Presence Of Heterotrophic Bacteria Research Articles

ISOLATION AND DIAGNOSIS OF CADMIUM-RESISTANT BACTERIA AND ITS POTENTIAL PHYTOREMEDIATION WITH THE BROAD BEAN PLANT

Results of the study proved that phytoremediation can be a promising technique to treat cadmium (Cd)-contaminated soil. Four bacteria types were isolated from the soil; two are autotrophic and others are heterotrophic. Autotrophic bacteria were dominant in soils with 42 mg Cd Kg-1. The total count and diversity of both bacteria types decreased with the increase of Cd in media and reached their minimum limit of tolerance at 60 mg Cd L-1 in terms of the heterotrophic bacteria, while the minimum limit of tolerance in the case of autotrophic bacteria was at 110 mg Cd L-1. The four isolates can form biofilms that ranged in thickness between 2.8–4.3 mm. The tolerant isolates belong to Rhizobium leguminosarum, Pseudomonas fluorescens, Actinobacteria, and Corynebacterium. Shoot and dry weight significantly varied according to the changes in Cd concentrations and isolate types. The level in either shoot or root exceeded critical levels, however, its concentration was higher in the root compared with the shoot. The effect of Cd on broad bean plants began at 80 and 100 mg Cd L-1. The broad bean plant was resistant to growing in the contaminated area by Cd even at 120 mg Cd Kg-1 DW. The presence of heterotrophic bacteria was noticeably useful for autotrophic bacteria, as well as, for enhancing Cd resistance. The study showed that cooperative phytoremediation could be a safe and active technique to apply in the field soil contaminated with heavy metals.

16S rRNA Gene-Based Profiling of the Microbial Community in an Acid Mine Drainage Fe Precipitate at Libiola Mine (Liguria, Italy)

Acid mine drainage (AMD) is a common environmental problem in many sulphide mines worldwide, and it is widely accepted that the microbial community plays a major role in keeping the process of acid generation active. The aim of this work is to describe, for the first time, the microbial community thriving in goethite and jarosite Fe precipitates from the AMD of the Libiola mine. The observed association is dominated by Proteobacteria (>50%), followed by Bacteroidetes (22.75%), Actinobacteria (7.13%), Acidobacteria (5.79%), Firmicutes (2.56%), and Nitrospirae (1.88%). Primary producers seem to be limited to macroalgae, with chemiolithotrophic strains being almost absent. A phylogenetic analysis of bacterial sequences highlighted the presence of heterotrophic bacteria, including genera actively involved in the AMD Fe cycle and genera (such as Cytophaga and Flavobacterium) that are able to reduce cellulose. The Fe precipitates constitute a microaerobic and complex environment in which many ecological niches are present, as proved by the wide range of bacterial species observed. This study is the first attempt to quantitatively characterize the microbial community of the studied area and constitutes a starting point to learn more about the microorganisms thriving in the AMD of the Libiola mine, as well as their potential applications.

Physicochemical, microbiological quality, and risk assessment of water consumed by a quilombola community in midwestern Brazil.

The quality of the water consumed by a given community is related to its quality of life. In this sense, this study aimed to evaluate, from the perspective of health risk, the physical, chemical, and microbiological quality of drinking water, in a quilombola community, and the qualitative aspects intrinsic to its use and storage. For this, water samples, collected at the exits of the collective water supply system and from eight cisterns that store rainwater, used for human consumption, were analyzed. The samples were subjected to physical, chemical, and microbiological analysis, including adenovirus (HAdV) and enterovirus (EV). The probability of an individual acquiring infection through water consumption was determined by quantitative microbiological risk analysis using HAdV and Escherichia coli (EC) as reference pathogens. The results showed that the water in the deep tubular well had 270.8 mg/L of total hardness, leading to the rejection of its consumption by ingestion. Alternativity, the people in the community consume rainwater stored in cisterns. For this type of water, the presence of heterotrophic bacteria was found in 75%, total coliform was present in 100%, and Enterococci were detected in 25%. Furthermore, EC was present in 25%, EV in 50%, and HAdV in 100% of the samples. The probability of annual infection with HAdV and EC was, in the worst situation, 100% and 1.3%, respectively. Regarding the qualitative and quantitative aspects, there was a significant positive correlation between the absence of EC and the withdrawal of water from the cistern using a pump and the opposite when the withdrawal was carried out using a bucket or hose. Based on the results found, it is important to carry out actions aimed at improving water quality and, consequently, the quality of life of people living in the study community.

Dental Unit Waterlines in Quito and Caracas Contaminated with Nontuberculous Mycobacteria: A Potential Health Risk in Dental Practice.

Three cases of severe odontogenic infections due to nontuberculous mycobacteria (NTM) in Venezuela that were directly associated with dental procedures and the finding of dental unit waterlines (DUWLs) in dental offices that were colonized with mycobacteria species was the reason for assessing the water quality of DUWLs in dental offices in two capital cities in South America, namely, Quito and Caracas. The main water supplies and the water from 143 DUWLs in both cities were sampled and especially checked for contamination with NTM. To measure the overall bacteriological quality of the water also the presence of heterotrophic bacteria, coliform bacteria, and Pseudomonas was determined. Results showed that respectively 3% and 56% of the DUWLs in Quito and Caracas yielded NTM species (up to 1000 colony-forming units (CFU)/mL). Furthermore, high and unacceptable total viable counts of heterotrophic bacteria and/or coliform bacteria and Pseudomonas were detected in 73% of the samples. We conclude that, in both cities, the water in the majority of DUWLs was contaminated with NTM and other potential pathogens, presenting a risk to human health. The detection of NTM in DUWL water with acceptable heterotrophic bacteria counts shows the need to include NTM in water quality testing. Mycobacteria are more resistant to disinfection procedures than other types of vegetative bacteria, and most testing protocols for DUWLs do not assess mycobacteria and thus do not guarantee risk-free water.

Biomass segregation in the granules and flocs affects the role of heterotrophic bacteria in the ANAMMOX process

• Biomass was segregated in the form of granules and flocs. • Biomass segregation affects ANAMMOX reactor efficiency. • Model was developed to simulate the biomass segregation in ANAMMOX reactor. • Heterotrophic bacteria predominantly occupied the flocs. • Heterotrophic bacteria in the flocs promote nitrogen removal. The autotrophic nitrogen removal could be achieved in the one-stage or two-stage PN-ANAMMOX (Partial nitrification –anaerobic ammonium oxidation) systems. A number of researches were carried out to study the impact of HET (heterotrophic bacteria) on the one-stage PN-ANAMMOX system. It is still not clear about the role of HET in the ANAMMOX process of the two-stage system. The granule sludge system used for the ANAMMOX process also included the flocs, resulting in the segregation of biomass between the flocs and granules. How the HET is segregated between the flocs and granules is still unknown. In this study, we examined the role of HET in the two-stage system ANAMMOX process and how the biomass segregation affects its role. The increase of floc SRT (Sludge Retention Time) from 7 h (the same as HRT (Hydraulic Retention Time)) to 30 d increased the floc/granule ratio by 150–200%, depending on the influent COD concentration. The biomass segregation affected the role of heterotrophic bacteria in the ANAMMOX process of the two-stage PN-ANAMMOX system. When there was no biomass segregation (granules alone), the heterotrophic bacteria negatively impacted the TN removal as the presence of HET within the granules reduced the number of ANAMMOX bacteria, reducing the nitrogen removal capacity. Under biomass floc/granule segregation conditions, the HET predominantly resided in the flocs and increased nitrogen removal by providing additional nitrite through the denitrification process. Compared to the TN removal without biomass segregation, the segregation of HET between the floc and granules caused 3% to 40% more TN removal depending on the influent COD concentration.

Characterization of bacterial population during composting of municipal solid waste

Composting is a natural biological process that degrades organic matter which is carried out spontaneously by aerobic microorganisms, whose metabolic action leads to the mineralization and partial humification of organic residue. The aim of this study was to investigate survival of potentially pathogenic bacterial species throughout the process and detection of enterotoxigenic Escherichia coli (ETEC) in the compost using PCR. The presence of heterotrophic bacteria, total total and fecal coliforms, and bacteria succession were also de detrermined. Out of the total 222 bacterial colonies isolated, 33 different genera and 56 different species were identified, being Bacillus, Escherichia, Enterobacter, and Pseudomonas , the prevailing genera . Total coliform counts ranged between 9.0 x 10 4 and 3.0 x 10 6 cfu/g, and fecal coliform counts between 1.0 x 10 4 and 2.3 x 10 6 cfu/g. The composting process was partially efficient, since even though coliform counts were reduced, enterotoxigenic E. coli was detected in mature compost.

FACTORS AFFECTING THE CONDITIONS OF SULFATE REDUCTION AND MERCURY METHYLATION IN THE RIVER AMUR ICE

Results of the layer-by-layer studies of distribution of organic matter (OM) and mercury in ice cores sampled from the Amur River near the Khabarovsk city: its mainstream and the Pemzenskaya and Amurskaya branches, are presented. Comprehensive investigation of ice performed at the end of the freeze-up period allows making a retrospective analysis of the river ecosystem pollution during winter. Analysis of the total content of dissolved organic substances and aromatic compounds, determining a level of humification of the aquatic environment, was carried out with a spectrophotometer Shimadzu UV-3600 at 254 and 275 nm. The mercury content was determined by inductively coupled plasmamass spectrometry (ICP-MS). The number of cultured heterotrophic bacteria, sulfate-reducing bacteria (SRB) and their resistance to mercury (0.0005 and 0.001 mg/L) were used as indicators of biogeochemical processes going on in vitro. The maximum resistance to mercury at concentration of 0.001 mg/l was revealed from the sulfate-reducing bacteria in cores taken from the upper ice layer (0-10 cm) near the right bank of the Amurskaya branch. Periodical high mercury contamination of ice (up to 0.71 mkg/L) is estimated as a risk factor. In Pemzenskoy branch, the main factors for the mercury methylation in the ice were fine detritus, coming at the reservoir discharges, and the SRB resistant to mercury. These microorganisms were found in upper layers of the ice (10-35 cm) near the left bank and in the middle of the water stream (60–80 cm). A layer of ice (70–117 cm) with conditions also favourable for the sulfate reduction and the mercury methylation had been revealed in the mainstream of the Amur River near its right bank that is the cross-boundary area in the zone of influence of the Songhua river runoff. Among these conditions are high levels of OM, the presence of heterotrophic bacteria, which are destructors of high-molecular compounds, the potential producers of metabolites with methyl radicals, and the activity of the SRB resistant to mercury.

Quantification of heterotrophic bacteria during the growth of Synechocystis sp. PCC 6803 using fluorescence activated cell sorting and microscopy

The presence of heterotrophic bacteria in microalgal cultures can dilute the microalgal content of the harvested biomass, compete for nutrients, and be associated with culture crashes. Being able to detect and quantify heterotrophic bacteria would be of high value for monitoring culture health and reducing deleterious effects. Here, we developed and applied a new method that combines flow cytometry (FC) and fluorescence activated cell sorting (FACS) for the quantification of heterotrophic bacteria in cultures of the cyanobacterium Synechocystis sp. PCC 6803. Particles not containing chlorophyll – heterotrophic bacteria and cell debris – were separated from mixed cultures using FACS based on autofluorescence of Synechocystis. Heterotrophic bacteria were differentiated from cell debris using FC with SYTOX green fluorescence. Using microscopy, we verified that FACS was able to quantify heterotrophic bacteria in Synechocystis cultures effectively. Applying these methods to batch cultures of Synechocystis showed that the count proportions of heterotrophic bacteria were significant (3–13%) and that depletion of inorganic P in the culture favored Synechocystis over heterotrophic bacteria, but led to more cell lysis.

Investigation of Heterotrophic Bacteria, Legionella and Free - Living amoeba in Cooling Tower Samples by FISH and Culture Methods

The microorganisms living in the cooling towers water can affect both human health through inhalation of aerosolized water as well as industrial processes. In order to analyse such man-made water systems, microbiological tests that can give results in a short time are needed. In this study, the presence of heterotrophic bacteria, Legionella bacteria and free - living amoeba, FLA, including Acanthamoeba, in cooling-tower water and biofilm samples were investigated using two different methods, fluorescent in situ hybridization (FISH), and culture. For this, a total of 40 water and biofilm samples were taken from 16 different cooling towers in Istanbul. FISH and culture analysis have revealed that the number of heterotrophic bacteria within the water and the biofilm samples was above the threshold values (>105 cell. mL-1), generally. Despite Acanthamoeba were present in all cooling tower specimens, Legionella pneumophila serogroup 1 were only detected in the biofilm of one cooling tower. According to the results of this study, both methods are recommended to be used in conjunction. Due to the the large biodiversity of FLA such as Hartmanella sp. and Naeglaria sp, there is a need for new studies utilizing FISH method for sensitive, reliable results in a short period of time.

Effects of Bacterial Community Members on the Proteome of the Ammonia-Oxidizing Bacterium Nitrosomonas sp. Strain Is79.

Microorganisms in the environment do not exist as the often-studied pure cultures but as members of complex microbial communities. Characterizing the interactions within microbial communities is essential to understand their function in both natural and engineered environments. In this study, we investigated how the presence of a nitrite-oxidizing bacterium (NOB) and heterotrophic bacteria affect the growth and proteome of the chemolithoautotrophic ammonia-oxidizing bacterium (AOB) Nitrosomonas sp. strain Is79. We investigated Nitrosomonas sp. Is79 in co-culture with Nitrobacter winogradskyi, in co-cultures with selected heterotrophic bacteria, and as a member of the nitrifying enrichment culture G5-7. In batch culture, N. winogradskyi and heterotrophic bacteria had positive effects on the growth of Nitrosomonas sp. Is79. An isobaric tag for relative and absolute quantification (iTRAQ) liquid chromatography-tandem mass spectrometry (LC-MS/MS) proteomics approach was used to investigate the effect of N. winogradskyi and the co-cultured heterotrophic bacteria from G5-7 on the proteome of Nitrosomonas sp. Is79. In co-culture with N. winogradskyi, several Nitrosomonas sp. Is79 oxidative stress response proteins changed in abundance, with periplasmic proteins increasing and cytoplasmic proteins decreasing in abundance. In the presence of heterotrophic bacteria, the abundance of proteins directly related to the ammonia oxidation pathway increased, while the abundance of proteins related to amino acid synthesis and metabolism decreased. In summary, the proteome of Nitrosomonas sp. Is79 was differentially influenced by the presence of either N. winogradskyi or heterotrophic bacteria. Together, N. winogradskyi and heterotrophic bacteria reduced the oxidative stress for Nitrosomonas sp. Is79, which resulted in more efficient metabolism. Aerobic ammonia-oxidizing microorganisms play an important role in the global nitrogen cycle, converting ammonia to nitrite. In their natural environment, they coexist and interact with nitrite oxidizers, which convert nitrite to nitrate, and with heterotrophic microorganisms. The presence of nitrite oxidizers and heterotrophic bacteria has a positive influence on the growth of the ammonia oxidizers. Here, we present a study investigating the effect of nitrite oxidizers and heterotrophic bacteria on the proteome of a selected ammonia oxidizer in a defined culture to elucidate how these two groups improve the performance of the ammonia oxidizer. The results show that the presence of a nitrite oxidizer and heterotrophic bacteria reduced the stress for the ammonia oxidizer and resulted in more efficient energy generation. This study contributes to our understanding of microbe-microbe interactions, in particular between ammonia oxidizers and their neighboring microbial community.

Low affinity of heterotrophic bacteria to loose deposits in drinking water distribution systems

Loose deposits (LD) accumulate in drinking water distribution systems (DWDS) and may lead to tap water discoloration incidents upon resuspension. While inconvenient for the consumers and the water companies, discoloration may be accompanied by degradation of the microbiological quality of the water, and possibly to the transport of bacteria. The presence of heterotrophic bacteria towards LD with different characteristics was investigated. Bacterial loads in discoloured water samples and LD concentrated over different settling times were analysed. Total heterotrophic (TH) bacteria numbers did not relate to turbidity or to suspended solids in discoloured waters. Higher affinities of TH were observed for slower-settling LD (

CONTAMINATION OF THE HANDLES AND BASES OF SHOPPING CARTS BY PATHOGENIC AND MULTI-DRUG RESISTANT BACTERIA

Background and Aims: Shopping carts (SCs) are considered as highly contaminated public surfaces, and may play a role in transmission of some harbor heterotrophic bacteria to human being. Therefore, this study aimed to examine the hygienic conditions and presence of heterotrophic bacteria on the surface of the handles and bases of SCs taken from shopping stores in Al-Mafraq city, Jordan. Methods: Five different SCs were selected randomly from four shopping stores (designated as A, B, C and D) during May through June, 2011. Two dry swab samples were taken from each SC, one from the handle and another one from the base. All samples were cultured on nutrient agar as none selective medium and incubated aerobically at 37 °C for 48 hours. The resulting number of colony forming units (CFUs) in each plate was converted to CFU per cm 2 surface area. The species of bacterial isolates were determined by biochemical tests and 16S rDNA sequencing. Results: The number of heterotrophic bacteria per SC range between 6 to 133 CFU/cm 2 surface area for the cart handles and between 6 to 300 CFU/cm 2 surface area for the cart bases, indicating higher numbers of heterotrophic bacteria in the cart bases as well as more fluctuations in the number of heterotrophic bacteria at the handles and bases of SCs. These analyses also confirmed the presence of seven coliform and three noncoliform species on the tested surface of the handles and bases of the selected stores. These include E. coli spp., Acinetobacter calcoaceticus, Burkholderia cepacia, Yersinia enterocolitica, Tatumeella ptyseas, Pseudomonas aeruginosa, Shigella sonnei, Bacillus cereus, and Bacillus pumilus.

Response of Prochlorococcus ecotypes to co-culture with diverse marine bacteria

Interactions between microorganisms shape microbial ecosystems. Systematic studies of mixed microbes in co-culture have revealed widespread potential for growth inhibition among marine heterotrophic bacteria, but similar synoptic studies have not been done with autotroph/heterotroph pairs, nor have precise descriptions of the temporal evolution of interactions been attempted in a high-throughput system. Here, we describe patterns in the outcome of pair-wise co-cultures between two ecologically distinct, yet closely related, strains of the marine cyanobacterium Prochlorococcus and hundreds of heterotrophic marine bacteria. Co-culture with the collection of heterotrophic strains influenced the growth of Prochlorococcus strain MIT9313 much more than that of strain MED4, reflected both in the number of different types of interactions and in the magnitude of the effect of co-culture on various culture parameters. Enhancing interactions, where the presence of heterotrophic bacteria caused Prochlorococcus to grow faster and reach a higher final culture chlorophyll fluorescence, were much more common than antagonistic ones, and for a selected number of cases were shown to be mediated by diffusible compounds. In contrast, for one case at least, temporary inhibition of Prochlorococcus MIT9313 appeared to require close cellular proximity. Bacterial strains whose 16S gene sequences differed by 1-2% tended to have similar effects on MIT9313, suggesting that the patterns of inhibition and enhancement in co-culture observed here are due to phylogenetically cohesive traits of these heterotrophs.

Morphological and physiological changes in Microcystis aeruginosa as a result of interactions with heterotrophic bacteria

Pg1. To reveal the role of aquatic heterotrophic bacteria in the process of development of Microcystis blooms in natural waters, we cocultured unicellular Microcystis aeruginosa with a natural Microcystis-associated heterotrophic bacterial community. 2. Unicellular M. aeruginosa at different initial cell densities aggregated into colonies in the presence of heterotrophic bacteria, while axenic Microcystis continued to grow as single cells. The specific growth rate, the chl a content, the maximum electron transport rate (ETR(max)) and the synthesis and secretion of extracellular polysaccharide (EPS) were higher in non-axenic M. aeruginosa than in axenic M. aeruginosa after cell aggregation, whereas axenic and non-axenic M. aeruginosa displayed the same physiological characteristic before aggregation. 3. Heterotrophic bacterial community composition was analysed by PCR-denaturing gradient gel electrophoresis (PCR-DGGE) fingerprinting. The biomass of heterotrophic bacteria strongly increased in the coinoculated cultures, but the DGGE banding patterns in coinoculated cultures were distinctly dissimilar to those in control cultures with only heterotrophic bacteria. Sequencing of DGGE bands suggested that Porphyrobacter, Flavobacteriaceae and one uncultured bacterium could be specialist bacteria responsible for the aggregation of M. aeruginosa. 4. The production of EPS in non-axenic M. aeruginosa created microenvironments that probably served to link both cyanobacterial cells and their associated bacterial cells into mutually beneficial colonies. Microcystis colony formation facilitates the maintenance of high biomass for a long time, and the growth of heterotrophic bacteria was enhanced by EPS secretion from M. aeruginosa. 5. The results from our study suggest that natural heterotrophic bacterial communities have a role in the development of Microcystis blooms in natural waters. The mechanisms behind the changes of the bacterial community and interaction between cyanobacteria and heterotrophic bacteria need further investigations.

Microbial endolithic colonization and the geochemical environment in young seafloor basalts

The colonization and weathering of young seafloor basaltic glass from the mid-Atlantic Ridge was examined. Microorganisms were localised to fractures in the surface of the basalt and grew on the surfaces of material in the fractures. XAS, Raman spectroscopy and NanoSIMS analysis of the fracture-filling material shows that it contains non-crystallised iron-enriched altered glass and poorly ordered iron oxides. Organisms, which in places develop into contiguous biofilms, develop on the surface of the material. No putative biogenic alteration textures were observed in the basaltic glass at the fracture boundaries suggesting that the microbial community is restricted to the secondary alteration products. Microbial culturing shows the presence of heterotrophic bacteria including Sufitobacter and Halomonas consistent with observations of photic zone detritus associated with fracture-filling material. These data show that the interior of fresh basaltic glass is an endolithic habitat for microorganisms, but that the glass itself is not a primary source of cations or energy for the developing communities.

BACTÉRIAS E BIOINDICADORES DE QUALIDADE DE ÁGUAS DE ECOSSISTEMAS ORIZÍCOLAS DA REGIÃO SUL DO BRASIL

The presence of heterotrophic bacteria in aquatic environments, such as those in the agricultural systems of irrigated rice fields, is determined by biotic and abiotic processes, with the focus on physical-chemical factors and highly complex interactions with other organisms. In this study, we address aspects related to these bacteria, such as: bacterial diversity in rice growing areas, total coliforms and thermotolerant as environmental indicators. Are also mentioned topics related to natural and artificial wetlands, the viability of enteric bacteria, the environmental impacts, reuse and monitoring of water in rice fields ecosystems.

Isoprene production by Prochlorococcus, a marine cyanobacterium, and other phytoplankton

The oceans are a small source of light (C 2–C 6) non-methane hydrocarbons (NMHC), which influence the photo-oxidant chemistry of the remote marine atmosphere. Previous work has shown that water column sources of alkenes include photochemical processes, and that various phytoplankton species can produce isoprene. However, only a few phytoplankton species have been studied, and no assessment has been performed of the effects of other pelagic microorganisms on NMHC cycling. The dependence of phytoplanktonic isoprene production on light, temperature, and organism size has also not been investigated. In this work, laboratory cultures of five different marine phytoplankton species ( Prochlorococcus, Synechococcus, Micromonas pusilla, Pelagomonas calceolata, and Emiliania huxleyi) were examined for NMHC production capabilities. All species were found to produce isoprene at constant rates during the balanced exponential growth phase; rates ranged from 1×10 −21 to 4×10 −19 mol cell −1 day −1 over all cell species and growth conditions tested. No other NMHC was consistently produced or consumed by these cells. The presence of heterotrophic bacteria in phytoplankton cultures had no effect on isoprene production rates per phytoplankton cell. A positive allometric relationship was observed between isoprene production rate and cell volume; highest production rates were found for the largest cell, E. huxleyi, and lowest rates for Prochlorococcus, the smallest cell. Isoprene production was a function of light intensity and temperature in Prochlorococcus, with patterns that were similar to those between growth rate and these environmental variables. The maximum production with light intensity occurred in the photoinhibited regime, and the maximum with temperature was at the maximum of growth rate for this species, near 23 °C. Nanoflagellate grazing by Cafeteria roenbergensis on, and phage infection of, Prochlorococcus controlled total isoprene produced in the flask by controlling cell abundances. Phage infection also decreased the isoprene production rate per cell during latent period of infection as compared to healthy cells. With certain assumptions, combining the measured laboratory isoprene production rates with observed water column phytoplankton abundances resulted in a maximum estimated sea-to-air flux of isoprene that was on the same order of magnitude as previously reported values determined using in situ measured seawater and atmospheric measurements.

Relationships between bacteria and cyanobacteria in the Marrakech waste stabilisation ponds

In waste stabilisation pond systems the interactions between algae and bacteria have an important ecological effect and appeared to play a key role in the self-purification process. The aim of the present study is to evaluate the interactions between two axenic cyanobacteria: Synechocystis sp. and Pseudanabaena sp. with heterotrophic bacteria and some pathogenic bacteria: E. coli, Salmonella sp. and non-O1 V. cholerae. The results obtained showed that Synechocystis sp. (planktonic cyanobacterium) and Pseudanabaena sp. (benthic cyanobacterium) stimulated the growth and the survival of heterotrophic bacteria and non-O1 V. cholerae and reduced the survival of E. coli and Salmonella. Blooms of these cyanobacteria during hot periods which are a particularity in stabilisation ponds of Marrakech, could explain the dynamics of bacteria studied in this sewage treatment process. The presence of heterotrophic bacteria, showing relative high densities during hot periods, could be considered as an important bioticfactor which led to the cyanobacteria blooms in the Marrakech ponds which function under an arid Mediterranean climate.

Influence of atmospheric pollutants on the biodeterioration of stone

Studies have been carried out on specimens of Saltrio stone, Carrara and Candoglia marbles, exposed for some years to the polluted atmosphere of Milan. The test specimens, which were directly exposed to the washing away, showed alterations in the form of grey-black stains which were different in dimensions and quantity according to the stone material, while those sheltered showed only a uniform grey deposit of particulate matter. The decay on the exposed specimens has been tested by gravimetric analyses and scanning electron microscopy (SEM) observations. Microbiological investigations evidenced that microorganisms, either chemoautotrophic or photosynthetic, were not present in any sample. On the washed out test specimens, the presence of heterotrophic bacteria was considerable, while the sheltered specimens showed negligible values. Chemical analysis, carried out through gas chromatography–mass spectrometry (GC/MS), of the particulate deposited on the test specimens, evidenced the presence of a wide range of aromatic and aliphatic hydrocarbons and fatty acids. Cultural tests of mixed cultures and isolated strains were carried out by using a mineral medium added with 14 organic compounds, typical representatives of atmospheric pollution, as a sole source of carbon and energy. The results evidenced that the mixed cultures in particular, as well as some of the isolated strains, are capable of using many of the tested molecules (fatty acid, aliphatic compounds, p-xylene).