Biosynthesis of polyketides. Purification and inhibition studies of 6-methylsalicylic acid synthase

6-MSA³ synthase has been purified 190-fold with 33% yield. The purification was found to be dependent on the presence of glycerol. The acetylenic inhibitors 3-pentynoyl- and 2-hexynoyl-NAC completely inhibit 6-MSA production at concentrations in which fatty acid synthesis, TAL production as well as NADPH oxidation are only partially affected. These results confirm earlier studies on the specificity of inhibition by acetylenic inhibitors and support a mechanism wherein the NADPH-mediated reduction step occurs on a 6-carbon rather than on an 8-carbon intermediate.     

One Step forward: Benthic Pelagic Coupling and Indicators for Environmental Status

A large data set from the Eastern Mediterranean was analyzed to explore the relationship between seawater column variables and benthic community status. Our results showed a strong quantitative link between the seawater column variables (Chlorophyll a and Eutrophication Index) and various indicators describing benthic diversity and community composition. The percentage of benthic opportunistic species increased significantly in the stations with high trophic status of the seawater column and so did the strength of the coupling between values of seawater column and benthic indicators. The Eutrophication Index threshold level of 0.85, separating the “Bad and Poor” from “Moderate to High” conditions could serve as an acceptable critical value above which there is a readily observable change in benthic community composition.     

The effect of organic loading rate on foam initiation during mesophilic anaerobic digestion of municipal wastewater sludge

The impact of increasing organic load on anaerobic digestion foaming was studied at both full and bench scale. Organic loadings of 1.25, 2.5 and 5 kg VS m⁻³ were applied to bench-scale digesters. Foaming was monitored at a full scale digester operated in a comparable organic loading range over 15 months. The bench scale batch studies identified 2.5 kg VS m⁻³ as a critical threshold for foam initiation while 5 kg VS m⁻³ resulted in persistent foaming. Investigation of a full scale foaming event corroborated the laboratory observation that foaming may be initiated at a loading rate of ?2.5 kg VS m⁻³. Experimental findings on foam composition and differences in the quality characteristics between foaming and non-foaming sludges indicated that foam initiation derived from the combined effect of the liquid and gas phases inside a digester and that the solids/biomass ultimately stabilized foaming.     

Porins and lipopolysaccharide of Escherichia coli ATCC 25922 and isogenic rough mutants

Abstract The lipopolysaccharide and porin profile of Escherichia coli ATCC 25922, a smooth strain commonly used in antibiotic susceptibility testing, and five isogenic rough mutants was examined. The lipopolysaccharide of the parent strain had the characteristic ladder pattern on polyacrylamide gels, while that of the mutants appeared similar to chemotypes Ra and Rc of Salmonella typhimurium with some changes in chemical composition. Of the porins, OmpC appeared markedly reduced in the parent strain while OmpF appeared markedly reduced in the mutants. In addition, a new outer-membrane protein of size intermediate to that of OmpC and OmpF was detected in all mutants. Neither parent nor mutants were susceptible to the LPS core-specific P1 phage or the porin-specific PA2 and K20 phages.     

On B12 biosynthesis and evolution

The paper describes a standard form of the initial rate equation for isotope transfer from a substrate to a product in an enzyme-catalysed reaction. This form of the equation facilitates the prediction of transfer behaviour because it can be used either in association with automatic methods for determining the rate equation of product formation, or in association with the set nomenclature of enzymic mechanisms (Ainsworth, 1975).     

The Pattern of Change in the Abundances of Specific Bacterioplankton Groups Is Consistent across Different Nutrient-Enriched Habitats in Crete

A common source of disturbance for coastal aquatic habitats is nutrient enrichment through anthropogenic activities. Although the water column bacterioplankton communities in these environments have been characterized in some cases, changes in α-diversity and/or the abundances of specific taxonomic groups across enriched habitats remain unclear. Here, we investigated the bacterial community changes at three different nutrient-enriched and adjacent undisturbed habitats along the north coast of Crete, Greece: a fish farm, a closed bay within a town with low water renewal rates, and a city port where the level of nutrient enrichment and the trophic status of the habitat were different. Even though changes in α-diversity were different at each site, we observed across the sites a common change pattern accounting for most of the community variation for five of the most abundant bacterial groups: a decrease in the abundance of the Pelagibacteraceae and SAR86 and an increase in the abundance of the Alteromonadaceae, Rhodobacteraceae, and Cryomorphaceae in the impacted sites. The abundances of the groups that increased and decreased in the impacted sites were significantly correlated (positively and negatively, respectively) with the total heterotrophic bacterial counts and the concentrations of dissolved organic carbon and/or dissolved nitrogen and chlorophyll α, indicating that the common change pattern was associated with nutrient enrichment. Our results provide an in situ indication concerning the association of specific bacterioplankton groups with nutrient enrichment. These groups could potentially be used as indicators for nutrient enrichment if the pattern is confirmed over a broader spatial and temporal scale by future studies.     

Anaerobic digestion foaming causes – A review

Anaerobic digestion foaming has been encountered in several sewage treatment plants in the UK. Foaming has raised major concerns for the water companies due to significant impacts on process efficiency and operational costs. Several foaming causes have been identified over the past few years by researchers. However, the supporting experimental information is limited and in some cases absent. The present report aims to provide a detailed review of the current anaerobic digestion foaming problem and to identify gaps in knowledge regarding the theory of foam formation in anaerobic digesters.     

Chitin synthase in Candida albicans: comparison of digitonin-permeabilized cells and spheroplast membranes.

The treatment of Candida albicans (yeast form) with digitonin or dimethyl sulfoxide permeabilized cells and caused the activation of chitin synthase in situ. Endogenous activation was completely prevented by the sulfhydryl reagents N-ethylmaleimide, p-chloromercuribenzoate, and 5,5'-dithiobis(2-nitrobenzoic acid); partially prevented by the protease inhibitors antipain, leupeptin, and N alpha-tosyl-L-lysyl chloromethyl ketone; and also partially prevented by EDTA. Thus, a clostripain-like protease may be involved in the endogenous activation phenomenon. The pH activity profile, cofactor requirements, and kinetic parameters of the endogenously activated chitin synthase were identical to those of the trypsin-activated enzyme in protoplast membranes.     

Interrelationships of bacteria,meiofauna and macrofauna in a Mediterranean sedimentary beach (Maremma Park,NW Italy)

Collelungo beach (Maremma Park, NW Italy), was sampled quantitatively for macrofauna, meiofauna and bacteria in May 2003; several physicochemical variables and variables associated with food availability and sediment structure were also measured. Replicated samples were collected from three sites representing natural conditions, an erosion regime, and the influence of the Ombrone River, respectively, as well as from four stations each located in the surf and sublittoral zones. Both uni- and multivariate techniques were used to assess the benthic community structure and the associated environmental variables. Different diversity indices revealed no pattern; in contrast, multivariate techniques applied on the macrobenthic fauna and the polychaete taxocommunity distinguished between the sites located in natural and eroding conditions from the one located nearby the discharges of the Ombrone river. Τhe community patterns deriving from meio- and macrofauna are clearly divergent. The overall benthic faunal community appears to be influenced by both groups of organisms. The patterns of the meio- and macrofaunal communities seem to be affected synergistically by a number of environmental variables, in accordance with the multicausal environmental severity hypothesis. Meiofaunal patterns are more often correlated with bacteria and the protein concentration than are macrofaunal patterns, indicating a potential utilization of bacteria as a food source by the meiofaunal organisms. Total bacterial numbers are associated with the macrofaunal pattern under the erosion regime, probably as a consequence of competition for food between macrofauna and meiofauna.     

N,N-Dichloroaminosulfonic acids as novel topical antimicrobial agents

2-Dichloroamino-2-methyl-propane-1-sulfonic acid sodium salt (2a), a stable derivative of endogenous N,N-dichlorotaurine (1), has been identified and is under development as a topical antimicrobial agent. Structure–activity relationships of analogs were explored to achieve optimal antimicrobial activity with minimal mammalian toxicity while maintaining the desired stability. All the analogs synthesized showed antimicrobial activity against Staphylococcus aureus, Escherichia coli, and Candida albicans in the range of 1–128 μg/mL and cytotoxicity against mammalian L929 cells in the range 80–1900 μg/mL.