Background: The bacterial cell wall is the target of many antibiotics and cell envelope constituents are critical to host-pathogen interactions. To combat resistance development and virulence, a detailed knowledge of the individual factors involved is essential. Members of the LytR-CpsA-Psr family of cell envelope-associated attenuators are relevant for β-lactam resistance, biofilm formation, and stress tolerance, and they are suggested to play a role in cell wall maintenance. However, their precise function is still unknown. This study addresses the occurrence as well as sequence-based characteristics of the LytR-CpsA-Psr proteins.

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Among the large number of hypothetical proteins within the genomes of Helicobacter pylori, there is a family of unique and highly disulfide-bridged proteins, designated family 12, for which no function could originally be assigned. Sequence analysis revealed that members of this family possess a modular architecture of ␣/␤-units and a stringent pattern of cysteine residues. The H. pylori cysteine-rich protein A (HcpA), which is a member of this family, was expressed and refolded from inclusion bodies. Six pairs of cysteine residues, which are separated by exactly seven residues, form disulfide bridges. HcpA is a ␤-lactamase. It slowly hydrolyzes 6-aminopenicillinic acid and 7-aminocephalosporanic acid (ACA) derivatives. The turnover for 6-aminopenicillinic acid derivatives is 2-3 times greater than for ACA derivatives. The enzyme is efficiently inhibited by cloxacillin and oxacillin but not by ACA derivatives or metal chelators. We suggest that all family 12 members possess similar activities and might be involved in the synthesis of the cell wall peptidoglycan. They might also be responsible for amoxicillin resistance of certain H. pylori strains.

A push-pull method, previously used in groundwater analyses, was successfully adapted for measuring sulfide turnover rates in situ at different depths in the meromictic Lake Cadagno. In the layer of phototrophic bacteria at about 12 m in depth net sulfide consumption was observed during the day, indicating active bacterial photosynthesis. During the night the sulfide turnover rates were positive, indicating a net sulfide production from the reduction of more-oxidized sulfur compounds. Because of lack of light, no photosynthesis takes place in the monimolimnion; thus, only sulfide formation is observed both during the day and the night. Sulfide turnover rates in the oxic mixolimnion were always positive as sulfide is spontaneously oxidized by oxygen and as the rates of sulfide oxidation depend on the oxygen concentrations present. Sulfide oxidation by chemolithotrophic bacteria may occur at the oxicline, but this cannot be distinguished from spontaneous chemical oxidation.Lakes, like most ecosystems, are open systems in a steady state with different trophic levels. To understand the interactions between organisms and the environment, inputs and outputs of the nutrients at each trophic level must be known. Rates describe the turnover of chemical species at specific sites and therefore describe elemental fluxes in biogeochemical cycles as well as microbial activities in an ecosystem.In physiology and ecology several methods for evaluating rates have been described. In sediments microbial reaction rates are calculated from concentration-depth profiles by using flux calculations based on a modified Fick's first law; however, as incubations of several days are necessary, only a low temporal resolution is achieved. Primary production rates from phytoplankton are obtained by the use of radioactive carbon isotopes. Samples are collected in a depth profile and incubated with 14 CO 2 at the originating depth for a few hours. But such results will also not give the actual in situ reaction rates for rapidly cycling elements.In this paper we present a new approach for determining in situ reaction rates for production and consumption of sulfide in the open water. Experiments were done in a meromictic alpine lake with a pronounced biological sulfur cycle (7,11,12,15,20). Under anoxic conditions sulfide is produced by sulfatereducing bacteria, which reduce sulfate to sulfide at the expense of organic substrates. At the same time, if light is present, sulfide is oxidized by anoxygenic phototrophic bacteria, which use it as an electron donor. Concentration profiles for Lake Cadagno often show no sulfide in the layer with the highest biomass concentration of the water column and thus cannot give information on actual turnover rates of the sulfur compounds because, in a steady state, sources and sinks are balanced. The "push-pull" technique, which has been previously applied in groundwater systems (9, 10, 17) was used to obtain real in situ sulfide turnover rates with a high temporal resolution in an undisturbed ecosystem. MATERIALS...