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Journal: Canadian journal of microbiology


Polyhexamethylene biguanide (PHMB) is a cationic biocide. The antibacterial mode of action of PHMB (at concentrations not exceeding its minimal inhibitory concentration) upon Listeria innocua LRGIA 01 was investigated by Fourier transformed infrared spectroscopy and fluorescence anisotropy analysis. Fourier transformed infrared spectra of bacteria treated with or without PHMB presented some differences in the lipids region: the CH(2)/CH(3) (2924 cm(-1)/2960 cm(-1)) band areas ratio significantly increased in the presence of PHMB. Since this ratio generally reflects membrane phospholipids and membrane microenvironment of the cells, these results suggest that PHMB molecules interact with membrane phospholipids and, thus, affect membrane fluidity and conformation. To assess the hypothesis of PHMB interaction with L. innocua membrane phospholipids and to clarify the PHMB mode of action, we performed fluorescence anisotropy experiments. Two probes, 1,6-diphenyl-1,3,5-hexatriene (DPH) and its derivative 1-[4-(trimethyl-amino)-phenyl]-6-phenylhexa-1,3,5-triene (TMA-DPH), were used. DPH and TMA-DPH incorporate inside and at the surface of the cytoplasmic membrane, respectively. When PHMB was added, an increase of TMA-DPH fluorescence anisotropy was observed, but no changes of DPH fluorescence anisotropy occurred. These results are consistent with the hypothesis that PHMB molecules perturb L. innocua LRGIA 01 cytoplasmic membrane by interacting with the first layer of the membrane lipid bilayer.

Concepts: Spectroscopy, Cell membrane, Lipid, Membrane biology, Lipid bilayer, Infrared spectroscopy, Fourier transform spectroscopy, PAPB


This study evaluated the cholesterol-lowering property of lactic acid bacteria (LAB) isolated from mink. Two strains, Enterococcus faecium MDF1104 and Lactobacillus plantarum MDL1118, were shown to remove cholesterol from broths of natural hen egg yolk and skimmed milk. The cholesterol in hen egg yolk was reduced by 58.15% and 38% by L. plantarum and E. faecium, respectively. When the bacteria were used in combination, 48.95% (p < 0.01) of cholesterol was removed from skimmed milk. Experimental mice remained healthy when fed different doses of the LAB, and the total serum cholesterol concentration was the lowest (0.90 mmol/L) (p < 0.01) when a combination of L. plantarum and E. faecium was used. Based on our results, we suggest that L. plantarum MDL1118, E. faecium MDF1104, or a combination of the 2 strains could be considered as promising cholesterol-lowering probiotics.

Concepts: Bacteria, Microbiology, In vivo, Lactic acid, Lactobacillus, Lactobacillus plantarum, Enterococcus, Egg yolk


Mandarin orange (MO) is an important fruit crop of tropical and subtropical regions of the world. A total of 217 morphologically distinct rhizobacteria from MO orchards in 3 states of northeastern India were isolated and analyzed for 4 plant-growth-promoting (PGP) attributes: nitrogen fixation, production of indole acetic acid like substances, solubilization of phosphate, and ability to antagonize pathogenic fungi. Isolates were ranked based on in-vitro-assayed PGP attributes, and 10 superior isolates were selected to test their effect on seedling emergence and seedling growth in a completely randomized pot experiment. These 10 isolates increased seedling emergence over a noninoculated control within 45 days after sowing. Five isolates, namely RCE1, RCE2, RCE3, RCE5, and RCE7, significantly increased shoot length, shoot dry biomass, and root dry biomass of 120-day-old seedlings over the noninoculated control. The beneficial effects of 4 selected strains, namely Enterobacter hormaechei RCE-1, Enterobacter asburiae RCE-2, Enterobacter ludwigii RCE-5, and Klebsiella pneumoniae RCE-7, on growth of the seedlings were visible up to 1 year after their transfer to 8 kg capacity pots. These strains were superior both in terms of in-vitro-assayed PGP attributes and of their beneficial effect in low phosphorus soil and, thus, may be promising bioinoculants for promoting early emergence and growth of MO seedlings.

Concepts: Ethanol, Citrus, Orange, Tangerine, Rutaceae, Mandarin orange, Clementine, Tangor


The dynamic interaction of bacteria within bed sediment and suspended sediment (i.e., floc) in a wave-dominated beach environment was assessed using a laboratory wave flume. The influence of shear stress (wave energy) on bacterial concentrations and on the partitioning and transport of unattached and floc-associated bacteria was investigated. The study showed that increasing wave energy (0.60 and 5.35 N/s) resulted in a 0.5 to 1.5 log increase in unattached cells of the test bacterium Pseudomonas sp. strain CTO7::gfp-2 in the water column. There was a positive correlation between the bacterial concentrations in water and the total suspended solids, with the latter increasing from values of near 0 to up to 200 mg/L over the same wave energy increase. The median equivalent spherical diameter of flocs in suspension also increased by an order of magnitude in all experimental trials. Under both low (0.60 N/s) and high (5.35 N/s) energy regime, bacteria were shown to preferentially associate with flocs upon cessation of wave activity. The results suggest that collecting water samples during periods of low wave action for the purpose of monitoring the microbiological quality of water may underestimate bacterial concentrations partly because of an inability to account for the effect of shear stress on the erosion and mobilization of bacteria from bed sediment to the water column. This highlights the need to develop a more comprehensive beach analysis strategy that not only addresses presently uncharacterized shores and sediments but also recognizes the importance of eroded flocs as a vector for the transport of bacteria in aquatic environments.

Concepts: Bacteria, Water, Sediment, Pseudomonas aeruginosa, Force, Erosion, Wind, Sediment transport


The present investigation was aimed to scrutinize the salt tolerance potential of plant-growth-promoting rhizobacteria (PGPR) isolated from rhizospheric soil of selected halophytes (Atriplex leucoclada, Haloxylon salicornicum, Lespedeza bicolor, Suaeda fruticosa, and Salicornica virginica) collected from high-saline fields (electrical conductivity 4.3-5.5) of District Mardan, Pakistan. Five PGPR strains were identified using 16S rRNA amplification and sequence analysis. Bacillus sp., isolated from rhizospheric soil of Atriplex leucoclada, and Arthrobacter pascens, isolated from rhizospheric soil of Suaeda fruticosa, are active phosphate solubilizers and bacteriocin and siderophore producers; hence, their inoculation and co-inoculation on maize (‘Rakaposhi’) under induced salinity stress enhanced shoot and root length and shoot and root fresh and dry mass. The accumulation of osmolytes, including sugar and proline, and the elevation of antioxidant enzymes activity, including superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase, were enhanced in the maize variety when inoculated and co-inoculated with Bacillus sp. and Arthrobacter pascens. The PGPR (Bacillus sp. and A. pascens) isolated from the rhizosphere of the mentioned halophytes species showed reliability in growth promotion of maize crop in all the physiological parameters; hence, they can be used as bio-inoculants for the plants growing under salt stress.

Concepts: Bacteria, Ribosomal RNA, Antioxidant, Superoxide dismutase, 16S ribosomal RNA, Maize, Catalase, Halophyte


Great attention has been focused on Gram-negative bacteria in the application of microbial fuel cells. In this study, the Gram-positive bacterium Enterococcus faecalis was employed in microbial fuel cells. Bacterial biofilms formed by E. faecalis ZER6 were investigated with respect to electricity production through the riboflavin-shuttled extracellular electron transfer. Trace riboflavin was shown to be essential for transferring electrons derived from the oxidation of glucose outside the peptidoglycan layer in the cell wall of E. faecalis biofilms formed on the surface of electrodes, in the absence of other potential electron mediators (e.g., yeast extract).

Concepts: Archaea, Bacteria, Enzyme, Organism, Microbiology, Cell membrane, Cell wall, Bacteriology


Here we report the production of the cyclic macrotetrolide nonactin from the fermentation culture of Streptomyces griseus subsp. griseus. Nonactin is a member of a family of naturally occurring cyclic ionophores known as the macrotetrolide antibiotics. Our fermentation procedure of Streptomyces griseus was performed at 30 °C and 200 rev·min(-1) for 5 days on a rotary shaker. Diaion HP-20 and Amberlite XAD-16 were added to the fermentation medium. Isolated yield of nonactin was up to 80 mg·L(-1) using our methodology. Nonactin is commonly known as an ammonium ionophore and also exhibits antibacterial, antiviral, and antitumor activities. It is also widely used for the preparation of ion-selective electrodes and sensors. Chemical synthesis of nonactin has been achieved by some groups; however, overall yields are very low, making efficient biosynthesis an attractive means of production.

Concepts: Immune system, Bacteria, Chemical reaction, Antibiotic, Yield, Streptomyces, Ionophore, Streptomyces griseus


As stories of microbiological and infectious disease discoveries are told, one of the most charming of these in Canadian history is the recognition of verotoxigenic Escherichia coli (VTEC) and associated disease. The considerable burden and impact of VTEC-associated infections is currently experienced worldwide. Jack Konowalchuk, Joan Speirs, and their collaborators in Ottawa, Ontario, defined the E. coli verotoxin. Mohamed Karmali, Martin Petric, and colleagues at The Hospital for Sick Children in Toronto, Ontario, established the association of VTEC and hemolytic-uremic syndrome. Nationwide, and with the dissemination of knowledge through the central health directorate in Ottawa, numerous scientists and clinicians were motivated to focus on this theme, and within a relatively brief chronology, much became known about the biology of VTEC and the pathogenesis, epidemiology, and clinical aspects of disease. Many Canadian investigators, but especially those in the veterinary school at Guelph, Ontario, also contributed to the science of VTEC among animals. The interactions between clinical and veterinary researchers led to a then unprecedented exponential growth in the knowledge base of VTEC. Canadians also participated in a better understanding of the origin and potential of the E. coli O157 serogroup. Whereas not exclusively Canadian, the contributions of our national scientists in this field must be seen as a vital part of medical and microbiological Canadiana; this essence is captured in this historical review.

Concepts: Medicine, Epidemiology, Infectious disease, Bacteria, Infection, Escherichia coli, Escherichia coli O157:H7, Canada


Antibiotic discovery is in crisis. Despite a growing need for new drugs resulting from the increasing number of multi-antibiotic-resistant pathogens, there have been only a handful of new antibiotics approved for clinical use in the past 2 decades. Faced with scientific, economic, and regulatory challenges, the pharmaceutical sector seems unable to respond to what has been called an “apocalyptic” threat. Natural products produced by bacteria and fungi are genetically encoded products of natural selection that have been the mainstay sources of the antibiotics in current clinical use. The pharmaceutical industry has largely abandoned these compounds in favor of large libraries of synthetic molecules because of difficulties in identifying new natural product antibiotics scaffolds. Advances in next-generation genome sequencing, bioinformatics, and analytical chemistry are combining to overcome barriers to natural products. Coupled with new strategies in antibiotic discovery, including inhibition of resistance, novel drug combinations, and new targets, natural products are poised for a renaissance to address what is a pressing health care crisis.

Concepts: DNA, Pharmacology, Medicine, Bacteria, Virus, Antibiotic resistance, Drug discovery, Antibiotic


A sampling trip to Central Gold Mine, Nopiming Provincial Park, Canada, was taken in September 2011. Abundance, distribution, and physiology of aerobic anoxygenic phototrophs (AAP) from 4 locations were studied. Enumeration revealed 14.6% of culturable microbes were AAP. Five strains (NM4.16, NM4.18, C4, C9, C11) were chosen for analysis. All grow best on complex media without vitamin requirements and with an optimal pH 7.0-8.0, with strain C4 preferring pH 6.0. Strain NM4.18 tolerates the highest pH 11.0. Optimal temperature for all is 28 °C (range of 2-37 °C except NM4.16, which survives 45 °C). Strains C9, C11, and NM4.18 grew in 1.0%, 2.0%, and 5.0% NaCl, respectively, while NM4.16 and C4 grew only without NaCl. Isolates were all highly resistant to toxic metal(oid) oxides: tellurite (1500 μg/mL, all), tellurate (1500 μg/mL, C11), selenite (5000 μg/mL, C9, C11, and NM4.18), selenate (1000 μg/mL, C9 and C11), and orthometavanadate and metavanadate (5000 μg/mL, C11 and NM4.18). They could reduce tellurite to the less toxic elemental tellurium. Full 16S rRNA gene sequencing revealed all strains are Alphaproteobacteria, with C4 and NM4.16 closely related to Porphyrobacter colymbi (99.4% and 99.7% sequence similarity, respectively), C9 to Brevundimonas variabilis (99.1%), C11 to Brevundimonas bacteroides (98.6%), and NM4.18 to Erythromonas ursincola (98.5%).

Concepts: Ribosomal RNA, 16S ribosomal RNA, 30S, Gold, Selenium, Tellurium, Park, Tailings