Intestinal luminal putrescine is produced by collective biosynthetic pathways of the commensal microbiome

The intestinal microbiome produces various metabolites that may harm or benefit the host. However, the production pathways of these metabolites have not been well characterised. The polyamines putrescine and spermidine required for physiological process are also produced by intestinal microbiome. The production and release of these polyamines by microbiome are poorly understood, though we have confirmed that intestinal bacteria produced putrescine from arginine. In this study, we characterised polyamine synthesis by analysing the collective metabolic functions of the intestinal microbiome. In particular, we analysed polyamines and their intermediates in faecal cultures, as well as the colonic contents of rats injected with isotope-labelled arginine through a colon catheter, using mass spectrometry. Isotope-labelled putrescine was detected in faecal cultures and colonic contents of rats injected with isotope-labelled arginine. Putrescine is produced through multiple pathways, and its extracellular intermediates are exchanged between bacterial species. Additionally, we demonstrated that the collective metabolic pathway depends on a complex exchange of metabolites released into the colonic lumen. This study demonstrates the existence of putrescine biosynthetic pathways based on the collective metabolic functions of the intestinal microbial community. Our findings provide knowledge to manipulate the levels of intestinal microbial products, including polyamines, that may modulate host health.

Influence of arginine on the growth, arginine metabolism and amino acid consumption profiles of Streptococcus thermophilus T1C2 in controlled pH batch fermentations

AIMS

The aim of this study was to elucidate the effect of arginine on the growth, arginine metabolism and amino acid consumption profiles of Streptococcus thermophilus T1C2.

METHODS AND RESULTS

The growth kinetics, intracellular pH, extracellular osmotic pressure, expression of key genes in the arginine metabolism pathway and amino acid consumption profiles were analysed in chemically defined medium with different initial arginine concentrations. The results showed that arginine stimulated the growth of Strep. thermophilus T1C2 under low intracellular pH and high extracellular osmotic pressure. The expression of key genes in the arginine degradation pathway indicated that arginine relieved the drop in the intracellular pH by consuming protons and generating NH3 . Additionally, the results showed that arginine degradation did not occur via the arginine deiminase pathway but through the arginine decarboxylase-urease pathway. Furthermore, the utilization efficiency of amino acids was improved in the presence of arginine.

CONCLUSIONS

Arginine improved the growth of Strep. thermophilus due to protecting Strep. thermophilus against intracellular acid stress, which was revealed at the transcriptional level of key genes. This study showed that the acid resistance of Strep. thermophilus was achieved through the arginine decarboxylase-urease pathway.

SIGNIFICANCE AND IMPACT OF THE STUDY

The arginine-stimulated growth of Strep. thermophilus improved the utilization efficiency of amino acids and reduced nitrogen waste, which could be useful for the optimization of cultivation media.

Overexpression, purification, crystallization and preliminary structural studies of catabolic ornithine transcarbamylase from Lactobacillus hilgardii

The catabolic ornithine transcarbamylase (cOTC; EC 2.1.3.3) from the lactic acid bacteria Lactobacillus hilgardii is a key protein involved in the degradation of arginine during malolactic fermentation. cOTC containing an N-terminal His6 tag has been overexpressed in Escherichia coli, purified and crystallized under two different experimental conditions using the hanging-drop vapour-diffusion method. Crystals obtained from a solution containing 8% (w/v) PEG 4000, 75 mM sodium acetate pH 4.6 belong to the trigonal space group P321 and have unit-cell parameters a = b = 157.04, c = 79.28 A. Conversely, crystals grown in 20% (v/v) 2-methyl-2,4-pentanediol, 7.5% (w/v) PEG 4000, 100 mM HEPES pH 7.8 belong to the monoclinic space group C2 and have unit-cell parameters a = 80.06, b = 148.90, c = 91.67 A, beta = 100.25 degrees. Diffraction data were collected in-house to 3.00 and 2.91 A resolution for trigonal and monoclinic crystals, respectively. The estimated Matthews coefficient for the crystal forms were 2.36 and 2.24 A3 Da(-1), respectively, corresponding to 48% and 45% solvent content. In both cases, the results are consistent with the presence of three protein subunits in the asymmetric unit. The structure of cOTC has been determined by the molecular-replacement method using the atomic coordinates of cOTC from Pseudomonas aeruginosa (PDB code 1dxh) as the search model.