Non-species-specific effects of unacylated homoserine lactone and hexylresorcinol, low molecular weight autoregulators, on the growth and development of bacteria

We conducted a comparative study of the effects of alpha-amino-gamma-butyrolactone, the common structural element of extracellular microbial regulators of the homoserine lactone (HSL) group, and of 4-n-hexylresorcinol, an autoregulator of the alkylhydroxybenzene (AHB) group, on the growth and development of gram-positive and gram-negative bacteria. We revealed non-species-specific effects of HSL and AHB and characterized their concentration dependencies. The addition of 10(-5)-10(-3) M HSL or 10(-5)-10(-4) M AHB during the exponential growth phase of the cultures grown on balanced media resulted in cell division arrest and accelerated the transition to the stationary phase that culminated in endospore formation in Bacillus cereus, Alicyclobacillus tolerans, and Sulfobacillus thermosulfidooxidans. When bacilli grew under the cultivation conditions that resulted in a low-zero spore percentage, 10(-4)-10(-3) M HSL cancelled the inhibition of spore formation. In the gram-negative bacteria Pseudomonas aurantiaca and Azotobacter vinelandii, AHB at concentrations of 10(-4) to (1.5-2.5) 10(-4) M induced the formation of dormant cells. Studies with the actinobacterium Streptomyces avermitilis revealed that the HSL effect varied depending on the age of the test cultures. The addition of 10(-4) M HSL during the lag phase of a submerged streptomycete culture accelerated its transition to the stationary phase and induced the formation of endospores, the dormant cells that are regarded as alternatives to exospores (conidia). If HSL (3.64 and 4.55 mg per 1cm2 disc) was locally added to a surface S. avermitilis culture, the growing mycelium formed rings that differed in their density, in the extent of the development of aerial mycelium, and in the presence/absence of exospores. Ring-shaped growth of streptomycete mycelia was also induced by 0.075-0.75 mg of AHB; however, unlike HSL, AHB repressed exospore formation. The data on non-species-specific effects of HSL and AHB suggest that they may perform regulatory functions on the microbial community level.     

A comparative study of the inducing effect of homoserine lactone and hexylresorcinol on phenotypic dissociation in bacteria

It has been shown that the phenotypic dissociation of Bacillus subtilis SK1 and Salmonella typhimurium TA100 is induced by hexylresorcinol, an exogenous non-species-specific autoregulator of pleiotropic action, which is genotoxic for both pro-and eukaryotes. Nongenotoxic homoserine lactone, a chemical analogue of cell-density-responsive species-specific regulators, does not induce bacterial dissociation. The phage resistance of the S-and R-type variants of S. typhimurium TA100 induced by hexylresorcinol has been found to be the same as that of the S-and R-type salmonella variants obtained by the routine subculturing method.     

Synergistic effects of antibiotics and an N-acyl homoserine lactone analog on Porphyromonas gingivalis biofilms

Aims: To investigate the effects of the combined application of an N‐acyl homoserine lactone (HSL) analog and antibiotics on biofilms of Porphyromonas gingivalis, a major pathogen of periodontal disease. Methods and Results: Antibiotics used were cefuroxime, ofloxacin and minocycline. A flow‐cell model was used for biofilm formation. Samples were divided into four groups: control, analog‐treated, antibiotic‐treated and combined application groups. Biofilm cell survival was determined using adenosine triphosphate (ATP) bioluminescence and confocal laser microscopy (CLSM). In the combined application group, the ATP count in biofilm cells was significantly decreased compared with the antibiotic‐treated group (Games–Howell test, P < 0·05). A combination of cefuroxime and the analog was most effective against the P. gingivalis biofilm. CLSM observations revealed that the proportion of dead cells was highest in the combined application group. Conclusions: The combined application of the N‐acyl HSL analog and antibiotics was effective at reducing the viability of P. gingivalis cells in biofilms. Significance and Impact of the Study: The combined application of the N‐acyl HSL analog and antibiotics may be successful for eradicating infections involving bacterial biofilms, such as periodontitis.     

Effect of microbial cell‐free meat extract on the growth of spoilage bacteria

Aims: This study examined the effect of microbial cell‐free meat extract (CFME) derived from spoiled meat, in which quorum sensing (QS) compounds were present, on the growth kinetics (lag phase, and growth rate) of two spoilage bacteria, Pseudomonas fluorescens and Serratia marcescens. Methods and Results: Aliquots of CFME from spoiled meat were transferred to Brain Heart Infusion broth inoculated with 10³ CFU ml^?1 of 18 h cultures of Ps. fluorescens or Ser. marcescens, both fresh meat isolates; CFME derived from unspoiled fresh meat (‘clean’ meat) served as a control. Changes in impedance measurements were monitored for 48 h, and the detection time (Tdet) was recorded. It was found that in the absence of CFME containing QS compounds the Tdet was shorter (P < 0·05) than that in broth samples with added CFME from spoiled meat. The rate of growth of Ps. fluorescens, recorded as the maximum slope rate of conductance changes (MSrCC), after Tdet, was higher (P < 0·05) in samples with CFME containing QS compounds compared to samples without CFME or CFME derived from ‘clean’ meat. Similar results in MSrCC of impedance changes were obtained for Ser. marcescens. Conclusions: The study indicated that the growth rate (expressed in MSrCC units) of meat spoilage bacteria in vitro was enhanced in samples supplemented with CFME containing QS compounds compared to control samples (i.e., without CFME or with CFME from ‘clean’ meat). This behaviour may explain the dominant role of these two bacteria in the spoilage of meat. Significance and Impact of the Study: These results illustrate the potential effect of signalling compounds released during storage of meat on the behaviour of meat spoilage bacteria. Understanding such interactions may assist in the control of fresh meat quality and the extension of its shelf life.     

Stimulative and inhibitory effects of bacteria on the growth of microalgae

Several examples of stimulative and inhibitoryeffects of bacteria on microalgal growth areintroduced, and the importance of bacteria in algalmass culture is investigated. Diatoms are often usedas live food for planktonic larvae of sea urchin andbivalves. Monodispersed Chaetoceros ceratosporum hasbeen cultivated by using clean, high nutrient content,deep seawater (DSW). However, the growth rate and cellyield of diatoms fluctuated, to relatively largeextent, with the season that DSW was collected. Whensome bacterial strains isolated from DSW were added tothe culture, diatom growth was often stimulated and arelatively constant cell yield was obtained. Anotherdiatom species, C. gracilis, was also stimulated byadding some bacterial strains to cultures. Thepositive effect of bacteria on diatoms was observednot only for planktonic species, but also on attachedspecies. A benthic diatom, Nitzschia sp., wasstimulated by a bacterial film of Alcaligenes on thesurface of the substratum. On the other hand, a strainof Flavobacterium sp. isolated from natural seawaterduring the decline period of an algal bloom had a strongalgicidal effect on the red tide plankton,Gymnodinium mikimotoi. Recent reports demonstratethat many bacterial strains have significantalgicidal effects on many species of red tideplankton. These results indicate that bacterialeffects should be taken into account to obtain stablemass culture of food microalgae.     

A randomized clinical trial on the antitumoral effects of low molecular weight heparin in the treatment of esophageal cancer

The current treatment approaches for esophageal cancer are associated with poor survival, and there are ongoing efforts to find new and more effective therapeutic strategies. There are several reports on the antitumoral effects of low-molecular-weight heparins (LMWHs). We have assessed the possible survival benefit of LMWHs in esophageal malignancies. This was a randomized, single-blind, multicenter, Phase II clinical trial on nonmetastatic esophageal cancer candidate for neoadjuvant chemoradiotherapy. Patients were randomly assigned to the chemoradiotherapy-only arm or chemoradiotherapy plus enoxaparin arm using 1:1 allocation. Radiotherapy was delivered in 1.8-Gy daily fractions to a dose of 50.4 Gy in both groups. Paclitaxel 50 mg/m² and carboplatin (AUC 2) were administered weekly, concurrent with radiotherapy. In the intervention group, patients received enoxaparin (40 mg) and chemoradiation daily. 4–6 weeks after treatment, all patients underwent esophagectomy. After a median follow up of 7 months, estimated 1 year disease-free survival (DFS) in the intervention group was 78.9% and was 70% in the control groups ( p = 0.5). Toxicity from the experimental treatment was minimal, and there were no treatment-related deaths. A pathologically complete response in intervention and control group was 64.8% and 62.5%, respectively ( p = 0.9). There was a nonsignificant trend toward improved survival by the addition of enoxaparin to the concurrent chemoradiotherapy regimen. However, 1 y DFS of both groups were high as expected. A longer follow-up and a larger sample size are required.     

Effects of different molecular weight fractions of dissolved organic matter on the growth of bacteria,algae and protozoa from a highly humic lake

Effects of different molecular size fractions (< 1000 MW, < 10 000 MW, < 100 000 MW and <0.1 μm) of dissolved organic matter (DOM) on the growth of bacteria, algae and protozoa from a highly humic lake were investigated. DOM from catchment drainage water as well as from the lake consisted mostly (59–63%) of high molecular weight (HMW) compounds (> 10 000 MW). With excess inorganic nutrients, the growth rate and yield of bacteria were almost identical in all size fractions. However, in < 1000 MW fractions and with glucose added, a longer lag phase occurred. Without added nutrients both the growth rates and biomasses of bacteria decreased towards the smaller size fractions and the percentage of dissolved organic carbon (DOC) used during the experiment and the growth efficiency of bacteria were lower than with excess nutrients. The growth efficiency of bacteria was estimated to vary between 3–66% in different MW fractions, largely depending on the nutrient concentrations, but the highest growth efficiencies were observed in HMW fractions and with glucose. The growth of algae was clearly lowest in the < 1000 MW fraction. In dim light no net growth of algae could be found. In contrast, added nutrients substantially enhanced algal growth and in deionized water with glucose, algae achieved almost the same growth rate and biomass as in higher MW fractions of DOM. The results suggested that bacteria and some algae were favoured by DOM, but protozoans seemed to benefit only indirectly, through bacterial grazing. The utilization of DOM by bacteria and algae was strongly affected by the availability of phosphorus and nitrogen.     

合成生物学时代基于非模式细菌的工业底盘细胞研究现状与展望

工业微生物底盘细胞的开发将为工业生物技术的发展提供优良的细胞工厂,有利于实现环境保护及经济可持续发展.基于合成生物学"设计-构建-测试-学习"(Design-Build-Test-Learn,DBTL)策略,对底盘细胞进行多维度的理性或半理性改造是实现"建物致知"以及"建物致用"目标的重要手段.文中简述了合成生物学DB...     

Effect of plant growth conditions, plating density, and genotype on the anther culture response of soft white spring wheat hybrids

Ten soft white spring wheat (Triticum aestivum L.) F₁ hybrids were grown under three temperature regimes, and anthers were cultured at two plating densities to investigate the effect of plant growth conditions, plating density, and genotype on embryo induction and plant regeneration. Anthers from plants grown at high temperature (25 °/18 °C) or from plants transferred from low (15 °/12 °C) to high temperature generally produced more embryos and green shoots, with a lower frequency of albinos, than did anthers from plants grown at low temperature. However, plating densities of 10 versus 20 anthers per milliliter, had little effect on anther response. Four of the five hybrids with `Fielder' as the female parent produced more embryos and green shoots than did hybrids with `AC Reed' as the female parent. Received: 12 July 1996 / Revision received: 1 April 1997 / Accepted: 30 April 1997     

The combined effects of temperature and salinity on hatching success and the survival,growth, and development of the larval stages of Metapenaeus bennettae (Racek & Dall)

During the spawning season of the estuarine prawn Metapenaeus bennettae (Racek & Dall), laboratory and field experiments were conducted to examine the combined effects of temperature and salinity on hatching success of eggs and the survival, growth and development of larvae. Response surface analysis showed that optimal levels of temperature and salinity for maximum hatching success varied depending on conditions during spawning. Similarly, temperature and salinity conditions that produced maximum survival and growth of larvae depended on conditions during rearing prior to experimental temperature/salinity treatments. At the onset of feeding, larvae showed the lowest tolerance to changes in temperature and salinity. Supplementary feeding experiments in the laboratory, and survival rates in field experiments indicated that starvation was a more potent factor than the effects of temperature and salinity in determining survival through the protozoeal larval stages. Late larval stages were relatively indifferent to the effects of temperature and salinity. It is suggested that, during early development, adaptive response to the prevailing physical conditions enhances survival in an estuarine environment.     

Temperature and humidity affecting development, survival and weight loss of the pupal stage of Drosophila melanogaster, and the influence of alternating temperature on the larvae

1. 1. The mean durations of development in the pupae of Drosophila melanogaster (Meigen) and their survival were measured at combinations of six constant temperatures (15, 20, 22.5, 25, 27.5 and 30°C) and up to 11 levels of relative humidity. The thermal survival range for the pupae is between 15 and 30°C, and the humidity viable range is between 60 and 100% RH.

2. 2. The percentage water loss of the pupae was measured at six constant temperatures and four levels of relative humidity. There was a rapid increase in the percentage of water lost during the first 24 h exposure at all tested conditions. However, pupae reared at 100% RH at each constant temperature, sustained the lowest water loss. The percentage water loss increased as temperature increased, as humidity decreased and also with time.

3. 3. The duration of larval development studied at six constant temperatures (15, 20, 22.5, 25, 27.5 and 30°C) was inversely related to temperature. A wide range of alternating temperature regimes had a small, though statistically significant, accelerative effect on larval developmental time. Thus, the present results may be used as a basis for modelling development under changing temperatures, with the assumption that the developmental rate is nearly identical to that from a series of constant temperatures.

     

Influence of spectral quality on the growth response of intact bean plants to brassinosteroid, a growth-promoting steroidal lactone. II. Chlorophyll content and partitioning of assimilate

The chlorophyll content and partitioning of assimilate of bean ( Phaseolus vulgaris L. 'Pinto') plants were determined 6 days after treatment of the second internode (I₂ with 5 μg of brassinosteroid (BR), a growth-promoting steroidal lactone. Plants were grown for 6 days under equal levels (90 μmol s^-1 m^-2) of photosynthetic photon flux density (PPFD) provided by cool white fluorescent (CWF) or incandescent (INC) lamps and equal levels of far-red (28 W m^-2, 700–800 nm) radiation provided by the same INC or far-red (FR) fluorescent lamps. Brassinosteroid treatment had no appreciable effect on total biomass production but caused a decrease of 15–20% dry matter distribution in the upper portion of the shoot, a small (4%) but constant increase in dry matter in l₂ and a large (11–16%) increase in dry matter in the lower portion of the shoot (especially I₁). Treatment with BR increased assimilate accumulation in the primary leaves, especially under INC and FR lamps, and reduced dry matter in the trifoliate leaves. BR also caused a 16–21% reduction in total leaf area and even a greater reduction in area of the trifoliate leaves, but significantly increased specific leaf weight of the primary leaves and the first trifoliate leaf and the amount of dry matter in the lateral shoots under all radiation sources. In comparison to controls, BR treatment increased dry matter accumulation in the treated internode 3.3x under CWF and 1.6x under INC or FR. BR treatment also increased chlorophyll content in the primary leaves under all radiation sources and in the trifoliate leaves under CWF and INC lamps. These findings suggest a possible mobilization role of BR and establish the importance of adequate PPFD (and photosynthate) for maximum swelling and splitting response to brassinosteroid.     

Effects of brief exposures to low temperature on the development, longevity and fecundity of the grain aphid Sitobion auenae (Hemiptera: Aphididae)

First instar nymphs and adults of the grain aphid Sirobion auenae that had been reared at 10°C and 20°C over a number of generations, were cooled to -5°C and -10°C for 1 h and 6 h and returned to 20°C to assess the effects of brief exposures to low temperatures (cold-pulses) on their survival. rate of development, longevity and fecundity. A strong acclimation response was observed in first instar nymphs, with significantly less mortality in groups reared to 10°C compared to 20°C. Mean development time from first instar to adult was not significantly affected by low temperature exposure at the first nymphal stage. Longevity in all groups cooled as first instars was reduced by the sub-zero cold-pulses, and was also dependent on temperature and exposure time. Acclimated aphids survived longer than non-acclimated individuals. Reproductive rate, in terms of the number of nymphs born per aphid per day, was unaffected by cold stress applied at the first instar stage. Total fecundity was however reduced, being a function of the number and longevity of the survivors. Adult aphids were less cold hardy than nymphs; mortality was higher at -10°C than -5°C increasing with duration of exposure from 1 h to 6 h. Mean fecundity was reduced significantly in aphids cooled at the adult stage, the number of aphids born per day decreasing as the exposure period of the cold-pulse increased, suggesting that low temperature had affected embryogenesis. All the nymphs born to adults surviving exposure to -5°C for 6 h died within 48 h of birth, indicating that low temperature has a pre-natal effect on mortality.     

Biochemical markers for measurement of predation effects on the biomass,community structure,nutritional status,and metabolic activity of microbial biofilms

Chemical measures for the biomass, community structure, nutritional status, and metabolic activities of microbes in biofilms attached to detrital or sediment surfaces based on analysis of components of cells and extracellular polymers represent a quantitative and sensitive method for the analysis of predation. These methods require neither the quantitative removal of the organisms from the surfaces nor the efficient culture of each group of microbes for analysis of predation effects on the biofilm. The biomass of microbes can be determined by measuring the content of cellular components found universally in relatively constant amounts. If these components have a high natural turnover or are rapidly lost from viable cells, they can be utilized to measure the viable cell mass. The membrane phospholipids have a naturally high turnover, are found in all cellular membranes, are rapidly hydrolyzed on cell death, and are found in reasonably constant amounts in bacterial cells as they occur in nature. Estimates of the viable biomass by phospholipid content correspond to estimates from the content of muramic acid, ATP, several enzyme activities, direct cell counts, and in some cases viable counts of subsurface sediments. The analysis of the ester-linked fatty acids of the phospholipids (PLFA) using capillary gas chromatography/mass spectrometry (GC/MS) provides sufficient information for the detection of specific subsets of the microbiota based on patterns of PLFA. With this technique shifts in community structure can be quantitatively assayed. Some of the microbiota form specific components such as poly beta-hydroxyalkanoate (PHA) under conditions of unbalanced growth. Others form polysaccharide glycocalyx when subjected to mechanical or chemical stress. The combination of analysis of phospholipids, PLFA, PHA, and glycocalyx provides a definition of the biomass, community structure, and metabolic status of complex microbial communities. These methods involve chromatographic separation and analysis so rates of incorporation or turnover into specific components can be utilized as measures of metabolic activities. With these methods it has proved possible to show that amphipod grazing can induce shifts in biofilm community structure, nutritional status, and metabolic activities. With this technology it proved possible to show resource partitioning amongst sympatric detrital feeding amphipods, prey specificity of feeding of benthic microvores, effects of sedimentary microtopology on predation, and shifts in the microbiota by exclusion of top epibenthic predators.     

Inhibitory effects of Chinese traditional herbs and herb-modified clays on the growth of harmful algae,Phaeocystis globosa and Prorocentrum donghaiense

In order to develop an improved method of mitigating harmful algal blooms (HABs), we assessed the inhibitory effects of five Chinese traditional herbs, Andrographis paniculata (Burm.f.) Nees, Galla chinensis, Punica granatum L., Cortex phellodendri chinensis and Radix scutellariae, as well as clay modified with herb extract on the growth of two harmful algae, Phaeocystis globosa and Prorocentrum donghaiense. The results showed that the five Chinese herbs had varying effects on the target microalgae and inhibitory rates ranged from −35% to 100% at concentration of 0.3 g dry wt./L during 96 h treatments. Among the five herbs, G. chinensis exhibited the strongest inhibitory effect, almost 100% on P. globosa and P. donghaiense. The growth of P. globosa and P. donghaiense was completely inhibited by G. chinensis extracts (0.3 g dry wt./L) during all growth phases, and lag phase cultures were more sensitive than exponential phase and stationary phase cultures. The highest inhibitory rate (100% inhibition) on P. globosa was observed at lag phase, followed by exponential phase (73.1% inhibition), and stationary phase (57% inhibition). The highest inhibitory rate of 100% on P. donghaiense was also found at lag phase, 40.3% at exponential phase, and 23.4% at stationary phase. Furthermore, modified clay with G. chinensis extract significantly enhanced the inhibitory impact. Modified clay (0.3 g L⁻¹) produced 95% of growth inhibition for both algae species at 24 h, and maintained the inhibition thereafter. Our study demonstrated that G. chinensis and clays modified with its extract significantly inhibited the growth of harmful species, therefore may provide ideas and another option for control of harmful algal blooms.     

草地贪夜蛾幼虫耐饥力及饥饿对其生长发育和繁殖的影响

本文旨在明确草地贪夜蛾Spodoptera frugiperda(J.E.Smith)幼虫耐饥力及饥饿处理对其生长发育、繁殖力的影响.选取初孵幼虫(幼虫孵化1 h内)、2、4、6、8和10日龄的幼虫进行饥饿处理,测定存活率和存活时间分析其耐饥力;进一步选取8日龄幼虫分别饥饿1、2、3和4d后再复食,分别统计和分析饥饿胁...     

The effects of low,regulated supplies of nitrate and ammonium nitrogen on the growth and composition of perennial ryegrass

Summary Perennial ryegrass was grown in flowing solution culture with nitrogen supplied in amounts that increased exponentially,i.e. in parallel with the rate of increase in growth. Nitrogen was supplied as either NO ₃ ⁻ or NH ₄ ⁺ , and the amounts to be added were calculated on the basis of extrapolated values for dry weights obtained from fitted curves. There were two rates of addition for each form of N aimed at providing adequate (5.0 per cent) and less than adequate (2.75 per cent) contents in the plants in each case. Measured plant weights and N concentrations were in close agreement with predicted values over a four week experimental period. There was no effect of N-form at high N, and these plants produced 46 per cent more dry matter than the plants at low N. Only minor differences in overall growth occurred with NO ₃ ⁻ or NH ₄ ⁺ plants at low N, but the NH ₄ ⁺ plants had a greater shoot:root ratio. The absorption rate (m mol Ng⁻ root d⁻¹) for NH ₄ ⁺ -N was therefore greater than for NO ₃ ⁻ -N. The cation/anion composition of the plants was affected in a predicable way, and to a greater or lesser extent at high or low N, respectively, in NO ₃ ⁻ or NH ₄ ⁺ plants. The major changes in cation composition came through effects on potassium absorption. Plants with low NO ₃ ⁻ appeared to be under greater N stress than those with low NH ₄ ⁺ because of the lower shoot:root ratio and the greater C∶N ratio in the shoots.