A thin line between plankton and biofilm

<p>Planktonic bacterial cells are by definition not aggregated. However, our previous work, where we have demonstrated the invisible mechanical connections between bacterial cells in dilute planktonic suspensions, challenged this assumption. Here we provide an experimental evidence using autocorrelation analysis of micrographs that in planktonic suspensions of <em>B. subtilis</em> a size continuum of aggregated structures is formed. In the microbial aggregates viable cells were embedded in the nucleic acid network. The eDNA was released during regular cell lysis events. To determine the size distribution of planktonic bacterial aggregates a pair-wise spatial correlations of bacterial cells in microscopic images were calculated. The monotonously decreasing shape of the autocorrelation function indicated a continuous distribution of bacterial aggregate sizes from monomer to multimers. Soft bacterial aggregates in dilute suspensions provide a missing link in a continuum of organic matter in aqueous environments and can significantly improve our understanding how non-attached biofilms form during planktonic growth.</p>

NEW BACTERIAL AGGREGATE-FORMING PRODUCER OF POLY-3-HYDROXYBUTYRATE

The growth and accumulation of carotenoid pigment and poly-3-hydroxybutyrate by a new strain of pink-colored facultative methylotrophic bacterium Methylorubrum extorquens LP in suspension culture and in cell aggregates were studied. The parameters that promote cell aggregation and the formation of poly-3-hydroxybutyrate have been determined.

Killing two birds with one stone: simultaneous extraction of DNA and RNA from activated sludge biomass

DNA and RNA are usually extracted from activated sludge samples using two separate methods developed for soil and sediment samples. However, activated sludge differs from soil and sediment in at least three aspects: high biomass density, low humic acid content, and the presence of bacterial aggregate flocs. Taking these characteristics into consideration, we developed a simple and rapid method allowing simultaneous DNA and RNA extraction from activated sludge samples. This method combines (i) mini-bead beating, which is most efficient in breaking bacterial aggregate flocs and cells, (ii) protection of RNA with diethyl pyrocarbonate, and (iii) precipitation of impurities with ammonium acetate. Phenol/chloroform extraction and column purification are not necessary. The resulting DNA and RNA are suitable for PCR and reverse transcriptase - PCR, respectively. The efficiencies of cell lysis and nucleic acid recovery were high enough to permit detection by PCR of 102cells/mL of mixed liquor. By simultaneously extracting both DNA and RNA from a single sample, this method eliminates variability in cell lysis between extraction of DNA and RNA using two different methods. This extraction method is rapid, and within 1 h, one person can process four or more samples. This simple method makes it easier to analyze a large number of activated sludge samples.Key words: activated sludge, DNA, extraction, PCR, RNA.

Interaction of Bartonella henselae with endothelial cells results in bacterial aggregation on the cell surface and the subsequent engulfment and internalisation of the bacterial aggregate by a unique structure, the invasome

Vascular colonisation by Bartonella henselae may cause vaso-proliferative tumour growth with clumps of bacteria found in close association with proliferating endothelial cells. By using B. henselae-infected human umbilical vein endothelial cells as an in vitro model for endothelial colonisation, we report here on a novel mechanism of cellular invasion by bacteria. First, the leading lamella of endothelial cells establishes cellular contact to sedimented bacteria and mediates bacterial aggregation by rearward transport on the cell surface. Subsequently, the formed bacterial aggregate is engulfed and internalised by a unique host cellular structure, the invasome. Completion of this sequence of events requires 24 hours. Cortical F-actin, intercellular adhesion molecule-1 and phosphotyrosine are highly enriched in the membrane protrusions entrapping the bacterial aggregate. Actin stress fibres, which are anchored to the numerous focal adhesion plaques associated with the invasome structure, are typically found to be twisted around its basal part. The formation of invasomes was found to be inhibited by cytochalasin D but virtually unaffected by nocodazole, colchicine or taxol, indicating that invasome-mediated invasion is an actin-dependent and microtubuli-independent process. Bacterial internalisation via the invasome was consistently observed with several clinical isolates of B. henselae, while a spontaneous mutant obtained from one of these isolates was impaired in invasome-mediated invasion. Instead, this mutant showed increased uptake of bacteria into perinuclear localising phagosomes, suggesting that invasome-formation may interfere with this alternative mechanism of bacterial internalisation. Internalisation via the invasome represents a novel paradigm for the invasion of bacteria into host cells which may serve as a cellular colonisation mechanism in vivo, e.g. on proliferating and migrating endothelial cells during Bartonella-induced vaso-proliferative tumour growth.

Freshwater Bacterial Aggregate Development: Effect of Dissolved Organic Matter

Suspended sediment particles and bacteria because of their surface area and charge, may play a role in the binding of aquatic contaminants. Little is known, as to what degree each of these factors play in the formation of suspended aggregates. Flocculation of particles can alter their hydrodynamic properties in aquatic environments and therefore may have significant implications for contaminant transport. In this study, we examine the role dissolved organic carbon plays in the production of bacterial aggregates as a first step to gaining a better understanding of bacterial-particle interactions and suspended particulate formation. Data indicated that an order of magnitude increase in bacterial population occurred due to the utilization of algal organic matter. This increase in bacterial density was closely accompanied by an increase in the size of the median bacterial aggregate from approximately 8 µm to 16 µm. This observation suggests that there is a greater potential for the sorption of aquatic contaminants by the aggregates.