Gut microflora of two saltmarsh detritivore thalassinid prawns,Upogebia africana andCallianassa kraussi

The presence and digestive capabilities of bacteria associated with the digestive systems and habitats of two saltmarsh-burrowing detritivore thalassinid prawns (Upogebia africana andCallianassa kraussi) was examined.U. africana is a filter-feeding prawn inhabiting muddy deposits, whereasC. kraussi, a deposit feeder, inhabits coarser more sandy deposits. Scanning electron microscopy was used to examine the gut lining and associated microflora and the nature of the ingested food of both prawns. The gut contents of both prawns included plant fragments, fragmented diatoms, partially degraded protozoa, and bacteria attached to organic matter. In bothU. africana andC. kraussi the midgut walls and gut contents were extensively coated by filamentous bacteria which were absent in the hindgut. The hindgut epithelium ofU. africana was coated by mats of rodshaped bacteria, not reported in marine invertebrates previously. The digestive glands of both species contained bacteria in the lumen. Isolation of gut and habitat bacteria suggests that bothU. africana andC. kraussi maintain a gut microflora distinct from the habitat microflora. Bacteria isolated from the guts of both species of prawn differed from those isolated from their respective habitats with regards to both the genera isolated and their digestive capabilities. The dominant genera isolated from the guts of bothU. africana andC. kraussi wereVibrio andPseudomonas, with an unidentified fermenter andPseudomonas, respectively dominating in the digestive glands. Bacteria of the genusAcinetobacter dominated the isolates from the habitats of both species of prawn. Resident gut bacteria isolated from the guts of both species of prawn exhibited lipase, protease, chitinase, and lysozyme, but not cellulase activity, and may contribute to nitrogen aquisition by the prawns. Isolates from the prawns' habitat exhibited alginase, gelatinase, and lipase activity, a few (3%) fromU. africana habitat having cellulases. In this study a distinction between resident gut bacteria and transient gut bacteria was made. Results suggest that some habitat bacteria remain viable in the guts ofU. africana, but not inC. kraussi.     

Screening of marine bacteria for fucoidanases

Twenty-five strains of epiphytic marine bacteria isolated from the brown algaeFucus evanescens andChorda filum and fifty-three bacteria isolated from the sea cucumberApostichopus japonicus were screened for fucoidanases using fucoidans prepared from the brown algaeF. evanescens, Laminaria cichorioides, andL japonica. Eighteen bacterial epiphytes and thirty-eight bacterial isolates from the sea cucumber were found to contain fucoidanases, which were able to hydrolyze either all of the fucoidans studied or some of them. Bacteria of the generaCytophaga andAlteromonas/Pseudoalteromonas exhibited the highest fucoidanase activities, which, however, did not exceed the activity of fucoidanases from the already known sources.     

Nitrogen-fixing bacteria associated with bark beetles

Nitrogen-fixingEnterobacter agglomerans andEnterobacter spp. were consistently isolated from the bark beetleDendroctonus terebrans. Large populations of nitrogen-fixing bacteria were found with the beetle, although no in situ acetylene reduction was demonstrated. The constant occurrence of nitrogenfixing bacteria withD. terebrans suggests a symbiotic relationship. Nitrogen-fixing bacteria were also isolated from the bark beetlesDendroctonus frontalis andIps avulsus.Mention of trade names is not an endorsement by the U.S. Department of Agriculture.     

Recent developments inRhizobium taxonomy

Recent developments inRhizobium taxonomy are presented from a molecular and evolutionary point of view. Analyses of ribosomal RNA gene sequences provide a solid basis to infer phylogenies in the Rhizobiaceae family. These studies confirmed thatRhizobium andBradyrhizobium are only distantly related and showed thatRhizobium andBradyrhizobium are related to other groups of bacteria that are not plant symbionts.Rhizobium andAgrobacterium species are intermixed. Differences in plasmid content may explain to a good extent the different behavior ofRhizobium andAgrobacterium as symbionts or pathogens. Other approaches to identify and classify bacteria such as DNA-DNA hybridization, fatty acid analysis, RFLP and RPD-PCR techniques and phylogenies derived from other genes are in general agreement to the groupings derived by ribosomal sequences. Only a small proportion of nodulated legumes have been sampled for their symbionts and more knowledge is required on the systematics and taxonomy ofRhizobium andBradyrhizobium species.     

Antigenic affinities of the root-nodule bacteria of legumes

Antisera prepared against 58 strains of root-nodule bacteria and against 16 strains belonging to the genusAgrobacterium were tested against 113 strains ofRhizobium, 20 strains ofAgrobacterium and 20 strains of other, possibly related, bacteria.Three serologically distinct groups of root-nodule bacteria were noted: (1)Rh. trifolii, Rh. leguminosarum andRh. phaseoli; (2)Rh. lupini, Rh. japonicum andRhizobium spp.; (3)Rh. meliloti. Strains ofRh. meliloti showed serological affinities withA. radiobacter andA. tumefaciens. All groups showed wider flagellar than somatic agglutination, and many different serotypes were apparent.The groupings obtained from this investigation are compared with those derived from other taxonomic studies, and the use of serological methods in rhizobial classification is discussed.     

Grazing of attached bacteria by heterotrophic microflagellates

Four species of heterotrophic microflagellates were examined for their ability to graze attached and unattached bacteria. The species tested displayed pronounced differences in their ability to graze the bacteriumPseudomonas halodurans attached to chitin particles. Two species of microflagellates (Monas andCryptobia sp.) efficiently grazed unattached bacteria but showed little or no ability to graze attached or aggregated cells. In contrast,Rhynchomonas nasuta andBodo sp. showed marked preferences for attached and aggregated bacteria and a limited ability to graze unattached cells. The density of attached bacteria was reduced by an order of magnitude due to grazing byBodo andR. nasuta, even though the density of unattached bacteria was 5–90× the density of attached cells. The maximum densities attained by microflagellates in the cultures were related to the density of unattached bacteria forMonas andCryptobia but not forBodo andR. nasuta. Growth of the latter two species appeared to be related to the density of attached or aggregated bacteria. Based on the results of these experiments, it is concluded that the pelagic existence of microflagellates that graze attached bacteria may be strongly linked to the distribution of suspended particles and their associated bacteria. In addition, the removal of attached bacteria by microflagellates can significantly affect the density of bacteria attached to particles in the plankton. This activity may have important implications for the controversy concerning the relative importance of attached and free-living bacteria in the plankton.     

The role of bacteria in the nutrition of aquatic detritivores

Summary Bacteriological analyses of the guts of four common lotic invertebrates are described. The results from these analyses suggest thatSimulium andChironomus digest at least half of the bacteria that they ingest in situ, but no evidence has been found for the digestion of bacteria byBaëtis or byEphemerella. Moreover,Simulium andChironomus do not appear to be selective, with regard to bacterial type, in their digestion. The limitations of the method are discussed and the relative importance of bacteria compared with other components of the insects' diet is assessed. Evidence is presented which supports the hypothesis that bacteria are not as quantitatively important as other components of the detrital food material.Sandwich student from the University of Bath     

An orphan gyrB in the Mycobacterium smegmatis genome uncovered by comparative genomics

DNA gyrase is an essential topoisomerase found in all bacteria. It is encoded bygyrB andgyrA genes. These genes are organized differently in different bacteria. Direct comparison ofMycobacterium tuberculosis andMycobacterium smegmatis genomes reveals presence of an additionalgyrB inM. smegmatis flanked by novel genes. Analysis of the amino acid sequence of GyrB from different organisms suggests that the orphan GyrB inM. smegmatis may have an important cellular role.     

Lytic effect ofVibrio cholerae elastase on Gram-positive and-negative bacteria

Elastase ofVibrio cholerae caused the lysis of freshly grown cells of Gram-negative (Pseudomonas aeruginosa, Proteus vulgaris, Salmonella paratyphi A andKlebsiella pneumoniae) bacteria. Gram-positive (Staphylococcus aureus andS. epidermidis) organisms were resistant to this enzyme. Heat killed and lyophilized Gram-positive and-negative bacteria (exceptS. aureus andS. epidermidis) showed higher sensitivity to elastase. Both Gram-negative and-positive bacteria were lyzed maximally by elastase at pH 8.0. At this pH, lytic activity of elastase was maximum in Tris-HCl and glycine-NaOH buffers followed by Tris-maleate and cacodylate buffers.     

Paramecium calkinsi andP. putrinum (Ciliophora, Protista) harboring alpha-subgroup bacteria in the cytoplasm

Summary New intracellular bacteria were detected in the cytoplasm ofParamecium calkinsi andP. putrinum. Some of the bacteria were not evenly distributed in the cytoplasm of the host but were found in the center of the cell, eventually near the nuclei, but not in the cortex area, whereas another species was found in the cortex area. These peculiarities of intracellular bacteria localization in the host suggest that the conditions in various parts of the cytoplasm favor bacterial maintenance to different extent. Due to the results obtained by transmission electron microscopy and in situ hybridization using appropriate oligonucleotide probes, the bacteria, three or possibly four species, are Gram-negative and belong to the alpha-subgroup of proteobacteria. Bacteria from one stock ofP. calkinsi were found to be infectious for bacteria-free cells ofP. calkinsi andP. nephridiatum.     

Characterization of microbial communities in anaerobic bioreactors using molecular probes

The microbial community structure of twenty-one single-phase and one two-phase full-scale anaerobic sewage sludge digesters was evaluated using oligonucleotide probes complementary to conserved tracts of the 16S rRNAs of phylogenetically defined groups of methanogens and sulfate-reducing bacteria. These probe results were interpreted in combination with results from traditional chemical analyses and metabolic activity assays. It was determined that methanogens in healthy mesophilic, single-phase sewage sludge digesters accounted for approximately 8–12% of the total community and thatMethanosarcinales andMethanomicrobiales constituted the majority of the total methanogen population.Methanobacteriales andMethanococcales played a relatively minor role in the digesters. Phylogenetic groups of mesophilic, Gram-negative sulfate-reducing bacteria were consistently present at significant levels:Desulfovibrio andDesulfobulbus spp. were the dominant sulfate-reducing populations,Desulfobacter andDesulfobacterium spp. were present at lower levels, andDesulfosarcina, Desulfococcus, andDesulfobotulus spp. were absent. Sulfate reduction by one or more of these populations played a significant role in all digesters evaluated in this study. In addition, sulfate-reducing bacteria played a role in favoring methanogenesis by providing their substrates. The analysis of the two-phase digester indicated that true phase separation was not accomplished: significant levels of active methanogens were present in the first phase. It was determined that the dominant populations in the second phase were different from those in the single-phase digesters.     

Anaerobic dissolution of iron-phosphorus complexes in sediment due to the activity of nitrate-reducing bacteria

Nitrate-reducing bacteria (Pseudomonas fluorescens andAlcaligenes sp.) as well as extracellular compounds from these bacteria increased the dissolution rate of iron and phosphorus sorbed to iron precipitates during anaerobic, nitrate-free conditions in experimental sediment-water systems. It is suggested that the influence of the bacteria is due to enzymatic catalyzation of chemical iron reduction.     

A bacteriological profile of bottled water sold in Bangladesh

Four different brands of bottled water had counts of aerobic bacteria ranging from 10³ to 10⁶ colony forming units/100 ml. Pathogens isolated includedPseudomonas (in all brands),Alcaligenes andEscherichia coli (each in three brands), andKlebsiella, Enterobacter andShigella (each in two brands). All four brands were judged to be unsatisfactory by accepted health standards.     

Nitrate production in the rhizosphere of Plantago species

Summary The production of nitrate in an old established dune grassland soil and its uptake by plants was studied by comparing amounts of mineral nitrogen and numbers of nitrifying bacteria in the rhizosphere on the one hand, and on the other accumulated nitrate and levels of nitrate reductase (NaR) of individual plants of three Plantago species,i. e., P. major, P. lanceolata andP. coronopus. For these three Plantago species andP. media basal levels of NaR in the absence of nitrate were determined in plants grown in culture solutions. The basal NaR levels ofP. major andP. media (species occurring on nutrient-rich soils) were significantly higher than those ofP. lanceolata andP. coronopus (species found on nutrient-poor soils). NaR activity increased in the presence of nitrate and was suppressed by ammonium.From the numbers of nitrifying bacteria in the rhizosphere and NaR activity in the leaves it was concluded that nitrate was produced in the root environments of the three Plantago species and that the compound was taken up by the plants. NaR activities and numbers of nitrifying bacteria were higher for individuals ofP. major than for those ofP. lanceolata andP. coronopus. No correlation was found between the ammonium levels and the numbers of nitrifying bacteria in the soil, and no indications of inhibition of nitrifying bacteria in the rhizosphere were obtained. For individuals ofP. lanceolata a correlation was found between the numbers of nitrifying bacteria in the soil and NaR activity in the leaves. The results are discussed in relation to the ecological habitats of the three species.Grassland Species Research Group Publication No.38.     

Bacteriolytic activities of the free-living soil amoebae,Acanthamoeba castellanii,Acanthamoeba polyphaga andHartmannella vermiformis

Bacteriolytic activities of axenically grown free-living soil amoebaeAcanthamoeba castellanii, Acanthamoeba polyphaga andHartmannella vermiformis towards various Gram-positive and Gram-negative bacteria were determined. A spectrophotometric assay revealed that the specific bacteriolytic activities of bothAcanthamoeba species were higher as those of the threeHartmannella strains.Bacillus megaterium, Bacillus subtilis, Chromatium vinosum, Micrococcus luteus andPseudomonas fluorescens were more easily lysed than the other bacteria tested.Agrobacterium tumefaciens, Klebsiella aerogenes andSerratia marcescens were hardly affected at all by the amoebal bacteriolytic activities. Among the Gram-negative bacteria we observed differences in lysis sensitivity while the Gram-positive bacteria tested were sensitive to lysis. Isoelectric focusing (IEF) gel-electrophoresis in the pH range 3–10 was performed to separate the bacteriolytic isoenzymes of amoebae. Bacteriolytic patterns were shown by using an activity assay in which lysis bands were formed in the agar/bacteria gel-overlay. The activity assay revealed remarkable differences in typical banding patterns for bacteriolytic activities among amoebae. Distinct differences between typical pI points of bacteriolytic activities inAcanthamoeba andHartmannella were shown. Bacteriolytic activities ofHartmannella were more pronounced and observed in the isoelectric points (pI) range of 4.0–9.3 while forAcanthamoeba the range was pI 4.5–8.9.Abbreviations IEF isoelectric focusing - PAA-IEF polyacrylamide-isoelectric focusing - CCAP culture collection of algae and protozoa - AS amoeba saline medium - pI isoelectric points     

茅尾海红树根际土壤可培养细菌多样性及抑菌活性研究

为挖掘茅尾海红树植物根际土壤可培养细菌资源,研究其抑菌活性,该文使用培养基对茅尾海5种红树植物(红海榄、黄槿、无瓣海桑、桐花树、阔苞菊)的7份根际土壤进行富集培养,选用6种不同分离培养基对富集样品进行可培养细菌的分离纯化,基于菌株16S rRNA基因序列信息进行物种多样性分析,并采用纸片法筛选具有抑制表皮葡萄球菌、耐甲氧西林金黄色葡萄球菌、铜绿假单胞菌活性的菌株。结果表明:(1)从7份红树植物根际土壤样品中分离到120种可培养细菌,隶属于35科47属,其中链霉菌属(Streptomyces sp.)占菌种总数的 14.2%,同时发现5种潜在新菌株。(2)通过抑菌活性初筛,发现9种细菌的发酵粗提物对至少一种致病菌具有抑菌活性。综上表明,茅尾海红树植物根际土壤可培养细菌多样性丰富,并且部分菌株具有抑制人类致病菌活性。该研究结果为新型抗生素的开发与利用提供了菌种资源。     

Characteristics of aSerratia plymuthica isolate from plant rhizospheres

An isolate (G15) of a bacterium, frequently isolated from roots of various plant species, was identified asSerratia plymuthica. At low temperature (viz. 2–8°C), the studied isolated readily produced a red pigment which proved useful in recognizing the bacteria on reisolation. In laboratory tests it exhibited strong antagonism againstBotrytis cinerea andGerlachia nivalis and moderate antagonism againstRhizoctonia solani, Fusarium culmorum andPythium sp. The bacterium significantly increased growth of lettuce plants when applied to the roots under non-sterile conditions in greenhouse tests. Various strains ofSerratia plymuthica are supposed to be common as rhizosphere bacteria under Swedish conditions.     

Phylogenetic studies of two rubredoxins from sulfate reducing bacteria

Summary The sequences of two rubredoxins isolated from the sulfate reducing bacteria:Desulfovibrio vulgaris andDesulfovibrio gigas have been elucidated. They have similar sequences but many more differences occur than would be expected from two bacteria of the same genus. Of the 52 sites, only 37 are occupied by identical residues. The primary structures are compared with those of the anaerobic bacteria rubredoxins ofClostridium pasteurianum, Micrococcus aerogenes, Pseudomonas oleovorans andPeptostreptococcus elsdenii: only 12 identities are found, mostly in the two clusters that contain two iron-bound cysteines each. A phylogenetic tree based on the primary structures is presented and possible relations with plant and bacterial ferredoxins are discussed. A secondary and tertiary structure, stereochemically compatible with the sequence data, is proposed.To whom reprint requests should be addressed     

The speciation of coliform genera from above and below a sewer outfall and their susceptibilities to antimicrobial agents

The occurrence of coliforms in a small water course was shown to increase by a factor of thirty six below the outfall of a sewage treatment plant. Speciation of the bacteria from above and below the sewer outfall showed thatEscherichia coli andEnterobacter species predominated. Drug resistance levels were significant in microorganisms from both sampling sites and the occurrence of a significant number of multiple-resistant microorganisms, particularlyE. coli, is reported. BothE. coli andEnterobacter species from below the sewer outfall show a statistically significant increase in resistance to ampicillin andE. coli from below the outfall also shows a statistically significant increase in resistance to sulphamethoxazole as compared with isolates from above the outfall.     

Microbiological characterization of a fuel-oil contaminated site including numerical identification of heterotrophic water and soil bacteria

Seven soil samples and seven groundwater samples from a site contaminated with fuel-oil were investigated using several chemical and microbiological techniques. In soil samples, 500 to 7,500 mg/kg of total hydrocarbons were found. These samples contained no n-alkanes but iso- and branched chain alkanes. No polychlorinated biphenyls could be detected. Microbiological investigations included estimations of total cell counts, viable cell counts on different media, and numbers of methylotrophic, denitrifying, sulphate reducing, anaerobic (with the exception of methanogenic organisms), and hydrocarbon degrading bacteria. Viable and hydrocarbon degrading bacteria were found in all samples. A total of 1,366 pure cultures was characterized morphologically and physiologically and identified by numerical identification using a data base of more than 4,000 reference strains. Groundwater samples were dominated by gram-negative bacteria of the generaPseudomonas, Comamonas, Alcaligenes, andAcinetobacter, which were also found in soil samples. In addition, more grampositive bacteria belonging to the generaArthrobacter, Nocardia, andBacillus could be isolated from soil samples.