Resistance to chlorine of freshwater bacterial strains

The disinfectant properties of chlorine have been known for centuries but in the last few years water chlorination has attracted some criticism due to its secondary effects and the increased resistance of bacterial strains to chlorine inactivation. In this paper the kinetics of inactivation by chlorine of different Gram-positive and Gram-negative bacterial strains isolated from chlorinated water is studied. The Gram-positive strains were more resistant to chlorine and the behaviour of some of them in the presence of chloramphenicol suggests either the synthesis of unique proteins or aggregation of the bacteria as mechanisms of resistance to inactivation. The concept of K _i, the inactivation rate constant, by comparison with K _s in Michaelis-Menten enzyme kinetics (considering enzymic saturation), or with K _s in Monod growth kinetics (considering limiting rates of transport and metabolism of substrates), may be an interesting parameter to define microbial resistance to disinfectants and toxics.     

多环芳烃降解菌筛选及其降解特性

通过选择性富集培养,从辽河油田稠油污染土壤4号土样中,获得了能以高浓度菲(2000mg·L^-1)为唯一碳源和能源快速生长的优势菌系和优良菌株ZL5．16S rDNA核苷酸序列分析表明,ZL5菌株归类于鞘氨醇单胞菌属,分得的菌系和菌株有较强的降解菲能力,120h混合菌系降解了投加菲的95．28％,菌株降解了69．24％,但它们对芘的降解能力均较低,外加碳源葡萄糖可提高菌系和菌株的菲、芘降解能力,加量多。提高幅度大,但超过一定量。降解速率开始下降,表现出抑制效应。所以,应用时需控制适宜的浓度。     

Isolation of strains belonging to the cosmopolitan Polynucleobacter necessarius cluster from freshwater habitats located in three climatic zones

More than 40 bacterial strains belonging to the cosmopolitan Polynucleobacter necessarius cluster (Betaproteobacteria) were isolated from a broad spectrum of freshwater habitats located in three climatic zones. Sequences affiliated with the freshwater P. necessarius cluster are among the most frequently detected in studies on bacterial diversity in freshwater ecosystems. Despite this frequent detection with culture-independent techniques and the cosmopolitan occurrence of members affiliated with this cluster, no isolates have been reported thus far. The isolated strains have been obtained from lakes, ponds, and rivers in central Europe, the People's Republic of China, and East Africa by use of the filtration-acclimatization method. The 16S rRNA gene sequences of the isolates are 98.8 to 100% identical to reference sequences obtained by various authors by use of culture-independent methods. The isolates, aerobic heterotrophs, grew on a wide range of standard complex media and formed visible colonies on agar plates. Thus, the previous lack of isolates cannot be explained by a lack of appropriate media. Most of the isolates possess, under a wide range of culture conditions, very small cells (<0.1 micro m(3)), even when grown in medium containing high concentrations of organic substances. Thus, these strains are obligate ultramicrobacteria. The obtained strains have a C-shaped cell morphology which is very similar to that of recently isolated ultramicrobacterial Luna cluster strains (Actinobacteria) and the SAR11 cluster strains (Alphaproteobacteria).     

The characterization and ultrastructure of two new strains of Butyrivibrio

Strains B-385-1 and 2-33 are numerically important components rumen bacterial populations , but they have remained (taxonomically) undefined. In spite of some resemblance to Selenomonas ruminantium in their cell size and in their formation of tufts of flagella, they more closely resemble Butyrivibrio fibrisolvens in the subpolar location of their flagella, in their guanine + cytosine content, and in most biochemical characteristics, including butyrate formation. Cells of these strains stain Gram negative, as do both Selenomonas and Butyrivibrio, but their cell walls closely resemble those of Butyrivibrio in their Gram-positive type of molecular architecture and in their cleavage pattern in freeze-etching. Cells of these strains and of B. fibrisolvens have a very thin (ca. 12 nm) peptidoglycan cell wall; thus, they fail to retain the crystal violet complex of the Gram stain and stain Gram negative. This important structural characteristic of their cell walls places strains B-385-1 and 2-33 within the genus Butyrivibrio and certain morphological and biochemical characteristics distinguish them from B. fibrisolvens.     

Analytical studies of the ultrastructure and movement of the spermatozoa of freshwater triclads

Fourteen phyllopod (Branchiopoda: Crustacea) species were collected from numerous temporary pools in north-eastern Natal, South Africa. Physical and chemical data for 10 pools, and results for hourly (over 41 hours) and 3-day interval (throughout periods when phyllopods were present) monitoring of 3 study pools are presented. Comparisons were made with other pools with phyllopods in Africa. The data reveal the broad tolerance to variation and extremes in both physical and chemical conditions in African temporary waterbodies. Species diversity appears to be related to pool size and vegetation. Phyllopod distribution does not follow a pattern associated with physical and chemical conditions.     

Isolation of Candida albicans from freshwater and sewage.

The isolation and identification of Candida albicans from polluted aquatic environments were facilitated by the inclusion of a selective medium and a differential screening medium to detect the reduction of 2,3,5-triphenyltetrazolium chloride. C. albicans occurred commonly in low numbers in sewage influents, rivers, and streams.     

Histology and ultrastructure of the olfactory organ of the freshwater pulmonate Helisoma trivolvis

Summary The olfactory organ of Helisoma trivolvis is located on the surface of the body at the base of the cephalic tentacles. An evagination of skin, the olfactory plica, at the base of the tentacle extends over the olfactory organ dorsally. The epithelium of the olfactory organs contains unspecialized epithelial cells, ciliated epithelial cells, basal cells, mucous secretory cells, and sensory dendrites. The surface of the epithelium has a complex brush border of thick plasmatic processes, which branch to form several terminal microvillar twigs. Long slender cytoplasmic processes form a dense spongy layer among the plasmatic processes beneath the level of the terminal twigs. Bipolar primary sensory neurons clustered beneath the epithelium of the olfactory organ send dendrites through the epithelium to the free surface. Some sensory endings have a few short cilia, but most bear only microvilli. Cilia of sensory endings and epithelial cells extend beyond the brush border of the epithelium. Small axons arise from the perikarya of the sensory neurons and enter a branch of the olfactory nerve. HRP tracing indicates that the axons pass to the cerebral ganglion without interruption. Histochemical tests indicate that the sensory neurons are neither aminergic nor cholinergic.     

Isolation of unbalanced growth forms from Listeria and their ultrastructure

As the result of the action of penicillin, LiCl and UV irradiation on Listeria culture in the logarithmic phase, unbalanced growth forms (UGF) were obtained. Their viability was determined by the number of colony-forming units per ml. In this investigation the action of the above factors in a single cultivation and in consecutive subcultures was studied. Viable UGF were obtained under the action of all the above factors. UGF obtained under the action of penicillin were found to convert easily into L-forms in the process of subculturing. On the contrary, UGF obtained under the action of UV irradiation and LiCl produced no L-forms and reverted easily when the action of these factors stopped. In all three cases the formation of UGF was accompanied by changes in the structure of the cell wall and, partially, the cytoplasmic membrane, but in each case these changes had different character.     

Morphology and ultrastructure of helical and nonhelical strains of Spiroplasma citri.

Cells of the nonhelical strain of Spiroplasma citri underwent changes of morphology comparable to those which occurred in the normal helical strain. Cells of the nonhelical strain had the same ultrastructural features as helical cells and released long flexible fibrils similar to those seen in other spiroplasmas. Nonhelical organisms showed an increased tendency to aggregate, forming cell clusters of an unusual annular form. The cytoplasmic membrane of the nonhelical strain lacked a single protein present in all helical strains. Loss of helicity associated with the senescence of spiroplasma cells was not accompanied by the disappearance of this protein. Differences in colony morphology were shown to be a consequence of motility, and a technique was developed which facilitated the identification of nonmotile organisms.     

Interspecific variations in the surface ultrastructure of the gills of freshwater mullets

SEM studies were made on the gills of freshwater mullets,Rhinomugil corsula andSicamugil cascasia, to correlate surface ultrastructure of various gill units with their probable functions. Two types of lamellated gill rakers of the former fish are suited for plankton feeding and the short, stumpy and transversely beaded gill rakers of the latter reflect the varied food and feeding habit of the fish.R. corsula has numerous mucous glands on the epithelium covering the gill arch and gill filaments,S. cascasia has fewer. In accordance with the differences in the density and distribution of the mucous glands, the microridged epithelial cells also show variations in their architectural plan. In both species the epithelium of the secondary lamellae is smooth, probably an adaptation for better gaseous exchange.     

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     

Amoebic grazing of freshwater Synechococcus strains rich in phycocyanin

Fifteen strains of naked amoebae were presented with 19 strains of Synechococcus on an agar surface. After 14 days of incubation, each of the 285 combinations yielded one of three responses. 42.1% of combinations showed clearing (digestion) of the Synechococcus (C), 56.5% of combinations showed no clearing of the Synechococcus (N) while 1.4% of combinations showed partial clearing of the Synechococcus (P). In general, the Synechococcus strains showed variability in their susceptibility to digestion by the amoebae and the amoebae showed variability in their ability to digest the Synechococcus strains. There was no evidence for amoebae actively selecting profitable prey and equivalent-sized Synechococcus strains were ingested at the same rate, irrespective of their fate. There was some evidence of 'size-selective' grazing in that amoebae ingested the smaller Synechococcus strains at higher rates than the larger strains. However, there was no correlation between prey size and their ultimate fate. These data suggest that amoebae are not selective with regard to the ingestion of synechococci, but that 'selection' occurs at the digestion stage, i.e. whether the synechococci are digested or not.     

Effect of medium composition on the ultrastructure of Lactobacillus strains

The growth of some locally isolated Lactobacillus strains forming D(-) or L(+) lactic acid, Lactobacillus helveticus ATCC 15009 and Lactobacillus delbrueckii subsp. bulgaricus ATCC 11842 was examined in different media. L. helveticus and Lactobacillus LBL strains formed atypical protoplast-like cells in LAPT medium, sensitive to SDS and proteinase. Specific morphological changes in the cell wall structure of these variants were revealed by transmission and scanning electron microscopy. The effect of glucose and various salts on their appearance was investigated. The prevalent role of metal cations, especially of Mg²⁺, was established.     

Isolation and characterization of cold-adapted strains producing beta-galactosidase

beta-Galactosidase is extensively employed in the manufacture of dairy products, including lactose-reduced milk. Here, we have isolated two gram-negative and rod-shaped coldadapted bacteria, BS 1 and HS 39. These strains were able to break down lactose at low temperatures. Although two isolates were found to grow well at 10 degrees , the BS 1 strain was unable to grow at 37 degrees . Another strain, HS-39, evidenced retarded growth at 37 degrees . The biochemical characteristics and the results of 16S rDNA sequencing identified the BS 1 isolate as Rahnella aquatilis, and showed that the HS 39 strain belonged to genus Buttiauxella. Whereas the R. aquatilis BS 1 strain generated maximal quantities of beta-galactosidase when incubated for 60 h at 10 degrees , Buttiauxella sp. HS-39 generated beta-galactosidase earlier, and at slightly lower levels, than R. aquatilis BS 1. The optimum temperature for beta-galactosidase was 30 degrees for R. aquatilis BS-1, and was 45 degrees for Buttiauxella sp. HS-39, thereby indicating that R. aquatilis BS-1 was able to generate a cold-adaptive enzyme. These two cold-adapted strains, and most notably the beta-galactosidase from each isolate, might prove useful in some biotechnological applications.     

Isolation and characterization of ethanol tolerant yeast strains

Yeast strains are commonly associated with sugar rich environments. Various fruit samples were selected as source for isolating yeast cells. The isolated cultures were identified at Genus level by colony morphology, biochemical characteristics and cell morphological characters. An attempt has been made to check the viability of yeast cells under different concentrations of ethanol. Ethanol tolerance of each strain was studied by allowing the yeast to grow in liquid YEPD (Yeast Extract Peptone Dextrose) medium having different concentrations of ethanol. A total of fifteen yeast strains isolated from different samples were used for the study. Seven strains of Saccharomyces cerevisiae obtained from different fruit sources were screened for ethanol tolerance. The results obtained in this study show a range of tolerance levels between 7%-12% in all the stains. Further, the cluster analysis based on 22 RAPD (Random Amplified polymorphic DNA) bands revealed polymorphisms in these seven Saccharomyces strains.