A Study of Bacterial Linear Growth Using A Microcalorimetric Method

By using an LKB-2277 bioactivity monitor, we have determined the thermogenesis curves of four kinds of anaerobes linear growth. From the thermogenesis curves, we established the growth thermokinetic equation:dp/dt = km Pn,the order of growth metabolism n=0, and calculated the mean specific rate constant of multiplication μ. It is a new kind of bacterial growth,it was compared with exponential growth.

The impact of heavy metals on bacterial tolerance of antibiotic resistance and growth in the aquatic environment of Vietnam

Heavy metals may induce bacterial antibiotic resistance and affect their growth in the ecosystem.In this study,we aim to determine bacterial growth and antibiotic resistance in the pressure of heavy metals.Observed the changing morphology by gram staining was checked for bacterial toleration with heavy metal,developing of the colony form unit(CFU)was analysed bacterial kinetic growths and their biofilm formation.The disk diffusion test was used to perform bacterial susceptibility profiles with Ceftazidime(30μg),Ceftriaxone(30μg),Colistin sulfate(10μg),Meropenem or Imipenem(10μg),Ciprofloxacin(5μg)and Azithromycin(15μg)and the CLSI was applied for interpreting the data.The bacterial morphology remarkably changed from normal to short,round shape at a high concentration of heavy metals after 1 month.Their changing shape adapted to heavy metals by survival growing and resisted to Azithromycin,Ciprofloxacin,and Colistin without biofilm formation after 1 month,that was continued increasing after 2 months.The bacterial growth and antibiotic resistance were significant differences between provinces(P=0.01),type of bacterial species,and concentration of heavy metals.These results indicate that heavy metals are a crucial factor-driven for enhancing bacterial adaptation in pollution water resources and inducing their antimicrobial resistance in the aquatic environment.

Novel Mannich Bases of Benzimidazole Derivatives: An Antibacterial Study of Environmental Bacterial Strains

A previous study was conducted on the synthesis and antibacterial evaluation of Mannich bases of 2-(thioalkyl)-1H-methylbenzimidazole derivatives. The results of this study showed that certain 2-(thioalkyl)-1H-methylbenzimidazole and 2-(thioalkyl)-methyl-1-(piperidin-1-ylmethyl)benzimidazole derivatives possess antibacterial activities against clinical strains, such as Escherichia coli, Klebsiella pneumonia (Gram-negative bacteria), Staphylococcus aureus and Pseudomonas aeruginosa (Gram-positive bacteria). Following these favorable results, we extended the antibacterial evaluation of this series of molecules to environmental strains. The aim of this study was to assess the impact of the methyl-piperidine group fixed at position-1 of this new series of benzimidazoles on the antibacterial activity of environmental strains. In addition, we first evaluated the antibacterial activity of four 2-(thioalkyl)methylbenzimidazole derivatives and then that of five 2-(thioalkyl)-methyl-1-(piperidin-1-ylmethyl) benzimidazole derivatives. This study allowed us to show that compounds 1d and 1e could inhibit bacterial growth in vitro of the Enterobacteria P1 strain with inhibition diameters of 17.3 ± 0.6 mm and 10 ± 0.0 mm, respectively. However, addition of methyl-piperidinyl in this series showed that five (5) of 2-(thioalkyl)-methyl-1-(piperidin-1-ylmethyl) benzimidazole derivatives had an inhibitory effect on the in vitro growth of bacterial strains used except on Enterobacteria P2 with inhibition diameters between 10.0 ± 0.8 mm and 27.9 ± 1.4 mm. The introduction of the methyl-piperidinyl group at the 1-position of 2-(thioalkyl)-1H-methylbenzimidazole derivatives greatly improved the antibacterial activity against environmental bacteria such as Escherichia coli A1, A2, A3, and A4 and two Enterobacteria P1.

Stacking Dishes Wet May Promote Bacterial Growth

这是一个为我们所忽略的问题:餐具洗净后,堆叠一处,届时拿出来就用。这似乎是很自然,很卫生的。本文告戒读者:当心！洗净后而未净干燥处理的餐具,在48小时后,即细菌丛生！成为一个重要的污染源。文章的末尾称: …consumers and food-preparers should pay attention not just to what they eatbut to whether or not what they eat is safely prepared。 读者朋友,在餐馆里你是consumer,在家里,你是food-preparer,你可曾注意到这个问题?】

Thermochemical Studies of SeleniumⅠ.Microcalorimetric Study of Effect of Na_(2)SeO_(3) on Bacillus subtilis Growth

By using LKB2277 bioactivity monitor, we have studied the effect of Na 2SeO 3 on Bacillus subtilis Growth at two different media and found the antagonism of protein on its toxicity. Low concentration of Na 2SeO 3 has promoting action, and high concentration of Na 2SeO 3 has inhibitory action. Half inhibitory concentration ( IC 50 ) of BPY medium is 4.2×10 -1 g / L, and IC 50 of PD medium is 2.2×10 -2 g / L.

Resazurin as an indicator of reducing capacity for analyzing the physiologic status of deep-sea bacterium Photobacterium phosphoreum ANT-2200

Resazurin(RZ)is a weakly fl uorescent blue dye and can be reduced irreversibly to highly fl uorescent pink resorufi n(RF)that is reduced reversibly to colorless dihydroresorufi n(hRF)by photodeoxygenation,chemical reaction and reductive organic compounds produced through cell metabolism.Because of the reliable and sensitive fl uorescence-color change and noninvasive features,RZ has been used widely as a redox indicator in cell viability/proliferation assays for bacteria,yeast,and mammalian cells.However,RZ is used rarely for physiological characterization of marine microorganisms.Here,we developed a custom-made irradiation and absorption-analysis device to assess the reducing capacity and physiologic status of marine bacterial cultures.We measured the absorption spectra of RZ,RF,and hRF in the presence of the reducing compound Na 2 S and under visible-light irradiation.After establishing appropriate parameters,we monitored the color changes of RZ and its reduced derivatives to evaluate the coherence between reducing capacity,bioluminescence and growth of the deep-sea bacterium Photobacterium phosphoreum strain ANT-2200 under various conditions.Emission of bioluminescence is an oxidation process dependent upon cellular reducing capacity.Growth and bioluminescence of ANT-2200 cell cultures were impeded progressively with increasing concentrations of RZ,which suggested competition for reducing molecules between RZ at high concentration with reductive metabolism.Therefore,caution should be applied upon direct addition of RZ to growth media to monitor redox reactions in cell cultures.Analyses of the instantaneous reduction velocity of RZ in ANT-2200 cell cultures showed a detrimental eff ect of high hydrostatic pressure and high coherence between the reducing capacity and bioluminescence of cultures.These data clearly demonstrate the potential of using RZ to characterize the microbial metabolism and physiology of marine bacteria.

Making comparable measurements of bacterial respiration and production in the subtropical coastal waters

Accurate estimates of bacterial carbon metabolic rates are indispensable for understanding the regulation of carbon fluxes in aquatic environments.Here,changes in bacterial growth,production,and cell volume in both pre-filtered and unfiltered seawater during 24 h incubation were monitored.The methodological artifacts during Winkler bacterial respiration(BR)measurements in subtropical Hong Kong coastal waters were assessed.Bacterial abundance increased by 3-and 1.8-fold in the pre-filtered and unfiltered seawater after incubation,respectively.Bacterial production(BP)and cell volume also showed significant enhancement.Compared with the BR measurements obtained by the Winkler method,the instantaneous free-living BR measurements,after correction,decreased by~70%.The time-integrated free-living BR and BP during 24 h incubation in the pre-filtered sample provided an improved estimate of bacterial growth efficiency,which increased by~52%compared to the common estimations using the noncomparable measurements of integrated free-living BR and instantaneous total BP.The overestimation of BR also exaggerated the contribution of bacteria to community respiration,affecting the understanding on the metabolic state of the marine ecosystems.Furthermore,the BR estimates by the Winkler method may be more biased in environments with a higher bacterial growth rate and tightly coupled grazing mortality,as well as in those with higher nutrient concentrations.These results reveal obvious problems associated with the BR methodology and raise a warning for caution when comparing BP and BR,as well as when making estimations of carbon flow through the complex microbial networks in aquatic ecosystems.

Bacterial Sample Concentration and Culture Monitoring Using a PEG-Based Osmotic System with Inline Impedance and Voltammetry Measurements

Impedance measurements using graphite electrodes were used to detect the increase in culture medium conductivity due to bacteria growth in real time along with simultaneous voltammetric monitoring of pyocyanin concentration.Electrochemical methods were compared to conventional continuous monitoring of bacterial cultures using turbidity measurement at an optical density of 600 nm(OD600).A practical osmotic system was further designed for concentrating bacterial cultures during growth to enable earlier detection using the electrochemical methods.Bacterial cultures,starting from an initial culture density of 1×10^(8) cells/mL,were grown inside a sealed cellulose ester dialysis membrane,while polyethylene glycol in LB medium was used as the draw solution outside the membrane to gradually concentrate the growing cultures.0.7-mm-diameter graphite for mechanical pencils was utilized as working and counter electrodes with a platinum wire reference electrode for electrochemical measurements with and without the osmotic system.In the absence of forward osmosis,impedance meas-urements detected culture growth~1 h faster than conventional OD600.Integrating osmosis showed a twofold decrease in the time to detect pyocyanin production as an indicator for bacterial growth.For impedance monitoring,removal of water by osmosis was conflated with the impedance decrease due to cell growth;however,the results show a promising ability to detect bacteria growth via an observed shift in osmotic impedance profile when bacteria are present in a sample.By monitoring the deviation in the impedance profile,a threefold improvement in detection time was achieved when compared to conventional OD600 measurements.

Integrated identification of growth pattern and taxon of bacterium in gut microbiota via confocal fluorescence imaging‐oriented single‐cell sequencing

Despite the fast progress in our understanding of the complex functions of gut microbiota,it is still challenging to directly investigate the in vivo microbial activities and processes on an individual cell basis.To gain knowledge of the indigenous growth/division patterns of the diverse mouse gut bacteria with a relatively high throughput,here,we propose an integrative strategy,which combines the use of fluorescent probe labeling,confocal imaging with single‐cell sorting,and sequencing.Mouse gut bacteria sequentially labeled by two fluorescent D‐amino acid probes in vivo were first imaged by confocal microscopy to visualize their growth patterns,which can be unveiled by the distribution of the two fluorescence signals on each bacterium.Bacterial cells of interest on the imaging slide were then sorted using a laser ejection equipment,and the collected cells were then sequenced individually to identify their taxa.Our strategy allows integrated acquirement of the growth pattern knowledge of a variety of gut bacteria and their genomic information on a single‐cell basis,which should also have great potential in studying many other complex bacterial systems.

Biodegradation of Crude Oil in Contaminated Soils by Free and Immobilized Microorganisms

The efficiencies of free and immobilized bacterial cultures of petroleum hydrocarbon degraders were evaluated and compared in this study. Hydrocarbon-degrading microbial communities with high tolerance to and high degrading ability of crude oil were obtained from the soil contaminated with crude oil in the Yellow River Delta. Then, the microbial cells were immobilized in sodium alginate （SA） beads and sodium Mginate-diatomite （SAD） beads. The biodegradation of crude oil in soil by immobilized cells was compared with that by free cells at three inoculation concentrations, 1× 104 colony forming units （cfu） kg-^（-1）（low concentration, L）, 5 × 104 cfu kg^（-1） （medium concentration, M）, and 1× 105 cfu kg^（-1） （high concentration, H）. At 20 d after inoculation, the maximum degradation rate in the immobilized systems reached 29.8% （SAD-M）, significantly higher （P 〈 0.05） than that of the free cells （21.1%）, and the SAD beads showed greater degradation than the SA beads. Moreover, both microbial populations and total microbial activity reached significantly higher level （P 〈 0.05） in the immobilized systems than free cell systems at a same initial inoculation amount. The scanning electronic microscope （SEM） images also confirmed the advantages of the immobilized microstructure of SAD beads. The enhanced degradation and bacterial growth in the SAD beads indicated the high potential of SAD beads as an effective option for bioremediation of crude oil-contaminated soils in the Yellow River Delta.

Soil microbial community structure and activity in a 100-year-old fertilization and crop rotation experiment

Aims Nitrogen(N)fertilization and lime addition may affect soil micro-bial and nematode communities and ecosystem functions through changing environmental conditions,such as soil pH and soil organic carbon.The objectives of this experiment were to examine the impact of N input and liming on soil microbial and nematode communities and to identify the key environmental determinant of community composition in a century-old fertilization and crop rota-tion experiment.Methods The field experiment consisting of a 3-year crop rotation regime was established in 1911 in southeastern USA.Four treatments,(i)no-input control,(ii)NPK with winter legume,(iii)PK with legume and lime and(iv)NPK with legume and lime,were included in this study.soil samples collected at the 0-5 cm depth were used to determine the bacterial growth rate by the 3H-thymidine incorporation technique.Incorporation of 13C into neutral lipids,glycolipids and phospholipid fatty acids(PlFas)was measured after incubation of soil with 13C-labeled acetate for 24 h.Free-living nematodes in fresh soil were extracted using a density sucrose centrifugal flotation method and identified to trophic group level.Important Findingsliming resulted in a 10-fold increase in bacterial growth rates compared with the no-input control,whereas N fertilization had no significant effect.multivariate analysis of PlFa profiles showed that soil microbial community composition was different among the four treatments;the difference was primarily driven by soil pH.PlFas indicative of gram-negative bacteria covaried with soil pH,but not those of fungi and actinobacteria.liming enhanced 13C incorpora-tion into neutral lipids,glycolipids and phospholipids by 2-15 times.In addition,13C incorporation into 16:0,16:1ω9,18:1ω9,18:1ω7 and 18:2ω6 were greater than other PlFas,suggesting that gram-negative bacteria and fungi were more active and sensitive to simple C input.bacterivorous nematodes were the dominant trophic group in the soil,but no significant differences in nematode communities were found among the treatments.our results suggest that soil pH had a greater impact than N fertilization on soil microbial community composition and activity in a crop rotation system including legumes.

Cu(Ⅱ), Fe(Ⅲ) and Mn(Ⅱ) combinations as environmental stress factors have distinguishing effects on Enterococcus hirae

Pollution by various heavy metals as environmental stress factors might affect bacteria. It was established that iron（Fe（Ⅲ））, manganese（Mn（Ⅱ）） and copper（Cu（Ⅱ）） ion combinations caused effects on Enterococcus hirae that differed from the sum of the effects when the metals were added separately. It was shown that the Cu2＋–Fe3＋combination decreased the growth and ATPase activity of membrane vesicles of wild-type E. hirae ATCC9790 and atp D mutant（with defective FoF1-ATPase） MS116. Addition of Mn2＋–Fe3＋combinations within the same concentration range had no effects on growth compared to control（without heavy metals）. ATPase activity was increased in the presence of Mn2＋–Fe3＋, while together with0.2 mmol/L N,N′-dicyclohexylcarbodiimide（DCCD）, ATPase activity was decreased compared to control（when only 0.2 mmol/L DCCD was present）. These results indicate that heavy metals ion combinations probably affect the FOF1-ATPase, leading to conformational changes. Moreover the action may be direct or be mediated by environment redox potential.The effects observed when Fe3＋was added separately disappeared in both cases, which might be a result of competing processes between Fe3＋and other heavy metals. These findings are novel and improve the understanding of heavy metals ions effects on bacteria,and could be applied for regulation of stress response patterns in the environment.

Experimental study using the dilution incubation method to assess water biostability

Water biostability is of particular concern to water supply as a major limiting factor for heterotrophic bacterial growth in water distribution systems. This study focused on bacterial growth dynamics in the series dilution of water samples with TOC（total organic carbon） values determined beforehand. The results showed that the specific growth rate of Pseudomonas fluorescens P17 varied dramatically and irregularly with TOC value when TOC concentrations were low enough during the initial periods of incubation under given conditions. According to this relationship between bacterial growth rate and TOC, a dilution incubation method was designed for the study of water biostability. With the method under a given condition, a turning-point TOC value was found at a relatively fixed point in the curve between bacterial growth rate and TOC of water sample, and the variation of growth rate had different characteristics below the turning-point TOC value relative to that over this value. A turning-point TOC value similarly existed in all experiments not only with tap water, but also with acetate and mixed solutions. And in the dilution incubation method study, the affections were analyzed by condition factors such as inoculum amount,incubation time and nature of the organic carbon source. In very low organic carbon water environments, the variation characteristics of bacterial growth rate will be useful to further understand the meaning of water biostability.