Starvation induces shrinkage of the bacterial cytoplasm

Environmental fluctuations are a common challenge for single-celled organisms; enteric bacteria such as Escherichia coli experience dramatic changes in nutrient availability, pH, and temperature during their journey into and out of the host. While the effects of altered nutrient availability on gene expression and protein synthesis are well known, their impacts on cytoplasmic dynamics and cell morphology have been largely overlooked. Here, we discover that depletion of utilizable nutrients results in shrinkage of E. coli’s inner membrane from the cell wall. Shrinkage was accompanied by an ∼17% reduction in cytoplasmic volume and a concurrent increase in periplasmic volume. Inner membrane retraction after sudden starvation occurred almost exclusively at the new cell pole. This phenomenon was distinct from turgor-mediated plasmolysis and independent of new transcription, translation, or canonical starvation-sensing pathways. Cytoplasmic dry-mass density increased during shrinkage, suggesting that it is driven primarily by loss of water. Shrinkage was reversible: upon a shift to nutrient-rich medium, expansion started almost immediately at a rate dependent on carbon source quality. A robust entry into and recovery from shrinkage required the Tol-Pal system, highlighting the importance of envelope coupling during shrinkage and recovery. Klebsiella pneumoniae also exhibited shrinkage when shifted to carbon-free conditions, suggesting a conserved phenomenon. These findings demonstrate that even when Gram-negative bacterial growth is arrested, cell morphology and physiology are still dynamic.

Design and Application of Silica Micro-Clusters for Microalgae Separation

Eutrophication has attracted social’s attention as it is a worldwide problem in freshwater aquatic ecosystem. Therefore, cultivation of microalgae in nutrient-rich medium can serve as wastewater treatment as they remove the pollutants from aquatic environment and the microalgal biomass can produce biofuels or other valuable bioproducts. Although microalgae harvesting by gravity sedimentation method is less expensive but it promotes slow sedimentation rate and increases the possibility of biomass deteriorates during harvesting process. In this research, the silica micro-clusters (SMCs) was being synthesized and surface functionalized by positively charged chitosan to improve the attachment with microalgal cells in order to promote rapid microalgae removal through sedimentation. The cell removal efficiency of Chlorella sp. can reach up to 99.41 ± 0.64 % by using 1 g/L of surface functionalized SMCs (SF-Si). Moreover, it also tended to promote high rate of cell sedimentation at 22.71 ± 3.02 cm/h which was about 162 times faster than self-sedimentation. This method of silica-aided-sedimentation (SAS) had proven effective to harvest the multi-species microalgal cells which collected from Tualang lake, Perak, and achieved cell separation efficiency up to 100% by 80 mg/L of SF-Si.

Effects of Bile Acids and Nisin on the Production of Enterotoxin byClostridium perfringensin a Nutrient-Rich Medium

Clostridium perfringensis the second most common cause of bacterial foodborne illness in the United States, with nearly a million cases each year.C. perfringensenterotoxin (CPE), produced during sporulation, damages intestinal epithelial cells by pore formation, which results in watery diarrhea. The effects of low concentrations of nisin and bile acids on sporulation and toxin production were investigated inC. perfringensSM101, which carries an enterotoxin gene on the chromosome, in a nutrient-rich medium. Bile acids and nisin increased production of enterotoxin in cultures; bile acids had the highest effect. Both compounds stimulated the transcription of enterotoxin and sporulation-related genes and production of spores during the early growth phase. They also delayed spore outgrowth and nisin was more inhibitory. Bile acids and nisin enhanced enterotoxin production in some but not all otherC. perfringensisolates tested. Low concentrations of bile acids and nisin may act as a stress signal for the initiation of sporulation and the early transcription of sporulation-related genes in some strains ofC. perfringens, which may result in increased strain-specific production of enterotoxin in those strains. This is the first report showing that nisin and bile acids stimulated the transcription of enterotoxin and sporulation-related genes in a nutrient-rich bacterial culture medium.

RpoN Modulates Carbapenem Tolerance in Pseudomonas aeruginosa through Pseudomonas Quinolone Signal and PqsE

ABSTRACTThe ability ofPseudomonas aeruginosato rapidly modulate its response to antibiotic stress and persist in the presence of antibiotics is closely associated with the process of cell-to-cell signaling. The alternative sigma factor RpoN (σ54) is involved in the regulation of quorum sensing (QS) and plays an important role in the survival of stationary-phase cells in the presence of carbapenems. Here, we demonstrate that a ΔrpoNmutant grown in nutrient-rich medium has increased expression ofpqsA,pqsH, andpqsRthroughout growth, resulting in the increased production of thePseudomonasquinolone signal (PQS). The link betweenpqsAand its role in carbapenem tolerance was studied using a ΔrpoNΔpqsAmutant, in which the carbapenem-tolerant phenotype of the ΔrpoNmutant was abolished. In addition, we demonstrate that another mechanism leading to carbapenem tolerance in the ΔrpoNmutant is mediated throughpqsE. Exogenously supplied PQS abolished the biapenem-sensitive phenotype of the ΔrpoNΔpqsAmutant, and overexpression ofpqsEfailed to alter the susceptibility of the ΔrpoNΔpqsAmutant to biapenem. The mutations in the ΔrpoNΔrhlRmutant and the ΔrpoNΔpqsHmutant led to susceptibility to biapenem. Comparison of the changes in the expression of the genes involved in QS in wild-type PAO1 with their expression in the ΔrpoNmutant and the ΔrpoNmutant-derived strains demonstrated the regulatory effect of RpoN on the transcript levels ofrhlR,vqsR, andrpoS. The findings of this study demonstrate that RpoN negatively regulates the expression of PQS in nutrient-rich medium and provide evidence that RpoN interacts withpqsA,pqsE,pqsH, andrhlRin response to antibiotic stress.

Technological Potential ofLactobacillusStrains Isolated from Fermented Green Olives:In VitroStudies with Emphasis on Oleuropein-Degrading Capability

Technological properties of two strains ofLactobacillus plantarum(B3 and B11) and one ofLactobacillus pentosus(B4), previously isolated from natural fermented green olives, have been studiedin vitro. Acidifying ability, salt, temperature, and pH tolerances of all strains were found in the range reported for similar strains produced in Italy and optimal growth conditions were found to be 6.0–8.0 pH, 15–30°C temperature, and less than 6% NaCl. Moreover, all strains showed very good tolerance to common olive phenol content (0.3% total phenol) and high oleuropein-degrading capability. It was found that medium composition affected the bacterial oleuropein degradation. B11 strain grown in a nutrient-rich medium showed a lower oleuropein-degrading action than when it was cultivated in nutrient-poor medium. Furthermore, enzymatic activity assays revealed that oleuropein depletion did not correspond to an increase of hydroxytyrosol, evidencing that bacterial strains could efficiently degrade oleuropein via a mechanism different from hydrolysis.

The Corrosion Behavior of Cu-Ni-Si Alloy in Sea Water with Deep-Sea Bacteria

The corrosion behavior of Cu-Ni-Si alloy exposed to a nutrient-rich simulated seawater-based nutrient-rich medium in the presence of a deep-sea bacterial (Erythrobacter pelagi sp.nov) was investigated by metallographic microstructure observation, electrochemical impedance spectroscopy (EIS) measurement. It was demonstrated that the charge transfer resistance (Rct) and the resistance of oxide film (Rf) dramatically increased within 2 days then gradually decrease and becoming stable because of an patchy or blotchy biofilm formed on the surface of the alloy.

Thermococcus kodakarensis Genetics: TK1827-Encoded β-Glycosidase, New Positive-Selection Protocol, and Targeted and Repetitive Deletion Technology

ABSTRACT Inactivation of TK1761, the reporter gene established for Thermococcus kodakarensis, revealed the presence of a second β-glycosidase that we have identified as the product of TK1827. This enzyme (pTK1827) has been purified and shown to hydrolyze glucopyranoside but not mannopyranoside, have optimal activity at 95°C and from pH 8 to 9.5, and have a functional half-life of ∼7 min at 100°C. To generate a strain with both TK1761 and TK1827 deleted, a new selection/counterselection protocol has been developed, and the levels of β-glycosidase activity in T. kodakarensis strains with TK1761 and/or TK1827 deleted and with these genes expressed from heterologous promoters are described. Genetic tools and strains have been developed that extend the use of this selection/counterselection procedure to delete any nonessential gene from the T. kodakarensis chromosome. Using this technology, TK0149 was deleted to obtain an agmatine auxotroph that grows on nutrient-rich medium only when agmatine is added. Transformants can therefore be selected rapidly, and replicating plasmids can be maintained in this strain growing in rich medium by complementation of the TK0149 deletion.

SleC Is Essential for Germination of Clostridium difficile Spores in Nutrient-Rich Medium Supplemented with the Bile Salt Taurocholate

ABSTRACT Clostridium difficile is the major cause of infectious diarrhea and a major burden to health care services. The ability of this organism to form endospores plays a pivotal role in infection and disease transmission. Spores are highly resistant to many forms of disinfection and thus are able to persist on hospital surfaces and disseminate infection. In order to cause disease, the spores must germinate and the organism must grow vegetatively. Spore germination in Bacillus is well understood, and genes important for this process have recently been identified in Clostridium perfringens; however, little is known about C. difficile. Apparent homologues of the spore cortex lytic enzyme genes cwlJ and sleB (Bacillus subtilis) and sleC (C. perfringens) are present in the C. difficile genome, and we describe inactivation of these homologues in C. difficile 630Δerm and a B1/NAP1/027 clinical isolate. Spores of a sleC mutant were unable to form colonies when germination was induced with taurocholate, although decoated sleC spores formed the same number of heat-resistant colonies as the parental control, even in the absence of germinants. This suggests that sleC is absolutely required for conversion of spores to vegetative cells, in contrast to CD3563 (a cwlJ/sleB homologue), inactivation of which had no effect on germination and outgrowth of C. difficile spores under the same conditions. The B1/NAP1/027 strain R20291 was found to sporulate more slowly and produce fewer spores than 630Δerm. Furthermore, fewer R20291 spores germinated, indicating that there are differences in both sporulation and germination between these epidemic and nonepidemic C. difficile isolates.