Characterization of the beneficial properties of lactobacilli isolated from bullfrog (<Emphasis Type="Italic">Rana catesbeiana</Emphasis>) hatchery

The present work addresses the isolation and partial identification of the microbial population of a R. catesbeiana hatchery in spring and summer as well as some beneficial properties of Lactobacillus strains isolated in different seasons and hatchery areas. The bacterial population was grouped into the following taxa: Lactobacillus spp., Pediococcus spp., Enterococcus faecalis and Ent. faecium, and Enterobacteriaceae (Enterobacter spp., Escherichia coli) while Pseudomonas aeruginosa and Staphylococcus epidermidis were isolated from frogs displaying red-leg syndrome. The Lactobacillus plantarum and L. curvatus strains isolated showed to inhibit the growth of red-leg syndrome associated pathogens and food-borne bacteria by organic acids. While L. plantarum CRL 1606 also inhibited red-leg syndrome related pathogens by hydrogen peroxide, meat spoilage bacteria were only inhibited by acidity. However, by using a MRS medium added with tetramethyl-benzidine and peroxidase, a high percentage of H₂O₂-producing lactobacilli were detected. The surface properties of Lactobacillus strains showed that a few strains were able to agglutinate ABO human erythrocytes, while the highest number of strains had a low to medium degree of hydrophobicity. This paper constitute the first study related to the beneficial properties of Lactobacillus isolated from a bullfrog hatchery, as well as the selection criteria applied to a group of strains, which could help to control or prevent bacterial infectious diseases in raniculture.     

Dynamics of Seawater Bacterial Communities in a Shellfish Hatchery

Bacterial disease is a significant issue for larviculture of several species of shellfish, including oysters. One source of bacteria is the seawater used throughout the hatchery. In this study carried out at a commercial oyster hatchery in Tasmania, Australia, the diversity of the bacterial community and its relationship with larval production outcomes were studied over a 2-year period using terminal restriction fragment length polymorphism and tag-encoded pyrosequencing. The bacterial communities were very diverse, dominated by the Alphaproteobacteria, Gammaproteobacteria, Flavobacteria and Cyanobacteria. The communities were highly variable on scales of days, weeks and seasons. The difference between the intake seawater and treated clean seawater used in the hatchery was smaller than the observed temporal differences in the seawater throughout the year. No clear correlation was observed between production outcomes and the overall bacterial community structure. However, one group of Cyanobacterial sequences was more abundant when mass mortality events occurred than when healthy spat were produced although they were always present.     

Novel alternative to antibiotics in shrimp hatchery: effects of the essential oil of Cinnamosma fragrans on survival and bacterial concentration of Penaeus monodon larvae

Aims: The activity of two essential oils (EOs) of Cinnamosma fragrans, an endemic plant to Madagascar (B8: linalool‐type and B143: 1,8‐cineole‐type), against bacterial isolates from a shrimp hatchery of Penaeus monodon and their effects on the survival and bacterial concentration of larvae were determined. Methods and Results: Minimum inhibitory concentrations were determined using a broth dilution technique. The bacterial concentrations of both larvae and water tank were assessed on Marine agar and Thiosulfate Citrate Bile Sucrose agar. The assays took place in OSO Farming’s shrimp hatchery in Madagascar. EOs were directly added to the water tank. Regarding the survival, the assays in larval culture (four replicates each of B8, B143, E and control) showed that B8 oil had a similar effect (P > 0·05) as the antibiotic (Erythromycin) and was more active than B143 (P < 0·05). A negative correlation was observed between the bacterial concentration and the survival of larvae for all assays. Conclusion: Both C. fragrans essential oils, as antibiotic, exhibited significantly higher survival rates and lower bacterial concentrations of the larvae than the control (oil and antibiotic free). Significance and impacts of the study: The potential of C. fragrans essential oil to control the bacterial load in in vivo conditions, thereby enhancing survival rate of P. monodon larvae, makes it a relevant option for developing a novel alternative to antibiotics in shrimp hatchery culture.     

Culturable bacterial communities on leaf sheaths and panicles of rice plants in Japan

Culturable bacterial communities on rice plants were investigated from 2001 to 2003. In total, 1,394 bacterial isolates were obtained from the uppermost leaf sheaths at 1 month before heading time and from leaf sheaths and panicles at heading time. The average culturable bacterial population on the leaf sheaths was larger at heading time than at 1 month previously. Furthermore, the population was significantly larger on panicles than on leaf sheaths, suggesting that the bacterial population is influenced by the organs of rice plants. Larger proportions of bacteria were obtained from the macerates of leaf sheaths after washing with phosphate buffer, and most culturable bacteria were verified to inhabit the inside or inner surface, rather than the outer surface, of the tissues. Verification of the bacterial composition based on 16S rRNA gene sequences revealed that genera of Sphingomonas, Microbacterium, Methylobacterium, and Acidovorax tended to be dominant colonizers on leaf sheaths, whereas Pseudomonas and Pantoea were isolated mainly from the panicles, indicating that leaf sheaths and panicles harbor distinct communities. Furthermore, the richness of bacterial genera was less on both leaf sheaths and panicles at heading time compared with that observed 1 month before heading time. Phylogenetic analyses using bacterial isolates belonging to the four dominant genera inhabiting leaf sheaths at heading time revealed that particular bacterial groups in each genus colonized the leaf sheaths.     

Crown Gall Development Stimulated by Wound Washing

A number of experiments on the effect of wound washing on the development of crown gall were made varying the following factors: Host species; bacterial strain; non-washing versus washing for different periods; sterile versus inoculated wound; time of inoculation. Washing did not have a recognizable effect on the healing of sterile wounds. Neither did it seem to overcome incompatibility between host and bacterial strain. Washing promoted tumor growth significantly under the following conditions: Vicia faba inoculated with T37 20 hours after washing for 1 hour; Helianthus annuus inoculated with B6 immediately after washing for 2 hours.     

Bacterial community and decomposition rate in long term fed-batch composting using woodchip and Polyethylene terephthalate (PET) as bulking agents

Long term fed-batch composting experiments were conducted for 200 days using two types of bulking agents; woodchip and PET flake, with periodic compost withdrawal through a washing process. The bacterial communities of composting materials in the two different bulking agents were also investigated by 16S rRNA gene clone analysis. The decomposition rate in both composting reactors was 86.1% and 88.2% of the total organic load, respectively. The control experiment of dead-end operation without compost withdrawal by washing process could not be maintained for more than 102 days because of its low performance. The reactor with compost withdrawal, however, improved the decomposition rate in the composting process, and could be applied in the long run. There was a significant difference in the bacterial community between the FBC reactor with woodchip and another with PET flake as the bulking agent though the decomposition rates were similar. The reactor with woodchip as the bulking agent consisted of 95% Bacillales while the PET flake reactor contained 54% of total bacteria count. In addition, Lactobacillales was dominant at 38% in the PET flake reactor and the bacterial community in general significantly differed from the woodchip reactor. Furthermore, there was a difference in the species composition in the Bacillales and the bacterial community showed a significant difference at the species level between the two reactors. Although bacterial community differed, the decomposition rates between the two reactors were similar and PET flake showed greater viability than woodchip as a bulking agent due to its high abrasion resistance and non-biodegradability.     

The attachment of Enteromorpha zoospores to a bacterial biofilm assemblage

This study has investigated the relationship between bacterial biofilms and the attachment of zoospores of the green macroalga Enteromorpha. Zoospore attachment to glass slides was enhanced in the presence of a bacterial biofilm assemblage, and the number attaching increased with the number of bacteria present. Zoospores also attached to control surfaces, but at lower numbers; glass surfaces conditioned in autoclaved seawater had the same number of zoospores attached as new glass surfaces. The spatial relationship between bacterial cells and attached zoospores was quantified by image analysis. The hypothesis tested was that zoospores attached preferentially to, or in the very close vicinity of, bacterial cells. Spatial microscopic analysis showed that more bacteria were covered by zoospores than would be expected if zoospore attachment was a random process and zoospores appeared to attach to bacterial clusters. The most likely explanation is that zoospores are attracted to bacterial cells growing on surfaces and the presence of a bacterial biofilm enhances their settlement. The possibility is discussed that Enteromorpha zoospores respond to a chemical signal produced by bacteria, i.e. that there may be prokaryote‐eukaryote cell signalling.     

ADHERENCE OF AGROBACTERIA TO MOSS PROTONEMA AND GAMETOPHORES VIEWED BY SCANNING ELECTRON MICROSCOPY

The attachment of certain Agrobacterium species to moss protonema was examined by scanning electron microscopy. The bacteria cultured with the moss adhered to the protonemal filaments of Pylaisiella selwynii and Funaria hygrometrica throughout the fixation and washing procedure prior to examination. The number of bacteria adhering per unit length of filament did not correlate with the ability of four species (A. tumefaciens, A. rubi, A. rhizogenes, A. radiobacter) to induce gametophore formation in P. selwynii. Little difference was found between the number of A. tumefaciens on P. selwynii or on F. hygrometrica, and although this bacterial species induced gametophores on P. selwynii, it had no effect on F. hygrometrica. A. rhizogenes, which is capable of inducing rhizoid formation on both P. selwynii and F. hygrometrica without physical attachment, did associate with filaments of both mosses. Larger numbers of A. tumefaciens and A. rubi, which induce gametophores or callus, were associated with the spore and germ tube of P. selwynii than were A. rhizogenes or A. radiobacter which do not initiate these changes. These results suggest that the germ tube may constitute the site where effective attachment occurs. The number of A. tumefaciens adhering to P. selwynii was greatest at 2–6 h after addition and then decreased by 26 h, raising the possibility that some bacteria lyse following attachment. None of the bacteria adhered to the gametophore walls of either moss, indicating that a change in cell wall surface may occur. The four species of Agrobacterium differed in their orientation when adhering to the moss. These results suggest that the process of bacterial adherence to higher plant cells in Agrobacterium infection is similar to that which we observe in mosses and which leads to developmental changes.     

Enumeration of phagocytosed Staphylococcus aureus inside cells of the mouse macrophage cell line J774 by bioluminescence,fluorescence and viable counting techniques

In order to quantify intracellular Staphylococcus aureus within a macrophage-like cell line by a bioluminescence technique, the mouse cell line J774 and opsonized Staphylococcus aureus were incubated together to allow phagocytosis to occur. Experiments using UV microscopy and fluorescent stained S. aureus were performed to determine an estimate of the mean intracellular bacterial numbers. For enumeration of intracellular bacteria by a bioluminescence technique, extracellular bacteria were removed by washing, the macrophages lysed mechanically and osmotically and treated with apyrase to remove somatic ATP. Bacterial cells were washed and the intracellular ATP measured by firefly luciferase bioluminescence in a luminometer. This new method of enumerating intracellular bacteria was compared to the conventional method of viable counts and found to correlate (r = 0.78). The bioluminescence assay developed was found to be a relatively rapid alternative method to the techniques currently used to enumerate intracellular bacteria and could prove advantageous in studies of intracellular killing and effects of antimicrobial agents on intracellular pathogens.     

Bacterial hand contamination and transfer after use of contaminated bulk-soap-refillable dispensers

Bulk-soap-refillable dispensers are prone to extrinsic bacterial contamination, and recent studies demonstrated that approximately one in four dispensers in public restrooms are contaminated. The purpose of this study was to quantify bacterial hand contamination and transfer after use of contaminated soap under controlled laboratory and in-use conditions in a community setting. Under laboratory conditions using liquid soap experimentally contaminated with 7.51 log(10) CFU/ml of Serratia marcescens, an average of 5.28 log(10) CFU remained on each hand after washing, and 2.23 log(10) CFU was transferred to an agar surface. In an elementary-school-based field study, Gram-negative bacteria on the hands of students and staff increased by 1.42 log(10) CFU per hand (26-fold) after washing with soap from contaminated bulk-soap-refillable dispensers. In contrast, washing with soap from dispensers with sealed refills significantly reduced bacteria on hands by 0.30 log(10) CFU per hand (2-fold). Additionally, the mean number of Gram-negative bacteria transferred to surfaces after washing with soap from dispensers with sealed-soap refills (0.06 log(10) CFU) was significantly lower than the mean number after washing with contaminated bulk-soap-refillable dispensers (0.74 log(10) CFU; P < 0.01). Finally, significantly higher levels of Gram-negative bacteria were recovered from students (2.82 log(10) CFU per hand) than were recovered from staff (2.22 log(10) CFU per hand) after washing with contaminated bulk soap (P < 0.01). These results demonstrate that washing with contaminated soap from bulk-soap-refillable dispensers can increase the number of opportunistic pathogens on the hands and may play a role in the transmission of bacteria in public settings.     

Pathogenic bacteria associated with lesions and thallus bleaching symptoms in the Japanese kelp Laminaria religiosa Miyabe (Laminariales,Phaeophyceae)

During early Spring (April–May) when the seawater salinity drops suddenly and the seawater temperature increases drastically, severe lesions and thallus bleaching were observed in the Laminaria religiosa population at Oshoro Bay, Otaru, Hokkaido, Japan. The healthy and diseased kelp blades were collected and subjected to enumeration of total number of culturable bacteria and bacterial species. Bacterial enumerations were done using 3 different media formulations; high-nutrient media (Media 1), low-nutrient media (Media 2) and modified low-nutrient media with 5% kelp extract (Media 3). Seven bacterial species were isolated from the healthy kelp. These were Alcaligenes aquamarinas, Alteromonas sp., Azomonas agilis, Azotobacter beijerinckii, Escherichia coli, Halobacterium sp. and Halococcus sp. All 7 bacterial species were isolated on Media 2 and Media 3, but only 5 species were isolated using Media 1 with the absence of Halobacterium sp. and Halococcus sp. Highest total number of culturable bacteria was 2050 CFU/cm² on Media 3. Eight species of bacteria were isolated from the diseased kelp thallus with the addition of Erwinia amylovora. All 8 bacteria grew on Media 2 and Media 3, but only 6 species were isolated using Media 1 with the absence of Halobacterium sp. and Halococcus sp. Highest total number of culturable bacteria was 5830 CFU/cm² on Media 3. However, only 3 species were isolated from the lesioned area. The most abundant species was Alteromonas sp. followed by Halococcus sp. and Alcaligenes aquamarinas. The surface bacteria showed best growth on Media 3. Scanning Electron Microscopic images of the healthy and diseased thallus gave distinctive evidence of the severity of the lesions as well as the relative abundance in the bacterial population. In an effort to identify the symptoms causative organism, the isolated bacterial species were cultured and used to test Koch's postulates. Out of the 8 species, only Alteromonas sp. induced lesions on the axenic kelp blades. The inoculated bacteria were also re-isolated without any significant contamination. Hence, Alteromonas sp. is suggested as the possible disease causing organism.     

Quantitation of Adsorption of Rhizobia in Low Numbers to Small Legume Roots

Bacteria adsorbed in low numbers to alfalfa or clover root surfaces were counted after incubation of seedlings in mineral solution with very dilute inocula (less than 10⁵ bacteria per ml) of an antibiotic-resistant strain under defined conditions. After specified washing, bacteria which remained adsorbed to roots were selectively quantitated by culturing the roots embedded in yeast extract-mannitol-antibiotic agar and counting the microcolonies along the root surface; the range was from about 1 bacterium per root (estimated as the most probable number) to 50 bacteria per cm of root length (by direct counting). This simple procedure can be used with any pair of small-rooted plant and antibiotic-resistant bacterium, requires bacterial concentrations comparable to those frequently found in soils, and yields macroscopic localization and distribution data for adsorbed bacteria over the root surface. The number of adsorbed bacteria was proportional to the size of the inoculum. One of every four Rhizobium meliloti cells adsorbed in very low numbers to alfalfa roots resulted in the formation of a nodule. Overall adsorption of various symbiotic and nonsymbiotic bacterial strains to alfalfa and clover roots did not reflect the specificities of these legumes for their respective microsymbionts, R. meliloti and R. trifolii.     

Purification and characterization of antibacterial substances produced by a marine bacterium Pseudoalteromonas haloplanktis strain

Aims: To purify and characterize compounds with antimicrobial activity from Pseudoalteromonas haloplanktis inhibition (INH) strain. Methods and Results: The P. haloplanktis isolated from a scallop hatchery was used to analyse antibacterial activities. Crude extracts were obtained with ethyl acetate of the cultured broth, after separation of bacterial cells, and assays against six strains of marine bacteria and nine clinically important pathogenic bacteria. The active compounds were purified from ethyl acetate extracts, by a combination of SiO₂ column and thin layer chromatography. Two active fractions were isolated, and chemical structures of two products from the major one were unambiguously identified as isovaleric acid (3-methylbutanoic acid) and 2-methylbutyric acid (2-methylbutanoic acid), by comparing their mass spectra and ¹H- and ¹³C-nuclear magnetic resonance spectra to those of authentic compounds. Conclusions: In the antibacterial activity of P. haloplanktis INH strain, extra cell compounds are involucred, mainly isovaleric and 2-methylbutyric acids. Significance and Impact of the Study: Production of antimicrobial compounds by marine micro-organisms has been widely reported; however, the efforts not always are conducted to purification and applications of these active compounds. This study is a significant contribution to the knowledge of compounds unique from marine bacteria as potential sources of new drugs in the pharmacological industry.     

Quantitative study, identification and antibiotics sensitivity of someVibrionaceae associated to a marine fish hatchery

This study characterises the bacteria associated with a marine hatchery in Tunisian coastal marine waters. Presumptive vibrios (TCBS agar) and heterotrophic aerobic microflora (CFU) were studied at different stages within the hatchery: seawater, batches of algal cultures, rotifers andArtemia culture tanks. The bacterial strains were isolated on TCBS Agar plates and described using different bacteriological tests (standardised micromethods “API 20 E Strips”, exoenzymes production, growth at different temperatures, pH and salinity, vibriostatic agent O/129 and antibiotics susceptibility). Two dominant genera of bacteria were found (Vibrio andAeromonas) associated with some strains of thePseudomonadaceae family.Vibrio alginolyticus was the dominant bacteria (75% of total isolates) found in rotifers (Brachionus plicatilis) andArtemia cultures (Artemia salina). In larvae rearing tanks, an increase ofVibrionaceae was noted after larvae were fed withArtemia. Most of the studied bacteria used the skin mucus ofSparus aurata larvae as their sole source of carbon. All theV. alginolyticus strains were β-haemolytic, hydrolyse the DNA and were susceptible to several tested antibiotics.     

烟草种子内生细菌群落结构与多样性

【目的】为了解烟草种子内生细菌的群落结构和多样性。【方法】分别对3个品种(K326、云烟85、云烟87)烟草种子内生细菌的16S rRNA基因V3–V4区进行扩增,采用Illumina MiSeq测序技术对扩增片段进行高通量测序,并对3个品种烟草种子内生细菌群落结构和多样性进行分析。【结果】3个品种种子共获得的V3–V4区高质量序列片段128558条,Shannon指数计算为2.03–3.73,K326和云烟85内生菌多样性指数高于云烟87。3品种烟草种子内生细菌的优势门均为变形菌门Proteobacteria、放线菌门Actinobacteria、厚壁菌门Firmicute和拟杆菌门Bacteroidete。3个品种烟草种子内生细菌共有菌属共有27个,K326和云烟85的最优势菌属为假单胞菌属(Pseudomonas),云烟87的最优势菌属为大肠杆菌志贺菌属(Escherichia-shigella)。16S功能预测显示各种子中产生了丰度较高的蛋白质、核苷酸、糖类、辅酶及代谢产物合成的有益功能信息。【结论】烟草种子内生细菌多样性丰富,不同品种种子细菌群落组成基本相似,其丰度存在一定差异性。种子中存在的潜在有益细菌包括假单胞菌、类芽孢杆菌、根瘤菌、马赛菌、藤黄单胞菌、萨勒河菌、Lelliottia菌等,具有大量代谢相关的有益功能。研究结果为今后烟草种子内生菌的功能研究和利用以及种子病害生物防控提供参考信息。     

Growth Inhibition of Helicobacter pylori by Monoclonal Antibody to Heat-Shock Protein 60

The H20mAb recognizing the 60-kilodalton protein, which existed in the outer membrane and was induced by heat shock at 42 C, was established. The molecule recognized with the mAb was a heat-shock protein 60 (HSP60) of Helicobacter pylori. To understand the role of HSP60 on the cell surface of H. pylori, whether or not H20mAb affects the growth of H. pylori was investigated. When bacteria were cultured with H20mAb, growth was markedly inhibited after 24 hr, although an initial 5 hr-incubation with the mAb induced no significant inhibition of H. pylori growth. The 24- and 48 hr growth of the bacteria after washing to remove the mAb at 5 hr was also inhibited though the inhibitory effect was not strong. In electron microscopical analysis, the spots with high electron density in the cytoplasm of the bacteria treated with H20mAb were increased, depending on the length of incubation time from 5 to 24 hr. After 24 hr treatment with H20mAb, bacterial destruction was also observed, indicating bactericidal activity by H20mAb. These results suggest that the HSP60 on the cell surface of H. pylori might have an essential role in the growth of the bacteria.     

郫县豆瓣细菌多样性及群落结构动态变化北大核心

【目的】通过检测郫县豆瓣在不同发酵阶段细菌的种类、丰度及数量,探究郫县豆瓣的不同发酵产品发酵过程中细菌的动态变化情况。【方法】采用16S rRNA基因测序对郫县豆瓣4个发酵阶段中细菌种类及丰度进行分析,利用荧光定量PCR(quantitative real-time PCR,qPCR)方法检测不同发酵阶段的细菌总数。【结果】郫县豆瓣在初期的发酵过程中细菌群落处于动态稳定,在不同发酵阶段细菌群落组成相对丰富,从郫县豆瓣整个初期的发酵过程来看,细菌群落多样性呈现升高的趋势,Shannon指数从1.25升高到3.50;在郫县豆瓣初期发酵过程中细菌群落的数量以及多样性与发酵环境息息相关,不同发酵阶段细菌群落的多样性也有所不同,其中在干辣椒发酵阶段中泛菌属(Pantoea)为最优势菌属,占比为20%;在蚕豆瓣发酵阶段中葡萄球菌属(Staphylococcus)的相对丰度最高,占比为38%;混合发酵后,在红油豆瓣发酵阶段的最优势菌属是乳酸杆菌属(Lactobacillus),占比达到27%,郫县豆瓣发酵阶段的最优势菌属是乳酸杆菌属(Lactobacillus),占比为62%。【结论】推断在郫县豆瓣不同发酵阶段初期相对丰度较大的菌属对郫县豆瓣的质量以及产量可能会产生重大影响。     

Do stocked hatchery‐reared juveniles ecologically suppress wild juveniles in Salvelinus leucomaenis?

The dominancy of semi‐wild and hatchery‐reared white‐spotted charr Salvelinus leucomaenis juveniles was evaluated using pair‐wise enclosure tests and field stocking tests. The semi‐wild S. leucomaenis originated in a hatchery, being stocked into the test stream as eyed‐eggs. In the pair‐wise enclosure test, the semi‐wild S. leucomaenis dominated the hatchery S. leucomaenis that were of a similar standard length (L_S). The semi‐wild S. leucomaenis were subordinate to hatchery S. leucomaenis that were > 11% larger in L_S. In the field stocking test, the abundance and growth of semi‐wild S. leucomaenis was decreased in the presence of larger hatchery S. leucomaenis (14% larger L_S). Taken together, these results suggest that larger hatchery S. leucomaenis ecologically suppress the smaller semi‐wild S. leucomaenis. Salvelinus leucomaenis juveniles that are stocked with the intention of supplementing natural populations should be < 10% larger than their wild counterparts at the time of stocking to minimize their competitive advantage. The semi‐wild and hatchery S. leucomaenis used in both tests were genetically similar individuals, suggesting that the differences are due to the early rearing environment of either a natural stream or hatchery. The hatchery S. leucomaenis have lower levels of aggression as a result of selection in the hatchery rearing environment. Rearing in a natural stream from the eyed‐egg stage is likely to increase their lowered aggression.     

Multiplication of Pseudomonas syringae pv. phaseolicola"in planta"

In the compatible combination of the halo blight disease of bean Pseudomonas phaseolicola was able to colonize large areas of the intercellular space of leaves, such that these confluent water congested areas became visible as water-soaked spots. Most of the plant cell walls in the infected region maintained their normal shape, even when the cytoplasm had collapsed. Some inward bending of plant cell walls preceded their rather slow degradation and final replacement by bacterial masses. Neighbouring plant cells appeared to be metabolically active. In resistant leaves no indications of active bacterial attachment or encapsulation could be observed. However, bacteria appeared to be more densely packed in resistant leaves, and relatively more plant cells completely collapsed as compared with susceptible leaves. From 8—14 days after inoculation, the bacterial concentration did not change much in susceptible or resistant leaves, indicating the absence of bactericidal components. Even Pseudomonas pisi snowed some multiplication in bean leaves (immune reaction), but its growth stopped earlier than that of P. phaseolicola. in the resistant cultivars, probably due to a different mechanism of resistance. Although less bacteria were determined in the intercellular washing fluid (IF) compared with leaf homogenates, the high bacterial concentrations in the IF supported our observation that an effective encapsulation of bacteria in resistant leaves did not occur.     

Diversity of Bacterial Communities in the Snowcover at Tianshan Number 1 Glacier and its Relation to Climate and Environment

The bacterial distribution, and its relationship with climate and environment factors were investigated in the snowcover at Tianshan Number 1 Glacier. The results showed that psychrotrophs were the preponderant bacteria in pit samples, though they were not the dominant species in the new fallen snow. The quantity and diversity of the cultivable bacteria decreased with the passage of time, indicating that the bacterial community acclimatized to low temperature by changing its structure. During this time, the peak number of the cultivable bacteria was associated with dirt layers, indicating that the bacterial input came with dust. Concurrently, the quantity and diversity of the cultivable bacteria showed a trend of variation similar to that shown by the δ¹⁸O values and the soluble ion concentrations, indicating that the bacterial distribution was related to both temperature and the amount of dust transported onto the glacier. Phylogentic analyses of 16S rRNA indicated that all the isolates fell into six categories: α-Proteobacteria, β-Proteobacteria, γ-Proteobacteria, Cytophaga-Flavobacterium-Bacteroides (CFB) group bacteria, high G+C gram-positive bacteria, and low G+C gram-positive bacteria. In the snow pit, the abundance of the CFB group bacteria (mainly of the genus Flavobacterium) decreased from 55.5% to 1.49% with age, and fluctuated similar to the ion concentrations and the δ¹⁸O value. Meanwhile the α-Proteobacteria (mainly of the genus Brevundimonas) increased from 0.9% to 88.1%, indicating that Brevundimonas was the dominant psychrotroph in the study area, whose abundance varied inversely compared to the above-mentioned chemical properties. All the results suggest that bacterial abundance and diversity vary with climate and the physical chemical microenvironment. The pattern of bacterial distribution could be a biological index for the record of climate and environment change in the Tianshan Number 1 Glacier.