Immunochemistry and localization of the enzyme disaggregatase in Methanosarcina mazei

Mechanical and cell-to-cell adhesive properties of aggregated Methanosarcina

The mechanical and adhesive properties as well as the turgor pressure of microbes play an important role in cell growth and aggregation. By applying AFM together with finite element modelling, one can determine the cell wall structural homogeneity, mechanical and cell-to-cell adhesive properties for aggregated Methanosarcina barkeri cells. This also allows a novel approach to determine in-aggregate turgor pressure determination. Analyzing the AFM force-indentation response of the aggregates under loads less than 10 nN, our study reveals structural inhomogeneity of the polymeric part of the cell wall material and suggests that the cell wall consists of two layers of methanochondroitin (external: with a thickness of 3 ± 1 nm and internal: with a thickness of 169 ± 30 nm). On average, the hyperelastic finite element model showed that the internal layer is more rigid (μ = 14 ± 4 MPa) than the external layer (μ = 2.8 ± 0.9 MPa). To determine the turgor pressure and adhesiveness of the cells, a specific mode of indentation (under a load of 45 nN), aimed towards the centre of the individual aggregate, was performed. By modelling the AFM induced decohesion of the aggregate, the turgor pressure and the cell-to-cell adhesive interface properties could be determined. On average, the turgor pressure is estimated to be 59 ± 22 kPa, the interface strength is 78 ± 12 kPa and the polymer network extensibility is 2.8 ± 0.9 nm. We predict that internal cell wall comprised highly compressed methanochondroitin chains and we are able to identify a conceptual model for stress dependent inner cell wall growth.

Identification of the gene for disaggregatase from Methanosarcina mazei

The gene sequences encoding disaggregatase (Dag), the enzyme responsible for dispersion of cell aggregates of Methanosarcina mazei to single cells, were determined for three strains of M. mazei (S-6(T), LYC and TMA). The dag genes of the three strains were 3234 bp in length and had almost the same sequences with 97% amino acid sequence identities. Dag was predicted to comprise 1077 amino acid residues and to have a molecular mass of 120 kDa containing three repeats of the DNRLRE domain in the C terminus, which is specific to the genus Methanosarcina and may be responsible for structural organization and cell wall function. Recombinant Dag was overexpressed in Escherichia coli and preparations of the expressed protein exhibited enzymatic activity. The RT-PCR analysis showed that dag was transcribed to mRNA in M. mazei LYC and indicated that the gene was expressed in vivo. This is the first time the gene involved in the morphological change of Methanosarcina spp. from aggregate to single cells has been identified.

Effect of Sulfur Source on the Performance and Metal Retention of Methanol-Fed UASB Reactors

The effect of a sulfur source on the performance and metal retention of methanol-fed upflow anaerobic sludge bed (UASB) reactors was investigated. For this purpose, two UASB reactors were operated with cobalt preloaded granular sludge (1 mM CoCl2; 30 degrees C; 24 h) at an organic loading rate (OLR) of 5 g COD.L reactor(-1).d(-1). One UASB reactor (R1) was operated without a sulfur source in the influent during the first 37 days. In this period the methanol conversion to methane remained very poor, apparently due to the absence of a sulfur source, because once cysteine, a sulfur-containing amino acid, was added to the influent of R1 (day 37) a full conversion of methanol to methane occurred within 6 days. The second reactor (R2) was operated with sulfate (0.41 mM) in the influent during the first 86 days of operation, during which no limitation in the methanol conversion to methane manifested. Cobalt washed out from the sludge at similar rates in both reactors. The leaching of cobalt occurred at two distinct rates, first at a high rate of 22 microg.g TSS(-1).d(-1), which proceeded mainly from the exchangeable and carbonate fraction and later at a relatively slow rate of 9 mug.g TSS(-1).d(-1) from the organic/sulfide fraction. This study showed that the supply of the sulfur source L-cysteine has a pronounced positive effect on the methanogenic activity and the retention of metals such as iron, zinc and molybdenum.

Proteomic and computational analysis of secreted proteins with type I signal peptides from the Antarctic archaeon Methanococcoides burtonii

LC-MS/MS was used to identify secreted proteins in the Antarctic archaeon Methanococcoides burtonii. Seven proteins possessing a classical class 1 signal peptide were identified in the supernatant from cultures grown at 4 and 23 degrees C. The proteins included a putative S-layer cell surface protein, cell surface protein involved with cell adhesion, and trypsin-like serine protease. Protease activity was detected in the secreted fraction, and the signal peptide cleavage site of the protease was confirmed using Edman sequencing. The expression profile of putative cell surface proteins suggests a requirement for cell interactions during growth at low temperature. Sequences of the secreted proteins were used to compile a dataset containing a further 32 predicted secreted proteins from the Methanosarcinaceae. Many of these proteins were also S-layer cell surface proteins with a variety of predicted roles, particularly in cell-cell interaction. Computational analysis of signal peptides revealed a preference for lysine in the n-region, leucine in the h-region, and a eucaryal-type cleavage site, highlighting the mosaic nature of signal peptides in Archaea. This is the first study to experimentally characterize secreted proteins from a cold-adapted archaeon and provides new insight and a functional dataset for studying secretion in Archaea.

Thinking about bacterial populations as multicellular organisms

It has been a decade since multicellularity was proposed as a general bacterial trait. Intercellular communication and multicellular coordination are now known to be widespread among prokaryotes and to affect multiple phenotypes. Many different classes of signaling molecules have been identified in both Gram-positive and Gram-negative species. Bacteria have sophisticated signal transduction networks for integrating intercellular signals with other information to make decisions about gene expression and cellular differentiation. Coordinated multicellular behavior can be observed in a variety of situations, including development of E. coli and B. subtilis colonies, swarming by Proteus and Serratia, and spatially organized interspecific metabolic cooperation in anaerobic bioreactor granules. Bacteria benefit from multicellular cooperation by using cellular division of labor, accessing resources that cannot effectively be utilized by single cells, collectively defending against antagonists, and optimizing population survival by differentiating into distinct cell types.

Functions of S-layers

Although S-layers are being increasingly identified on Bacteria and Archaea, it is enigmatic that in most cases S-layer function continues to elude us. In a few instances, S-layers have been shown to be virulence factors on pathogens (e.g. Campylobacter fetus ssp. fetus and Aeromonas salmonicida), protective against Bdellovibrio, a depository for surface-exposed enzymes (e.g. Bacillus stearothermophilus), shape-determining agents (e.g. Thermoproteus tenax) and nucleation factors for fine-grain mineral development (e.g. Synechococcus GL 24). Yet, for the vast majority of S-layered bacteria, the natural function of these crystalline arrays continues to be evasive. The following review up-dates the functional basis of S-layers and describes such diverse topics as the effect of S-layers on the Gram stain, bacteriophage adsorption in lactobacilli, phagocytosis by human polymorphonuclear leukocytes, the adhesion of a high-molecular-mass amylase, outer membrane porosity, and the secretion of extracellular enzymes of Thermoanaerobacterium. In addition, the functional aspect of calcium on the Caulobacter S-layer is explained.

Identification of an ATP-binding cassette transport system required for translocation of lipopolysaccharide O-antigen side-chains across the cytoplasmic membrane of Klebsiella pneumoniae serotype O1

The rfbKpO1 gene cluster of Klebsiella pneumoniae O1 directs synthesis of the D-galactan I component of the lipopolysaccharide O-antigen. The first two genes in the rfbKpO1 cluster encode RfbAKpO1 and RfbBKpO1, with predicted sizes of 29.5 or 30.0 kDa and 27.4 kDa, respectively. RfbBKpO1 contains a consensus ATP-binding domain and shares homology with several proteins which function as ATP-binding components of cell surface polysaccharide transporters. RfbAKpO1 is predicted to be an integral membrane protein with five putative membrane-spanning domains and its transmembrane topology was confirmed by TnphoA mutagenesis. The hydropathy plot of RfbAKpO1 resembles KpsM, the transcytoplasmic membrane component of the capsular polysaccharide transporter from Escherichia coli K-1 and K-5. These relationships suggest that RfbAKpO1 and RfbBKpO1 belong to a family of two-component ABC (ATP-binding cassette) transporters. E. coli K-12 containing a plasmid carrying an rfbKpO1 gene cluster deleted in rfbAKpO1 and rfbBKpO1 expresses rough lipopolysaccharide molecules on its surface and accumulates cytoplasmic O-antigen. When RfbAKpO1 and RfbBKpO1 are supplied in trans by a compatible plasmid, O-polysaccharide transport is restored and smooth D-galactan I-substituted lipopolysaccharide is produced. RfbAKpO1 and RfbBKpO1 are, therefore, proposed to constitute a system required for transport of D-galactan I across the cytoplasmic membrane, where RfbAKpO1 represents the membrane-spanning translocator and RfbBKpO1 couples the energy of ATP hydrolysis ot the transport process.