Total Bacterial Population Size Research Articles

Long-term low dissolved oxygen accelerates the removal of antibiotics and antibiotic resistance genes in swine wastewater treatment

In this study, a novel process for swine wastewater treatment, anoxic and four-stage micro oxygen aerated sequence coupled with a coagulation process (AO4) was investigated in the pilot scale to determine its capacity in the removal of antibiotics and antibiotic resistance genes (ARGs). Results showed that long-term low dissolved oxygen (DO) operational condition played a significant role in decreasing the antibiotics and relative abundance of ARGs. Around 98% of the total antibiotics were removed along with 4–6 orders magnitude reductions of the ARGs copy numbers in AO4 process. Reduction of bacterial endogenous decay rate in AO4 process with low DO (0.15mg/L and 0.10mg/L) might result in the increase in the total bacterial population size and the concentration of sludge. As a result, high biomass accelerated the accumulation of antibiotics in sludge. In addition, real-time polymerase chain reaction amplification (qPCR) assays indicated that the long-term low DO could reduce the relative abundance of ARGs via enriching the 16S rDNA in activated sludge and inhibiting the emergence or distribution of ARGs. Our findings imply that the AO4 process could not only achieve a significant reduction of conventional contaminants such as chemical oxygen demand (COD), chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP) but also antibiotics and ARGs.

Changes in the activity and abundance of the soil microbial community in response to the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP)

The application of organic and inorganic fertilizers to soil can result in increased gaseous emissions, such as NH3, N2O, CO2, and CH4, as well as nitrate leaching, contributing to climate warming and ground and surface water pollution, particularly in regions with hot climates, where high temperatures and high soil nitrification rates often occur. The use of nitrification inhibitors (NIs) has been shown to effectively decrease nitrogen (N) losses from the soil-plant system. Non-disruptive laboratory incubation experiments were conducted to assess the extent to which temperature (20 and 30 °C) and nutrient source (mineral and organic fertilizers) influence the rate of carbon (C)- and N-related microbial processes in soil in response to the NI 3,4-dimethylpyrazole phosphate (DMPP). Furthermore, short-term changes in the ability of microbes to degrade C substrates were evaluated in disruptive soil microcosms using microbial community-level physiological profiling and the abundance of the bacterial 16S rRNA gene as a measure of total bacterial population size. DMPP reduced net nitrification after 2 and 4 weeks of incubation at 30 and 20 °C by an average of 78.3 and 84.5 %, respectively, and with similar dynamics for mineral or organic fertilization. The addition of labile organic matter with cattle effluent led to a rapid increase in C mineralization that was significantly reduced by DMPP at both temperatures, whereas no changes could be detected after the addition of mineral fertilizer. The culturable heterotrophic microorganisms showed metabolic diversification in the oxidation of C sources, with organic fertilizer playing a major role in the substrate utilization patterns during the first week of incubation and the DMPP effects prevailing from day 14 until day 28. Furthermore, the copy number of the bacterial 16S rRNA gene was reduced by the application of DMPP and organic fertilizer after 28 days. Our results show the marked efficiency of DMPP as an NI at elevated temperatures of incubation and when associated with both mineral and organic fertilization, providing support for its use as a tool to mitigate N losses in Mediterranean ecosystems. However, we also observed impaired C respiration rates and bacterial abundances, as well as shifts in community-level physiological profiles in soil, possibly indicating a short-term effect of DMPP and organic fertilizers on non-target C-related processes and microorganisms.

Interaction of rumen bacteria as assumed by colonization patterns on untreated and alkali‐treated rice straw

Colonization patterns of representative rumen bacteria were compared between untreated rice straw (UTS) and sodium hydroxide-treated rice straw (SHTS). UTS and SHTS were incubated in the rumen of sheep for 10 min, 1, 2, 6, 12, 24, 48 and 96 h using the nylon bag method. The population sizes of 13 representative bacterial species or groups were quantified by real-time PCR. The total bacterial population size (abundance) was similar in both UTS and SHTS. Fibrobacter succinogenes showed a higher population size compared to other fibrolytic species and was detected at a higher level in SHTS (3.7%) than in UTS (2.6%). Ruminococcus albus and Ruminococcus flavefaciens were also detected at higher levels in SHTS (0.15% and 0.29%) than in UTS (0.03% and 0.18%). Population sizes of non-fibrolytic species, such as Selenomonas ruminantium, Anaerovibrio lipolytica and Succinivibrio dextrinosolvens were higher in UTS than in SHTS. Coefficient of determination (r(2) ) on population changes between bacterial species or groups were higher in UTS than in SHTS, suggesting the necessity of stronger bacterial interactions for UTS digestion. Therefore, not only colonization of fibrolytic species, but also synergistic interactions between different bacterial species may be key to the ruminal digestion of rice straw.

Effect of solar UV-B radiation on a phyllosphere bacterial community.

The effect of solar UV-B radiation on the population dynamics and composition of the culturable bacterial community from peanut (Arachis hypogeae L.) was examined in field studies using plants grown under UV-B-transmitting (UV-B+) or UV-B-excluding (UV-B-) plastic filters. Our data demonstrate that solar UV-B selection alters phyllosphere bacterial community composition and that UV tolerance is a prevalent phenotype late in the season. The total bacterial population size was not affected by either UV-B treatment. However, isolates from the UV-B+ plots (n = 368) were significantly more UV tolerant than those from the UV-B- (n = 363) plots. UV sensitivity was determined as the minimal inhibitory dose of UV that resulted in an inhibition of growth compared to the growth of a nonirradiated control. The difference in minimal inhibitory doses among bacterial isolates from UV-B+ and UV-B- treatments was mainly partitioned among nonpigmented isolates, with pigmented isolates as a group being characterized as UV tolerant. A large increase in UV tolerance was observed within isolate groups collected late (89 and 96 days after planting) in the season. Identification of 200 late-season isolates indicated that the predominant UV-tolerant members of this group were Bacillus coagulans, Clavibacter michiganensis, and Curtobacterium flaccumfaciens. We selected C. michiganensis as a model UV-tolerant epiphyte to study if cell survival on UV-irradiated peanut leaves was increased relative to UV survival in vitro. The results showed an enhancement in the survival of C. michiganensis G7.1, especially following high UV-C doses (300 and 375 J m(-2)), that was evident between 24 and 96 h after inoculation. A dramatic increase in the in planta/in vitro survival ratio was observed over the entire 96-h experiment period for C. michiganensis T5.1.

Biological Control of Pseudomonas syringae pv. glycinea by Epiphytic Bacteria under Field Conditions.

The efficacy of a bacterial strain as a biocontrol agent in the field may be related to the ecological similarity between the biocontrol agent and the target pathogen. Therefore, a number of different Pseudomonas syringae strains were evaluated for their antagonistic activities in vitro (agar-diffusion assay) and in planta (greenhouse assay) against the target pathogen, Pseudomonas syringae pv. glycinea. Six strains of five different pathovars were found to be antagonistic in vitro as well as in planta. The epiphytic fitness of the antagonistic Pseudomonas syringae strain 22d/93 and its two antibiotic-resistant mutants were examined on soybean plants in the fields. After adaptation the parental strain and its mutants had the ability to establish and maintain large epiphytic populations (about 106 cfu/g FW) over the whole growing season after a single spray inoculation. The epiphytic behaviors of the mutants and the parent were not significantly different. The introduced bacteria did not influence the total bacterial population size. When the antagonist was coinoculated with the pathogen, the development of the pathogen was significantly reduced during the whole growing season. When the antagonistic strain was inoculated 4 weeks in advance of the pathogen, this antagonistic effect could be markedly enhanced. The final population size of the pathogen reached just 104 cfu/g FW and was significantly reduced to 0.12% compared to the pathogen alone. This study demonstrates that biological control of foliar pathogens through colonization of the host plants with near isogenic or ecologically similar antagonistical strains seems to be a realistic goal.

Plant Species and Plant Incubation Conditions Influence Variability in Epiphytic Bacterial Population Size.

The influences of plant species and plant incubation conditions on the variability in bacterial population sizes among leaves were investigated in field and growth chamber studies. Pseudomonas syringae strains TLP2 and Cit7 were inoculated onto plants and population sizes were measured at intervals after inoculation. Total bacterial population sizes were also assessed in field studies. Levels of leaf-to-leaf variability in both P. syringae population size and bacterial community size differed significantly among plant species. For all plant species, variability among leaves in population sizes of inoculated bacteria was consistently greater than the leaf-to-leaf variability in numbers of total bacteria. Considering levels of variability in population size immediately prior to and following incubation under either wet or dry physical conditions, leaf-to-leaf variability in the population sizes of inoculated P. syringae strains increased significantly following incubation under dry, but not under wet, conditions. Measurements of leaf-to-leaf variability immediately prior to and following incubation were positively correlated regardless of whether the incubation was under wet or dry conditions, though the correlation was greater following dry incubation. These data provide insight into the biological and physical factors that may be important in generating variability in bacterial population sizes among leaves, and they have important implications for the design of appropriate strategies for sampling leaf surface microbial populations. </hea

Role of leaf surface sugars in colonization of plants by bacterial epiphytes.

The relationship between nutrients leached onto the leaf surface and the colonization of plants by bacteria was studied by measuring both the abundance of simple sugars and the growth of Pseudomonas fluorescens on individual bean leaves. Data obtained in this study indicate that the population size of epiphytic bacteria on plants under environmentally favorable conditions is limited by the abundance of carbon sources on the leaf surface. Sugars were depleted during the course of bacterial colonization of the leaf surface. However, about 20% of readily utilizable sugar, such as glucose, present initially remained on fully colonized leaves. The amounts of sugars on a population of apparently identical individual bean leaves before and after microbial colonization exhibited a similar right-hand-skewed distribution and varied by about 25-fold from leaf to leaf. Total bacterial population sizes on inoculated leaves under conditions favorable for bacterial growth also varied by about 29-fold and exhibited a right-hand-skewed distribution. The amounts of sugars on leaves of different plant species were directly correlated with the maximum bacterial population sizes that could be attained on those species. The capacity of bacteria to deplete leaf surface sugars varied greatly among plant species. Plants capable of supporting high bacterial population sizes were proportionally more depleted of leaf surface nutrients than plants with low epiphytic populations. Even in species with a high epiphytic bacterial population, a substantial amount of sugar remained after bacterial colonization. It is hypothesized that residual sugars on colonized leaves may not be physically accessible to the bacteria due to limitations in wettability and/or diffusion of nutrients across the leaf surface.

Occurrence of Indole-3-Acetic Acid-Producing Bacteria on Pear Trees and Their Association with Fruit Russet

ABSTRACT A relatively high percentage of epiphytic bacteria on pear leaf and fruit surfaces had the ability to produce indole-3-acetic acid (IAA) in culture media supplemented with tryptophan. While over 50% of the strains produced at least small amounts of IAA in culture, about 25% of the strains exhibited high IAA production as evidenced by both colorimetric and high-performance liquid chromatography analysis of culture supernatants. A majority of the strains that produced high amounts of IAA were identified as Erwinia herbicola (Pantoea agglomerans), while some strains of Pseudomonas syringae, Pseudomonas viridiflava, Pseudomonas fluorescens, Pseudomonas putida, and Rahnella aquaticus that produced high amounts of IAA also were found on pear. Fruit russeting was significantly increased in 39 out of 46 trials over an 8-year period in which IAA-producing bacteria were applied to trees compared with control trees. A linear relationship was observed between fruit russet severity and the logarithm of the population size of different IAA-producing bacteria on trees in the 30 days after inoculation, when normalized for the amount of IAA produced by each strain in culture. On average, the severity of fruit russet was only about 77% that on control trees when trees were treated at the time of bloom with Pseudomonas fluorescens strain A506, which does not produce IAA. Both total bacterial populations on pear in the 30-day period following full bloom and fruit russet severity varied greatly from year to year and in different commercial orchards over a 10-year period. There was a strong linear correlation between the logarithm of total bacterial population sizes and fruit russet severity.

Forest soil community responses to plant growth-promoting rhizobacteria and spruce seedlings

The influence of plant-growth-promoting rhizobacteria (PGPR) and spruce seedlings on the composition and activity of forest soil microbial communities was studied in a microcosm experiment in which sterile, sand-filled 25mm×150mm glass tubes were treated with a forest soil suspension containing Bacillus or Pseudomonas PGPR and 2-week-old spruce seedlings. Eighteen weeks after treatments were established, bacterial, actinomycete and fungal population sizes were determined by dilution plating, as were seedling dry weights and soil carbon substrate utilization profiles using Biolog plates. PGPR inoculation had little influence on the population sizes of actinomycetes or fungi. However, significant effects were detected on the total bacterial population size, primarily in microcosms without seedlings. Euclidean distances between treatments plotted on two dimensions by multidimensional scaling showed that the introduction of PGPR strains changed the type of microbial community, particularly when inoculated into soil without seedlings. Significant changes were also detected in one soil type in the presence of seedlings. Our results suggest that the type of soil community and the presence of seedlings are significant factors influencing the responses of soil communities to bacterial inoculation, and that for some soil communities, the presence of seedlings may mitigate perturbations caused by the introduction of PGPR.

Influence of the Hydrological Cycle on the Bacterioplankton of an Impacted Clear Water Amazonian Lake

Free-living and attached bacterial population sizes were determined fortnightly from December 1991 to December 1992 in natural and disturbed areas of an Amazonian clear water lake (Batata Lake, Para, Brazil) impacted by bauxite tailings. The bacterioplankton showed distinct patterns during different phases of the hydrological cycle. Total bacterial population size and rates of thymidine incorporation (measured during high and low water phases) were high during low water, with values ranging from 3.3 × 105 to 1.1 × 106 cells ml−1, and from 0.28 to 4.01 μg C l−1 h−1, respectively. The population size of free-living bacteria was larger at the natural station, while no differences were observed between attached bacterial populations at both stations. However, production and turnover rate of attached bacteria were high at the disturbed area. During low water, bacterial growth appeared to be driven mainly by the input of dissolved organic carbon (DOC) from phytoplankton origin. During high water, bacterial abundance was reduced, probably as the result of dilution and the input of less labile DOC from floodplains. The presence of bauxite tailings seems to influence bacterial dynamics in an indirect way, probably due to shading of phytoplankton cells and, hence, reducing the DOC supply for bacterial growth. This study, the first on the microbial ecology of an Amazonian clear water lake, demonstrated that water level variations exert a strong influence on the bacterioplankton dynamics.

Population Sizes, Immigration, and Growth of Epiphytic Bacteria on Leaves of Different Ages and Positions of Field-Grown Endive (Cichorium endivia var. latifolia)

Total, fluorescent, and pectolytic epiphytic bacterial population sizes were quantified on leaves of different age groups of broad-leaved endive during field cultivation from leaf emergence until harvest. Greater bacterial population densities (log(inf10) CFU per square centimeter) were observed on outer leaves than on inner leaves of the plants throughout the growing season. These differences were statistically significant for total bacterial populations at all sampling times and were often significant for fluorescent and pectolytic bacterial populations. At harvest, a linear gradient of decreasing densities of epiphytic bacteria from outer (older) to inner (younger) leaves of the head was significant. Leaf age influenced the frequency distribution and variability of bacterial population sizes associated with leaves of broad-leaved endive. Total bacterial population sizes were greater at leaf emergence for leaves emerging during the second half of the cultivation period than for leaves emerging earlier. The size of fluorescent and pectolytic bacterial populations on newly emerged leaves increased throughout the season as plants aged. To assess the importance of plant age on bacterial immigration at leaf emergence, bacterial densities were quantified on leaves emerging simultaneously on plants of different ages. In two of the three experiments, greater bacterial population sizes were observed on leaves emerging on younger plants. This indicates that factors other than an increase in concentration of airborne bacteria can lead to increases in population sizes at leaf emergence as plants age in the field. Results of leaf pruning experiments suggested that adjacent leaves may act as a barrier for immigration of fluorescent bacteria on newly emerged leaves. Survival of an inoculated strain of Pseudomonas fluorescens on newly emerged leaves generally did not vary with the age of plants. However, these effects were not consistent among experiments, suggesting that interactions among micro- and macroenvironmental conditions, physiological condition of leaves, and accessibility of leaves to airborne bacteria are important in controlling epiphytic bacterial population sizes.