A partial metabolic pathway enables group b streptococcus to overcome quinone deficiency in a host bacterial community

Aerobic respiration metabolism in Group B Streptococcus (GBS) is activated by exogenous heme and menaquinone. This capacity enhances resistance of GBS to acid and oxidative stress and improves its survival. In this work, we discovered that GBS is able to respire in the presence of heme and 1,4‐dihydroxy‐2‐naphthoic acid (DHNA). DHNA is a biosynthetic precursor of demethylmenaquinone (DMK) in many bacterial species. A GBS gene (gbs1789) encodes a homolog of the MenA 1,4‐dihydroxy‐2‐naphthoate prenyltransferase enzyme, involved in the synthesis of demethylmenaquinone. In this study, we showed that gbs1789 is involved in the biosynthesis of long‐chain demethylmenaquinones (DMK‐10). The Δ gbs1789 mutant cannot respire in the presence of heme and DHNA, indicating that endogenously synthesized DMKs are cofactors of the GBS respiratory chain. We also found that isoprenoid side chains from GBS DMKs are produced by the protein encoded by the gbs1783 gene, since this gene can complement an Escherichia coli ispB mutant defective for isoprenoids chain synthesis. In the gut or vaginal microbiote, where interspecies metabolite exchanges occur, this partial DMK biosynthetic pathway can be important for GBS respiration and survival in different niches.     

<Superscript>15</Superscript>N, <Superscript>13</Superscript>C and <Superscript>1</Superscript>H backbone resonance assignments of an artificially engineered TEM-1/PSE-4 class A β-lactamase chimera and its deconvoluted mutant

The widespread use of β-lactam antibiotics has given rise to a dramatic increase in clinically-relevant β-lactamases. Understanding the structure/function relation in these variants is essential to better address the ever-growing incidence of antibiotic resistance. We previously reported the backbone resonance assignments of a chimeric protein constituted of segments of the class A β-lactamases TEM-1 and PSE-4 (Morin et al. in Biomol NMR Assign 4:127–130, 2010. doi: 10.1007/s12104-010-9227-8). That chimera, cTEM17m, held 17 amino acid substitutions relative to TEM-1 β-lactamase, resulting in a well-folded and fully functional protein with increased dynamics. Here we report the ¹H, ¹³C and ¹⁵N backbone resonance assignments of chimera cTEM-19m, which includes 19 substitutions and exhibits increased active-site perturbation, as well as one of its deconvoluted variants, as the first step in the analysis of their dynamic behaviours.     

Proteolytic processing of human L-type pyruvate kinase increases its ability to be phosphorylated

Red cell soluble cyclic 3′-5′ AMP-dependent protein kinase phosphorylates more efficient L₄ liver pyruvate kinase or the L_b partially proteolysed form of erythrocyte enzyme than the L′₄ precursor. Affinity of protein kinase for liver L₄ and L′₄ as substrates is similar (10 μM at 0.1 M ATP and 1 μM cyclic AMP), but maximal velocity of the phosphorylation reaction is twice higher with L₄ than L′₄. Thus it appears that proteolytic processing of pyruvate kinase increases its ability to be phosphorylated, in the same way that it increases its allosteric properties.     

Morphogenetic sequences of the rooting process after in vitro culture or Agrobacterium rhizogenes inoculation

Abstract

After a brief review dealing with the factors inducing adventitious rhizogenesis, the morphogenetic patterns of the rooting process induced by in vitro culture or after Agrobacterium rhizogenes inoculations are described. In vitro cultures of Nicotiana tabacum, Datura innoxia and Crepis capillaris leaf explants on Murashige and Skoog's medium supplemented with sucrose and IAA or NAA have been used in order to identify the target cells for direct and indirect rooting. The structural and functional features of the prerhizogenetic cells are described and the ploidy levels of both direct and indirect root meristems are examined by means of DNA microspectrophotometry. Data on the synergistic effects between auxin, sucrose and amino acids (particularly L-ornithine) for the reactivation of the prerhizogenetic cells are also given.

Transformed roots from carrct root discs or pea epicotyls after Agrobacterium rhizogenes inoculation arise indirectly from cambium-like layers differentiated inside a previously formed callus. Numerous auxin-like symptoms at the cell level are detected after the inoculation, suggesting modifications in the endogenous contents of auxin prior to the rooting process. It is also shown that initially non-susceptible cells (fully differentiated tobacco pith) can be induced to become susceptible by in vitro treatments resulting in cell reactivation before inoculation with the bacteria. Further work is in progress to extend these observations to non-susceptible species in order to check, via the occurrence of transformed roots, their ability to react positively to foreign Ri T-DNA.     

Effects of hydrostatic pressure per se (101 ATA) on energetic processes in fish

Nucleotides concentrations (ATP, ADP, AMP) have been measured in brain and muscle of eels exposed to 101 ATA of hydrostatic pressure (HP) for 3 hr. Survival times (ST) and oxygen arterial content (CaO2) have been measured in trouts exposed to HP = 101 ATA. The results show that at HP = 101 ATA, AMP increases (P less than 0.05) and ATP decreases (-12%; NS) in muscle but are not modified in brain; ST values are similar in normoxic and hyperoxic conditions, and CaO2 are similar at 1 ATA and 101 ATA of HP. It is concluded that HP tends to decrease aerobic production of energy. This phenomenon is not due to a failure in O2 transport from ambient medium to the cell but to a possible perturbation of the aerobic cellular processes leading to energy production (Krebs cycle and/or respiratory chain coupled to oxidative phosphorylation.     

Hormonal Contraception and the Risk of HIV Acquisition: An Individual Participant Data Meta-analysis

BackgroundObservational studies of a putative association between hormonal contraception (HC) and HIV acquisition have produced conflicting results. We conducted an individual participant data (IPD) meta-analysis of studies from sub-Saharan Africa to compare the incidence of HIV infection in women using combined oral contraceptives (COCs) or the injectable progestins depot-medroxyprogesterone acetate (DMPA) or norethisterone enanthate (NET-EN) with women not using HC.ConclusionsThis IPD meta-analysis found no evidence that COC or NET-EN use increases women’s risk of HIV but adds to the evidence that DMPA may increase HIV risk, underscoring the need for additional safe and effective contraceptive options for women at high HIV risk. A randomized controlled trial would provide more definitive evidence about the effects of hormonal contraception, particularly DMPA, on HIV risk.