Microbial Growth Rate Research Articles

The biogeography of soil microbiome potential growth rates

Soil microbial growth, a vital biogeochemical process, governs both the accrual and loss of soil carbon. Here, we investigate the biogeography of soil microbiome potential growth rates and show that microbiomes in resource-rich (high organic matter and nutrients) and acid-neutral soils from cold and humid regions exhibit high potential growth. Conversely, in resource-poor, dry, hot, and hypersaline soils, soil microbiomes display lower potential growth rates, suggesting trade-offs between growth and resource acquisition or stress tolerance. In addition, the potential growth rates of soil microbiomes positively correlates with genome size and the number of ribosomal RNA operons but negatively correlates with optimum temperature, biomass carbon-to-phosphorus and nitrogen-to-phosphorus ratios. The spatial variation of microbial potential growth rates aligns with several macroecological theories. These findings not only enhance our understanding of microbial adaptation to diverse environments but also aid in realistically parameterizing microbial physiology in soil carbon cycling models.

Asymmetric winter warming reduces microbial carbon use efficiency and growth more than symmetric year-round warming in alpine soils

Asymmetric seasonal warming trends are evident across terrestrial ecosystems, with winter temperatures rising more than summer ones. Yet, the impact of such asymmetric seasonal warming on soil microbial carbon metabolism and growth remains poorly understood. Using 18O isotope labeling, we examined the effects of a decade-long experimental seasonal warming on microbial carbon use efficiency (CUE) and growth in alpine grassland ecosystems. Moreover, the quantitative stable isotope probing with 18O-H2O was employed to evaluate taxon-specific bacterial growth in these ecosystems. Results show that symmetric year-round warming decreased microbial growth rate by 31% and CUE by 22%. Asymmetric winter warming resulted in a further decrease in microbial growth rate of 27% and microbial CUE of 59% compared to symmetric year-round warming. Long-term warming increased microbial carbon limitations, especially under asymmetric winter warming. Long-term warming suppressed the growth rates of most bacterial genera, with asymmetric winter warming having a stronger inhibition on the growth rates of specific genera (e.g., Gp10, Actinomarinicola, Bosea, Acidibacter, and Gemmata) compared to symmetric year-round warming. Bacterial growth was phylogenetically conserved, but this conservation diminished under warming conditions, primarily due to shifts in bacterial physiological states rather than the number of bacterial species and community composition. Overall, long-term warming escalated microbial carbon limitations, decreased microbial growth and CUE, with asymmetric winter warming having a more pronounced effect. Understanding these impacts is crucial for predicting soil carbon cycling as global warming progresses.

A Kinetic Study on Chronic Response of Activated Sludge to Diclofenac by Respirometry

The present study investigated the chronic response of activated sludge to the emerging pollutant diclofenac as well as its aerobic biodegradation potential at different sludge retention times (SRTs). The impact of prolonged exposure to diclofenac on microbial process kinetics was explored with respirometric modelling. The long-term operation of lab-scale reactors revealed that continuous feeding of diclofenac at relevant concentrations observed in municipal wastewaters did not affect carbon removal efficiency independentl of SRT. However, in case of diclofenac removal, 34% efficiency could be achieved at a higher SRT of 20 days. Kinetic evaluation showed that the increment in diclofenac dosing resulted in no adverse effect on the microbial growth rate except that high concentrations of diclofenac exposure decreased the growth rate at SRT of 10 days. A significant increase in hydrolysis rate was determined in the diclofenac-acclimated biomass for both SRTs; even at high concentrations of diclofenac exposure, the hydrolysis rate remained unchanged. Long-term acclimation to diclofenac had a progressive impact on the hydrolysis kinetics, which could be attributed to an alteration in the microbial culture profile. Overall, the results suggest that the operation with diclofenac-acclimated biomass at higher SRTs could enrich a microbial culture capable of overcoming the adverse effect of the pollutant and improve the biodegradation potential as well.

Basil essential oil-incorporated bacterial nanocellulose foam: Fabrication, characterization, and application in extending ground beef shelf life

Bacterial nanocellulose (BNC) is a sustainable antimicrobial material for food packaging. To enhance its antimicrobial properties, basil (Ocimum basilicum L.) essential oil (BEO) was incorporated into the BNC porous foam. A spray method was used with low BEO concentrations (1 and 2 μL/cm2) based on foam surface to optimize BEO usage while maintaining its antimicrobial effectiveness. BNC was synthesized using Komagataeibacter xylinus. The minimum inhibitory concentrations were 128 and 64 μg/mL for Pseudomonas aeruginosa and Listeria monocytogenes, respectively, demonstrating greater sensitivity of Gram-positive bacteria compared to Gram-negative bacteria. The use of BEO in spray form increased the antimicrobial and antioxidant activities (as measured by DPPH and ABTS methods) of foams. The absorption bands related to BEO in Fourier transform infrared spectroscopy analysis of the BNC-BEO foam confirmed the incorporation of BEO into the BNC foam. Impregnation with BEO at 1 and 2 μL/cm2 significantly increased the water contact angle to 31.62° and 33.19°, respectively, thereby enhancing the hydrophobicity of the foam, but reduced the mechanical strength of the BNC-BEO foams. Foams were used in active packaging of ground beef to improve shelf life by controlling microbial and oxidative processes. The BNC-BEO foam showed a slower microbial growth rate, with bacterial populations about 1–2 log₁₀ CFU/g lower than control. Meat samples packaged with BNC-BEO foams scored higher in terms of taste and odor. A significantly lower amount of BEO was used in the foam form of BNC, which is favorable for improving sensory parameters. Therefore, BNC-BEO can be applied to the active packaging of meat.

Growth rate as a link between microbial diversity and soil biogeochemistry.

Measuring the growth rate of a microorganism is a simple yet profound way to quantify its effect on the world. The absolute growth rate of a microbial population reflects rates of resource assimilation, biomass production and element transformation-some of the many ways in which organisms affect Earth's ecosystems and climate. Microbial fitness in the environment depends on the ability to reproduce quickly when conditions are favourable and adopt a survival physiology when conditions worsen, which cells coordinate by adjusting their relative growth rate. At the population level, relative growth rate is a sensitive metric of fitness, linking survival and reproduction to the ecology and evolution of populations. Techniques combining omics and stable isotope probing enable sensitive measurements of the growth rates of microbial assemblages and individual taxa in soil. Microbial ecologists can explore how the growth rates of taxa with known traits and evolutionary histories respond to changes in resource availability, environmental conditions and interactions with other organisms. We anticipate that quantitative and scalable data on the growth rates of soil microorganisms, coupled with measurements of biogeochemical fluxes, will allow scientists to test and refine ecological theory and advance process-based models of carbon flux, nutrient uptake and ecosystem productivity. Measurements of in situ microbial growth rates provide insights into the ecology of populations and can be used to quantitatively link microbial diversity to soil biogeochemistry.

Changes in microbial physiology and carbon-use efficiency upon improving soil habitat conditions in conservation farming systems

The interplay between soil microbial anabolism and metabolism has recently been postulated as an important lever for carbon sequestration in soils. Theoretical considerations suggest that high microbial growth rates and a high carbon-use efficiency (CUE) are associated with increased soil organic carbon (SOC) build-up in arable soils. Nature-oriented conservation agricultural practices are believed to facilitate this microbial-driven process of SOC accrual; a practical validation of this postulation is however missing. Against this background, we evaluated the effect of agricultural management and site-specific soil chemical and physical properties on microbial physiology (i.e., respiration, bacterial and fungal growth rates, and microbial biomass turnover) and CUE by an on-farm comparison of conventional farming, conservation farming and unmanaged reference soil systems (i.e., adjacent field margins) at twenty-one sites across three soil depths. We show that a change in agricultural management towards soil health regeneration has a significant impact on microbial physiology. Bacterial growth, respiration and microbial biomass turnover increased from conventional farming towards conservation farming systems to reference soils. The opposite trend however was found for fungal growth and microbial CUE, with highest values observed in conventional farming systems. This clearly contradicts the prevailing idea that higher microbial CUE in conservation farming systems may be associated with higher SOC contents. Our results further show that soil physical and chemical parameters such as soil pH, texture and dissolved carbon compounds strongly predict microbial CUE. In line with these results, functional pore domains showed specific optima for microbial growth and CUE. For example, a high share of small pore domains hampered fungal growth and reduced microbial CUE but facilitated microbial biomass turnover at the same time. Thus, we suggest that – superimposed upon agricultural management effects – habitat structural conditions and microbial carbon limitation mainly shape microbial physiology and CUE in arable soil systems.

Single-cell measurement of microbial growth rate with Raman microspectroscopy.

Rates of microbial growth are fundamental to understanding environmental geochemistry and ecology. However, measuring the heterogeneity of microbial activity at the single-cell level, especially within complex populations and environmental matrices, remains a forefront challenge. Stable isotope probing (SIP) is a method for assessing microbial growth and involves measuring the incorporation of an isotopic label into microbial biomass. Here, we assess Raman microspectroscopy as a SIP technique, specifically focusing on the measurement of deuterium (2H), a tracer of microbial biomass production. We correlatively measured cells grown in varying concentrations of deuterated water with both Raman spectroscopy and nanoscale secondary ion mass spectrometry (nanoSIMS), generating isotopic calibrations of microbial 2H. Relative to Raman, we find that nanoSIMS measurements of 2H are subject to substantial dilution due to rapid exchange of H during sample washing. We apply our Raman-derived calibration to a numerical model of microbial growth, explicitly parameterizing the factors controlling growth rate quantification and demonstrating that Raman-SIP can sensitively measure the growth of microorganisms with doubling times ranging from hours to years. The measurement of single-cell growth with Raman spectroscopy, a rapid, nondestructive technique, represents an important step toward application of single-cell analysis into complex sample matrices or cellular assemblages.

Biokinetic and microbial insights into regulatory mechanisms of long-chain fatty acid degradation during food waste-lipid co-digestion within anaerobic membrane bioreactor

This study investigated the effects of varying lipid ratios on the anaerobic co-digestion of high-lipid food waste (FW) in a mesophilic anaerobic membrane bioreactor (AnMBR). At a lipid concentration of 5 %, optimal biogas production (3.84 L/L/d) and lipid removal efficiency (78 %) were achieved; however, increasing lipid concentrations resulted in significant accumulations of long-chain fatty acids (LCFAs) and volatile fatty acids (VFAs). Batch tests further demonstrated the impact of various types of LCFAs, with stearic acid showing the slowest microbial growth rate (0.033d-1), confirming its role in the accumulation of acetate-dominated VFAs, potentially limiting the methanogenesis process at elevated lipid levels. Furthermore, at 8 % lipid content, the downregulation of key LCFA degradation enzymes and dominance of hydrogenotrophic methanogens indicated adverse conditions. The importance of the intricate interplay between LCFA degradation kinetics and microbial community for the system efficiency was evidenced, offering insights for optimizing and managing high-lipidic wastes.

Environment and microbiome drive different microbial traits and functions in the macroscale soil organic carbon cycle.

Soil microbial traits and functions play a central role in soil organic carbon (SOC) dynamics. However, at the macroscale (regional to global) it is still unresolved whether (i) specific environmental attributes (e.g., climate, geology, soil types) or (ii) microbial community composition drive key microbial traits and functions directly. To address this knowledge gap, we used 33 grassland topsoils (0-10 cm) from a geoclimatic gradient in Chile. First, we incubated the soils for 1 week in favorable standardized conditions and quantified a wide range of soil microbial traits and functions such as microbial biomass carbon (MBC), enzyme kinetics, microbial respiration, growth rates as well as carbon use efficiency (CUE). Second, we characterized climatic and physicochemical properties as well as bacterial and fungal community composition of the soils. We then applied regression analysis to investigate how strongly the measured microbial traits and functions were linked with the environmental setting versus microbial community composition. We show that environmental attributes (predominantly the amount of soil organic matter) determined patterns of MBC along the gradient, which in turn explained microbial respiration and growth rates. However, respiration and growth normalized for MBC (i.e., specific respiration and growth) were more linked to microbial community composition than environmental attributes. Notably, both specific respiration and growth followed distinct trends and were related to different parts of the microbial community, which in turn resulted in strong effects on microbial CUE. We conclude that even at the macroscale, CUE is the result of physiologically decoupled aspects of microbial metabolism, which in turn is partially determined by microbial community composition. The environmental setting and microbial community composition affect different microbial traits and functions, and therefore both factors need to be considered in the context of macroscale SOC dynamics.

Interactions of graphene oxide with the microbial community of biologically active filters from a water treatment plant

With widespread occurrence and increasing concern of emerging contaminants (CECs) in source water, biologically active filters (BAF) have been gaining acceptance in water treatment. Both BAFs and graphene oxide (GO) have been shown to be effective in treating CECs. However, studies to date have not addressed interactions between GO and microbial communities in water treatment processes such as BAFs. Therefore, in the present study, we investigated the effect of GO on the properties and microbial growth rate in a BAF system. Synthesized GO was characterized with a number of tools, including scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Raman spectrometry. GO exhibited the characteristic surface functional groups (i.e., C-OH, C=O, C-O-C, and COOH), crystalline structure, and sheet-like morphology. To address the potential toxicity of GO on the microbial community, reactive oxygen species (ROS) generation was measured using nitro blue tetrazolium (NBT) assay. Results revealed that during the exponential growth phase, ROS generation was not observed in the presence of GO compared to the control batch. In fact, the adenosine triphosphate (ATP) concentrations increased in the presence of GO (25 μg/L - 1000 μg/L) compared to the control without GO. The growth rate in systems with GO exceeded the control by 20 % to 46 %. SEM images showed that GO sheets can form an effective scaffold to promote bacterial adhesion, proliferation, and biofilm formation, demonstrating its biocompatibility. Next-generation sequencing (Illumina MiSeq) was used to characterize the BAF microbial community, and high-throughput sequencing analysis confirmed the greater richness and more diverse microbial communities compared to systems without GO. This study is the first to report the effect of GO on the microbial community of BAF from a water treatment plant, which provides new insights into the potential of utilizing a bio-optimized BAF for advanced and sustainable water treatment or reuse strategies.

A mathematical model-based evaluation of yeast extract’s effects on microbial growth and substrate consumption for lactic acid production by Bacillus coagulans

The microbial production of lactic acid, a crucial platform chemical for the development of biobased products, aims to replace fossil-based materials, although current production costs remain relatively high. Fermentation requires the addition of yeast extract (YE) to exclude nutritional lag, which increases the cost of production; therefore, optimizing its amount is essential. This study explores batch fermentation with varying concentrations of YE (5 %, 10 %, 15 % and 20 %) in a medium using the strain Bacillus coagulans A166 to produce lactic acid from glucose. The results reveal that the level of YE significantly influences the product yield, substrate consumption rate, and process productivity. The kinetic model applied to experimental data indicates that higher YE concentrations lead to increased glucose uptake and microbial growth rates, while concentrations exceeding 10 % result in reduced performance. It was determined that a concentration of 10 % YE in the medium delivered the highest maximum specific rates for glucose consumption and microbial growth, leading to a 0.99 g/g yield of glucose lactic acid. Furthermore, a real-time monitoring strategy for glucose consumption and lactic acid formation was established using a mathematical model based on the rate of alkaline consumption throughout fermentation. The cross-validation results demonstrate the reliability of this approach, with mean absolute errors (expressed as a percentage of the concentration range) for the prediction of glucose ranging from 2.8 % to 5.0 % and for the prediction of lactic acid ranging from 3.4 % to 5.4 %.

Environment-independent distribution of mutational effects emerges from microscopic epistasis.

Predicting how new mutations alter phenotypes is difficult because mutational effects vary across genotypes and environments. Recently discovered global epistasis, where the fitness effects of mutations scale with the fitness of the background genotype, can improve predictions, but how the environment modulates this scaling is unknown. We measured the fitness effects of ~100 insertion mutations in 42 strains of Saccharomyces cerevisiae in six laboratory environments and found that the global-epistasis scaling is nearly invariant across environments. Instead, the environment tunes one global parameter, the background fitness at which most mutations switch sign. As a consequence, the distribution of mutational effects is predictable across genotypes and environments. Our results suggest that the effective dimensionality of genotype-to-phenotype maps across environments is surprisingly low.

Compared to histamine-2 receptor antagonist, proton pump inhibitor induces stronger oral-to-gut microbial transmission and gut microbiome alterations: a randomised controlled trial

ObjectiveWe aim to compare the effects of proton pump inhibitors (PPIs) and histamine-2 receptor antagonists (H2RAs) on the gut microbiota through longitudinal analysis.DesignHealthy volunteers were randomly assigned to receive either...

Microbial central carbon metabolism in a tidal freshwater marsh and an upland mixed conifer soil under oxic and anoxic conditions.

The central carbon (C) metabolic network is responsible for most of the production of energy and biosynthesis in microorganisms and is therefore key to a mechanistic understanding of microbial life in soil communities. Many upland soil communities have shown a relatively high C flux through the pentose phosphate (PP) or the Entner-Doudoroff (ED) pathway, thought to be related to oxidative damage control. We tested the hypothesis that the metabolic organization of the central C metabolic network differed between two ecosystems, an anoxic marsh soil and oxic upland soil, and would be affected by altering oxygen concentrations. We expected there to be high PP/ED pathway activity under high oxygen concentrations and in oxic soils and low PP/ED activity in reduced oxygen concentrations and in marsh soil. Although we found high PP/ED activity in the upland soil and low activity in the marsh soil, lowering the oxygen concentration for the upland soil did not reduce the relative PP/ED pathway activity as hypothesized, nor did increasing the oxygen concentration in the marsh soil increase the PP/ED pathway activity. We speculate that the high PP/ED activity in the upland soil, even when exposed to low oxygen concentrations, was related to a high demand for NADPH for biosynthesis, thus reflecting higher microbial growth rates in C-rich soils than in C-poor sediments. Further studies are needed to explain the observed metabolic diversity among soil ecosystems and determine whether it is related to microbial growth rates.IMPORTANCEWe observed that the organization of the central carbon (C) metabolic processes differed between oxic and anoxic soil. However, we also found that the pentose phosphate pathway/Entner-Doudoroff (PP/ED) pathway activity remained high after reducing the oxygen concentration for the upland soil and did not increase in response to an increase in oxygen concentration in the marsh soil. These observations contradicted the hypothesis that oxidative stress is a main driver for high PP/ED activity in soil communities. We suggest that the high PP/ED activity and NADPH production reflect higher anabolic activities and growth rates in the upland soil compared to the anaerobic marsh soil. A greater understanding of the molecular and biochemical processes in soil communities is needed to develop a mechanistic perspective on microbial activities and their relationship to soil C and nutrient cycling. Such an increased mechanistic perspective is ecologically relevant, given that the central carbon metabolic network is intimately tied to the energy metabolism of microbes, the efficiency of new microbial biomass production, and soil organic matter formation.

The size and diversity of microbes determine carbon use efficiency in soil.

Soil is home to a multitude of microorganisms from all three domains of life. These organisms and their interactions are crucial in driving the cycling of soil carbon. One key indicator of this process is Microbial Carbon Use Efficiency (CUE), which shows how microbes influence soil carbon storage through their biomass production. Although CUE varies among different microorganisms, there have been few studies that directly examine how biotic factors influence CUE. One such factor could be body size, which can impact microbial growth rates and interactions in soil, thereby influencing CUE. Despite this, evidence demonstrating a direct causal connection between microbial biodiversity and CUE is still scarce. To address these knowledge gaps, we conducted an experiment where we manipulated microbial body size and biodiversity through size-selective filtering. Our findings show that manipulating the structure of the microbial community can reduce CUE by approximately 65%. When we restricted the maximum body size of the microbial community, we observed a reduction in bacterial diversity and functional potential, which in turn lowered the community's CUE. Interestingly, when we included large body size micro-eukarya in the soil, it shifted the soil carbon cycling, increasing CUE by approximately 50% and the soil carbon to nitrogen ratio by about 25%. Our metrics of microbial diversity and community structure were able to explain 36%-50% of the variation in CUE. This highlights the importance of microbial traits, community structure and trophic interactions in mediating soil carbon cycling.

Soil cover shapes organic matter pools and microbial communities in soils of maritime Antarctica

Bryophytes and biological soil crusts (biocrusts) are the two major biological soil cover types of maritime Antarctica and play a crucial role for key ecosystem functions in the barely vegetated and little developed soils. Besides their profound impacts on nutrient cycling, they also provide habitats and activity hotspots for unique soil microbial communities. Yet, the effects of biological soil cover on the physical and chemical soil environment and belowground microbial communities have not been comprehensively studied in this fragile ecosystem.We here address the research question how biocrusts and mosses shape the quantity and structure of the soil organic matter pool, and the activity and composition of subjacent microbial communities. Towards this end, we sampled soils under two common, but physiologically distinct moss species, Polytrichastrum alpinum and Sanionia unicinata, and adjacent biological soil crusts at two sites on Deception Island, South Shetland Islands.We found that biocrusts and mosses differentially influenced central soil properties and subjacent soil microbial communities. All major SOM compound groups (carbohydrates, aromatics and phenols, lipids, N-containing polymers) as well as microbial biomass were more abundant in soil under biocrusts. However, microbial mass-specific growth rates were higher in soil under mosses. Our results showed moss-species-specific effects in addition to effects of soil cover type, as P. alpinum affected the activity and structure of soil microbial communities and the composition of soil organic matter stronger than S. unicinata.Our study highlights the interconnectedness between soil cover and soil biogeochemistry, which is crucial for deepening our understanding of belowground functioning in Antarctic soils. This linkage is of particular importance in the context of ongoing rapid climate change on the Antarctic Peninsula, as future shifts in the distribution and abundance of soil cover may substantially impact multiple soil processes in this vulnerable ecosystem.

Exploring the potential of melittin peptide: Expression, purification, anti-pathogenic properties, and promising applications as a bio-preservative for beef slices

Melittin peptide is a short cationic linear peptide derived from honey bee venom with 26 amino acids, demonstrates potential in controlling and eliminating pathogens. In this study, the genetic sequence of melittin was inserted into the pcDNA3.1+ plasmid and expressed in HEK-293 cells with a His-tag. Purification was done through affinity chromatography and a nickel column. In this study, the antimicrobial effect of melittin in beef sirloin was first investigated, and the minimum inhibitory concentration (MIC) was determined. Then, the effect of combining it with nanochitosan (n-CH) coating, melittin (0.1% and 0.2%v/v), and nanochitosan alone on the physicochemical, microbiological, and sensory properties of beef was examined over a 9-day at 4 °C. At the end of the storage period, the coated samples effectively prevented an increase in pH (5.75 ± 0.06) and showed a significant decrease in the peroxide value (PV) (4.50 ± 0.07). The most favorable result was observed when using the n-CH+0.2%M, which led to malondialdehyde level of 0.44 ± 0.0.05 mg/kg in the amount of thiobarbituric acid reactant. Additionally, the total volatile base nitrogen content in the treatment involving 0.2%M and n-CH+0.2% and 0.1%M was deemed acceptable. Although the total viable count (TVC) of microorganisms in samples covered with melittin increased over time (7.88 ± 0.12 CFU/g), the microbial growth rate in these samples was lower than the control sample (12.10 ± 0.13 CFU/g). Therefore, the use of nanochitosan based edible coatings in combination with melittin in meat packaging reduces microbial population and increases its shelf life.

Whole genome sequencing revealed the capability of Paenarthrobacter sp. KN0901 to simultaneously remove atrazine and corn straw at low temperatures: From gene identification to empirical validation

Corn planting is often associated with serious atrazine pollution and excessive corn straw amounts, causing severe threats to environmental and ecological security, as well as to green agricultural development. In this context, a Paenarthrobacter sp. KN0901 strain was applied to simultaneously remove atrazine and straw at low temperatures. The results of whole genome sequencing indicated that KN0901 encoded over nine straw biodegradation-related enzymes. In addition, 100 % and 27.3 % of atrazine and straw were simultaneously degraded by KN0901 following an incubation period of seven days at 15 ºC and 180 rpm in darkness. The KN0901 strain maintained high atrazine and straw biodegradation rates under temperature and pH ranges of 4–25 ºC and 5–9, respectively. The simultaneous atrazine and corn straw additions improved the microbial growth and biodegradation rates by increasing the functional gene expression level, cell viability, inner membrane permeability, and extracellular polymeric substance contents of KN0901. The hydroponic experiment results demonstrated the capability of the KN0901 strain to mitigate the toxicity of atrazine to soybeans in four days under the presence of corn straw. The present study provides a new perspective on the development of bioremediation approaches and their application to restore atrazine-polluted cornfields with large straw quantities, particularly in cold areas.

Role of phosphate in microalgal-bacterial symbiosis system treating wastewater containing heavy metals

Phosphorus is one of the important factors to successfully establish the microalgal-bacterial symbiosis (MABS) system. The migration and transformation of phosphorus can occur in various ways, and the effects of phosphate on the MABS system facing environmental impacts like heavy metal stress are often ignored. This study investigated the roles of phosphate on the response of the MABS system to zinc ion (Zn2+). The results showed that the pollutant removal effect in the MABS system was significantly reduced, and microbial growth and activity were inhibited with the presence of Zn2+. When phosphate and Zn2+ coexisted, the inhibition effects of pollutants removal and microbial growth rate were mitigated compared to that of only with the presence of Zn2+, with the increasing rates of 28.3% for total nitrogen removal, 48.9% for chemical oxygen demand removal, 78.3% for chlorophyll-a concentration, and 13.3% for volatile suspended solids concentration. When phosphate was subsequently supplemented in the MABS system after adding Zn2+, both pollutants removal efficiency and microbial growth and activity were not recovered. Thus, the inhibition effect of Zn2+ on the MABS system was irreversible. Further analysis showed that Zn2+ preferentially combined with phosphate could form chemical precipitate, which reduced the fixation of MABS system for Zn2+ through extracellular adsorption and intracellular uptake. Under Zn2+ stress, the succession of microbial communities occurred, and Parachlorella was more tolerant to Zn2+. This study revealed the comprehensive response mechanism of the co-effects of phosphate and Zn2+ on the MABS system, and provided some insights for the MABS system treating wastewater containing heavy metals, as well as migration and transformation of heavy metals in aquatic ecosystems.

Effect of Dietary Supplementation with Lactiplantibacillus plantarum I On Queen Scallop Aequipecten opercularis Under Simulated Climate Change Conditions

Abstract This study examined the effects of dietary supplementation of queen scallop Aequipecten opercularis with an indigenous strain of lactic acid bacteria (LAB), Lactiplantibacillus plantarum I, previously isolated from its digestive tract, on gut microbial populations and growth rates during cultivation under simulated climate change conditions (pH 7.8, T = 16 ± 2 °C). After one month of feeding, the results showed a noticeable reduction in aquaculture diseases causing pathogens while maintaining sufficient viable Lpb. plantarum I cells. A higher pH and temperature resulted in higher growth rates, measured by the weight and length of scallops, compared to the control group. The results obtained shed light on the influence of the addition of lactic acid bacteria on the growth of bivalve mollusks under normal and climate change conditions, and provide control of pathogenic microorganisms. In the context of climate change, host-pathogen interactions need to be recognized and put under control by applying natural solutions to minimize the environmental footprint.