreement on the pH for the cultivation of T. novellus, values ranging between 6.8 and 9.0 having been used (2,6,13,15). Our control experiments, in which the culture pH was maintained constant during growth by means of a pH stat (see below), showed that the...

Pressure effects on sulfur‐oxidizing activity of Thiobacillus thioparus

“…We obtained the highest growth at 5 g.l −1 of thiosulfate (31.6 mM). This agrees well with the observations of Perez and Matin (1980) who studied the growth of the closely related species Thiobacillus novellus on mixotrophic media, using thiosulfate and/or glucose at different concentrations. They observed that the use of thiosulfate as an electron donor decreases the growth rate of T. novellus at any concentration tested and concluded to a negative correlation between initial thiosulfate concentration and growth rate although T. novellus utilized thiosulfate.…”

Regulation of Glucose Transport and Metabolism in Thiobacillus novellus

“…Under such conditions, energy overproduction could become a serious problem if unrestricted use of the two substrates were to take place. These considerations suggest a rationale for the regulatory strategy employed by T. novellus in a mixotrophic environment, i.e., a decrease in the rate of substrate utilization and a partial uncoupling of substrate oxidation from energy generation (10). We may infer that this strategy is designed to protect the organism from excessive energy generation in an environment containing a superabundance of energy substrates.…”

“…Heterotrophic, autotrophic, and mixotrophic media used were obtained by supplementing the basal medium (7,9) with 0.4% glucose, 1% Na2S203, or both, respectively. The organism was grown with automatic pH control exactly as described previously (10).…”

“…The column was first eluted with 5 ml of water, 10 equal-volume fractions (0.5 ml each) were collected by using an LKB Instruments Inc. (Rockville, Md.) fraction collector, the subsequent elution was with 5 ml (0.5 M) of i39 on October 3, 2020 by guest http://jb.asm.org/ Downloaded from 640 MATIN, SCHLEISS, AND PEREZ ammonium formate (0.2 M)-formic acid solution, 10 equal-volume samples being again collected. The fractions, which were collected directly in scintillation vials, were counted in a Searle ISOCAP Scintillation Counter after mixing with 10 ml of Bray scintillation fluid.…”

Comparison of Autotrophic and Mixotrophic Biofilters for H 2 S Removal

“…Hence, these bacteria are apparently adaptable to different environments, i.e., autotrophic, heterotrophic, or mixotrophic conditions (Matin 1978). Studies have shown adaptive physiologic/metabolic response of T. novellus to mixotrophic environments (Leefeldt and Matin 1980;Perez and Matin 1980), but little engineering information, such as desired control mechanisms, and proper design and maintenance of biofilters for H 2 S removal is available.…”