Formation of a functional electron transport system during growth of penicillin-induced spheroplasts of Haemophilus parainfluenzae

Methanogenesis inhibitors used in bio-electrochemical systems: A review revealing reality to decide future direction and applications

Microbial fuel cell (MFC) is a robust technology capable of treating real wastewaters by utilizing mixed anaerobic microbiota as inoculum for producing electricity from oxidation of the biodegradable matters. However, these mixed microbiota comprises of both electroactive microorganisms (EAM) and substrate/electron scavenging microorganisms such as methanogens. Hence, in order to maximize bioelectricity from MFC, different physio-chemical techniques have been applied in past investigations to suppress activity of methanogens. Interestingly, recent investigations exhibit that methanogens can produce electricity in MFC and possess the cellular machinery like cytochrome c and Type IV pili to perform extracellular electron transfer (EET) in the presence of suitable electron acceptors. Hence, in this review, in-depth analysis of versatile behaviour of methanogens in both MFC and natural anaerobic conditions with different inhibition techniques is explored. This review also discusses the future research directions based on the latest scientific evidence on role of methanogens for EET in MFC.

Release of membrane components from viable Haemophilus parainfluenzae by ethylenediaminetetraacetic acid-tris(hydroxymethyl)-aminomethane

Logarithmically growing Haemophilus parainfluenzae lost 15 to 20% of the phospholipids, demethyl vitamin K(2), cytochrome b, and cytochrome c, and 50% of the lipopolysaccharide when incubated in ethylenediaminetetraacetic acid (EDTA)-tris-(hydroxymethyl)aminomethane (Tris) for 10 min. This loss of membrane components occurred without loss in viability, and the lost components were recovered as membrane fragments in the surrounding buffer. The phospholipids recovered in the membrane fragments had a slightly lower specific activity than the phospholipids in the residue. Lysis of a portion of the cells could not account for the release of membrane components, as the cells lost neither glucose-6-phosphate dehydrogenase activity not deoxyribonucleic acid. The treated cells were osmotically stable and contained the same proportions of the individual phospholipids as pretreatment cells. Prolongation of the EDTA-Tris treatment did not induce further loss of phospholipid or demethyl vitamin K(2), but caused a decrease in viability. If the cells were returned to the growth medium after 10 min, the cells immediately resumed growth at the pretreatment rate. During growth in the recovery period, the phospholipids increased logarithmically in the pretreatment rate. During growth in the recovery period, the phospholipids increased logarithmically in the pretreatment proportions, although there was a marked decrease in the turnover and a shift from the use of extracellular lipid precursors to the use of intracellular pools of precursors.

Phospholipid metabolism during changes in the proportions of membrane-bound respiratory pigments in Haemophilus parainfluenzae

After a transition from high to low oxygen tension, there was a twofold to 50-fold increase in the content of membrane-bound respiratory pigments of Haemophilus parainfluenzae, and there were concurrent changes in the metabolism of the membrane phospholipids: (i) a twofold decrease in the rate of turnover of the phosphate in all the phospholipids; (ii) a shift from simple one-phase, linear incorporation of phosphate into phospholipids to a complex biphasic incorporation of phosphate into phospholipids; and (iii) an increase in the total phospholipids with a slight increase in the proportion of phosphatidylglycerol (PG) and a slight decrease in the proportion of phosphatidylethanolamine (PE). Changes in the rates of incorporation of phosphate into the phospholipids occurred without a change in the rate of bacterial growth. When the compensatory adjustment of the proportions of the respiratory pigments reached a steady state, the total phospholipid, the rate of incorporation of phosphate into phospholipids, and the proportion of PG fell. At steady-state proportions of cytochromes, the proportion of PE and the rate of turnover of the phosphate in the phospholipids increased. All through an incorporation experiment of 1.5 divisions, the specific activity of the phosphate of PG was twice that of phosphatidic acid (PA). The phosphate of PG turned over 1.2 to 1.5 times more rapidly than the phosphate of PA in cells with high and low cytochrome levels. If the PA was an accurate measure of the precursor for the cytidine-5'-diphosphate-diglyceride, which in turn was the precursor of all the lipids, then the results of these experiments suggested that exchange reactions, in addition to synthesis from PA, were involved in phospholipid metabolism. These reactions were more sensitive to changes in oxygen concentration than was the growth rate.

Lipid composition of the electron transport membrane of Haemophilus parainfluenzae

The principal lipids associated with the electron transport membrane of Haemophilus parainfluenzae are phosphatidylethanolamine (78%), phosphatidylmonomethylethanolamine (0.4%), phosphatidylglycerol (18%), phosphatidylcholine (0.4%), phosphatidylserine (0.4%), phosphatidic acid (0.2%), and cardiolipin (3.0%). Phospholipids account for 98.4% of the extractible fatty acids. There are no glycolipids, plasmalogens, alkyl ethers, or lipo amino acid esters in the membrane lipids. Glycerol phosphate esters derived from the phospholipids by mild alkaline methanolysis were identified by their staining reactions, mobility on paper and ion-exchange column chromatography, and by the molar glycerol to phosphate ratios. Eleven diacyl phospholipids can be separated by two-dimensional thin-layer chromatography. Each lipid served as a substrate for phospholipase D, and had a fatty acid to phosphate ratio of 2:1. Each separated diacyl phospholipid was deacylated and the glycerol phosphate ester was identified by paper chromatography in four solvent systems. Of the 11 separated phospholipids, 3 were phosphatidylethanolamines, 2 were phosphatidylserines, and 2 were phosphatidylglycerols. Phosphatidylcholine, cardiolipin, and phosphatidic acid were found at a single location. Phosphatidylmonomethylethanolamine was found with the major phosphatidylethanolamine. Three distinct classes of phospholipids are separable according to their relative fatty acid compositions. (i) The trace lipids consist of two phosphatidylethanolamines, two phosphatidylserines, phosphatidylcholine, phosphatidic acid, and a phosphatidylglycerol. Each lipid represents less than 0.3% of the total lipid phosphate. These lipids are characterized by high proportions of the short (C(10) to C(14)) and long (C(19) to C(22)) fatty acids with practically no palmitoleic acid. (ii) The major phospholipids (93% of the lipid phosphate) are phosphatidylethanolamine, phosphatidylmonomethylethanolamine, and phosphatidylglycerol. These lipids contain a low proportion of the short (<C(14)) and long (>C(19)) fatty acids. Palmitic and palmitoleic acids represent over 80% of the total fatty acids. (iii) The fatty acid composition of the cardiolipin is intermediate between the other two classes. Both palmitoleic and the longer fatty acids represent a significant proportion of the total fatty acid.