Aerobic Heterotrophic Bacteria Research Articles

Monitoring Dental-Unit-Water-Line Output Water by Current In-office Test Kits

The importance of monitoring contamination levels in the output water of dental-unit-water-lines (DUWLs) is essential as they are prone to developing biofilms that may contaminate water that is used to treat patients, with opportunistic pathogens such as species of Legionella, Pseudomonas and others. Dentists and practice staff are also at risk of being infected by means of cross-infection due to aerosols generated from DUWL water. The unit of measurement for the microbial contamination of water by aerobic mesophilic heterotrophic bacteria is the colony-forming unit per millilitre (cfu/ml) of water. The UK has its own guidelines set by the Department of Health for water discharged from DUWL to be between 100 and 200 cfu/ml of water. The benchmark or accepted standard laboratory test is by microbiological culture on R2A agar plates. However, this is costly and not convenient for routine testing in dental practices. A number of commercial indicator tests are used in dental surgeries, but they were not developed for the dental market and serve only to indicate gross levels of contamination when used outside of the manufacturer's recommended incubation period. The aim of this article is to briefly review the universal problem of DUWL contamination with microbial biofilms and to update dental professionals on the availability of currently available commercial in-office monitoring systems for aerobic mesophilic heterotrophic bacteria and to discuss their limitations for testing water samples in assuring compliance with recommended guidelines.

Management induced changes of antibiotic resistant strains of heterotrophic bacteria in shrimp farming ponds

Antibiotic resistant strains of heterotrophic bacteria and total aerobic heterotrophic bacteria were enumerated along with important water quality parameters in water and sediment samples collected from 3 shrimp farming ponds used for the monoculture of Penaeus monodon as well as from a control pond located outside the shrimp farm. The resistant strains of heterotrophic bacteria were screened against 3 antibiotics (ampicillin, chloramphenicol and oxytetracycline) at 25 and 50 μg/l. The counts of antibiotic resistant bacteria tended to rise in shrimp ponds with progressive rise in the days of culture, but were specially high during the period when both antibiotics and feed were applied in the system. It appears that antibiotics exerted a selective pressure in favour of antibiotic resistant bacterial strains and widespread use of antibiotics should be forbidden in shrimp ponds.

Aerobic Biodegradation of Hydrocarbons in High Temperature and Saline Groundwater

A series of laboratory microcosm experiments and a field pilot test were performed to evaluate the potential for aerobic biodegradation of aromatic hydrocarbons and methyl tert‐butyl ether (MtBE; a common oxygenate additive in gasoline) in saline, high temperature (>30° C) groundwater. Aquifer, sediment, and groundwater samples from two sites, one in Canada and another in Saudi Arabia, were incubated for 106 days to evaluate the changes in select hydrocarbon and MtBE concentrations and microbial community structure. Almost complete biodegradation of the aromatic hydrocarbons was found in the Saudi Arabian microcosm samples whereas the Canadian microcosm samples showed no significant biodegradation during the laboratory testing. MtBE degradation was not observed in either set of microcosms. Denaturing gradient gel electrophoresis analyses showed that, while the Canadian microorganisms were the most diverse, they showed little response during incubation. The microbial communities for the Saudi Arabian sample contained significant numbers of microorganisms capable of hydrocarbon degradation which increased during incubation.Based on the laboratory results, pilot‐scale testing at the Saudi Arabian field site was carried out to evaluate the effectiveness of enhanced aerobic biodegradation on a high temperature, saline petroleum hydrocarbon plume. Dissolved oxygen was delivered to the subsurface using a series of oxygen diffusion emitters installed perpendicular to groundwater flow, which created a reactive zone. Results obtained from the seven‐month field trial indicated that all the target compounds decreased with removal percentages varying between 33 percent for the trimethylbenzenes to greater than 80 percent for the BTEX compounds. MtBE decreased 40 percent on average whereas naphthalene was reduced 85 percent on average. Examination of the microbial population upgradient and downgradient of the emitter reactive zone suggested that the bacteria population went from an anaerobic, sulfate‐reducing dominated population to one dominated by a heterotrophic aerobic bacteria dominant population.These studies illustrate that field aerobic biodegradation may exceed expectations derived from simple laboratory microcosm experiments. Also, high salinity and elevated groundwater temperature do not appear to inhibit in situ aerobic biorestoration. © 2014 Wiley Periodicals, Inc.

Microbial contamination of dental unit waterlines and effect on quality of indoor air

The microbiological quality in dental unit waterlines (DUWLs) is considered to be important because patients and dental staff with suppressed immune systems are regularly exposed to water and aerosols generated from dental units (DUs). Opportunistic pathogens like Pseudomonas, Legionella, Candida, and Aspergillus can be present in DUWLs, while during consultations, bioaerosols can be dispersed in the air, thus resulting in effects on microbiological quality of indoor air. This present study represents microbiological air and water quality in dental offices (DOs) and also concerns the relationship between the quality of DO air and dental unit water. This study aimed to assess both the microbial quality of dental unit water and the indoor air in 20 DOs and to survey the effect on the quality of the indoor air with the existing microorganisms in dental unit water. Fourteen out of 20 (70 %) DUWLs were found to be contaminated with a high number of aerobic mesophilic heterotrophic bacteria. In terms of bacterial air contamination levels, in 90 % of DOs, a medium level (<500 colony-forming units (CFU)/m(3)) of contamination was determined, while in terms of microfungal air contamination, in all DOs, a low level (<100 CFU/m(3)) of contamination was determined. Potential infection or allergen agents, such as Pseudomonas, Micrococcus, Staphylococcus, Alternaria, Cladosporium, Penicillium, Aspergillus, and Paecilomyces were isolated from water and air samples. This study's determination of contamination sources and evaluation of microbial load in DOs could contribute to the development of quality control methods in the future.

The effect of carbon dioxide on the shelf life of ready-to-eat shredded chicken breast stored under refrigeration

The objective of the present study was to determine the shelf life of ready-to-eat cooked chicken breast fillets (shredded) stored in atmospheres that were modified with different concentrations of CO2 and to establish a relationship between the concentration of this gas and bacterial growth. The samples were divided into 7 groups with different packaging conditions: aerobiosis, vacuum, and 10, 30, 50, 70, and 90% CO2 (with the remaining volume filled with N2). All of the samples were stored at 4 ± 2°C for 28 d. During this period, pH tests and counts of aerobic heterotrophic mesophyll bacteria (AHMB), aerobic heterotrophic psychotropic bacteria (AHPB), Enterobacteriaceae, and lactic acid bacteria (LAB) were performed, and the gas compositions of the packaging atmospheres were verified. The pH of the aerobic packages increased during storage. However, the other treatments resulted in the opposite trend, with the CO2 concentration decreasing over the first 24 h and then remaining constant until the end of experiment. A gradual increase in the AHMB, AHPB, Enterobacteriaceae, and LAB counts was observed during storage; this increase was faster in the meat that was packed under aerobiosis conditions than in the other treatments. The treatments with a CO2 concentration above 10% exhibited lower Enterobacteriaceae growth, whereas LAB growth was discrete in all of the treatments, independent of the CO2 concentration. The shelf life of the samples packed with 90% CO2 was 28 d. Based on the AHMB and AHPB counts, the shelf life was 3 times longer than for the samples packed under aerobiosis conditions (9 d). The increased package CO2 concentration caused a reduction in the growth rate of the examined bacteria (r = 0.99), and treatment with 90% CO2 appears promising as a method with which to increase the product's shelf life.

Se (IV) triggers faster Te (IV) reduction by soil isolates of heterotrophic aerobic bacteria: formation of extracellular SeTe nanospheres

Selenium and Tellurium have many common chemical properties as both belong to group 16 of the periodic table. High toxicities of Se and Te oxyanions cause environmental problems in contaminated soils and waters. Three strains (C4, C6 and C7) of selenite reducing and nanoparticle forming aerobic bacteria which were isolated from agricultural soils of India containing high concentrations of Se were investigated after 3.5 months of freeze-storage for their resistance against the toxic oxyanion tellurite and its reduction to non toxic elemental form Te0 as well as nanoparticles formation. Strains C4, C6 and C7 reduced tellurite at maximum reduction rates of 2.3, 1.5 and 2.1 mg Te (IV)/L/d, respectively and produced extracellular Te0 nanospheres as revealed from SEM-EDX analysis. Production of extracellular Te nanospheres has been described seldom. Further, concurrent reduction of both selenite and tellurite by bacteria was examined as these toxic oxyanions are often present together in natural environments, mine tailings or wastewater from copper refining. Interestingly, bioreduction of 100 mg/L selenite in shake flasks was not much affected by the presence of 10 mg/L tellurite but tellurite reduction rate increased 13 fold with selenite in the medium. The concurrent reduction of these oxyanions resulted in rarely described bioformation of extracellular nanoparticles composed of both Se and Te, reported first time for aerobically growing heterotrophic non-halophilic bacterial cultures. Duganella violacienigra, the closely related strain to C4 was also found to be resistant to oxyanions of Se and Te. Selenite reducing heterotrophic non-halophilic aerobic bacteria revived from 3.5 months freeze storage could successfully reduce toxic tellurite to non toxic elemental form and produced extracellular nanospheres during detoxification. Presence of relatively less toxic selenite in the medium triggers bioreduction of more toxic tellurite leading to formation of extracellular SeTe nanospheres which are sought by solar and optical recording media industry because of their excellent photovoltaic and optical properties. The bacterial cultures investigated in this study could be exploited commercially to remediate not only selenite and tellurite-contaminated soil and water but also for green synthesis of extracellular Se, Te and Se + Te nanospheres.

Biodegradation of Total Petroleum Hydrocarbon by Aerobic Heterotrophic Bacteria Isolated from Crude Oil Contaminated Brackish Waters of Bodo Creek

Bodo creek is located in Gokana Local Government Area of Rivers state and is characterised by brackish water which is heavily contaminated with crude oil. Water samples collected from the creek were taken to Environmental Microbiology Laboratory of University of Portharcourt for isolation of aerobic heterotrophic bacteria using serial dilution spread plate technique. Isolation of morphologically distinct pure cultures was done and the isolates obtained were identified molecularly on the basis of 16S rRNA gene sequence analysis. 16S rRNA sequencing for identification of the isolates generated sequences ranging from 500 bp to 1700 bp and a 250 bp size PCR amplified fragment. The nucleotide sequence of the 16S rRNA gene was compared with published 16S rRNA sequences using BLAST search at the data base of National Centre for Biotechnology Information (NCBI). Biodegradation of petroleum hydrocarbon test on the isolates was conducted using Bony light crude oil obtained from Shell Petroleum Development Company and monitored using GC-FID (Agilent 6890 model) for 49 days. The initial quantity of TPH was 24091 and 6706 mg/l on day 0 for aerobic heterotrophic treatment and crude oil contaminated control and decreased progressively to 212.8 and 1174 mg/l respectively on day 49 indicating biodegradation in the treatment and control. Loss of TPH was statistically significant using one way analysis of variance (ANOVA) p<0.05 with time. Model for predicting TPH loss was developed and rate of biodegradation of the isolates determined using Trend line method of Microsoft Excel, 2010. The growth of bacteria cells increased progressively with decrease in TPH implying that the bacteria were responsible for biodegradation. Further application of bioremediation strategies in Bodo creek for biostimulation of the crude oil biodegrading bacteria for reclamation and restoration of an efficient ecosystem structure and function is suggested.

Diversity of bacterial forms in ice wedge of the Mamontova Gora glacial complex (Central Yakutiya)

Electron microscopic investigation of four samples of ancient ice wedge from the Pleistocene glacial complex of Mamontova Gora (Yakutiya, Russia) revealed high diversity of bacteriomorphic particles. Their structural features included the presence of electron-transparent zones, presumably inclusions containing storage compounds, and microenvironment (capsules or external sheaths). These features may be a result of adaptive strategies providing for microbial survival under permafrost conditions. Predominance of rod-shaped forms morphologically resembling coryneform actinobacteria was found. X-ray microanalysis revealed organic origin of bacteriomorphic particles. Some particles were characterized by incomplete spectra of the major biogenic elements, resulting probably from low-temperature damage to the cellular structures. Total numbers of aerobic heterotrophic bacteria determined by plating on nutrient media were comparable to the values obtained for permafrost soils and Arctic ice. Predominance of coryneform actinobacteria was observed. Abundance of these evolutionarily early groups of actinobacteria may indicate the ancient origin of the microflora of the relic frozen rocks.

Molecular Characterization of Aerobic Heterohophic Bacteria Isolated from Petroleum Hydrocarbon Polluted Brackish Waters of Bodo Creeks, Rivers State Nigeria

Surface water sources in the oil producing Niger Delta region of Nigeria are highly susceptible to pollution by petroleum hydrocarbons and so it is important to understand the microbial diversity of such ecosystems. Water and sediment samples were collected between April-August, 2013 from Bodo creeks and taken to Environmental Microbiology laboratory of University of Portharcourt for analysis. A total of thirty aerobic heterotrophic bacterial strains isolated ranged from 3.0 - 7.0 × 104 cfu for surface water and 1.6 - 5.6 × 104 cfu for sediment samples of Bodo creek using serial dilution and spread plate technique. Pure cultures of bacteria were obtained on the basis of their morphological characteristics and subjected to biochemical tests and further classified on the basis of 16S rRNA gene sequence analysis. The DNA was isolated from size fractionated samples and the diversity of bacteria in each fraction was studied using PCR amplification of partial 16S rRNA. The sequences were submitted to NCBIGen bank for identification and assigning of accession numbers. The isolated aerobic heterotrophic bacteria belong to the families of Enterobacteriaceae, Bacilliceae, Alcaligenaceae, Pseudomonadaceae, Flavobactericeae and Planococcaceae.

Biostimulation of Crude Oil Contaminated Soil Using Soybean Waste

The potential of soybean waste (SBW) in enhancing microbial breakdown of crude oil in soil was studied. The soybean waste contained 5.31% nitrogen and 33.2% crude protein while the soil used for the bioremediation study contained 1.89% organic matter, 1.10% organic carbon, 0.21% nitrogen and 0.08 ppm phosphorus. The textural composition of the soil was 76.58% sand, 8.28% silt, 15.16% clay and the soil was classified as sandy loam. The microbiological analysis revealed that aerobic heterotrophic bacteria counts in oil polluted soil amended with SBW ranged between 1.6 × 10 8 cfu/g and 8.9 × 10 8 cfu/g. These counts were higher than those of the unamended soil which ranged from 1.2 × 10 8

Processes Forming Daily Lamination in a Microbe-Rich Travertine Under Low Flow Condition at the Nagano-yu Hot Spring, Southwestern Japan

A daily rhythm of microbial processes, in terms of sub-mm order lamination, was identified for a microbe-rich aragonite travertine formed at a low-flow site of the Nagano-yu Hot Spring in Southwestern Japan. Continuous observation and sampling clearly showed that the lamination consisted of diurnal microbe-rich layers (M-layers) and nocturnal crystalline layers (C-layers). The M-layers originated from biofilm formed by growth and upward migration of filamentous cyanobacteria related to Microcoleus sp., which can rapidly glide and secrete extracellular polymeric substances (EPS). During the daytime, cyanobacterial biofilm development inhibited aragonite precipitation on the travertine surface due to the calcium-binding ability of EPS. After sunset, aragonite precipitation started on the surface where aerobic heterotrophic bacteria decomposed EPS, which induced precipitation of micritic crystals. This early stage of C-layer formation was followed by abiotic precipitation of fan-shaped aragonite aggregates. Despite their major role in lamina formation, the cyanobacteria were readily degraded within 6–10 days after embedding, and the remaining open spaces in the M-layers were sparsely filled with crystal clots. These lamina-forming processes were different from those observed in a high-flow site where the travertine has a dense texture of aragonite crystals. The microbial travertine at Nagano-yu is similar to some Precambrian stromatolites in terms of in situ mineral precipitation, regular sub-mm order lamination, and arrangement of filamentous microbes; therefore, the lamination of these stromatolites possibly occur with a daily rhythm. The microbial processes demonstrated in this study may revise the interpretation of ancient stromatolite formation.

Investigation of the bacterial load and antibiotic susceptibility of dental units

The aim of this study was to evaluate the bacterial contamination level and to determine the antibiotic susceptibility of the isolated bacteria from dental unit waterlines (DUWLs) in Istanbul. Bacterial quality of DUWLs is very important, as patients and dental staff are regularly exposed to water and aerosols generated by the unit. If opportunistic pathogens such as Staphylococcus aureus, Pseudomonas aeruginosa, and Legionella pneumophila are present in DUWLs, patient and dental staff can be infected. One hundred water samples were collected from high-speed drills and input waters from 50 dental units. Aerobic heterotrophic bacteria counts and the presence of Legionella, Pseudomonas, oral streptococci, and Staphylococcus were investigated in dental unit waters and aerosol samples. In addition, the antibiotic susceptibility of the isolated and identified bacteria from DUWLs was examined. This research found that 37 out of 50 dental unit water samples exceeded the American Dental Association's limit of 200colony-forming units (CFU)/mL(-1). Legionella, oral streptococci, and S. aureus were not detected in any water or aerosol samples, but P. aeruginosa was isolated in three DUWLs. Also, Pseudomonas and Staphylococcus were found in water and aerosol samples. Cefoperazone, ofloxacin, gentamicin, ciprofloxacin, and piperacillin were the most effective antibiotics against the isolated bacteria from DUWLs.

Effect of Ni2+ and Pb2+ on the efficiency of packed cage rotating biological contactor system

The research aimed to study the effects of Ni2+ and Pb2+ on the efficiencies of the packed cage rotating biological contractor (packed cage-RBC) system with synthetic industrial wastewater (SIW) containing various concentrations of Ni2+ or Pb2+ (SIW-Ni2+ or SIW-Pb2+) of 10, 20, 30, 40, 50mg/L at various hydraulic retention times (HRT) of 4, 6 and 8h. The results showed that the system efficiencies decreased with the increase of heavy metal (HM) concentrations or loadings. However, Ni2+ and Pb2+ concentrations of up to 10mg/L did not affect the system efficiencies. The COD, BOD5, TKN and Ni2+ or Pb2+ removal efficiencies of 89±1% and 93±0%, 87±1% and 87±1%, 80.2±0.3% and 80.0±0.8% and 85.7±0.7% or 89.8±1.5%, respectively, were obtained with SIW-10Ni2+ and SIW-10Pb2+, respectively, at a HRT of 8h. According to the increase of HM, the numbers of aerobic heterotrophic, nitrifying and denitrifying bacteria decreased while facultative heterotrophic bacteria dominated. Moreover, Ni2+ gave a greater repression effect than Pb2+ on the growth and activity of bio-film.

The distribution and diversity of culturable aerobic heterotrophic benthic bacteria in the continental slope of the Bay of Bengal: Linked abiotic factors, including a tsunami

The culturable aerobic heterotrophic benthic bacterial population and community structure in relation to the physico-chemical parameters in the continental slope of the Bay of Bengal was studied. In addition, diversity indices were calculated and pretsunami (in 2004) and post-tsunami (in 2005) diversity values were compared. Sediment samples were collected from two cruises in the depth zone of 214–1000 m (10°36′ N–20°01′ N and 79°59′ E–87°30′ E). The vertical distribution of the total heterotrophic bacterial population during both cruises was higher in the top section (0–3 cm) of the sediment. The average total heterotrophic bacterial population was in the range of 0.42–37.38 × 104 CFU/g to 1.66–19.73 × 104 CFU/g dry sediment weight during the two cruises, respectively. The limiting physico-chemical factors were sediment pH, sediment temperature, TOC, porosity, and clay as revealed from multiple regression (r = 0.75) and BIOENV (Partial Correlation ρω = 0.447) analyses. The shannon-Wiener index (H′ log e), Simpson index (D), Margalef index (d) and Pielou’s evenness index (J′) were found to be higher in the 1000 m depth stations. Cluster analysis showed that the 500 m depth stations clustered either with the 200 m or with the 1000 m stations. The 200 m depth stations never formed a cluster with the 1000 m stations. Pre-tsunami diversity indices at two depth ranges (200 m and 1000 m) were higher than those of the post-tsunami indices, which was quite evident from the cluster analysis as well. This study confirms the effect of the tsunami surge in the sediments of the continental slope of the Bay of Bengal in the marine ecosystem, which is also attributed to the temporal variation of the heterotrophic bacterial population and diversity.

Assessment of the Resistance to Uranium (VI) Exposure by Arthrobacter sp. Isolated from Hanford Site Soil

Production of nuclear fuel has resulted in hazardous waste streams that have contaminated the soil and groundwater. Arthrobacter strains, G975, G968, and G954 were used in the prescreening tests to evaluate their tolerance to UO2 2+ and investigate bacteria-U(VI) interactions under oxidizing pH-neutral conditions. Experiments have shown G975 is the fastest growing and the most uranium tolerant strain that removed about 90% of uranium from growth media. Atomic Force Microscopy images exhibited an irregular surface structure, which perhaps provided a larger surface area for uranium precipitation. The data indicate that aerobic heterotrophic bacteria may offer a solution to sequestering uranium in oxic conditions, which prevail in the vadose zone.

Oil waste management through large scale landfarming: a case study

The operational activities of the oil industry generate solid waste containing several classes of hydrocarbons. Landfarming enables the treatment of large amounts of oil waste through the disposal of waste in the reactive soil layer and hydrocarbon biodegradation. The aim of the present study was to evaluate oil waste management in a 1,000 m2 of landfarming area. The operational method used in the current investigation was biostimulation, including soil damping, fertilisation and aeration. In addition, a control cell was evaluated. To evaluate the performance of the proposed bioprocess, the moisture, total oil organic carbon, phosphorous, nitrogen, total petroleum hydrocarbon (TPH), heterotrophic aerobic bacteria (HAB), total fungi and heterotrophic anaerobic bacteria (HNB) contents were monitored, and the pH of the landfarming area was determined. The results indicated that the THP content of the treated soil decreased by 89.6%. The HAB, total fungi and HNB content presented average values of 1.4x107, 2.6x105 CFU.g–1 and 2.2x106 Cells.g–1, respectively.

First records and microgeographical variations of culturable heterotrophic bacteria in an inner sea (the Sea of Marmara) between the Mediterranean and the Black Sea, Turkey

The microdiversity and composition of culturable heterotrophic aerobic bacteria were investigated in seawater samples taken from the Sea of Marmara (an important basin between the Mediterranean and the Black Sea) in different time periods throughout 2002-2010. The bacterial isolates were identified with the automated microidentification system VITEK 2 Compact 30 (bioMerieux, France). The compositions of identified bacteria according to their exposure to environmental factors in the areas from which they were isolated were compared. The primary hydrographic parameters (temperature, salinity, and dissolved oxygen) were recorded at the sampling station. The highest heterotrophic aerobic bacteria abundance was found in the coastal stations. It was possible to isolate enteric bacteria species from the lower and upper stratification of various marine localities, which possessed salinity values between 24.0 psu and 39.2 psu during the study. Six bacterial classes were determined: Gammaproteobacteria (49%), Bacilli (34%), Alphaproteobacteria (9.09%), Betaproteobacteria (3.03%), Flavobacteria (3.03%), and Actinobacteria (3.03%). This study increases the knowledge of the composition and biochemical response of bacteria isolated from eutrophic and oligotrophic areas. Twenty-three bacteria species belonging to 16 families are reported in this study as the first records for the Sea of Marmara.

Hexavalent chromium reduction by aerobic heterotrophic bacteria indigenous to chromite mine overburden

Microbiological analysis of overburden samples collected from chromite mining areas of Orissa, India revealed that they are rich in microbial density as well as diversity and dominated by Gram-negative (58%) bacteria. The phenotypically distinguishable bacterial isolates (130) showed wide degree of tolerance to chromium (2–8 mM) when tested in peptone yeast extract glucose agar medium. Isolates (92) tolerating 2 mM chromium exhibited different degrees of Cr+6 reducing activity in chemically defined Vogel Bonner (VB) broth and complex KSC medium. Three potent isolates, two belonging to Arthrobacter spp. and one to Pseudomonas sp. were able to reduce more than 50 and 80% of 2 mM chromium in defined and complex media respectively. Along with Cr+6 (MIC 8.6–17.8 mM), the isolates showed tolerance to Ni+2, Fe+3, Cu+2 and Co+2 but were extremely sensitive to Hg+2 followed by Cd+2, Mn+2 and Zn+2. In addition, they were resistant to antibiotics like penicillin, methicillin, ampicillin, neomycin and polymyxin B. During growth under shake-flask conditions, Arthrobacter SUK 1201 and SUK 1205 showed 100% reduction of 2 mM Cr+6 in KSC medium with simultaneous formation of insoluble precipitates of chromium salts. Both the isolates were also equally capable of completely reducing the Cr+6 present in mine seepage when grown in mine seepage supplemented with VB concentrate.

Diversity and biosynthetic potential of culturable aerobic heterotrophic bacteria isolated from Magura Cave, Bulgaria

Biocapacity of bacteria inhabiting karstic caves to produce valuable biologically active compounds is still slightly investigated. A total of 46 culturable heterotrophic bacteria were isolated under aerobic conditions from the Gallery with pre-historical drawings in Magura Cave, Bulgaria. Phylogenetic analysis revealed that most of bacterial isolates aff iliated with Proteobacteria (63%), followed by Actinobacteria (10.9%), Bacteroidetes (10.9%), and Firmicutes (6.5%). A strong domination of Gram-negative bacteria (total 81%) belonging to nine genera: Serratia, Pseudomonas, Enterobacter, Sphingobacterium, Stenotrophomonas, Commamonas, Acinetobacter, Obesumbacterium, and Myroides, was observed. Gram-positive isolates were represented by the genera Bacillus, Arthrobacter, and Micrococcus. One isolate showed a signif icant phylogenetic distance to the closest neighbor and could represent а novel species. Heterotrophic bacterial isolates from Magura Cave were investigated for hydrolytic enzymes production, antimicrobial and hemolytic activity. Predominance of producers of protease (87%), followed by xanthan lyase (64%), lipase (40%), β-glycosidase (40%), and phytase (21%) was observed. Over 75% of the isolates demonstrated antimicrobial and hemolytic activity. The results suggest that heterotrophic bacteria isolated from Magura Cave could be a valuable source of industrially relevant psychrotolerant enzymes and bioactive metabolites. This study is a f irst report on the taxonomic composition and biological activity of culturable bacteria inhabiting a cave in Bulgaria.

Assessment of &lt;i&gt;in-situ&lt;/i&gt; abundance dynamics of enterobacteria and total heterotrophic aerobic bacteria in groundwater in the equatorial region of Central Africa

Assessment of &lt;i&gt;in-situ&lt;/i&gt; abundance dynamics of enterobacteria and total heterotrophic aerobic bacteria in groundwater in the equatorial region of Central Africa