Immunofluorescence assay for effects on field abundance of a naturally occurring pseudomonad during passage through the gut of a marine deposit feeder,Abarenicola pacifica

In a seasonal study we used immunofluorescence to follow a specific bacterial population, as well as total numbers, through the fore-, mid-, and hindgut of a deposit feeder, Abarenicola pacifica. We chose a pseudomonad because of its high ambient abundance. On five dates, we collected A. pacifica gut contents, with concurrent measurements of sedimentary food quality (chlorophyll a, protein, bacterial abundance), animal egestion rates (inversely proportional to gut residence time), and temperature. Increasing bacterial numbers from ingested sediment to foregut contents, and decreases from foregut to midgut indicate significant selection and digestion, respectively, of both the pseudomonad and the total bacterial community. Inverse correlations between egestion rate and digestive removal of bacteria offer some support for the prediction that digestion of bacteria is proportional to time spent exposed to digestive enzymes, although the significance of the associated statistical tests is marginal. No hindgut growth of the pseudomonad was observed, likely due to the short gut residence time of A. pacifica. The pseudomonad showed variation of less than a factor of 3 in its ambient sedimentary abundance over the year. Off print requests to: C. Plante.     

松墨天牛成虫室内外种群肠道细菌的多样性及功能分析

[目的]为明确松墨天牛Monochamus alternatus成虫中、后肠细菌群落结构,探索肠道细菌的潜在功能.[方法]分别提取室外和室内饲养的松墨天牛成虫各15头(室内和室外各15个中肠、15个后肠)的肠道DNA,利用二代测序技术对松墨天牛成虫肠道细菌的16S rDNA V3-V4区序列进行测序,统计操作分类单元(...     

The microbial environment of marine deposit-feeder guts characterized via microelectrodes

Microbial viability and growth in animal guts are dependent upon conditions influenced by both the physiological activities of the animal and the activities of the microbes themselves. To examine the relative contribution of these influences, the guts of Molpadia intermedia (a subtidal holothuroid) and a variety of other marine deposit feeders from diverse habitats were probed with mini- or microelectrodes to measure oxygen, Eh, and pH. In general, bulk oxygen and pH conditions of the gut mimicked those of ambient sediments, revealing nearly neutral pH and zero oxygen in sub- and intertidal animals, with more oxygen in bathyal animals ingesting oxygenated sediments. Eh in guts of subsurface deposit feeders that likely subduct and aerate sediments before ingestion did not mimic sediments. Axial Eh profiles, in contrast to those of pH and oxygen, revealed significant changes along the gut. In most deposit feeders, values decreased from mouth to midgut, suggesting high rates of microbial metabolism within the gut. Increases in Eh were observed in the most distal portion of guts, however, likely due to anal intake of aerated water, and throughout the guts of terebellid polychaetes that feed on highly reducing sediments. This addition of a strong oxidant by the animal may be necessary to avoid sulfide poisoning and may provide access to organic products by stimulating chemoautotrophy. Radial profiles of the gut revealed sharp gradients of Eh and oxygen. In general, steep redox gradients stimulate bacterial metabolism and may lead to exceptionally high respiratory rates. Radial diffusion calculations made using oxygen profiles surrounding the gut reveal that, as predicted by digestion theory, oxygen consumption rates are rapid and are higher in the hindgut, where the digestive products of the animal are available to microbes, than in the foregut.Offprint requests to: C. Plante.     

Importance of Gram-positive naphthalene-degrading bacteria in oil-contaminated tropical marine sediments

AIMS: The aim of this study was to isolate, characterize and evaluate the importance of naphthalene-degrading bacterial strains from oil-contaminated tropical marine sediments. METHODS AND RESULTS: Three Gram-positive naphthalene-degrading bacteria were isolated from oil-contaminated tropical intertidal marine sediments by direct isolation or enrichment using naphthalene as the sole source of carbon and energy. Bacillus naphthovorans strain MN-003 can also grow on benzene, toluene, xylene and diesel fuel while Micrococcus sp. str. MN-006 can also grow on benzene. Staphylococcus sp. str. MN-005 can only degrade naphthalene and was not able to use the other aromatic hydrocarbons tested. Strain MN-003 possessed the highest maximal specific growth rate with naphthalene as sole carbon source. An enrichment culture fed with naphthalene as sole carbon source exhibited a significant increase in the relative abundances of the three isolates after 21 days of incubation. The three isolates constituted greater than 69% of the culturable naphthalene-degrading microbial community. Strain MN-003 outcompeted and dominated the other two isolates in competition studies involving batch cultures inoculated with equal cell densities of the three isolates and incubated with between 1 and 10 mg l-1 of naphthalene. CONCLUSIONS: Three Gram-positive naphthalene-degrading bacteria were successfully isolated from oil-contaminated tropical marine sediments. Gram-positive bacteria might play an important role in naphthalene degradation in the highly variable environment of oil-contaminated tropical intertidal marine sediments. Among the three isolates, strain MN-003 has the highest maximal specific growth rate when grown on naphthalene, and outgrew the other two isolates in competition experiments. SIGNIFICANCE AND IMPACT OF THE STUDY: This research will aid in the development of bioremediation schemes for oil-contaminated marine environments. Strain MN-003 could potentially be exploited in such schemes.     

Barophilic Bacteria Associated with Digestive Tracts of Abyssal Holothurians

Abyssal holothurians and sediment samples were collected at depths of 4,430 to 4,850 m in the Demerara abyssal plain. Bacterial concentrations in progressive sections of the holothurian digestive tract, as well as in surrounding surface sediments, were determined by epifluorescence microscopy. Total bacterial counts in sediments recently ingested by the animals were 1.5- to 3-fold higher than in surrounding sediments at the deepest station. Lowest counts were observed consistently in the foregut, where the digestive processes of the holothurian are believed to occur. In most animals, counts increased 3- to 10-fold in the hindgut. Microbial activity at 3°C and in situ and atmospheric pressure were determined for gut and sediment samples by measuring the utilization of [¹⁴C]glutamic acid, the doubling time of the mixed-population of culturable bacteria, and the percentage of the total bacterial count responsive to yeast extract in the presence of nalidixic acid, using epifluorescence microscopy. A barophilic microbial population, showing elevated activity under deep-sea pressure, was detected by all three methods in sediments removed from the hindgut. Transmission electron micrographs revealed intact bacteria directly associated with the intestinal lining only in the hindgut. The bacteria are believed to be carried as an actively metabolizing, commensal gut flora that transforms organic matter present in abyssal sediments ingested by the holothurian. Using data obtained in this study, it was calculated that sediment containing organic matter altered by microbial activity cleared the holothurian gut every 16 h, suggesting that abyssal holothurians and their associated gut flora are important participants in nutrient cycles of the abyssal benthic ocean.     

Production of Industrial Enzymes (Amylase,Carboxymethylcellulase and Protease) by Bacteria Isolated from Marine Sedentary Organisms

The abilities of bacteria isolated from eight marine sedentary organisms, six marine sponges (Spirastrella sp., Phyllospongia sp., Ircinia sp., Aaptos sp., Azorica sp. and Axinella sp.), one soft coral (Lobophytum sp.) and one alga (Sargassum sp.) to produce industrial enzymes (amylase, carboxymethylcellulase and protease) were examined. The mean total viable counts of the bacterial isolates ranged from 8.7 × 10⁴ to 8.4 × 10⁵ cfu/g wet weight of the organism. All eight organisms harboured amylase (0.05–0.5 IU/ml), carboxymethylcellulase (0.05–0.5 IU/ml) and protease (0.1–0.5 IU/ml) producing bacteria. Of 56 bacterial strains tested, as many as 60 to 83% of the strains produced at least one of the three enzymes, and 47% of strains were able to produce all three enzymes. High activities (> 0.5 IU/ml) of the three enzymes were recorded in bacterial strains belonging to the genera Alcaligenes and Bacillus. From the results of this study, it appears that bacteria associated with marine sedentary organisms are the novel source of industrial enzymes for possible commercial applications and may play an important role in enzyme‐catalysed organic matter cycling in marine environments.     

Screening and Characterization of Several 2,2-Dicholoropropionic Acid–Degrading Bacteria Isolated from Marine Sediment of Danga Bay and East Coast of Singapore Island

Industries and agriculture activities extensively utilize halogenated compounds. These compounds were found to be toxic and pollute the environment. Thus, many studies have been done on microbial degradation of these chemicals. In this study, an attempt was made to isolate bacterial strains EK1–EK5 from marine sediments collected at Danga Bay and east coast of Singapore island. The 16S rRNA analysis suggested that the isolated bacteria had more than 96% sequence identity to the sequence in the database; therefore, they were designated as Bacillus sp., Rhodococcus sp., Lysinibacillus sp., Microbacterium sp., and Aminobacter sp. The results of molecular analysis were supported by biochemical and microscopic examinations. Bacterial isolates were able to grow slowly in minimal medium containing only 2,2-dichloropropionate as the sole carbon source. The cellular doubling times were 39.60 ± 0.1, 36.60 ± 0.2, 30.71 ± 0.1, 41.23 ± 0.1, and 36.70 ± 0.3 h for EK1, EK2, EK3, EK4, and EK5, respectively. In the future, it will be important to further investigate the presence of the dehalogenase gene in their genomic DNA for further characterization.     

16S rRNA metagenomic analysis of the symbiotic community structures of bacteria in foregut,midgut, and hindgut of the wood-feeding termite <Emphasis Type="Italic">Bulbitermes</Emphasis> sp.

The termite gut is a highly structured microhabitat with physicochemically distinct regions. It is generally separated into the foregut, midgut and hindgut. The distribution of gut microbiota is greatly influenced by varying physicochemical conditions within the gut. Thus, each gut compartment has a unique microbial population structure. In this study, the bacterial communities of foregut, midgut and hindgut of wood-feeding higher termite, Bulbitermes sp. were analyzed in detail via metagenomic sequencing of the 16S rRNA V3-V4 region. While the microbiomes of the foregut and midgut shared a similar taxonomic pattern, the hindgut possessed more diverse bacterial phylotypes. The communities in the foregut and midgut were dominated by members of the group Bacilli and Clostridia (Firmicutes) as well as taxon Actinomycetales (Actinobacteria). The main bacterial lineage found in hindgut was Spirochaetaceae (Spirochaetes). The significant difference among the three guts was the relative abundance of the potential lignin-degrading bacteria, Actinomycetales, in both the foregut and midgut. This suggests that lignin modification was probably held in the anterior part of termite gut. Predictive functional profiles of the metagenomes using 16S rRNA marker gene showed that cell motility, energy metabolism and metabolism of cofactors and vitamins were found predominantly in hindgut microbiota, whereas xenobiotics degradation and metabolism mostly occurred in the foregut segment. This was compatible with our 16S rRNA metagenomic results showing that the lignocellulose degradation process was initiated by lignin disruption, increasing the accessibility of celluloses and hemicelluloses.     

THE TOXIC DINOFLAGELLATE GYMNODINIUM CATENATUM (DINOPHYCEAE) REQUIRES MARINE BACTERIA FOR GROWTH1

Interactions with the bacterial community are increasingly considered to have a significant influence on marine phytoplankton populations. Here we used a simplified dinoflagellate‐bacterium experimental culture model to conclusively demonstrate that the toxic dinoflagellate Gymnodinium catenatum H. W. Graham requires growth‐stimulatory marine bacteria for postgermination survival and growth, from the point of resting cyst germination through to vegetative growth at bloom concentrations (10³ cells · mL^?1). Cysts of G. catenatum were germinated and grown in unibacterial coculture with antibiotic‐resistant or antibiotic‐sensitive Marinobacter sp. DG879 or Brachybacterium sp., and with mixtures of these two bacteria. Addition of antibiotics to cultures grown with antibiotic‐sensitive strains of bacteria resulted in death of the dinoflagellate culture, whereas cultures grown with antibiotic‐resistant bacteria survived antibiotic addition and continued to grow beyond the 21 d experiment. Removal of either bacterial type from mixed‐bacterial dinoflagellate cultures (using an antibiotic) resulted in cessation of dinoflagellate growth until bacterial concentration recovered to preaddition concentrations, suggesting that the bacterial growth factors are used for dinoflagellate growth or are labile. Examination of published reports of axenic dinoflagellate culture indicate that a requirement for bacteria is not universal among dinoflagellates, but rather that species may vary in their relative reliance on, and relationship with, the bacterial community. The experimental model approach described here solves a number of inherent and logical problems plaguing studies of algal‐bacterium interactions and provides a flexible and tractable tool that can be extended to examine bacterial interactions with other phytoplankton species.     

The larval alimentary canal of the Antarctic insect, Belgica antarctica

On the Antarctica continent the wingless midge, Belgica antarctica (Diptera, Chironomidae) occurs further south than any other insect. The digestive tract of the larval stage of Belgica that inhabits this extreme environment and feeds in detritus of penguin rookeries has been described for the first time. Ingested food passes through a foregut lumen and into a stomodeal valve representing an intussusception of the foregut into the midgut. A sharp discontinuity in microvillar length occurs at an interface separating relatively long microvilli of the stomodeal midgut region, the site where peritrophic membrane originates, from the midgut epithelium lying posterior to this stomodeal region. Although shapes of cells along the length of this non-stomodeal midgut epithelium are similar, the lengths of their microvilli increase over two orders of magnitude from anterior midgut to posterior midgut. Infoldings of the basal membranes also account for a greatly expanded interface between midgut cells and the hemocoel. The epithelial cells of the hindgut seem to be specialized for exchange of water with their environment, with the anterior two-thirds of the hindgut showing highly convoluted luminal membranes and the posterior third having a highly convoluted basal surface. The lumen of the middle third of the hindgut has a dense population of resident bacteria. Regenerative cells are scattered throughout the larval midgut epithelium. These presumably represent stem cells for the adult midgut, while a ring of cells, marked by a discontinuity in nuclear size at the midgut-hindgut interface, presumably represents stem cells for the adult hindgut.     

西太平洋多金属结核区12个站位沉积物中可培养潜在腐殖质转化菌的多样性

【背景】海洋环境作为地球上最大的有机碳库贮藏着大量腐殖质,其中可能蕴藏着丰富的腐殖质转化菌。【目的】从深海沉积物环境中分离具有潜在腐殖质转化能力的细菌,为难降解天然有机多聚物的生物转化提供菌种资源。【方法】利用以腐殖质为唯一碳源的培养基,对西太平洋多金属结核区12个站位沉积物样品中的腐殖质转化菌进行富集培养和纯化,通过16S rRNA基因测序分析比对初步确定分离菌株的分类地位,并利用含苯胺蓝的培养基筛选潜在的腐殖质转化菌。【结果】从12个沉积物样品中共分离获得菌株276株,隶属于放线菌纲(Actinobacteria)、纤维粘网菌纲(Cytophagia)、黄杆菌纲(Flavobacteria)、 α变形菌纲(Alphaproteobacteria)和γ变形菌纲(Gammaproteobacteria)中的14个目37个属56个种(含1个潜在新属和2个新种),其中49个种呈现木质素修饰酶阳性。【结论】利用以腐殖质为唯一碳源和能源的培养基可以分离获得具有较高多样性的潜在腐殖质转化菌。     

Screening of bromotyramine analogues as antifouling compounds against marine bacteria

Rapid and efficient synthesis of 23 analogues inspired by bromotyramine derivatives, marine natural products, by means of CuSO₄-catalysed [3+2] alkyne–azide cycloaddition is described. The final target was then assayed for anti-biofilm activity against three Gram-negative marine bacteria, Pseudoalteromonas ulvae (TC14), Pseudoalteromonas lipolytica (TC8) and Paracoccus sp. (4M6). Most of the synthesised bromotyramine/triazole derivatives are more active than the parent natural products Moloka’iamine (A) and 3,5-dibromo-4-methoxy-β-phenethylamine (B) against biofilm formation by the three bacterial strains. Some of these compounds were shown to act as non-toxic inhibitors of biofilm development with EC₅₀ < 200 μM without any effect on bacterial growth even at high concentrations (200 μM).     

Diversity Dynamics of Marine Bacteria Studied by Immunofluorescent Staining on Membrane Filters

Of 34 strains of marine bacteria isolated on a general seawater medium, 5 were selected for detailed studies of their population dynamics in the plankton. The isolates were characterized as Aeromonas sp., Chromobacterium cf. lividum, Vibrio sp., and two Pseudomonas spp. Specific antibodies were produced by immunization of rabbits, and bacterial cells were stained on black Uni-Pore membrane filters by an indirect immunofluorescent staining procedure. The method proved to be very specific and practical for use in a large-scale field sampling program. Growth of all five isolates was stimulated by high values for net primary production, chlorophyll a, and dissolved organic carbon. Calculation of a diversity index based on specific and total counts is proposed as a way of characterizing the dynamics of organotrophic bacterial populations in the sea.     

Isolation of sulfate‐reducing bacteria from deep sediment layers of the pacific ocean

Bacterial populations exist at great depths in marine sediments, but little is known about the type and characteristics of organisms in this unique bacterial environment. Cascadia Margin sediments from the Pacific Ocean have deep bacterial activity and bacterial populations, which are stimulated around a gas hydrate zone (215–225 m below sea floor [mbsf]). Bacterial sulfate reduction is the dominant anaerobic process within these sediments, and the depth distribution of sulfate‐reducing activity corresponds with distributions of viable sulfate‐reducing bacteria (SRB). Anaerobically stored sediments from this site were used to isolate sulfate‐reducing bacteria using a temperature‐gradient system, elevated pressure and temperatures, different media, and a range of growth substrates. A variety of enrichments on lactate were obtained from 0.5 and 222 mbsf, with surprisingly more rapid growth from the deeper sediments. The temperature range of enrichments producing strong growth from 222 mbsf was markedly wider than those from the near surface sediment (15–45°C and 9–19°C, respectively). This presumably reflects a temperature increase in deeper sediments. Only a few of these enrichments were successfully isolated due to very slow or no growth on subculture, despite the use of a wide range of different media and growth conditions. Psychrophilic and mesophilic sulfate‐reducing isolates were obtained from 0.5 m depth. As the minimum growth temperature of the mesophile (probably a Desulfotomaculum sp.) was above the in situ temperature of 3°C, it must have been present in the sediment as spores. A larger number of isolates (23) was obtained from 222 mbsf, and these barophilic SRB were closely related (based on 16S rRNA gene analysis), but not identical to, Desulfovibrio profundus, recently isolated from deep sediments from the Japan Sea. Bacteria related to D. profundus may be widespread in deep marine sediments.     

Ornamental fish: a potential source of pathogenic and multidrug-resistant motile Aeromonas spp.

Aeromonas spp. are ubiquitous bacteria that cause diseases in fish and other aquatic animals. They are the natural inhabitants of different aquatic environments, such as freshwater, brackishwater and marinewater. Extrinsic stressors, such as crowding, unhygienic handling, poor water quality, polluted feeding and inadequate nutrition, can predispose fish to Aeromonas infection. In ornamental fish, motile Aeromonas spp. are known as aetiological agents of motile aeromonad infections, which cause significant mortality in fish and economic loss in the ornamental fish industry. The existence of different virulence factors leads to the virulence potential of motile Aeromonas spp. There are several antimicrobials used to treat bacterial infections in ornamental fish. However, the extensive use of antimicrobials in the ornamental fish industry causes multidrug resistance. This article reviewed a multitude of virulence factors that are related to the ornamental fish-borne Aeromonas pathogenicity and the antimicrobial resistance determinants related to the multidrug resistance phenotypes of motile Aeromonas spp. in ornamental fish.     

Cryptic niche differentiation of novel sediment ecotypes of Ruegeria pomeroyi correlates with nitrate respiration

Marine intertidal sediments fluctuate in redox conditions and nutrient availability, and they are also known as an important sink of nitrogen mainly through denitrification, yet how denitrifying bacteria adapt to this dynamic habitat remains largely untapped. Here, we investigated novel intertidal benthic ecotypes of the model pelagic marine bacterium Ruegeria pomeroyi DSS-3 with a population genomic approach. While differing by only 1.3% at the 16S rRNA gene level, members of the intertidal benthic ecotypes are complete denitrifiers whereas the pelagic ecotype representative (DSS-3) is a partial denitrifier lacking a nitrate reductase. The intertidal benthic ecotypes are further differentiated by using non-homologous nitrate reductases and a different set of genes that allow alleviating oxidative stress and acquiring organic substrates. In the presence of nitrate, the two ecotypes showed contrasting growth patterns under initial oxygen concentrations at 1 vol% versus 7 vol% and supplemented with different carbon sources abundant in intertidal sediments. Collectively, this combination of evidence indicates that there are cryptic niches in coastal intertidal sediments that support divergent evolution of denitrifying bacteria. This knowledge will in turn help understand how these benthic environments operate to effectively remove nitrogen.     

Seasonal and spatial variability of sediment bacterial communities inhabiting the large shallow Lake Balaton

Seasonal studies of surface sediment bacterial communities, from two basins with differing trophic states within Lake Balaton (Hungary), were carried out using molecular (denaturing gradient gel electrophoresis, DGGE) and cultivation-based techniques. The presence of polyphosphate accumulates was tested using Neisser staining, and phosphatase activity was investigated on organic phosphorus (P) compound. Aerobic viable cell counts were significantly higher in the eutrophic than mesotrophic basin in each season. The lowest viable counts were observed in the autumn and the highest in spring and summer month in both basins. The DGGE fingerprints of the samples reflected that the composition of sediment bacterial communities in the two basins were distinct in spring and summer, and similar in autumn, but similarly diverse in all seasons. On the basis of partial 16S rDNA sequences, the 216 strains were affiliated with six major bacterial lineages: Firmicutes; Actinobacteria, Bacteroidetes, Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria. Common species characterized from both basins constituted up to 66% of all identified phylotypes. Strains related to Bacillus sp. were dominant in all but one sample. Isolates affiliated with Aeromonas sp. prevailed in the sample taken from the mesotrophic basin in spring. The majority of the strains showed excess poly-P accumulation. Association of Neisser staining and phosphatase activity test results suggested that excess poly-P accumulation serves as P storage for sediment bacteria. Our study implied the importance of Firmicutes, Actinobacteria, Alphaproteobacteria, and Aeromonas species in benthic bacterial P retention.     

Autochthonous bacterial flora indicated by PCR-DGGE of 16S rRNA gene fragments from the alimentary tract of Costelytra zealandica (Coleoptera: Scarabaeidae)

Aims: To locate and identify putative autochthonous bacteria within the grass grub gut that may have a role in symbiosis. Methods and Results: Polymerase chain reaction-denaturing gradient gel electrophoresis (DGGE) fingerprinting was used to investigate bacterial diversity in the grass grub larval gut. The microbial community profiles from five geographically distinct populations were compared and the influence of feeding was analysed. Bacterial community in the midgut was highly variable between locations and was affected by feeding. The hindgut contained a more diverse but stable bacterial community that was less affected by external conditions. Forty-seven distinct DGGE bands, representing different bacterial genotypes, could be distinguished from all samples, with 34 different bands occurring in the hindgut. The 22 most common bands were isolated and DNA was sequenced. Sequence analysis revealed that most bacteria (16/22) were affiliated to the Clostridiales with the predominant bacteria affiliated to the genus Clostridium. The remaining bacteria were aligned to the Betaproteobacteria, Deltaproteobacteria and Bacteroidetes. Conclusions: The grass grub larva has an autochthonous microflora with predominance of Clostridium spp. in the hindgut. Significance and Impact of the Study: Occurrence of an autocthonous microflora in the grass grub hindgut suggests a symbiotic relationship which could help explain the ability of larval scarabs to feed on recalcitrant organic matter.     

Different co-occurring bacteria enhance or decrease the growth of the microalga Nannochloropsis sp. CCAP211/78

Marine photosynthetic microalgae are ubiquitously associated with bacteria in nature. However, the influence of these bacteria on algal cultures in bioreactors is still largely unknown. In this study, eighteen different bacterial strains were isolated from cultures of Nannochloropsis sp. CCAP211/78 in two outdoor pilot-scale tubular photobioreactors. The majority of isolates was affiliated with the classes Alphaproteobacteria and Flavobacteriia. To assess the impact of the eighteen strains on the growth of Nannochloropsis sp. CCAP211/78, 24-well plates coupled with custom-made LED boxes were used to simultaneously compare replicate axenic microalgal cultures with addition of individual bacterial isolates. Co-culturing of Nannochloropsis sp. CCAP211/78 with these strains demonstrated distinct responses, which shows that the technique we developed is an efficient method for screening the influence of harmful/beneficial bacteria. Two of the tested strains, namely a strain of Maritalea porphyrae (DMSP31) and a Labrenzia aggregata strain (YP26), significantly enhanced microalgal growth with a 14% and 12% increase of the chlorophyll concentration, respectively, whereas flavobacterial strain YP206 greatly inhibited the growth of the microalga with 28% reduction of the chlorophyll concentration. Our study suggests that algal production systems represent a ‘natural’ source to isolate and study microorganisms that can either benefit or harm algal cultures.     

Virulence and antibiotic susceptibility of Aeromonas spp. isolated from drinking water

Aeromonas isolates from tap water, mineral water, and artesian well water were investigated for their ability to produce different potential virulence factors or markers such as hemolysins, cytotoxins, phospholipase, DNase, hydrophobicity and their ability to adhere to epithelial cells and to abiotic surfaces. The susceptibility to antibiotics of Aeromonas isolates was also examined. Majority of the isolates displayed hemolytic activity against sheep erythrocytes, while only 7 of the 23 Aeromonas strains displayed DNase activity and 4 of the 23 Aeromonas strains tested were regarded as positive for phospholipase production. Most of the isolates showed cytotoxic activities in culture filtrate dilutions at titer of 1/8 or lower. No general relation between the strain isolated and the ability to interact with epithelial cells could be established. Using the bacterial adherence to hydrocarbons method, most of the strains were classified as highly hydrophilic. All five Aeromonas jandaei strains isolates, 9 of the 12 Aeromonas sp strains and four of the five Aeromonas hydrophila were multidrug resistant. The most active antimicrobial was ciprofloxacin (susceptible in 100% of the isolates), and the least active antibiotic was ampicillin (resistance in 92% of the isolates). The majority of the isolates tested were not killed by chlorine at 1.2 mg/l. Whether the high tolerance to chlorine of Aeromonas isolates can be linked to greater virulence is not know.