Occurrence of the methylglyoxal bypass in halophilic Archaea

Redox and Thiols in Archaea

Low molecular weight (LMW) thiols have many functions in bacteria and eukarya, ranging from redox homeostasis to acting as cofactors in numerous reactions, including detoxification of xenobiotic compounds. The LMW thiol, glutathione (GSH), is found in eukaryotes and many species of bacteria. Analogues of GSH include the structurally different LMW thiols: bacillithiol, mycothiol, ergothioneine, and coenzyme A. Many advances have been made in understanding the diverse and multiple functions of GSH and GSH analogues in bacteria but much less is known about distribution and functions of GSH and its analogues in archaea, which constitute the third domain of life, occupying many niches, including those in extreme environments. Archaea are able to use many energy sources and have many unique metabolic reactions and as a result are major contributors to geochemical cycles. As LMW thiols are major players in cells, this review explores the distribution of thiols and their biochemistry in archaea.

Methylglyoxal synthase regulates cell elongation via alterations of cellular methylglyoxal and spermidine content in Bacillus subtilis

Methylglyoxal regulates cell division and differentiation through its interaction with polyamines. Loss of their biosynthesizing enzyme causes physiological impairment and cell elongation in eukaryotes. However, the reciprocal effects of methylglyoxal and polyamine production and its regulatory metabolic switches on morphological changes in prokaryotes have not been addressed. Here, Bacillus subtilis methylglyoxal synthase (mgsA) and polyamine biosynthesizing genes encoding arginine decarboxylase (SpeA), agmatinase (SpeB), and spermidine synthase (SpeE), were disrupted or overexpressed. Treatment of 0.2mM methylglyoxal and 1mM spermidine led to the elongation and shortening of B. subtilis wild-type cells to 12.38±3.21μm (P<0.05) and 3.24±0.73μm (P<0.01), respectively, compared to untreated cells (5.72±0.68μm). mgsA-deficient (mgsA^-) and -overexpressing (mgsA^OE) mutants also demonstrated cell shortening and elongation, similar to speB- and speE-deficient (speB^- and speE^-) and -overexpressing (speB^OE and speE^OE) mutants. Importantly, both mgsA-depleted speB^OE and speE^OE mutants (speB^OE/mgsA^- and speE^OE/mgsA^-) were drastically shortened to 24.5% and 23.8% of parental speB^OE and speE^OE mutants, respectively. These phenotypes were associated with reciprocal alterations of mgsA and polyamine transcripts governed by the contents of methylglyoxal and spermidine, which are involved in enzymatic or genetic metabolite-control mechanisms. Additionally, biophysically detected methylglyoxal-spermidine Schiff bases did not affect morphogenesis. Taken together, the findings indicate that methylglyoxal triggers cell elongation. Furthermore, cells with methylglyoxal accumulation commonly exhibit an elongated rod-shaped morphology through upregulation of mgsA, polyamine genes, and the global regulator spx, as well as repression of the cell division and shape regulator, FtsZ.

N5 ,N10 -methylenetetrahydromethanopterin reductase from Methanocaldococcus jannaschii also serves as a methylglyoxal reductase

In Methanocaldococcus jannaschii, methylglyoxal (MG) is required for aromatic amino acid biosynthesis. Previously, the reduction of MG to lactaldehyde in Methanocaldococcus jannaschii cell extracts using either NADPH or F₄₂₀ H₂ was demonstrated; however, the enzyme responsible was not identified. Using NADPH as the reductant, the unknown enzyme was purified from cell extracts of Methanocaldococcus jannaschii and determined to be the F₄₂₀ -dependent N⁵ ,N¹⁰ -methylenetetrahydromethanopterin reductase (Mer). Here, we report that the recombinantly overexpressed Mer is able to use NADPH and MG (K_M of 1.6 and 1.0 mm, respectively) to produce lactaldehyde. Additionally, Mer does not catalyze the reduction of MG to lactaldehyde in the presence of reduced Fo, the precursor of F₄₂₀ .

Glycerol metabolism of haloarchaea

Haloarchaea are heterotrophic members of the Archaea that thrive in hypersaline environments, often feeding off the glycerol that is produced as an osmolyte by eucaryotic Dunaliella during primary production. In this study we analyzed glycerol metabolism genes in closed genomes of haloarchaea and examined published data describing the growth properties of haloarchaea and experimental data for the enzymes involved. By integrating the genomic data with knowledge from the literature, we derived an understanding of the ecophysiology and evolutionary properties of glycerol catabolic pathways in haloarchaea.

Carbonyl Stress in Bacteria: Causes and Consequences

Pathways of synthesis of the α-reactive carbonyl compound methylglyoxal (MG) in prokaryotes are described in this review. Accumulation of MG leads to development of carbonyl stress. Some pathways of MG formation are similar for both pro- and eukaryotes, but there are reactions specific for prokaryotes, e.g. the methylglyoxal synthase reaction. This reaction and the glyoxalase system constitute an alternative pathway of glucose catabolism - the MG shunt not associated with the synthesis of ATP. In violation of the regulation of metabolism, the cell uses MG shunt as well as other glycolysis shunting pathways and futile cycles enabling stabilization of its energetic status. MG was first examined as a biologically active metabolic factor participating in the formation of phenotypic polymorphism and hyperpersistent potential of bacterial populations. The study of carbonyl stress is interesting for evolutionary biology and can be useful for constructing highly effective producer strains.

Methylglyoxal and glucose metabolism: a historical perspective and future avenues for research

Methylglyoxal, an alpha-oxoaldehyde discovered in the 1880s, has had a hectic scientific career, at times being considered of fundamental importance and at other times viewed as playing a very subordinate role. Much has been learned about methylglyoxal, but the function of its production in the metabolic machinery is still unknown. This paper gives an overview of the changing role of methylglyoxal from a historical aspect and arrives at the conclusion that methylglyoxal is tightly bound to glycolysis from an evolutionary perspective, its production therefore being inevitable. It is not situated in the main stream of the glycolytic sequence, but a role can be assigned to its production in the phosphate supply of operating glycolysis in some prokaryotes and yeast under conditions of phosphate deficiency. This function is presumed to be performed by the enzyme methylglyoxal synthase, which is specialized for the conversion of dihydroxyacetone-phosphate to methylglyoxal. However, it is still unknown whether this enzyme and this kind of regulation also exist in animals.

Identification of lactaldehyde dehydrogenase in Methanocaldococcus jannaschii and its involvement in production of lactate for F420 biosynthesis

One of the early steps in the biosynthesis of coenzyme F(420) in Methanocaldococcus jannaschii requires generation of 2-phospho-L-lactate, which is formed by the phosphorylation of L-lactate. Preliminary studies had shown that L-lactate in M. jannaschii is not derived from pyruvate, and thus an alternate pathway(s) for its formation was examined. Here we report that L-lactate is formed by the NAD(+)-dependent oxidation of l-lactaldehyde by the MJ1411 gene product. The lactaldehyde, in turn, was found to be generated either by the NAD(P)H reduction of methylglyoxal or by the aldol cleavage of fuculose-1-phosphate by fuculose-1-phosphate aldolase, the MJ1418 gene product.

Characterization of methylglyoxal synthase from Clostridium acetobutylicum ATCC 824 and its use in the formation of 1, 2-propanediol

A gene encoding a putative 150-amino-acid methylglyoxal synthase was identified in Clostridium acetobutylicum ATCC 824. The enzyme was overexpressed in Escherichia coli and purified. Methylglyoxal synthase has a native molecular mass of 60 kDa and an optimum pH of 7.5. The Km and Vmax values for the substrate dihydroxyacetone phosphate were 0.53 mM and 1.56 mmol min(-1) microgram(-1), respectively. When E. coli glycerol dehydrogenase was coexpressed with methylglyoxal synthase in E. coli BL21(DE3), 3.9 mM 1,2-propanediol was produced.

Pathways for utilization of carbon reserves in Desulfovibrio gigas under fermentative and respiratory conditions

The sulfate-reducing bacterium Desulfovibrio gigas accumulates large amounts of polyglucose as an endogenous carbon and energy reserve. In the absence of exogenous substrates, the intracellular polysaccharide was utilized, and energy was conserved in the process (H. Santos, P. Fareleira, A. V. Xavier, L. Chen, M.-Y. Liu, and J. LeGall, Biochem. Biophys. Res. Commun. 195:551-557, 1993). When an external electron acceptor was not provided, degradation of polyglucose by cell suspensions of D. gigas yielded acetate, glycerol, hydrogen, and ethanol. A detailed investigation of the metabolic pathways involved in the formation of these end products was carried out, based on measurements of the activities of glycolytic enzymes in cell extracts, by either spectrophotometric or nuclear magnetic resonance (NMR) assays. All of the enzyme activities associated with the glycogen cleavage and the Embden-Meyerhof pathway were determined as well as those involved in the formation of glycerol from dihydroxyacetone phosphate (glycerol-3-phosphate dehydrogenase and glycerol phosphatase) and the enzymes that catalyze the reactions leading to the production of ethanol (pyruvate decarboxylase and ethanol dehydrogenase). The key enzymes of the Entner-Doudoroff pathway were not detected. The methylglyoxal bypass was identified as a second glycolytic branch operating simultaneously with the Embden-Meyerhof pathway. The relative contribution of these two pathways for polyglucose degradation was 2:3. 13C-labeling experiments with cell extracts using isotopically enriched glucose and 13C-NMR analysis supported the proposed pathways. The information on the metabolic pathways involved in polyglucose catabolism combined with analyses of the end products formed from polyglucose under fermentative conditions provided some insight into the role of NADH in D. gigas. In the presence of electron acceptors, NADH resulting from polyglucose degradation was utilized for the reduction of sulfate, thiosulfate, or nitrite, leading to the formation of acetate as the only carbon end product besides CO2. Evidence supporting the role of NADH as a source of reducing equivalents for the production of hydrogen is also presented.

Diversity of lactate metabolism in halophilic archaea

D-Lactate is readily used as a substrate for the growth of species of halophilic archaea belonging to the genera Haloferax and Haloarcula. L-Lactate was used by Haloferax species (Haloferax volcanii, Haloferax mediterranei) only when a substantial concentration of the D-isomer was also present in the medium. On the enzymatic level, considerable diversity was found in the lactate metabolism of the different representatives of the Halobacteriaceae. At least three types of lactate dehydrogenases were detected in halophilic archaea. A high level of activity of an NAD-linked enzyme was present constitutively in Haloarcula species, and a low level of activity was also detected in Haloferax mediterranei. NAD-independent lactate dehydrogenases, oxidizing L-lactate and D-lactate with 2,6-dichlorophenol-indophenol as electron acceptor, were detected in all nine species tested, but L-lactate dehydrogenase activity in Halobacterium species was very low, and Haloarcula species, which possess a high level of activity of NAD-linked lactate dehydrogenase, showed very low activities of both NAD-independent D- and L-lactate dehydrogenase. An inducible lactate racemase, displaying an unusually high pH optimum, was found in Haloferax volcanii. Lactate racemase activity was found constitutively in Haloarcula species, but no activity was detected in Halobacterium species and in Haloferax mediterranei.