Aerobic Heterotrophic Bacteria Research Articles

Water physicochemical quality as driver of spatial and temporal patterns of microbial community composition in lake ecosystems

This study aimed at monitoring and management of the surface water and potentially pathogenic microbes of Lake Tonga (Algeria) with respect to. It characterized the main bacterial diversity patterns of Lake Tonga and predicted from water physicochemical parameters and water quality index (WQI) the distribution of bacterial species and the main indicator groups of faecal water contamination. Water samples were taken monthly at three sampling sites of different water depths. Several physicochemical parameters were measured; of which some were included in computing WQI to characterize the water quality of the lake. Counting, isolation and bacterial identification methods were used to characterize the existing aerobic heterotrophic bacteria. The composition of the microbial community of the waterbody of Lake Tonga included an abundant culturable bacterial flora belonging to several bacterial families and whose specific richness varied between water depths of the sites sampled. Species richness of the bacteria identified phenotypically varied between 7 and 11 per sample. The site with shallow water was the richest in bacterial species, compared to moderate and deep waters. The redundancy analysis showed the main physicochemical drivers of the microbial community composition. Our findings showed that high WQI scores indicated the water quality deterioration which triggered the increase in total load of faecal indicator bacterial groups. This study identified in Lake Tonga an important culturable aerobic bacterial flora whose specific richness and distribution varied spatially following the effects of water physicochemical parameters. Lake Tonga needs an integrated management plan to mitigate human disturbances declining water quality.

Bacterial load, multiple antibiotic-resistance patterns, and cytotoxic effects of coliform and coliform-related bacteria associated with the surface water of dhaka city

The surface water quality of Dhaka Metropolitan City was studied from June to December 2022, with special attention to coliform bacterial pollution. The aerobic heterotrophic bacteria, total coliform, and fecal coliform were high in Buriganga and Shitalakshya River water compared to other selected water bodies. The physico-chemical parameters of the selected rivers and lakes were unsatisfactory.  A total of 110 isolates were obtained, of which 26 were selected for further study. Twelve Gram-positive isolates belonged to the genera Enterococcus, Micrococcus, Planococcus and Bacillus. Fourteen Gram-negative isolates belonged to the genera Escherichia, Klebsiella, Enterobacter, Alcaligenes, Pseudomonas, Plesiomonas, Aeromonas and Salmonella. Most of the Gram-negative bacteria were multiple antibiotic resistant (MAR). Plesiomonas shigelloides showed the highest MAR (50%). Klebsiella oxytoca (MAR 40%) and E. coli (MAR 30%) showed a positive cytotoxic effect on the non-cancer cell line. Coliform bacteria associated with the surface water of Dhaka City pose a serious health threat to city dwellers.  Bangladesh J. Bot. 53(1): 41-48, 2024 (March)

Disease-suppressive soils induce systemic resistance in Arabidopsis thaliana against Pseudomonas syringae pv. tomato

Arabidopsis thaliana accession Col-0 seedlings were transferred into an autoclaved potting soil/sand mixture amended with either 10 or 20% (weight/weight) soil from fields in Washington State USA that are suppressive to take-all or Rhizoctonia root rot of wheat. Three weeks after transplanting, these plants had population sizes of 2,4-diacetylphloroglucinol (DAPG)- or phenazine-1-carboxylic acid (PCA)-producing pseudomonads of greater than 5 x 105 colony forming units per gram fresh weight of root with rhizosphere soil. When the plants were challenge-inoculated with Pseudomonas syringae pv. tomato, both soils displayed induced systemic resistance in the leaves against bacterial speck to a level similar to that induced by Pseudomonas simiae WCS417r, P. fluorescens Q2-87 (DAPG+), P. brassicacearum Q8r1-96 and L5.1-96 (both DAPG+), and P. synxantha 2-79 (PCA+). Pasteurization of the soils before adding them into the soil/sand mixture eliminated DAPG- and PCA-producing pseudomonads from the A. thaliana rhizosphere and significantly reduced induced systemic resistance activity. However, populations of total culturable heterotrophic aerobic bacteria were similar in the rhizosphere of plants grown in soil/sand mixes amended with untreated or pasteurized suppressive soils. This is the first report of induction of systemic resistance in A. thaliana by take-all and Rhizoctonia suppressive soils and the ability of PCA-producing P. synxantha 2-79 to induce resistance.

The specific molecular signature of dissolved organic matter extracted from different arctic plant species persists after biodegradation

Dissolved organic matter (DOM) is a small but very reactive pool of organic matter (OM) in the environment. Its role is related to its composition, which depends on its source. In soils, vegetation is the main source of DOM, and biodegradation is the main regulating mechanism. This study aims to characterise DOM produced by contrasted arctic vegetation species and their biodegradation products.The water-extractable organic matter (WEOM) was produced from C. stellaris (lichen), E. vaginatum (sedge), A. polifolia (dwarf evergreen shrub) and B. nana (deciduous dwarf shrub). The WEOM were inoculated with a common aerobic heterotrophic soil bacteria (P. aureofaciens) and incubated for 7 days. During the experiment, WEOM was characterised through a wide range of analytical methods (TOC, UV–Vis absorbance, high-performance ion chromatography and HRMS Orbitrap).The results showed bacteria consumed a significantly greater proportion of WEOM produced by C. stellaris than by A. polifolia and B. nana at the end of the experiment (p < 0.05). Furthermore, the number of features in WEOM decreased for C. stellaris and E. vaginatum, whereas it increased for B. nana. These findings shed light on the species-specific biodegradation processes that rely on the initial composition of DOM, specifically influenced by the vegetation's capacity to produce recalcitrant compounds. Furthermore, our results emphasised that even though bacterial activity greatly impacted molecular characteristics, the WEOM produced by different vegetation species maintained their distinct molecular signatures. As a result, it can be inferred that the DOM found in natural environments directly reflects the relevant vegetation cover despite the strong influence of biogeochemical processes on DOM molecular composition. This should be considered when developing models to assess the influence of climate change on vegetation cover composition and its subsequent effects on DOM dynamics in soil and surface waters.

Distinct mechanisms drive plant-nitrifier interactions in topsoil and subsoil

Plants can influence soil microbes through resource acquisition and interference competition, with consequences for ecosystem function such as nitrification. However, how plants alter soil conditions to influence nitrifiers and nitrification rates remains poorly understood, especially in the subsoil. Here, coupling the 15N isotopic pool dilution technique, high throughput sequencing and in situ soil O2 monitoring, we investigated how a deep-rooted perennial grass, miscanthus, versus an adjacent shallow-rooted turfgrass reference shapes nitrifier assembly and function along 1 m soil profiles. In topsoil, the suppression of ammonia (NH3) oxidizing archaea (AOA) and gross nitrification rates in miscanthus relative to the reference likely resulted from nitrifiers being outcompeted by plant roots and heterotrophic bacteria for ammonium (NH4+). The stronger tripartite competition under miscanthus may have been caused in part by the lower soil organic matter (SOM) content, which supported lower gross nitrogen (N) mineralization, the major soil process that produces NH4+. In contrast, below 10 cm soil depth, significantly greater gross nitrification rates were observed in miscanthus compared to the reference. This was likely driven by the significantly lower oxygen (O2) in miscanthus than reference subsoil, which selected against aerobic heterotrophic bacteria but in favor of AOA. Overall, we found that plants can regulate AOA community structure and function through different mechanisms in topsoil and subsoil, with suppression of nitrification in topsoil and enhancement of nitrification in subsoil.

Quality of Drinking Water Points in Ntui (Centre Region, Cameroon) Based on the Abundance Dynamics of Bacteria of the Genus Aeromonas

A study to assess the microbiological quality of drinking water in the town of Ntui was carried out from February to July 2022. The microbiological quality was assessed by monitoring the abundance dynamics of bacteria of the genus Aeromonas isolated from surface and ground water. Samples were taken from ten water points. The parameters considered were physicochemical and bacteriological. The samples were taken and analysed using standard methods. These include temperature and pH. Bacteriologically, Heterotrophic Aerobic Mesophilic Bacteria (HAMB) and bacteria of the genus Aeromonas were isolated on Plate Count Agar and Ampicillin Dextrin Agar culture media using surface spreading techniques respectively.  The data obtained was analysed using appropriate software. The results show that certain physico-chemical parameters such as temperature vary relatively little from one sampling point to another, remaining at around 23.14±2.69°C. There was also a slightly acidic average pH of 6.87 U.C. This acidity is a consequence of the nature of the soils leached by the water. Microbiologically, an average density of 215 CFU/100 ml was recorded for the HAMB. A total of 06 species of opportunistic Aeromonas pathogenic to humans were isolated during the study. These were A. hydrophila, A. salmonicida, A. schubertii, A. jandaei, A. média and A. veronii biovar veronii, with variable mean densities of up to 22 CFU/100ml. The most abundant species was A. veronii biovar veronii (22 CFU/100ml). In short, the presence of these Aeromonas makes the water unfit for human consumption without prior treatment.

Nitrate removal from industrial wastewater using six newly isolated strains of aerobic heterotrophic denitrifiers in an attached growth

ABSTRACTBackgroundThe objective of this study was to isolate specific heterotrophic aerobic denitrifying bacteria from a wastewater treatment plant and employ them in an attached growth system for wastewater denitrification.MethodsTo isolate and screen aerobic denitrifiers, Denitrifying Medium (DM) and Screen Medium (GN) were utilized. The Polymerase Chain Reaction (PCR) technique and 16S rDNA sequencing were used to identify the isolates. The formation of biofilms by selected isolates on ceramic media was examined using a Scanning Electron Microscope (SEM). This study also investigated various variables for nitrate removal, including temperature, Carbon/Nitrogen ratio (C/N), and the carbon source. A series of experiments were conducted to gauge nitrate removal under optimal variable values.ResultsSix purified strains exhibited the highest denitrification efficiency in less than 30 h. Pseudomonas species were chosen for additional experiments. Denitrification efficiencies ranged from a low of 71.4% (at a temperature of 30 °C, C/N ratio of 17, and citrate as the carbon source) to a high of 98.9% (at a temperature of 33 °C, C/N ratio of 8, and citrate as the carbon source). The average denitrification efficiency was 84.02%. Optimal nitrate removal occurred at temperatures around 30–31 °C and C/N ratios of approximately 5.8–6.5.ConclusionThis study demonstrates that aerobic denitrifying bacteria can effectively remove nitrate from aqueous solutions.

Assessment of spatio-temporal variation in microbial quality of groundwater for irrigation and drinking water: A case study in Santa Lucia canton, Ecuador

The community of Paipayales is placed in the Santa Lucía Canton of Guayas Province, Ecuador. The residents rely mainly on well water for irrigation of their agricultural products, as well as for consumption. This study aimed to evaluate the temporal and spatial variation in microbial quality among different wells in Paipayales. Additionally, the research aimed to identify potential sources of contamination by assessing the association between groundwater microbial sources and land use patterns. The microbiological and physicochemical quality of 26 water wells were studied across 16 months. Samples were taken at the end of dry season in November 2018 (ED), beginning of dry season June 2019 (BD), and rainy season February 2020 (RS). Overall, the mean values of all studied microorganisms were found to be lowest in ED, followed by BD and RS. Fecal indicators microorganisms displayed less variability compared to heterotrophic aerobic bacteria, and Pseudomonas, all of which showed significant differences between years (p < 0.01). No significant difference was found between microorganisms and well characteristics. Out of the analyzed E. coli strains, seven (16.66%) exhibited resistance to at least one antibiotic, and two strains were found to be multiresistant. These findings indicate the influence of activities such as rice cultivation and animal husbandry near the wells, as well as the absence of proper sanitation facilities in their vicinity. Turbidity increased from 2018 to 2020, while pH, temperature, and salinity showed minimal variation across all years, with only a few samples displaying correlation. Most wells met the Ecuadorian guidelines for drinking water after disinfection, with only one sample failing to meet the irrigation standards. The results suggest that microbial communities in groundwater aquifers are primarily influenced by external factors, notably anthropogenic activities related to agriculture and urbanization in the area.

Stable microbial community in compacted bentonite after 5 years of exposure to natural granitic groundwater.

The Materials Corrosion Test (MaCoTe) at the Underground Research Laboratory in Grimsel, Switzerland, assesses the microbiology and corrosion behavior of engineered barrier components of a deep geological repository (DGR) for long-term disposal of high-level nuclear waste. Diversity and temporal changes of bentonite-associated microbial community profiles were assessed under DGR-like conditions for compacted Wyoming MX-80 bentonite (1.25 g/cm3 and 1.50 g/cm3 targeted dry densities) exposed to natural groundwater. Using culture-dependent and molecular techniques, samples taken from the outside layer of 5-year borehole modules revealed up to 66% and 23% of 16S rRNA gene sequences affiliated with Desulfosporosinus and Desulfovibrio, respectively. Putatively involved in sulfate reduction, these taxa were almost undetectable within the bentonite core. Instead, microbial profiles of the inner bentonite core were similar to uncompacted bentonite used to pack modules years earlier, and were consistent with a previously published 1-year time point, revealing no detectable microbial growth. Abundances of culturable aerobic and anaerobic heterotrophic bacteria in the uncompacted bentonite were relatively low, with less than 1,000 and 100 colony-forming units (CFUs) per gram dry weight, respectively. Nearly 5 years after emplacement, culturable heterotrophic bacterial CFUs and sulfate-reducing bacteria did not change significantly inside the bentonite core. Phospholipid fatty acid data indicated similar lipid abundance, and corresponding cell abundance estimates, for inner 5-year MaCoTe bentonite samples compared to those previously obtained for 1-year incubations. Collectively, our results provide complementary evidence for microbial stability inside highly compacted bentonite exposed to conditions that mimic engineered barrier components of a deep geological repository. IMPORTANCE The long-term safety of a deep geological repository for used nuclear fuel is dependent on the performance of the engineered and natural barriers. Microbial activity can produce chemical species that can influence the corrosion of the disposal containers for used nuclear fuel. Although previous studies have evaluated the microbiology of compacted bentonite clay within subsurface environments, these have been limited to relatively short incubations (i.e., 1 year). The current study provides a unique 5-year perspective that reinforces previous findings of growth inhibition for bentonite clay exposed to in situ subsurface conditions.

Bioremediation of an industrial soil contaminated by hydrocarbons in microcosm system, involving bioprocesses utilizing co-products and agro-industrial wastes.

The present study describes practical implication of bioaugmentation and biostimulation processes for bioremediation of an industrial soil chronically contaminated by hydrocarbons. For this purpose, biomass production of six autochthonous hydrocarbon-degrading bacteria were evaluated as inoculum of bioaugmentation strategy, by testing carbon and nitrogen sources included co-products and agro-industrial waste as sustainable and low-cost components of the growth medium. Otherwise, biostimulation was approached by the addition of optimized concentration of nitrogen and phosphorus. Microcosm assays showed that total hydrocarbons (TH) were significantly removed from chronically contaminated soil undergoing bioremediation treatment. Systems Mix (bioaugmentation); N,P (biostimulation) and Mix + N,P (bioaugmentation and biostimulation) reached higher TH removal, being 89.85%, 91.00%, 93.04%, respectively, comparing to 77.83% of system C (natural attenuation) at 90days. The increased heterotrophic aerobic bacteria and hydrocarbon degrading bacteria counts were according to TH biodegrading process during the experiments. Our results showed that biostimulation with nutrients represent a valuable alternative tool to treat a chronically hydrocarbon-contaminated industrial soil, while bioaugmentation with a consortium of hydrocarbon degrading bacteria would be justified when the soil has a low amount of endogenous degrading microorganisms. Furthermore, the production of inoculum for application in bioaugmentation using low-cost substrates, such as industrial waste, would lead to the development of an environmentally friendly and attractive process in terms of cost-benefit.

Enumeration of Aerobic Heterotrophic Bacteria in Early-Stage of Biofilm Formed on Different Plastic Types

In this study, the total number of aerobic hetetotrophic bacteria (AHB) in early-stage of biofilm formed on different plastic types commonly used in daily life, namely polyethylene (PE), polypropylene (PP), polystyrene (PS) was investigated in a water recirculating test system. The Golden Horn Estuary’s water was used as a system water. The test system was operated continuously for 504 h and natural biofilm formation was ensured. The physicochemical properties of system water were measured each sampling time. Bacterial attachment was observed on all plastic surfaces even within the first hours. Also, macroscopic images proved that the biofilm layer formed and flourished on all plastic surfaces over time. After 504 h, the levels of AHB on the plastic coupons were detected as 1.4×105, 1.2×105 and 1.8×105 cells cm−2 for PE, PP and PS, respectively. To investigate the number of bacterial cells in early-stage of biofilm formation on plastic surfaces will create an important basis for future research in terms of evaluating the effects of microplastics on the environment and human health.

Methanotrophic oxidation of organic micropollutants and nitrogen upcycling in a hybrid membrane biofilm reactor (hMBfR) for simultaneous O2 and CH4 supply

Pharmaceuticals and other organic micropollutants (OMPs) present in wastewater effluents are of growing concern, as they threaten environmental and human health. Conventional biological treatments lead to limited removal of OMPs. Methanotrophic bacteria can degrade a variety of OMPs. By employing a novel bubble-free hybrid membrane biofilm bioreactor (hMBfR), we grew methanotrophic bacteria at three CH4 loading rates. Biomass productivity and CH4 loading showed a linear correlation, with a maximum productivity of 372 mg-VSS·L−1·d−1, with corresponding biomass concentration of 1117.6 ± 56.4 mg-VSS·L−1. Furthermore, the biodegradation of sulfamethoxazole and 1H-benzotriazole positively correlated with CH4 oxidation rates, with highest biodegradation kinetic constants of 3.58 L·g−1·d−1 and 5.42 L·g−1·d−1, respectively. Additionally, the hMBfR recovered nutrients as microbial proteins, with an average content 39% DW. The biofilm community was dominated by Methylomonas, while the bulk was dominated by aerobic heterotrophic bacteria. The hMBfR removed OMPs, allowing for safer water reuse while valorising CH4 and nutrients.

Phenanthrene Degradation by Photosynthetic Bacterial Consortium Dominated by Fischerella sp.

Microbial degradation of aromatic hydrocarbons is an emerging technology, and it is well recognized for its economic methods, efficiency, and safety; however, its exploration is still scarce and greater emphasis on cyanobacteria-bacterial mutualistic interactions is needed. We evaluated and characterized the phenanthrene biodegradation capacity of consortium dominated by Fischerella sp. under holoxenic conditions with aerobic heterotrophic bacteria and their molecular identification through 16S rRNA Illumina sequencing. Results indicated that our microbial consortium can degrade up to 92% of phenanthrene in five days. Bioinformatic analyses revealed that consortium was dominated by Fischerella sp., however different members of Nostocaceae and Weeksellaceae, as well as several other bacteria, such as Chryseobacterium, and Porphyrobacter, were found to be putatively involved in the biological degradation of phenanthrene. This work contributes to a better understanding of biodegradation of phenanthrene by cyanobacteria and identify the microbial diversity related.

Treatment of high-phosphorus load wastewater by column packed with non-burning compound filler/gravel/ceramsite: evaluation of performance and microorganism community.

Cost-effective and environmental-friendly substrates are essential for the constructed wetlands (CWs). In this study, the column test was used to explore the differences in pollutant purification performance, microbial community structure and abundance between non-burning compound filler and conventional CWs substrates (i.e. gravel and ceramsite) at low temperature (0-15℃). It was found that the maximum phosphorus removal efficiency of compound filler (99%) was better than gravel (18%) and ceramsite (21%). Besides, the proportion of aerobic heterotrophic bacteria capable of ammonium oxidation, nitrification and denitrification (i.e. Pseudomonas, Acinetobacter, and Acetoanaerobium) was enhanced by compound filler, which has an excellent potential for nitrogen removal in the subsequent purification process. These results demonstrated that the self-made non-burning compound filler was a potential substrate for CWs, which was of great significance for the resource utilization of solid wastes such as polyaluminum chloride residue.

Elucidating prioritized factor for mainstream partial nitritation between C/N ratio and dissolved oxygen: Response surface methodology and microbial community shifts

Recently, C/N ratio is suggested as a promising control factor with dissolved oxygen (DO) achieving mainstream partial nitritation (PN); however, their combined effects on mainstream PN are still limited. This study evaluated the mainstream PN with respect to the combined factors, and investigated the prioritized factor affecting the community of aerobic functional microbes competing with NOB. Response surface methodology was performed to assess the combined effects of C/N ratio and DO on the activity of functional microbes. Aerobic heterotrophic bacteria (AHB) played the greatest role in oxygen competition among functional microbes, which resulted in relative inhibition of nitrite-oxidizing bacteria (NOB). The combination of high C/N ratio and low DO had a positive role in the relative inhibition of NOB. In bioreactor operation, the PN was successfully achieved at ≥ 1.5 of C/N ratio for 0.5–2.0 mg/L DO conditions. Interestingly, aerobic functional microbes outcompeting NOB were shifted with C/N ratio rather than DO, suggesting C/N ratio is more prioritized factor achieving mainstream PN. These findings will provide insights into how combined aerobic conditions contribute to achieve mainstream PN.

Nitrogen removal enhancement through competitive inhibition of nitrite oxidizing bacteria in mainstream partial nitritation/anammox: Anammox seeding and influent C/N ratios

Mainstream partial nitritation/anaerobic ammonium oxidation (annamox) (PN/A) has received a lot of attention, but stable nitrite oxidizing bacteria (NOB) inhibition remains a key challenge. This study investigated the main parameters affecting the competitive inhibition of NOB. For stable nitrogen removal in single-stage PN/A, the addition of organic matter and anammox seeding ratio were considered as major variables. By increasing the influent C/N ratio to 3.0, the nitrogen removal efficiency (NRE) improved from 63.4 ± 1.5% to 71.4 ± 2.7%. In addition, increasing the anammox seeding ratio to 37.2% further stabilized PN/A-based nitrogen removal, resulting in an increase of NRE to 81.4 ± 4.2%. In batch experiments, the effects of these two variables on the nitrogen conversion pathway were investigated in depth. In mainstream PN/A, the addition of organic matter selectively deteriorated NOB in competition for oxygen with aerobic heterotrophic bacteria. In addition, at a C/N ratio greater than 1.5, the effect was more pronounced. The anammox seeding ratio is a major variable in nitrite competition with NOB. An increase in this ratio exacerbated the role of NOB in the nitrogen conversion pathway. These results indicate that in depth insights into microorganisms competing with NOB in various nitrogen conversion pathways may be key parameters for achieving stable nitrogen removal from mainstream flows.

Preemptive methodology determining operational parameters for mainstream PN: Evaluating biokinetics of three functional microbiome in seeding sludge

Chemical oxygen demand (COD)/N ratio is attracted as an alternative strategy selectively suppressing nitrite oxidizing bacteria (NOB) in mainstream partial nitritation (PN). We investigated a methodology that proper COD/N ratio is preemptively evaluated from seeding sludge through biokinetic analysis for three functional aerobic microbes. The COD/N ratio facilitating PN was preemptively determined as ≥3 from the biokinetic assay using seeding sludge, which was successfully verified in continuous bioreactors. Interestingly, the relative biokinetic properties of NOB in oxygen competition between aerobic microbes were the key indicators to achieve mainstream PN. Microbial community results show that some aerobic heterotrophic bacteria (AHB) became predominant at higher COD/N ratio conditions (≥3) with decreasing Nitrospira spp. In other words, the COD/N ratio, which could deteriorate the relative oxygen competition of NOB depending on the microbial community, could be determined preemptively. Our results could suggest that the proposed methodology can be helpful to provide operational guideline of mainstream PN.

Predicting Legionella contamination in cooling towers and evaporative condensers from microbiological and physicochemical parameters.

Inhalation of Legionella-containing aerosols generated by cooling towers (CT) and evaporative condensers (EC) where water risk management is not performed correctly has been linked to a high percentage of community outbreaks of Legionnaires' disease (LD). Likewise, microbiological and physicochemical characteristics of the water in these facilities have been associated with this bacterium. The main aim of this study was to assess the risk of Legionella colonization in CT and EC based on the data for microbiological and physicochemical water quality provided by the Environmental Health Department and Laboratory of the City Council of L'Hospitalet de Llobregat (Barcelona, Spain). Legionella was analysed in 789 samples collected from 127 CT and EC in 46 companies in Catalonia from 2002 to 2019. A two-step logistic regression analysis was carried out to assess the risk of colonization by Legionella in the studied facilities according to the microbiological (aerobic heterotrophic bacteria) and physicochemical (pH, alkalinity, hardness, turbidity, conductivity, total iron and Langelier Index) water parameters. The optimal cut-off points for the water parameters predictive of Legionella contamination were defined as the values on the receiver operating characteristic (ROC) curve where sensitivity and specificity were jointly maximized. Legionella was isolated in 8.49% of the 789 analysed samples, 22.39% of which were heavily contaminated (with counts higher than 1.0×104CFU/l). L. pneumophila was isolated in 82.09% of the samples, with 41.82% belonging to serogroup 1. Logistic regression analysis revealed that aerobic heterotrophic bacteria concentrations ≥6.90×102CFU/ml [Odds ratios (OR) (95% CI)=3.56 (1.39-9.43), p=0.01], a pH≥8.70 [OR (95% CI)=3.60 (1.34-10.09), p=0.01], and water hardness ≥5.72×102mg/l [OR (95% CI)=6.30 (2.34-18.56), p<0.001] were each independently associated with a higher risk of CT and EC colonization by Legionella. The present study shows the importance of risk assessment for improving the control measures aimed at preventing or reducing Legionella populations in CT and EC, thus minimizing potential dangers for public health.

Application Potential of Constructed Wetlands on Different Operation Mode for Biologically Pre-Treatment of Rural Domestic Wastewater

In order to satisfy the requirements of rural domestic sewage, a bio-ecological combination system was proposed, including a biological treatment section (anaerobic hydrolysis tank and aerobic tank) and an ecological post-treatment section. This study observed the application potential of constructed wetlands (CW) on different operation modes for biologically pre-treated rural domestic wastewater. The organics and nutrient removal efficiency of the tidal flow constructed wetland (TFCW) and the horizontal subsurface flow constructed wetland (HFCW) were compared at a temperature range of 20–40 °C. During the stable phase, the higher chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), and total phosphorus (TP) removal efficiencies existed in TFCW than HFCW, corresponding to the efficiency of COD 69.46%, NH4+-N 96.47%, and TP 57.38%, but lower performance on COD (61.43%), NH4+-N (84.99%), and TP (46.75%) removal in HFCW, which should be attributed to the increasement of aerobic heterotrophic bacteria (Arthrobact and Sphingomonas), nitrifiers (Nitrospira), and phosphate accumulating organisms (PAOs) (Pseudomonas). The microbial biomass was also increased from 2.13 ± 0.14 mg/g (HFCW) to 4.64 ± 0.18 mg/g (TFCW), which proved to strengthen the formation and growth of biofilm under a better oxygen supplement. Based on the relative abundance of functional genera in the microbial community, it showed that TFCW was more favorable for promoting the growth of heterotrophic bacteria, nitrifiers, and phosphate-accumulating organisms (PAOs). When temperature changed from −4 °C to 15 °C, the two-stage constructed wetlands (TFCW-HFCW and HFCW-TFCW) were used for improving the performance of pollutants removal. The results demonstrated that the effluent concentrations of TFCW-HFCW and HFCW-TFCW met the Class 1A discharge standard of DB32/3462-2020 in JiangSu Province, China. Therefore, this study will provide a useful and easy-to-implement technology for the operation as an ecological post-treatment section.

Survival of Inoculated Campylobacter jejuni and Escherichia coli O157:H7 on Kale During Refrigerated Storage

Campylobacter and pathogenic Escherichia coliillnesses have been attributed to the consumption of fresh produce. The leafy green, kale, is increasingly consumed raw. In comparison to other leafy greens, kale has a longer shelf-life. Due to the extended shelf-life of kale, it is warranted to examine the survival of pathogenic Campylobacter jejuni and E. coli O157:H7 inoculated on the surface of kale stored in a controlled environment at 4 ± 1.4°C, and average humidity of 95 ± 1.9% over a 23-day period. At predetermined time points (days 0, 1, 2, 3, 5, 7, 9, 11, 13, 15, 17, 19, and 21), inoculated kale was destructively sampled and the surviving bacteria determined by serial dilution and plating onto Tryptic soy agar, Charcoal cefoperozone deoxycholate agar, and Eosin methylene blue for total aerobic bacteria, C. jejuni, and E. coli O157:H7, respectively. Enrichment and PCR were used for detection when pathogens were not detected using serial dilution and plating. Aerobic heterotrophic bacteria increased over the 23-day period, in contrast, significant declines in the inoculated pathogens were observed. Inoculated E. coli O157:H7 survived longer on kale (up to 19 d); in comparison, C. jejuni was undetectable by day 13 using enrichment and PCR or plating. In conclusion, C. jejuni and E. coli O157:H7 declined on fresh kale over time when held at refrigerated temperatures but were still detected during the majority of the time when the kale would likely still be considered edible by consumers.