Formation of thionates by freshwater and marine strains of sulfate-reducing bacteria

The formation of thionates (thiosulfate, trithionate and tetrahionate) during the reduction of sulfate or sulfite was studied with four marine and four freshwater strains of sulfate-reducing bacteria. Growing cultures of two strains of the freshwater species Desulfovibrio desulfuricans formed up to 400 M thiosulfate and 100 M trithionate under conditions of electron donor limitation. Tetrathionate was observed in lower concentrations of up to 30 M. Uncoupler-treated washed cells of the four freshwater strains formed thiosulfate and trithionate at low electron donor concentrations with sulfite in excess. In contrast, only one of four marine strains formed thionates. The freshwater strain Desulfobulbus propionicus transformed sulfite almost completely to thiosulfate and trithionate. The amounts produced increased with time, concentration of added sulfite and cell density. Tetrathionate was detected only occasionally and in low concentrations, and was probably formed by chemical oxidation of thiosulfate. The results confirm the diversity of the sulfite reduction pathways in sulfate-reducing bacteria, and suggest that thiosulfate and trithionate are normal by-products of sulfate reduction.Abbreviations CCCP carbonyl cyanide m-chlorophenylhydrazone     

Oxidation of short-chain fatty acids by sulfate-reducing bacteria in freshwater and in marine sediments

Colony counts of acetate-, propionate- and l-lactate-oxidizing sulfate-reducing bacteria in marine sediments were made. The vertical distribution of these organisms were equal for the three types considered. The highest numbers were found just beneath the border of aerobic and anaerobic layers.Anaerobic mineralization of acetate, propionate and l-lactate was studied in the presence and in the absence of sulfate. In freshwater and in marine sediments, acetate and propionate were oxidized completely with concomitant reduction of sulfate. l-Lactate was always fermented. Lactate-oxidizing, sulfate-reducing bacteria, belonging to the species Desulfovibrio desulfuricans, and lactate-fermenting bacteria were found in approximately equal amounts in the sediments. Acetate-oxidizing, sulfate-reducing bacteria could only be isolated from marine sediments, they belonged to the genus Desulfobacter and oxidized only acetate and ethanol by sulfate reduction. Propionate-oxidizing, sulfate-reducing bacteria belonged to the genus Desulfobulbus. They were isolated from freshwater as well as from marine sediments and showed a relatively large range of usable substrates: hydrogen, formate, propionate, l-lactate and ethanol were oxidized with concomitant sulfate reduction. l-Lactate and pyruvate could be fermented by most of the isolated strains.     

Induction of luciferase synthesis in Beneckea harveyi by other marine bacteria

It has been previously demonstrated that luciferase synthesis in the luminous marine bacteria, Beneckea harveyi and Photobacterium fischeri is induced only when sufficient concentrations of metabolic products (autoinducers) of these bacteria accumulate in growth media. Thus, when cells are cultured in liquid medium there is a lag in luciferase synthesis. A quantitative bioassay for B. harveyi autoinducer was developed and it was shown that many marine bacteria produce a substance that mimics its action, but in different amounts, (20–130% of the activity produced by B. harveyi) depending on the species and strain. This is referred to as alloinduction. None of the bacteria tested produced detectable quantities of inducer for P. fischeri luciferase synthesis. These findings may have significance with respect to the ecology of B. harveyi and P. fischeri.Non-Standard Abbreviation AB medium autoinducer bioassay medium     

Enteric bacteria isolated from acute diarrheal patients in the Republic of Korea between the year 2004 and 2006

In an epidemiological survey of human enterobacterial infections in the Republic of Korea during three years from 2004 to 2006, we isolated 1,784 (6.2%, isolation rate of enteropathogens from stool samples) in 2004, 2,547 (9.5%) in 2005 and 3,506 bacteria (12.3%) from people who visited clinics. Among the isolated bacteria, pathogenic Escherichia coli, especially, EAEC was the most frequently identified pathogen in both urban and rural regions followed by Staphylococcus aureus, Salmonella species, Bacillus cereus, Vibrio parahaemolyticus, Campylobacter jejuni, Clostridium perfringens, and Shigella species. Distinct seasonality was found in V. parahaemolyticus species, while this pathogen showed no age-specific patterns. However, other bacteria, i.e., pathogenic E. coli, S. aureus, Salmonella spp., and B. cereus showed similar seasonality throughout the year, showing a slight increase in the infection rate during the summer months and high prevalence among children under 10 years of age and elder-age people. The antibiotic susceptibility patterns of pathogenic E. coli, Salmonella spp., and S. aureus showed high resistance to penicillins. However, both pathogenic E. coli and Salmonella spp. were susceptible to several cephems, imipenem, and amikacin. Moreover, S. aureus strains resistant to vancomycin were not found. In conclusion, these surveillances can play an important role for the control and prevention to the diseases originated by enteritis bacteria.     

Calibration of the impedance method for rapid quantitative estimation of Escherichia coli in live marine bivalve molluscs

AIM: Calibration of impedance measurement was performed vs the Association Fran?oise de Normalisation (AFNOR) MPN method with a view to rapid enumeration of Escherichia coli in live marine bivalve molluscs. METHODS AND RESULTS: Linear regression models between log10 MPN and detection time (DT) were adjusted for several shellfish types, growth media, and impedance instruments (BacTrac and Malthus systems). Escherichia coli concentrations could be estimated from DT using a single regression line for BacTrac 4100 with M1 medium (R2 = 87.8%) and Malthus with M2 medium (R2 = 86.7%), and two regression lines for BacTrac 4110 with M2 medium (R2 = 86.4 and 88.2%). The uncertainty of the predicted bacterial concentration was around +/-0.43 log unit for duplicate sample analysis. The impedance signal was attributable to E. coli in 99% of cases. All cultures containing E. coli produced an impedance signal with BacTrac 4100 and BacTrac 4110, whereas 5.6% did not exhibit a signal with Malthus. CONCLUSIONS: Impedance measurement is a possible alternative to the MPN method for rapid quantitative estimation of E. coli in live bivalve shellfish. SIGNIFICANCE AND IMPACT OF THE STUDY: The impedance method reduces analysis handling time considerably and is much easier to use than the MPN method. Moreover, results can be obtained within 5-10 h, allowing rapid intervention to ensure public health protection in case of shellfish contamination.     

Engineering alternative butanol production platforms in heterologous bacteria

Alternative microbial hosts have been engineered as biocatalysts for butanol biosynthesis. The butanol synthetic pathway of Clostridium acetobutylicum was first re-constructed in Escherichia coli to establish a baseline for comparison to other hosts. Whereas polycistronic expression of the pathway genes resulted in the production of 34 mg/L butanol, individual expression of pathway genes elevated titers to 200 mg/L. Improved titers were achieved by co-expression of Saccharomyces cerevisiae formate dehydrogenase while overexpression of E. coli glyceraldehyde 3-phosphate dehydrogenase to elevate glycolytic flux improved titers to 580 mg/L. Pseudomonas putida and Bacillus subtilis were also explored as alternative production hosts. Polycistronic expression of butanol biosynthetic genes yielded butanol titers of 120 and 24 mg/L from P. putida and B. subtilis, respectively. Production in the obligate aerobe P. putida was dependent upon expression of bcd-etfAB. These results demonstrate the potential of engineering butanol biosynthesis in a variety of heterologous microorganisms, including those cultivated aerobically.     

康氏菌科海洋细菌的系统发育与代谢潜能研究进展

康氏菌科(Kangillaceae)是海洋螺杆菌目(Oceanosprillales)下的科级分类单元,包含康氏菌属(Kangiella)、异康氏菌属(Aliikangiella)和Pleionea三个属.在康氏菌属高度精简的基因组中存在异常丰富的胞外蛋白酶编码基因,暗示此类海洋细菌对海洋颗粒有机物中的蛋白质成分降解具...     

Within-season reproductive and somatic energy allocation in a freshwater clam,Anodonta piscinalis

The effect of a change in the environment on reproductive and somatic energy allocation in an iteroparous freshwater clam Anodonta piscinalis was studied at different time of the seasonal reproductive cycle. Environmental change was produced by reciprocal transplant experiments among sites of varying productivity. In addition, clams were caged at high density to reduce the availability of resources. Transplanting females before fertilization (from May to June), or during the early development of the brood (from July to August) had no detectable effect on reproductive output. Early-season environment, however, affected body mass and percent fat content of females from two populations. This suggests that maintaining the level of reproductive allocation when resources are reduced early in the season leads to lower allocation to somatic growth and biochemical storage. Transplanting females late in the season (from September to November) had a substantial effect on reproductive output and body mass, but not on fat content, suggesting that late in the season allocation to biochemical energy storage is important. Hence, late in the season reproductive allocation may be adjusted to prevailing conditions in preparation for winter. Indeed, over-wintering site had a significant effect on percent fat content, body mass and shell growth when females were kept in a new environment from September to March. Variation among transplant sites in female body mass matched the estimated productivity of the sites, suggesting that it occurred in response to differences in the productivity of the habitats. The results emphasize the importance of taking seasonal changes in the priorities of energy allocation and the seasonality of reproductive processes into account when developing or testing models of optimal energy allocation.     

革兰氏阴性细菌蛋白分泌系统研究进展

革兰氏阴性细菌由于具有复杂的双层膜结构,其蛋白质分泌能力较差.这使得革兰氏阴性细菌的典型菌株——大肠杆菌作为最常用的受体细胞在生物制药工程和其他生物技术产品生产中受到一定的限制.因此,革兰氏阴性细菌蛋白分泌系统的研究具有重要意义.本文详细地归纳了革兰氏阴性细菌已知的蛋白分泌系统,分别从分泌系统的分泌过程、分泌蛋白类别、...     

Structure of visual pathways in the nervous system of freshwater pulmonate molluscs

Central nervous system of freshwater pulmonate molluscs Lymnaea stagnalis and Planorbarius corneus was stained using retrograde transport of neurobiotin in the optic tract fibers. In both species, perikarya and fibers of the stained neurons are found in all ganglia except the buccal ones. Afferent fibers of the optic nerve form dense sensory neuropil located in relatively small volume of cerebral ganglia. Typical neuronal groups sending their processes into the optic nerves of ipsilateral and contralateral body halves are described. Among them, neurons of visceral and parietal ganglia innervating both eyes concurrently as well as sending projections into peripheral nerves are revealed. These neurons, supposedly, have a function to integrate sensory signals, which may be a basis for regulation of light sensitivity of retina and functioning of peripheral organs. Bilateral links of the molluscan eye with the pedal ganglia cells and statocysts are found, which is, likely, a structural basis of certain known behavioral patterns related to stimulation of visual inputs in the studied gastropod molluscs.     

A note on the significance of larger bivalve molluscs (Anodonta spp. and Dreissena sp.) in the food of the eel (Anguilla anguilla) in Tjeukemeer

The stomach contents of 517 eels were analysed during 1979. In that particular year the diet consisted predominantly of chironomids, but large bivalve molluscs were of secondary importance. The meaning of this observation is discussed in relation to food conditions and the food preference of the eel.     

A dormancy state in nonspore-forming bacteria

While cultivation is a convenient way of proliferating and understanding bacteria, studies have shown the formation of nonculturable cells in nonspore-forming bacteria in response to environmental stress and thus in turn have generated immense interest. Whether these cells are in a state of dormancy or in a stage preceding cell death has been considered of paramount importance for the past couple of decades. In this study, osmotic-stress-induced dormant bacterial cells were separated by cell sorting and revived by osmotic down-shift in the absence of nutrients, source(s) that potentially could supply nutrients, and/or the external addition of resuscitation factor(s). Reversal of dormancy followed a definite pattern akin to population asynchrony of dormant cells, and the phenomenon was observed across three species, namely, Enterobacter sp. strain mcp11b, Klebsiella pneumonia strain mcp11d and Escherichia coli. In addition, our study precisely forecasted the presence of multiple subpopulations in dormant cells, which is explained by an emerging theory of survival mechanisms in stressful environments. These observations reveal that the state of dormancy induced by environmental stress in these nonspore-forming bacteria is “reversible” and also implies that it is an orderly and spontaneous adaptation to circumvent adverse conditions. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Faecal indicator bacteria enumeration in beach sand: a comparison study of extraction methods in medium to coarse sands

Aims:  The absence of standardized methods for quantifying faecal indicator bacteria (FIB) in sand hinders comparison of results across studies. The purpose of the study was to compare methods for extraction of faecal bacteria from sands and recommend a standardized extraction technique.
Methods and Results:  Twenty-two methods of extracting enterococci and Escherichia coli from sand were evaluated, including multiple permutations of hand shaking, mechanical shaking, blending, sonication, number of rinses, settling time, eluant-to-sand ratio, eluant composition, prefiltration and type of decantation. Tests were performed on sands from California, Florida and Lake Michigan. Most extraction parameters did not significantly affect bacterial enumeration. anova revealed significant effects of eluant composition and blending; with both sodium metaphosphate buffer and blending producing reduced counts.
Conclusions:  The simplest extraction method that produced the highest FIB recoveries consisted of 2 min of hand shaking in phosphate-buffered saline or deionized water, a 30-s settling time, one-rinse step and a 10 : 1 eluant volume to sand weight ratio. This result was consistent across the sand compositions tested in this study but could vary for other sand types.
Significance and Impact of the Study:  Method standardization will improve the understanding of how sands affect surface water quality.     

Identification of sources of Escherichia coli in South Carolina estuaries using antibiotic resistance analysis

Fecal pollution from nonhuman (pets, livestock or wildlife) and human sources is often one of the major factors associated with urbanization that contribute to the degradation of water quality. Methods to differentiate animal from human sources of fecal coliform contamination could assist resource managers in developing strategies to protect shellfish harvesting areas and recreational waters. In this study, surface water samples were collected from both a developed and an undeveloped watershed in coastal South Carolina. Influent and effluent samples from several wastewater treatment plants (WWTPs) in the same area were also collected. Most Probable Numbers (MPNs) of fecal coliforms were determined for all samples. Escherichia coli isolates were analyzed for antibiotic resistance (AR) to 10 antibiotics. Then, AR indices (no. of resistant/total no. of antibiotics tested), were calculated for each isolate and site. Results indicated that MPNs from the WWTP samples were significantly higher than those from the developed watershed which were significantly higher than those from the undeveloped watershed (p<0.0001). The AR analyses suggested that there was a trend toward increased antibiotic resistance in samples for the urbanized Broad Creek (BC) watershed. In the Okatee River (OR), E. coli isolates from three sites (20%) showed resistance to a single antibiotic (penicillin) but in BC, isolates from seven sites (47%) were resistant to multiple antibiotics, and the predominant resistance pattern was chlortetracycline-oxytetracycline-tetracycline. Raw sewage isolates from most WWTPs contained E. coli that exhibited resistance to multiple antibiotics. Cluster analysis indicated that all resistant OR sites had antibiotic resistant isolates that matched AR patterns found in isolates from WWTPs. Similarly, six of the seven sites in BC had AR patterns that matched with resistance patterns in WWTPs. These results suggest that AR testing may be a useful tool for differentiating E. coli from human and wildlife sources. Further testing of bacterial isolates from known animal sources is necessary to better assess the utility of this approach.     

Natural vitamin E enrichment of Artemia salina fed freshwater and marine microalgae

Three species of microalga, the freshwater Euglena gracilis and the marine Dunaliella salina and Tetraselmis suecica, were compared in terms of vitamin E enrichment and survival and growth of the brine shrimp Artemia salina. The tocopherol content was investigated using HPLC for the post-larval and pre-adult stages of Artemia fed the microalgae and the results compared to the initial content of unfed newly hatched nauplii. There was a markedly higher content of tocopherols (about two-fold) in Artemia fed Euglena. Since this microalga contains other antioxidants such as -carotene, vitamin C and glutathione, bioactive molecules such as PUFA, and the immunostimulant polysaccharide -glucan, it represents a valuable alternative for enriching the diets of Artemia and increase its nutritional value as a food item.     

Effect of Plumbago zeylanica extract and certain curing agents on multidrug resistant bacteria of clinical origin

Alcoholic extract of Plumbago zeylanica (root) was tested against multidrug-resistant clinical isolates of bacteria (Salmonella paratyphi, Staphylococcus aureus, Escherichia coli, Shigella dysenteriae and a R-plasmid-harbouring standard strain, E.coli x⁺). The extract exhibited strong antibacterial activity against all test bacteria irrespective of their antibiotic resistance behaviour. Phytochemical analysis of crude extract revealed the presence of flavonoids, saponins and naphthoquinone. A comparative evaluation of R-plasmid elimination from E. coli x⁺ (pUK 651) by the plant extract, DNA intercalating dyes (acridine orange and ethidium bromide) and a DNA gyrase antagonizing drug (pefloxacin) were made. All these agents could cure R-plasmid effectively at their respective sub-MIC concentrations. Maximum plasmid curing was observed by pefloxacin (88%), followed by ethidium bromide (36%), acridine orange (14%) and alcoholic extract of P. zeylanica (14%). Curing of plasmid pUK651 from E. coli x⁺ was confirmed by determining the loss of resistance markers in the cured derivative culture. This revised version was published online in November 2006 with corrections to the Cover Date.     

Tributyltin-resistant marine bacteria: a summary of recent work

Summary A tributyltin chloride (TBTCl)-resistant bacterium,Alteromonas sp. M-1, was isolated from coastal seawater. This bacterium grew in medium containing 125 M TBTCl. TBTCl added to the medium was taken up by this bacterium, however, the amount of TBTCl in the cellular fraction was low after the logarithmic phase, suggesting the existence of a TBTCl-efflux system. A genetic library was constructed using plasmid vector pUC 19. Three positive clones were obtained, by whichE. coli was transformed to TBTCl resistance. Of the three clones, the shortest fragment fromHindIII-library was analyzed. This fragment was 1.8 kb long and contained one complete open reading frame. The predicted amino acid sequence of this open reading frame had a homologous domain to transglycosylases of bacteriophage andE. coli. TBTCl-tolerant marine bacteria other thanAlteromonas sp. M-1 were obtained from natural seawater to which TBTCl was added. DNA-DNA hybridization was performed between the three cloned fragments fromAlteromonas sp. M-1 and chromosomal DNA of the TBTCl-tolerant bacteria. Some strains hybridized with the fragments and some did not, suggesting that several genes are responsible for TBTCl tolerance.     

The mechanism of secretion of hemolysin and other polypeptides from Gram-negative bacteria

In the secretion of polypeptides from Gram-negative bacteria, the outer membrane constitutes a specific barrier which has to be circumvented. In the majority of systems, secretion is two-step process, with initial export to the periplasm involving an N-terminal signal sequence. Transport across the outer membrane then involves a variable number of ancillary polypeptides including both periplasmic and outer membrane. While such ancillary proteins are probably specific for each secreted protein, the mechanism of movement across the outer membrane is unknown. In contrast to these systems, secretion of theE. coli hemolysin (HlyA) has several distinctive features. These include a novel targeting signal located within the last 50 or so C-terminal amino acids, the absence of any periplasmic intermediates in transfer, and a specific membrane-bound translocator, HlyB, with important mammalian homologues such as P-glycoprotein (Mdr) and the cystic fibrosis protein. In this review we discuss the nature of the HlyA targeting signal, the structure and function of HlyB, and the probability that HlyA is secreted directly to the medium through a trans-envelope complex composed of HlyB and HlyD.     

A comparison of protocols for the optimisation of detection of bacteria using a surface acoustic wave (SAW) biosensor

A dual channel surface acoustic wave (SAW) device has been used as a biosensor to detect two different microorganisms, Legionella and Escherichia coli, simultaneously. A series of experiments was conducted to optimise the use of the SAW for bacterial detection using a novel protocol of coating bacteria on the sensor surface prior to addition of the antibody. Results were compared with an experiment in which a conventional protocol was utilised, where antibody was coated on the sensor surface prior to exposure to bacteria. The concentration of bacteria that attached to the surface of the SAW device was related to the antibody that specifically bound to it and therefore to frequency in a dose dependent fashion. Unlike conventional microbiological techniques quantitative results can be obtained for Legionella and E. coli down to 10(6) cells per ml within 3 h. In addition E. coli was detected down to 10(5) cells per ml in a modified protocol using sheep IgG as a blocking agent.     

Change in the cellular localization of alkaline phosphatase by alteration of its carboxy-terminal sequence

Summary Alkaline phosphatase (AP) is secreted into the medium when the carboxy-terminal 25 amino acids are replaced by the 60 amino acid carboxy-terminal signal peptide (HlyA_s) ofEscherichia coli haemolysin (HlyA). Secretion of the AP-HlyA_s fusion protein is dependent on HlyB and HlyD but independent of SecA and SecY. The efficiency of secretion by HlyB/HlyD is decreased when AP carries its own N-terminal signal peptide. Translocation of this fusion protein into the periplasm is not observed even in the absence of HlyB/HlyD. The failure of the Sec export machinery to transport the latter protein into the periplasm seems to be due in part to the loss of the carboxy-terminal sequence of AP since even AP derivatives which do not carry the HlyA signal peptide but lack the 25 C-terminal amino acids of AP are localized in the membrane but not translocated into the periplasm.