Growth Of Microbial Populations Research Articles

A numerical approach for soil microbiota growth prediction through physics-informed neural network

In recent years, there has been a growing interest in leveraging Scientific Machine Learning (SciML) techniques to address challenges in solving Partial Differential Equations (PDEs). This study focuses on forecasting the growth of microbial populations in soil using a novel numerical methodology, the Physics-Informed Neural Network (PINN). This approach is crucial in overcoming the inherent challenges associated with the general unculturability of soil bacteria. PINNs can be used to model the growth of bacterial and fungal populations, considering environmental factors like temperature, solar radiation, air humidity, soil hydration status, and external weather conditions. In this paper, some stability issues related to the mathematical model have been analyzed. Moreover, by utilizing field data and applying equations that describe the biological mechanisms of microbial growth, a PINN was trained to predict the development of the microbiota over time. The results demonstrate that the use of PINNs for studying microbial growth and evolution is a promising tool for enhancing agriculture, optimizing cultivation processes, and facilitating efficient resource management.

The ecological hazards of profenofos revealed by soil beneficial-bacteria, plant seedlings, and plasmid nicking assays: A short-term toxicity investigation

Excessive and indiscriminate use of pesticides may adversely affect the growth and activity of both crop plants and soil microbial populations. The reported study was conducted to evaluate the toxicity of profenofos (PF; an organophosphate insecticide) using bacterial (Pseudomonas fluorescens PSB-3 and Enterobacter cloacae ZSB-8) and plant (Coriandrum sativum and Lactuca sativa L.) bioassays. PF was applied at rates of (0–100 µg mL−1) in vitro. Both bacterial strains were sensitive to PF but showed variable tolerance. Following PF exposure, cellular growth, morphology, survival, and inner membrane permeability of bacterial strains were significantly (p < 0.05) altered. Decreased population size coincided with decline in cellular respiration. The 100 µgmL−1 PF dosage imparted maximum impact on ZSB-8, inhibiting populations by 87%. PF also interfered with bacterial surface adherence (i.e., biofilm formation) in a concentration-dependent manner. Alterations in bacterial biomarker enzymatic activity and oxidative stress were also noted. PGP traits of bacterial strains were negatively and significantly (p ≤ 0.05) affected by insecticide. Under PF stress, reduction in indole-3-acetic and siderophore production followed the order: ZSB-8 > PSB-3. PF-induced phytotoxicity was confirmed via reduction in germination, seedling parameters, survival, tolerance, and vigor indices in both plant species. Additionally, PF caused distortion in morphology of root tips and root surfaces. Under CLSM, PF-exposed C. sativum and L. sativa roots exhibited increased oxidative stress. Cellular death in insecticide-treated roots was observed following staining with Evans blue dye. Insecticide concentration-dependent increase in stress markers (proline and MDA content), and antioxidant enzymatic activities in plant seedlings were observed. A dose-dependent conversion of super-coiled form of DNA to open circular in pBR-322 plasmid revealed the genotoxic potential of PF. These findings provide an understanding of toxic effects of profenofos on beneficial microbes and leafy edible vegetables, including their morphological, and cellular effects. Indeed, insecticidal applications deserve special attention due to their potential environmental hazards.

An approach for estimating microbial growth and chlorinated ethenes biotransformation in groundwater based on discrete observations

The bioremediation of chlorinated ethenes (CEs) contaminated groundwater is attracting increasingly attention in practical remediation projects. However, modelling of microbial metabolic processes under the constraints of substrate and environmental factors is inadequate. This study developed a new kinetic model, which incorporated the logistic model and Dual-Monod kinetic to represent the interaction between the controlled microbial growth and the bioavailable substrates in CE-contaminated groundwater. The proposed model was based on discrete observations to simulate microbial growth under the constraints of substrate and environmental conditions, reducing the amount of observational data required for the model. Meanwhile, the proposed model introduced two new kinetic parameters, the effective specific growth rate μeff and the real self-limiting coefficient of microbial growth keff,sl, to simplified the number of independent parameters. A parameter estimation method based on the quasi-Newton's algorithm for the proposed model was also developed. The model was validated based on the hypothetical data, experimental results, and a published dataset, demonstrated the successful simulation of microbial growth and the sequential biodegradation of PCE in groundwater systems (*E < 0.3). The monitoring duration and the sampling schedule have significant impacts on estimating the biological parameters, and large errors would be induced when the data from the periods of extremely low substrate concentration or microbial growth decline were involved in parameter estimation. The research suggested that the proposed kinetic model provided a new insight to express the limitation of microbial population growth due to the available substrates and environmental factors, and is hoping to be applied in actual CE-contaminated sites.

The fate and biostimulant potential of metal lactates in silt loam soil

AbstractConventional farming practices have negatively impacted micronutrient fertility and overall soil health. Metal lactates are an organic micronutrient amendment that provide both a labile carbon substrate as well as mineral nutrition for plant and microbial growth. To determine the ability of metal lactates to provide readily available micronutrients, Zn, Cu, Mn, Ni, and Co in lactate and chloride salt form were amended to soils and incubated for 28 days. Operationally defined speciation was determined using sequential extraction on samples incubated for 1, 5, or 28 days. The results show a comparable distribution of metals in chloride and lactate form; however, differences were detected in water‐soluble and exchangeable Ni and Zn at each timepoint. For example, in the water exchangeable fraction, there was 2.6%–2.9% less Ni and 0.2%–0.3% less Zn in the metal lactate‐treated soil compared to soil treated with metal chlorides. Furthermore, carbonate‐bound Ni averaged 4.1% and 4% less in metal lactate‐treated soils as compared to metal chloride‐treated soils on days 1 and 5, and Cu decreased 2.9%–3.3% during the treatment period for the lactate‐bound form. Additionally, microbial phospholipid fatty acid (PLFA) was performed and found a stimulatory effect of metal lactates on bacterial biomass with an increase of 12%–18% relative to the metal chloride treatment. Results from this study support the use of metal lactates as a sustainable alternative to conventional fertilizers by providing bioavailable micronutrients for plant nutrition in addition to a labile carbon source to support the growth of microbial populations.

Towards zero excess sludge discharge with built-in ozonation for wastewater biological treatment

In this study, a biological treatment process, which used a built-in ozonation bypass to achieve sludge reduction, was built to treat the industrial antifreeze production wastewater (mainly composed of ethylene glycol). The results indicated there is a positive correlation between ozone dosage and sludge reduction. At the laboratory level, the MLSS in the system can be stably controlled at around 3400 mg MLSS L−1 under the dosage of 0.18 g O3 g−1 MLSS. Ozonation can increase the compactness of sludge flocs (fractal dimension increased from 1.89 to 1.92). Ozone destroys microbial cell membranes and alters the structure of sludge flocs through direct oxidation through electrophilic reactions. It leads to the release of intracellular polysaccharides, proteins, and other biological macromolecules in microorganisms, thereby promoting the implicit growth of microbial populations. Some bacteria such as g_Pseudomonas, g_Gemmobacter, etc. have strong ethylene glycol degradation ability and tolerance to ozonation. The removal of ethylene glycol includes the glyoxylate cycle, glycine serine carbon cycle, and the glutamate-cysteine ligase pathway of assimilation. Gene KatG and gpx may be key factors in improving microbial tolerance to ozonation. The comprehensive evaluation from the perspectives of cost and carbon emission shows that choosing ozone cracking-implicit growth in wastewater treatment systems has significant cost advantages and application value.

Effect of selected agents for ochratoxin A biocontrol on the colour, texture and volatile profile of dry-cured fermented sausages.

Traditional dry-cured fermented sausages favour the growth of an autochthonous microbial population, which plays an important role in their sensory aspects. However, some moulds can produce mycotoxins such as ochratoxin A (OTA). The biocontrol agents (BCAs) Debaryomyces hansenii FHSCC 253H and Staphylococcus xylosus FHSCC Sx8 have been demonstrated to reduce OTA production in dry-cured meat products, but their influence in the sensory characteristics of sausages has to be tested. The aim of this study was to evaluate the effect of these BCAs on the colour, texture and volatile profile of dry-cured fermented sausages. D. hansenii caused few differences in the tested parameters with respect to the control batch. S. xylosus modified the texture and colour, although the values found were within the range expected for dry-cured fermented sausages 'salchichón'. Additionally, the volatile profile revealed the potential antioxidant effect of both BCAs and their ability to produce compounds associated with the ripened aroma that could increase product acceptability. The results indicate that there were no inconveniences in implementing both BCAs during the processing of dry-cured fermented sausages 'salchichón'. Moreover, D. hansenii FHSCC 253H could improve the volatile profile of this product. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

In situ cell division and mortality rates of SAR11, SAR86, Bacteroidetes, and Aurantivirga during phytoplankton blooms reveal differences in population controls.

Net growth of microbial populations, that is, changes in abundances over time, can be studied using 16S rRNA fluorescence in situ hybridization (FISH). However, this approach does not differentiate between mortality and cell division rates. We used FISH-based image cytometry in combination with dilution culture experiments to study net growth, cell division, and mortality rates of four bacterial taxa over two distinct phytoplankton blooms: the oligotrophs SAR11 and SAR86, and the copiotrophic phylum Bacteroidetes, and its genus Aurantivirga. Cell volumes, ribosome content, and frequency of dividing cells (FDC) co-varied over time. Among the three, FDC was the most suitable predictor to calculate cell division rates for the selected taxa. The FDC-derived cell division rates for SAR86 of up to 0.8/day and Aurantivirga of up to 1.9/day differed, as expected for oligotrophs and copiotrophs. Surprisingly, SAR11 also reached high cell division rates of up to 1.9/day, even before the onset of phytoplankton blooms. For all four taxonomic groups, the abundance-derived net growth (-0.6 to 0.5/day) was about an order of magnitude lower than the cell division rates. Consequently, mortality rates were comparably high to cell division rates, indicating that about 90% of bacterial production is recycled without apparent time lag within 1 day. Our study shows that determining taxon-specific cell division rates complements omics-based tools and provides unprecedented clues on individual bacterial growth strategies including bottom-up and top-down controls. IMPORTANCE The growth of a microbial population is often calculated from their numerical abundance over time. However, this does not take cell division and mortality rates into account, which are important for deriving ecological processes like bottom-up and top-down control. In this study, we determined growth by numerical abundance and calibrated microscopy-based methods to determine the frequency of dividing cells and subsequently calculate taxon-specific cell division rates in situ. The cell division and mortality rates of two oligotrophic (SAR11 and SAR86) and two copiotrophic (Bacteroidetes and Aurantivirga) taxa during two spring phytoplankton blooms showed a tight coupling for all four taxa throughout the blooms without any temporal offset. Unexpectedly, SAR11 showed high cell division rates days before the bloom while cell abundances remained constant, which is indicative of strong top-down control. Microscopy remains the method of choice to understand ecological processes like top-down and bottom-up control on a cellular level.

Experimental investigation on the effect of soil solarization incorporating black, silver, and transparent polythene, and straw as mulch, on the microbial population and weed growth

Soil solarization is a non-chemical method for eliminating crop-threatening weeds and selectively decontaminating soil. The effect of various soil solarization with black, silver, transparent polythene sheet and straw as mulching on the microbial count and weed growth was studied experimentally. The farm investigation comprised six soil solarization treatments: mulching with black, silver, and transparent polyethylene sheets of 25 μm (μ), organic mulch (soybean Straw), weed-free, and control. All six treatments were repeated in four sets in a Randomized Block Design (RBD) plot size of 5.4 m × 4.8 m. Black, silver, and transparent polythene mulches significantly reduced fungal count compared to non-solarized soil. Straw mulch significantly increased soil fungal count. Solarized treatments had much lower bacterial populations than straw mulch, weed-free, and control treatments. Black, silver, straw mulch, and transparent polythene had 18746, 22763, 23999, and 3048 weeds ha−1 at 45 days after transplanting (DAT). The analysis of dry weed weight demonstrated a significantly low weed dry weight of 0.44 t/ha for black polythene (T1) based soil solarization, representing an 86.66% reduction in dry weed biomass. Soil solarization had the lowest weed index (WI), with black polythene mulch (T1) reducing weed competition. Among various soil solarization treatments, black polythene (T1) showed the highest weed control efficiency of 85.84%, indicating its suitability for use in weed control. The results suggest that soil solarization is effective for soil disinfestation and weed control with polyethene mulch and summer heat in central India.

Mathematical Modeling of Microbial Electrolysis Cells for Enhanced Urban Wastewater Treatment and Hydrogen Generation

Conventional wastewater treatment plants (CWTPs) are intensive energy consumers. New technologies are emerging for wastewater treatment such as microbial electrolysis cells (MECs) that can simultaneously treat wastewater and generate hydrogen as a renewable energy source. Mathematical modeling of single and dual-chamber microbial electrolysis cells (SMEC and DMEC) has been developed based on microbial population growth in this study. The model outputs were validated successfully with previous works, and are then used for comparisons between the SMEC and DMEC regarding the hydrogen production rate (HPR). The results reveal that the daily HPR in DMEC is higher than in SMEC, with about 0.86 l H2 and 0.52 l H2, respectively, per 1 L of wastewater. Moreover, the results have been used to compare the HPR in water electrolysis (WE) processes and MECs. WE consume 51 kWh to generate 1 kg of hydrogen, while SMEC and DMEC require only 30 kWh and 24.5 kWh, respectively.

Development of peat microbial fuel cells (Peat MFCs) – the green and sustainable generators of electricity

Although deemed unsuitable for construction, Peat soils have remarkable applications in MFCs by generating electric power because of the microbial decomposition of rich organic matter. The demerits such as weak skeleton, high water content, acidic nature, and humus contamination of peat soil for civil engineering applications are considered merits in microbial fuel cell applications. Peat soil-based Microbial Fuel Cells (MFCs), the first of its kind among MFCs, are explored to generate electric power as high as 6 V when six MFCs connected in a series and lighted up an LED for 288 h. The performance of peat MFCs as a function of bamboo waste, fulvic acid, iron winding and surface area of the BC anode has been discussed in this work. The synergistic effect of organic decomposition by microbes and Fe complexation with humic substances (HS) has been detailed to be responsible for the cause of electric power in Peat MFCs. ATP measurement in peat soils after defined time periods confirmed the growth of microbial population, which successfully degraded the organic matter in MFCs. The characterization of BC anode and GAC cathode using FTIR, Raman, SEM with EDS, BET isotherm studies substantiated the structural modification and porous nature of the fresh and the used electrodes. The EIS study was performed to determine the dynamics of internal resistances due to the degradation kinetics in Peat MFCs. The cost effectiveness and the sustainability of Peat MFCs towards green technology are detailed in this paper.

Influence of Leachate Recirculation on Landfill Degradation and Biogas Production

Population growth combined with the rising standard of living of people around the world is the reason for the ever-increasing production of waste which management is costing states a lot of money for its disposal. Among available waste treatment techniques, landfill is one of the most promoted waste management techniques with the emergence of the bioreactor concept. However, the control of biodegradation parameters in order to accelerate waste stabilization is an important issue. For environmental and economic reasons, the technique of leachate recirculation by injection into the waste is increasingly used to improve the degradation of landfilled waste. The injection of leachate is possible using vertical boreholes, horizontal pipes, infiltration ponds or a combination of these. Indeed, moisture is the main factor in waste degradation and biogas production. The migration of leachate to the bottom of the landfill creates low moisture in the upper areas of the landfill reducing the growth of microbial populations. This results in low or no biogas production. The main objective of the present work is to develop a numerical model of leachate recirculation by injection into the waste to rewet the waste and restart biological activity. The analysis of the results shows that the diffusion of the wet front increases with time and depth. The lateral widening of the wet front is slow in relation to the progression of the wet front towards the bottom of the waste cell. This indicates the predominance of gravity effects over diffusion phenomena. The results reveal that the distributed re-injection is the best mode of leachate recirculation because the moisture distribution on the whole waste mass is totally satisfactory and the biogas generation is more important. Leachate recirculation campaigns should be done periodically to rewet the waste, boost microbial activity and hope for a quicker stabilization of the landfill.

Role of Genital Tract Bacteria in Promoting Endometrial Health in Cattle.

Microbiota regulate endometrial health in cattle. It is important to know what a 'good' microbiome is, in order to understand pathogeneses of uterine disease. Given that microbial influx into the genital tract of cows at calving is unavoidable, exploring the involvement of genital tract bacteria in promoting endometrial health is warranted. The dysbiosis of endometrial microbiota is associated with benign and malign uterine diseases. The present review discusses current knowledge about the altered endometrial microbiome and the implications of this modulation on endometrial inflammation, ovarian activity, fecundation, pregnancy, and postpartum complications. Intravaginal administration of symbiotic microbes in cattle is a realistic alternative to antibiotic and hormone therapy to treat uterine disease. Genital microbial diversity can be modeled by nutrition, as the energy balance would improve the growth of specific microbial populations. It may be that probiotics that alter the endometrial microbiome could provide viable alternatives to existing therapies for uterine disease in cattle.

Accelerated retting technology for the extraction of golden fibre from the Indian Tossa jute (Corchorus sp.)

Conventional retting over 20–25 d in stagnant water results in the production of poor-quality fibre in jute-growing countries which created a need for the development of an effective retting technology. Several retting technologies involving region-specific microbial consortia were reported with limited information on field effectiveness, storability, environmental impact, and cost analysis. In this study a retting formulation, NINFET-Sathi was introduced as a microbial food supplement to promote the growth of the retting microbial population irrespective of location. NINFET-Sathi resulted in 8–10.5% higher yield of jute fibre with 1–1.5 grade improvement within 10–12 d over conventional retting. Unlike earlier reported microbial-retting technologies, NINFET-Sathi did not introduce any new microbe into the retting system. It accelerated the growth of native pectinolytic and xylanolytic microbial populations in the retting water. This formulation improved bundle strength by 10.8–15.3%, fineness by 14.7–22.8%, and colour by 27.9–33.1% with low defects (0.56–0.61% by weight) and root content (7.11–7.68% by length) leading to higher fibre quality (TD-2) over conventional retting (TD-3) consistently for three years of storage. Long storability also offered scopes of distant transport of NINFET-Sathi formulation to jute growing areas with difficulty to reach. Post-retting water with NINFET-Sathi was found to meet water standards for aquaculture and irrigation and resulted in 9.1–24.7% high seed germination in rice, Bengal gram, green gram, and Indian mustard over the pre-retting water. Application of NINFET-Sathi retting technology holds potential for jute farmers to harness a net additional income of nearly USD 257 per ha.

APPLICATION OF GILLESPIE ALGORITHM FOR SIMULATING EVOLUTION OF FITNESS OF MICROBIAL POPULATION

In this study we present simulation system based on Gillespie algorithm for generating evolutionary events in the evolution scenario of microbial population. We present Gillespie simulation system adjusted to reproducing experimental data obtained in barcoding studies – experimental techniques in microbiology allowing tracing microbial populations with very high resolution. Gillespie simulation engine is constructed by defining its state vector and rules for its modifications. In order to efficiently simulate barcoded experiment by using Gillespie algorithm we provide modification - binning cells by lineages. Different bins define components of state in the Gillespie algorithm. The elaborated simulation model captures events in microbial population growth including death, division and mutations of cells. The obtained simulation results reflect population behavior, mutation wave and mutation distribution along generations. The elaborated methodology is confronted against literature data of experimental evolution of yeast tracking clones sub-generations. Simulation model was fitted to measurements in experimental data leading to good agreement.

EVALUATION OF ANTIMICROBIAL PROPERTY OF EXTRACT OF PUNICA GRANATUM (L.) ON ORAL PATHOGENS

The aim of the present research was the examination of the potential activity of various organic solvent extracts of Punica granatum on the important microbiota harbouring in the oral cavity. The dried peels and seeds of P. granatum were extracted using chloroform, methanol and nbutanol and their potential activity were studied. The inhibitory effect of crude extracts were observed on various microbial plates which were incubated with different bacterial species in terms of zone of inhibition as mm in diameter. The data was analysed by One Way Analysis of Variance for significance. The peel extract was more potent in inhibiting the microbial population growth as compared to seed extract. While all the four solvents were effective in case of peel extracts, the bioactivity was much higher in species such as Streptococcus mutants, Streptococcus sanguis, Staphylococcus aureus, Lactobacillus acidophilus and Actinomyces viscosus, among 8 species evaluated in the present investigation. The peel extract of P. granatum contains active biomolecule(s) against important oral microbial pathogens and thus holds promise as a potential bioactive molecule against Dental Caries. Based on the bioactivity analysis, the peel extract of P. granatum may further be subjected to purification and characterization of the bioactive compound(s) for regulating oral microbial contamination.

Herbal Antagonism of a Superbug – A Novel Approach

Background: This study was conducted to herbally antagonize the growth of a multi drug resistant Pseudomonas sp using ethanolic carrot rough fiber extractive. Materials and methods: The isolated strain of Pseudomonas sp was subjected to treatment with 5 different antibiotics-Chloramphenicol, penicillin, streptomycin, amoxycillin clavulanate along with monocef up to a concentration of 500µg/ml. The isolated organism was also treated with a mutagen Ethyl methane sulphonate. The antimicrobial property of the ethanolic carrot rough fiber extractive was tested by well diffusion method. MIC study of the ethanolic carrot rough fiber extractive was also performed. Result: The isolated strain was found to be resistant against 5 different antibiotics-Chloramphenicol, penicillin, streptomycin, amoxycillin clavulanate along with monocef up to a concentration of 500µg/ml. This organism was also found to grow at 44°C without any pigment production. This Pseudomonas sp also possess the ability of biofilm formation and antagonize the growth of other microbial population. There is reduced growth of this superbug under the influence of Ethyl methane sulphonate. It also became susceptible to the antibiotics monocef, streptomycin and higher concentration of amoxicillin. So the isolated strain is very much prone to induced mutation. The growth of this multi drug resistant strain of Pseudomonas sp has been antagonized by the ethanolic carrot fibre extractive. MIC study of the ethanolic carrot rough fibre extractive was performed which revealed that the MIC lies between 125µl-150µl i.e., 216.6-260mg/ml concentration of the extract. Conclusion: The ethanolic carrot rough fibre extractive has been found to antagonize the growth of the multidrug resistant Pseudomonas sp.

Potential Prebiotic and Anti-Obesity Effects of Codium fragile Extract

Polysaccharides from marine algae exhibit beneficial biological activities. In this study, we examined the effect of Codium fragile extract (CFE) on prebiotic and anti-obesity activity through in vitro experiments. CFE increases the growth of specific beneficial microbial populations with concomitant decrease in pathogenic microbes. Further, total phenolic content (TPC), total flavonoid content (TFC), and DPPH radical scavenging activity (DPPH activity) after fermentation with CFE as the carbon source were higher than for glucose as the control. Moreover, CFE inhibited adipocyte differentiation by inducing differentiation-related factors when the induction of 3T3-L1 preadipocytes into adipocytes was induced. Therefore, we suggest that CFE can be used as a prebiotic material with an anti-obesity effect for human health.

A Bayesian approach to modeling phytoplankton population dynamics from size distribution time series.

The rates of cell growth, division, and carbon loss of microbial populations are key parameters for understanding how organisms interact with their environment and how they contribute to the carbon cycle. However, the invasive nature of current analytical methods has hindered efforts to reliably quantify these parameters. In recent years, size-structured matrix population models (MPMs) have gained popularity for estimating division rates of microbial populations by mechanistically describing changes in microbial cell size distributions over time. Motivated by the mechanistic structure of these models, we employ a Bayesian approach to extend size-structured MPMs to capture additional biological processes describing the dynamics of a marine phytoplankton population over the day-night cycle. Our Bayesian framework is able to take prior scientific knowledge into account and generate biologically interpretable results. Using data from an exponentially growing laboratory culture of the cyanobacterium Prochlorococcus, we isolate respiratory and exudative carbon losses as critical parameters for the modeling of their population dynamics. The results suggest that this modeling framework can provide deeper insights into microbial population dynamics provided by size distribution time-series data.

Silicon substances for restoration of oil-contaminated areas

Numerous investigations demonstrate that active forms of silicon (Si) enhance the plant tolerance against abiotic stresses by several mechanisms, including increasing the antioxidant activities and minimizing oxidative damage. Soil contamination with oil and oil products relates to abiotic stress that detrimentally affects soil microbial population and plant growth. Considering the crucial role of microorganisms and plants in bioremediation of oil-polluted areas, Si substances can be beneficial to acceleration of soil reclamation. In greenhouse experiment, wheat was grown in Grey Forest Soil contaminated with used motor oil. The effect of fumed silica and monosilicic acid on soil enzymatic activity and plant growth was studied. Both Si substances provided increasing the plant biomass and the activities of catalase and dehydrogenase. As regards the plant growth, the effect of Si was more pronounced in polluted soil, while the enzyme activity was higher affected in unpolluted soil. The activities of catalase and dehydrogenase were closely correlated to the water-soluble Si in soil (R=0.91-0.92). Silicon substances with high content of, plant-and microorganism-available Si might be promising for involvement in bioremediation technology for oil-contaminated soil.

Predatory bacteria in the haemolymph of the cultured spiny lobster Panulirus ornatus.

Bdellovibrio and like organisms (BALOs) are Gram-negative obligate predators of other bacteria in a range of environments. The recent discovery of BALOs in the circulatory system of cultured spiny lobster P. ornatus warrants more investigation. We used a combination of co-culture agar and broth assays and transmission electron microscopy to show a Halobacteriovorax sp. strain Hbv preyed upon the model prey bacterium Vibrio sp. strain Vib. The haemolymph microbiome of juvenile P. ornatus was characterised following injection of phosphate buffered saline (control) or prey and/or predator bacteria for 3 d. The predator Hbv had no effect on survival compared to the control after 3 d. However, when compared to the prey only treatment group, lobsters injected with both prey and predator showed significantly lower abundance of genus Vibrio in the haemolymph bacterial community composition. This study indicates that predatory bacteria are not pathogenic and may assist in controlling microbial population growth in the haemolymph of lobsters.