Biochemical Basis of Obligate Autotrophy in Blue-Green Algae and Thiobacilli

Abstract

Differential rates of incorporation of sugars, organic acids, and amino acids during autotrophic growth of several blue-green algae and thiobacilli have been determined. In obligate autotrophs (both blue-green algae and thiobacilli), exogenously furnished organic compounds make a very small contribution to cellular carbon; acetate, the most readily incorporated compound of those studied, contributes about 10% of newly synthesized cellular carbon. In Thiobacillus intermedius, a facultative chemoautotroph, acetate contributes over 40% of newly synthesized cellular carbon, and succinate and glutamate almost 90%. In the obligate autotrophs, carbon from pyruvate, acetate, and glutamate is incorporated into restricted groups of cellular amino acids, and the patterns of incorporation in all five organisms are essentially identical. These patterns suggest that the tricarboxylic acid cycle is blocked at the level of a-ketoglutarate oxidation. Enzymatic analyses confirmed the absence of a-ketoglutarate dehydrogenase in the obligate autotrophs, and also revealed that they lacked reduced nicotinamide adenine dinucleotide oxidase, and had extremely low levels of malic and succinic dehydrogenase. These enzymatic deficiencies were not manifested by the two facultative chemoautotrophs examined. On the basis of the data obtained, an interpretation of obligate autotrophy in both physiological and evolutionary terms has been developed.

Cellular differentiation and the NtcA transcription factor in filamentous cyanobacteria

“…Consistently with its putative signaling role, determinations of 2-oxoglutarate levels in different cyanobacteria incubated under different conditions of nitrogen supply have indicated accumulation of 2-oxoglutarate under N-limiting conditions [22][23][24][25]. Because cyanobacteria lack 2-oxoglutarate dehydrogenase [26], the main metabolic role of 2-oxoglutarate in these organisms is incorporation of nitrogen through the glutamine synthetase-glutamate synthase cycle [27], which positions 2-oxoglutarate at the link of C and N metabolisms.…”

Biochemical and molecular characterization of the NAD+-dependent isocitrate dehydrogenase from the chemolithotroph Acidithiobacillus thiooxidans

“…It has been reported that the NAD-ICDH gene of Streptococcus mutans is encoded in an operon with citrate synthase and aconitase genes and is related to glutamate synthesis [14]. Although A. thiooxidans ICDH also can contribute to glutamate biosynthesis [8], the structure of the icd operon containing the putative succinyl-CoA synthetase gene is di¡erent from that of the icd operon of S. mutans. The complete analysis of the operon may reveal the physiological role of the 2-oxoglutarate-de¢cient TCA cycle containing NAD-ICDH of A. thiooxidans.…”

“…Some chemolithotrophs, that possess a 2-oxoglutarate dehydrogenase-de¢cient TCA cycle, contain NAD þ -dependent ICDH (NAD-ICDH) activity [7,8], though most bacteria contain NADP þ -dependent ICDH (NADP-ICDH) activity. It has been reported that the incomplete TCA cycle functions for CO 2 ¢xation [9] as well as glutamate synthesis [8]. Thus, the bacterial NAD-ICDH is expected to be metabolically and structurally (especially the coenzyme recognition) unique, but little is known about the properties of the enzyme.…”

The Biochemistry of Nitrifying Microorganisms

“…The poly-P-hydroxybutyrate fraction had almost 5 yo of the total 14C label recovered. This polymer has been shown to be an important constituent in the Nitrobacter cell functioning as an energy reserve (Tobback & Laudelout, 1965).…”

“…The debate on what constitutes the distinctive characteristics of the autotrophic mode of life continues and this now embraces not only nitrifying bacteria but also the sulphur oxidizing thiobacilli and the photosynthetic autotrophically grown, blue-green algae. Ever since the report of Smith, London & Stanier (1967) that several obligate autotrophs, blue-green algae and chemosynthetic bacteria, lacked a-ketoglutarate dehydrogenase and NADH oxidase many workers have not confirmed this evidence. Pearce & Carr (1967) noted the absence of the dehydrogenase from the blue-green alga Anabaena vulgaris, suggesting an incomplete tricarboxylic acid cycle.…”