Versatility in corrinoid salvaging and remodeling pathways supports corrinoid-dependent metabolism in Dehalococcoides mccartyi.

Corrinoids are cobalt-containing molecules that function as enzyme cofactors in a wide variety of organisms but are produced solely by a subset of prokaryotes. Specific corrinoids are identified by the structure of their axial ligands. The lower axial ligand of a corrinoid can be a benzimidazole, purine, or phenolic compound. Though it is known that many organisms obtain corrinoids from the environment, the variety of corrinoids that can serve as cofactors for any one organism is largely unstudied. Here, we examine the range of corrinoids that function as cofactors for corrinoid-dependent metabolism in Dehalococcoides mccartyi strain 195. Dehalococcoides bacteria play an important role in the bioremediation of chlorinated solvents in the environment because of their unique ability to convert the common groundwater contaminants perchloroethene and trichloroethene to the innocuous end product ethene. All isolated D. mccartyi strains require exogenous corrinoids such as vitamin B(12) for growth. However, like many other corrinoid-dependent bacteria, none of the well-characterized D. mccartyi strains has been shown to be capable of synthesizing corrinoids de novo. In this study, we investigate the ability of D. mccartyi strain 195 to use specific corrinoids, as well as its ability to modify imported corrinoids to a functional form. We show that strain 195 can use only specific corrinoids containing benzimidazole lower ligands but is capable of remodeling other corrinoids by lower ligand replacement when provided a functional benzimidazole base. This study of corrinoid utilization and modification by D. mccartyi provides insight into the array of strategies that microorganisms employ in acquiring essential nutrients from the environment.

Feeding characteristics of a golden alga (Poterioochromonas sp.) grazing on toxic cyanobacterium Microcystis aeruginosa.

Microcystis aeruginosa has quickly risen in infamy as one of the most universal and toxic bloom-forming cyanobacteria. Here we presented a species of golden alga (Poterioochromonas sp. strain ZX1), which can feed on toxic M. aeruginosa without any adverse effects from the cyanotoxins. Using flow cytometry, the ingestion and maximal digestion rates were estimated to be 0.2 approximately 1.2 and 0.2 M. aeruginosa cells (ZX1 cell)(-1)h(-1), respectively. M. aeruginosa in densities below 10(7)cells mL(-1) could be grazed down by ZX1, but no significant decrease was observed when the initial density was 3.2 x 10(7)cells mL(-1). ZX1 grazing was a little influenced by the light intensity (0.5 approximately 2500l x) and initial pH of the medium (pH=5.0 approximately 9.5). ZX1 could not survive in continuous darkness for longer than 10 days. The pH value was adjusted to 8 by ZX1 while to 10 by M. aeruginosa. This study may shed light on understanding the ecological interactions between M. aeruginosa and mixotrophic Poterioochromonas sp. in aquatic ecosystems.

[Effects of allelochemical EMA from reed on the production and release of cyanotoxins in Microcystis aeruginosa].

The growth inhibition of ethyl-2-methylacetoacetate (EMA) isolated from common reed (Phragmites australis Trin. or Phragmites communis Trin.) on the growth of Microcystis aeruginosa PCC7806 was investigated and the intracellular and extracellular concentration of cyanotoxin (MC-LR) after treatment of EMA were tested. The experimental results indicated that EMA has significant inhibitory effect on the growth of M. aeruginosa PCC7806, and the value of EC(50,7d) was 2.0 mg x L(-1). However, the inhibition declined with the cultivation time. During the whole cultivation period, EMA showed no significant effect on the release of MC-LR from cells to the culture. After 7 days, the amount of intracellular MC-LR per cell unit increased with the increasing of EMA concentration. The amount of MC-LR per cell unit was 25 ng x (10(6) cells)(-1) after the treatment with 1.5 mg x L(-1) EMA, which was increased by 39% compared with the control. The total MC-LR production (including intracellular and extracellular MC-LR) first slightly increased and then decreased significantly with the increase of EMA concentration. After the treatment with 3 mg x L(-1) EMA, the total MC-LR production was 28 microg x L(-1) (only half of that in the control). After 16 days, EMA showed no significant effect on both the amount of MC-LR per cell and the total MC-LR production.

[Effects of allelochemical EMA isolated from Phragmites communis on algal cell membrane lipid and ultrastructure].

In order to reveal the antialgal mechanisms of allelochemicals, effects of the allelochemical eathyl-2-methyl acetoacetate (EMA) on cell membrane lipid and ultrastructure of Chlorella pyrenoidosa, Microcystis aeruginosa and Chlorella vulagaris were studied in this paper. The lipid fatty acids of the algal membrane were isolated following the Bligh and Dye method and quantified by gas chromatograph/mass spectrometry. The ultrastructure of algal cells was observed with TEM. The results showed that EMA increased the contents of linolenic acid and linolic acid with increment of 14%, while decreased the content of myristic acid and cetylic acid in C. pyrenoidosa, membrane. The content of unsaturated fatty acids C18:1 and C18:2 increased 12% and 10% in M. aeruginosa with the addition of EMA, while the content of saturated fatty acids C18:0 and C16:0 decreased. EMA showed no significant change in the fatty acid composition in C. vulagaris under the experiment condition. EMA broke off cell wall of C. pyrenoidosa and M. aeruginosa. EMA damaged the cell membrane and the inclusion of algal cell leaked out. Nuclear and mitochondrial structure was damaged with the addition of EMA. EMA showed no significant change in the ultrastructure of C. vulgaris.

[Effects of allelochemical isolated from Phragmites communis on algal membrane permeability].

Efflux of K+, Mg2+, Ca2+ ions from algal cells as signals of cell membrane permeability, inductively coupled plasma mass spectrometry (ICP-MS) as detection method of ions, the present research investigated effects of allelochemical eathyl-2-methyl acetoacetate (EMA) isolated from Phragmites communis on cell membrane permeability of Microcystis aeruginosa, Chlorella pyrenoidosa and Chlorella vulagaris. The results showed that, when the cells were boiled for 10 min and the membrane was destroyed absolutely, the K+ efflux of M. aeruginosa and C. pyrenoidosa were 1.45 and 1.59 microg x (10(9) cell) (-1), respectively. When the concentration of EMA was 2 mg x L(-1), the K+ efflux of M. aeruginosa and C. pyrenoidosa were 1.38 and 1.40 microg x (10(9) cell)(-1), respectively. The K+ efflux of M. aeruginosa and C. pyrenoidosa reached 1.44 and 1.58 microg x (10(9) cell)(-1) while the EMA was 4 mg x L(-1). When the concentrations were 2 mg x L(-1) or 4 mg x L(-1) the K+ efflux reached more than 95% of the total ion amount in M. aeruginosa and C. pyrenoidosa cells. But when EMA concentration was 4 mg x L(-1), K+ efflux of C. vulagaris was 0.64 microg x (10(9) cell)(-1), which was only 31.5% of total K+ amount in C. vulagaris. Effects EMA on efflux of Mg2+ and Ca2+ were similar to those of K+. The results indicated that EMA destroyed the cell membrane of M. aeruginosa and C. pyrenoidosa but not C. vulagaris. This is one of the mechanisms of EMA species-selective antialgal.

[Effects of EMA on activities of algal antioxidant enzymes].

Using allelochemicals produced by macrophytes to control harmful algae is a novel antialgal method. The present research investigated effects of the species-specific antialgal allelochemical EMA on activities of antioxidant enzymes of Chlorella pyrenoidosa and Chlorella vulagaris. The results showed that 0.25 mg/L of EMA increased activities of superoxide dismutase (SOD), peroxidase (POD)and catalase (CAT) of C. pyrenoidosa and C. vulagaris. With the increase of EMA concentrations, activities of the 3 enzymes of C. pyrenoidosa decreased sharply. The activity of SOD of C. pyrenoidosa decreased to 0 when the EMA were 4 mg/L. With the increase of EMA concentrations, activities of the 3 enzymes of C. vulagaris increased to as higher as 3-4 folders of that of the control set. The results gave hints to elucidate the species-specific antialgal mechanisms of EMA.