Tolerant Bacteria Research Articles

Biofilm forming rhizobacteria affect the physiological and biochemical responses of wheat to drought

Plant growth promoting rhizobacteria (PGPR) can attenuate the adverse effects of water deficit on plant growth. Since drought stress tolerance of bacteria has earlier been associated to biofilm formation, we aimed to investigate the role of bacterial biofilm formation in their PGPR activity upon drought stress. To this end, a biofilm-forming bacterial collection was isolated from the rhizospheres of native arid grassland plants, and characterized by their drought tolerance and evaluated on their plant growth promoting properties. Most bacterial strains formed biofilm in vitro. Most isolates were drought tolerant, produced auxins, showed 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity and solubilized mineral phosphate and potassium, but at considerably different levels. Greenhouse experiments with the most promising isolates, B1, B2 and B3, under three levels of water deficit and two wheat varieties led to an increased relative water content and increased harvest index at both moderate and severe water deficit. However, the bacteria did not affect these plant parameters upon regular watering. In addition, decreased hydrogen peroxide levels and increased glutathione S-transferase activity occurred under water deficit. Based on these results, we conclude that by improving root traits and antioxidant defensive system of wheat, arid grassland rhizospheric biofilm forming bacilli may promote plant growth under water scarcity.

Changes in fatty acid composition as a response to glyphosate toxicity in Pseudomonas fluorescens

Excessive use of herbicides decreases soil biodiversity and fertility. The literature on the xenobiotic response by microorganisms is focused on herbicide biodegradation as a selective event. Non-degradation systems independent of selection could allow the survival of tolerant bacteria in contaminated environments, impacting xenobiotic turnover and, consequently, bioremediation strategies. However, it is uncertain whether the response based on these systems requires selective pressure to be effective. The objective here was to analyze non-degradation phenotypes, enzymatic and structural response systems, of Pseudomonas fluorescens CMA-55 strain, already investigated the production pattern of quorum sensing molecules in response to glyphosate, not present at the isolation site. One mode of response was associated with decrease in membrane permeability and effective antioxidative response for 0–2.30 mM glyphosate, at the mid-log growing phase, with higher activities of Mn-SOD, KatA, and KatB, and presence of fatty acids as nonadecylic acid, margaric and lauric acid. The second response system was characterized by lower antioxidative enzymes activity, presence of KatC isoform, and pelargonic, capric, myristic, stearic, palmitoleic and palmitic acid as principal fatty acids, allowing the strain to face stressful conditions in 9.20–11.50 mM glyphosate at the stationary phase. Therefore, the bacterial strain could modify the fatty acid composition and the permeability of membranes in two response modes according to the herbicide concentration, even glyphosate was not previously selective for P. fluorescens, featuring a generalist system based on physiological plasticity.

A systematic review on chlorine tolerance among bacteria and standardization of their assessment protocol in wastewater.

Though chlorine is a cost-effective disinfectant for water and wastewaters, the bacteria surviving after chlorination pose serious public health and environmental problems. This review critically assesses the mechanism of chlorine disinfection as described by various researchers; factors affecting chlorination efficacy; and the re-growth potential of microbial contaminations in treated wastewater post chlorination to arrive at meaningful doses for ensuring health safety. Literature analysis shows procedural inconsistencies in the assessment of chlorine tolerant bacteria, making it extremely difficult to compare the tolerance characteristics of different reported tolerant bacteria. A comparison of logarithmic reduction after chlorination and the concentration-time values for prominent pathogens led to the generation of a standard protocol for the assessment of chlorine tolerance. The factors that need to be critically monitored include applied chlorine doses, contact time, determination of chlorine demands of the medium, and the consideration of bacterial counts immediately after chlorination and in post chlorinated samples (regrowth). The protocol devised here appropriately assesses the chlorine-tolerant bacteria and urges the scientific community to report the regrowth characteristics as well. This would increase the confidence in data interpretation that can provide a better understanding of chlorine tolerance in bacteria and aid in formulating strategies for effective chlorination.

Isolation and Molecular identification of Phenol tolerating bacteria from petroleum contaminated sites

This research was conducted to isolate and identify phenol tolerating bacteria from petroleum contaminated sites. Two bacterial species were isolated from petroleum contaminated sites (NWPK and NWPKD). The isolation was based on morphological, microscopic and molecular identification. The total viable counts of phenol utilizing bacteria from NWPK and NWPKD are 2.71x107 and 4.0x106 cfu/g respectively. The isolates showed capacity of phenol tolerance at 500 mg/L, 1000 mg/L and 1500 mg/L when grown on phenol tolerant nutrient agar. The NWPK showed its capacity to tolerate phenol at 2.3x107, 2.5x107 and 1.0x107 cfu/g of 500, 1000 and 1500 mg/L of phenol concentration respectively while NWPKD tolerate 1.5x107, 3.8x107 and 1.0x107 cfu/g of 500, 1000 and 1500 mg/L of phenol respectively. The isolates were identified as Citrobacter and Acinetobacter species respectively based on 16S rRNA gene sequence analysis. These isolates showed their ability to withstand and survive high phenol concentrations in the environment.

Responsive change of crop-specific soil bacterial community to cadmium in farmlands surrounding mine area of Southeast China

In arable soils co-influenced by mining and farming, soil bacteria significantly affect metal (Cadmium, Cd) bioavailability and accumulation. To reveal the soil microecology response under this co-influence, three intersection areas (cornfield, vegetable field, and paddy field) were investigated. With a similar nutrient condition, the soils showed varied Cd levels (0.31–7.70 mg/kg), which was negatively related to the distance from mining water flow. Different soils showed varied microbial community structures, which were dominated by Chloroflexi (19.64–24.82%), Actinobacteria (15.49–31.96%), Acidobacteriota (9.46–20.31%), and Proteobacteria (11.88–14.57%) phyla. A strong correlation was observed between functional microbial taxon (e. g. Acidobacteriota), soil physicochemical properties, and Cd contents. The relative abundance of tolerant bacteria including Vicinamibacteraceae, Knoellia, Ardenticatenales, Lysobacter, etc. elevated with the increase of Cd, which contributed to the enrichment of heavy metal resistance genes (HRGs) and integration genes (intlI), thus enhancing the resistance to heavy metal pollution. Cd content rather than crop species was identified as the dominant factor that influenced the bacterial community. Nevertheless, the peculiar agrotype of the paddy field contributed to its higher HRGs and intlI abundance. These results provided fundamental information about the crop-specific physiochemical-bacterial interaction, which was helpful to evaluate agricultural environmental risk around the intersection of farmland and pollution sources.

Biosynthesis of a water solubility-enhanced succinyl glucoside derivative of luteolin and its neuroprotective effect.

SummaryThe natural flavonoids luteolin and luteoloside have anti‐bacterial, anti‐inflammatory, anti‐oxidant, anti‐tumour, hypolipidemic, cholesterol lowering and neuroprotective effects, but their poor water solubility limits their application in industrial production and the pharmaceutical industry. In this study, luteolin‐7‐O‐β‐(6″‐O‐succinyl)‐d‐glucoside, a new compound that was prepared by succinyl glycosylation of luteolin by the organic solvent tolerant bacterium Bacillus amyloliquefaciens FJ18 in an 8.0% DMSO (v/v) system, was obtained and identified. Its greater water solubility (2293 times that of luteolin and 12 232 times that of luteoloside) provides the solution to the application problems of luteolin and luteoloside. The conversion rate of luteolin (1.0 g l−1) was almost 100% at 24 h, while the yield of luteolin‐7‐O‐β‐(6″‐O‐succinyl)‐d‐glucoside reached 76.2%. In experiments involving the oxygen glucose deprivation/reoxygenation injury model of mouse hippocampal neuron cells, the cell viability was significantly improved with luteolin‐7‐O‐β‐(6″‐O‐succinyl)‐d‐glucoside dosing, and the expressions of the anti‐oxidant enzyme HO‐1 in the nucleus increased, providing a neuroprotective effect for ischemic cerebral cells. The availability of biosynthetic luteolin‐7‐O‐β‐(6″‐O‐succinyl)‐d‐glucoside, which is expected to replace luteolin and luteoloside, would effectively expand the clinical application value of luteolin derivatives.

Repeated introduction of micropollutants enhances microbial succession despite stable degradation patterns

The increasing-volume release of micropollutants into natural surface waters has raised great concern due to their environmental accumulation. Persisting micropollutants can impact multiple generations of organisms, but their microbially-mediated degradation and their influence on community assembly remain understudied. Here, freshwater microbes were treated with several common micropollutants, alone or in combination, and then transferred every 5 days to fresh medium containing the same micropollutants to mimic the repeated exposure of microbes. Metabarcoding of 16S rRNA gene makers was chosen to study the succession of bacterial assemblages following micropollutant exposure. The removal rates of micropollutants were then measured to assess degradation capacity of the associated communities. The degradation of micropollutants did not accelerate over time but altered the microbial community composition. Community assembly was dominated by stochastic processes during early exposure, via random community changes and emergence of seedbanks, and deterministic processes later in the exposure, via advanced community succession. Early exposure stages were characterized by the presence of sensitive microorganisms such as Actinobacteria and Planctomycetes, which were then replaced by more tolerant bacteria such as Bacteroidetes and Gammaproteobacteria. Our findings have important implication for ecological feedback between microbe-micropollutants under anthropogenic climate change scenarios.

Chimeric Ligands of Pili and Lectin A Inhibit Tolerance, Persistence, and Virulence Factors of Pseudomonas aeruginosa over a Wide Range of Phenotypes.

Bacteria readily form resilient phenotypes to counter environmental and antibiotic stresses. Here, we demonstrate a class of small molecules that inhibit a wide range of Pseudomonas aeruginosa phenotypes and enable antibiotics to kill previously tolerant bacteria, preventing the transition of tolerant bacteria into a persistent population. We identified two proteins, type IV pili and lectin LecA, as receptors for our molecules by methods including a new label-free assay based on bacterial motility sensing the chemicals in the environment, the chemical inhibition of bacteriophage adsorption on pili appendages of bacteria, and fluorescence polarization. Structure–activity relationship studies reveal a molecule that inhibits only pili appendage and a class of chimeric ligands that inhibit both LecA and pili. Important structural elements of the ligand are identified for each protein. This selective ligand binding identifies the phenotypes each protein receptor controls. Inhibiting LecA results in reducing biofilm formation, eliminating small colony variants, and is correlated with killing previously tolerant bacteria. Inhibiting pili appendages impedes swarming and twitching motilities and pyocyanin and elastase production. Because these phenotypes are controlled by a broad range of signaling pathways, this approach simultaneously controls the multiple signaling mechanisms preventing bacteria to elude antibiotic treatments.

Pseudomonas citronellolis alleviates arsenic toxicity and maintains cellular homeostasis in chickpea (Cicer arietinum L.)

Arsenic is a hazardous metalloid that causes detrimental effects on plant growth and metabolism. Plants accumulate arsenic in edible parts that consequently enter the food chain leading to many health problems. Metal tolerant plant growth-promoting bacteria (PGPB) ameliorate heavy metal toxicity. In this study, the effect of arsenic (As5+) and the role of PGPB Pseudomonas citronellolis (PC) in mitigating As5+ toxicity and associated metabolic alterations in chickpea were assessed. Five chickpea varieties (PBG1, GPF2, PDG3, PDG4 and PBG5) were evaluated for arsenic accumulation, translocation, and its interference with metabolic and defense processes. As5+ (40 mg kg−1) interfered with plant metabolism and enhanced the antioxidative and carbohydrate metabolizing enzyme's activity but PC treatment maintained the activity at par with control. PC also facilitated the accumulation of As5+ in the root system and restricted its translocation to the shoot. Further, to map the metabolic changes, Gas chromatography Mass Spectroscopy (GC-MS) based metabolite profiling and gene expression analysis (qRT-PCR) were performed in the best and worst-performing chickpea varieties (PBG1 and PBG5). 48 metabolites of various metabolic pathways (amino acid, carbohydrate, and fatty acid) were altered in As5+ and PC treatment. Gene expressions showed correlation with biochemical analysis of the antioxidative enzymes and carbohydrate metabolizing enzymes while PC treatment improved chlorophyll biosynthesis enzyme CaDALA expression in As5+ treated plants. Therefore, PC mitigates As5+ toxicity by restricting it in the roots thereby maintaining the cellular homeostasis under As5+ stress in chickpeas.

The Composition of Bile Acids under Fatty Liver Model in Chicken

Bile acids is synthesized by cholesterol in the liver and exert by two different pathways, classical and alternative pathway. Two major enzymes, CYP7A1 and CYP27A1 play regulatory roles in two pathways. CA (cholic acid) and CDCA (chenodeoxycholic acid) as known as the primary bile acids which means they are major products in these two pathways and then they can be modified by gut microbiome. After modifying, the metabolites are called secondary bile acids such as lithocholic acid (LCA)、deoxycholic acid (DCA). Some researchers found that total bile acids including primary and secondary bile acids elevate in serum from non‐alcoholic fatty liver (NAFL). However, the composition of bile acids in chickens upon fatty liver model is unclear.In current study, seven‐week‐old ISA chicken were assigned to two group, there are control group (C) (n=10) and cholesterol with low choline (CLC) group (n=10). The control group was fed with extra 0.05% choline and without cholesterol, the other group was fed with extra 2% cholesterol and without choline for six weeks to simulate as NAFL. After sacrificing, we collected serum and cecum contents to quantitation of bile acids by mass spectrometer and analyze gut microbiome by 16S amplicon sequencing. The gene expression pattern of bile acid synthetic enzymes and related transcription factors was also determined by real‐time PCR.The bile acids in serum, such as TCDCA (C:CLC=6080.15nM:14555.75nM)、TLCA (C:CLC=122.31nM:2122.62nM)、5β‐Cholenic Acid‐7α‐ol‐3‐one (C:CLC=1.04nM:3.87nM)、CDCA (C:CLC=3.93nM:38.13nM) are significantly elevated in CLC group and the bile acids in cecum contents such as, TLCA (C:CLC=109.8nM:8897.27nM)、TUDCA (C:CLC=15.82nM:985.0nM)、THDCA(C:CLC=718.72nM:3084.36nM)、LCA(C:CLC=4.32nM:22.88nM)、TDCA(C:CLC=10.12nM:172.28nM) are significantly increased in CLC group. The results of gene expression showed that CYP7A1 and CYP8B1 were increased in CLC group compared than control. For gut microbiome, the proportion of bile acid tolerance bacteria Alistipes in the CLC group is 9.13% which is 1.69% higher than the control group.The pleiotropic roles of bile acid have gradually been valued. In this study, we analyzed the composition of bile acids under the fatty liver of chickens. We also found that the concentration of taurine conjugated bile acid in chickens is much higher than that of glycine.

Bacterial inoculations mitigate different forms of iron (Fe) stress and enhance nutrient uptake in rice seedlings (Oryza sativa L.)

Iron (Fe) is an essential micronutrient required by plants for various physiological processes. However, the accumulation of excessive Fe affects plant growth and agricultural productivity. In the present study, 250 iron tolerant bacteria (ITB) were isolated from 25 soil samples, screened for plant growth-promoting properties and identified based on 16S rRNA gene sequencing. A pot study experiment using rice plants amended with three forms of Fe (FeSO4, FeCl3 and [Fe(NH4)2(SO4)2]) revealed the enhancement of root and shoot length ranged from 42.67%–177.35% and 88.10%–119.19% in FeSO4 amended soil, 64.25%–161.54% and 81.07%–124.46% in FeCl3 soil and 66.65%–159.60% and 69.04%–119.70% in Fe(NH4)2(SO4)2 compared to control and non-inoculated plants. Further, the ITB inoculated seedling showed enhanced N uptake 0-4 fold and P content 1-2 fold compared to control. Similar enhancement of Fe mobilization was also observed for soils amended with FeSO4 (2-4 fold in the root and 2-3.5 in the shoot), FeCl3 (2.5-6 and 2-5 fold) and Fe(NH4)2(SO4)2 (2-5 and 0-2 fold). The estimation of and Fe2＋ and Fe3＋ revealed that Fe2+ uptake in the ITB inoculated roots and shoots of rice plant ranged to 4-7.85 ppm compared to control (0.55-18.36 ppm). Whereas the Fe3＋ uptake was ranged to 20.52-58.15 ppm in roots and 0.70-47.61 ppm in shoots compared to control (0.67-1.95 and 0.25-3.12 ppm). Enhanced chlorophyll contents (p ≤ 0.05) was also observed in the inoculated plants. The present study demonstrated that the inoculation of ITB improved the sequestration of Fe from the soils and mitigated the Fe stress in rice plants.

Synthesis of silver nanoparticles with high efficiency and stability by culture supernatant of Bacillus ROM6 isolated from Zarshouran gold mine and evaluating its antibacterial effects

BackgroundThe use of bacteria to synthesize nanoparticles as an environment-friendly method has recently been considered by researchers. Bacteria residing in different mines have shown high potential in the synthesis of metal nanoparticles due to their compatibility with the environment. The aim of this study was to evaluate the ability of Zarshouran gold mine bacteria to synthesize silver nanoparticles and their antibacterial activity.MethodsAfter isolation of mine bacteria and several screening steps, silver ion tolerant bacteria that were able to synthesize extracellular silver nanoparticles were isolated and the most suitable isolate was selected and sequenced. The characteristics, stability, and production efficiency of silver nanoparticles were evaluated using UV–vis spectrophotometry, DLS, TEM, FTIR, and X-ray diffraction analysis. Finally, the antibacterial effect of silver nanoparticles against pathogenic bacteria was investigated.ResultsAmong the eight silver-tolerant bacteria, isolate No. 6 had high antibacterial activity and high potential in the synthesis and stabilization of silver nanoparticles. Therefore, this isolate was selected for the next experiments. The results of 16S rDNA sequencing showed that this isolate is related to Bacillus pumilus. We registered in the NCBI Bank called ROM6 with access number MW440543. The DLS and TEM analysis showed that silver nanoparticles produced by this isolate were most spherical with a size of less than 25 nm and were stable for at least 180 days. The efficiency at concentrations less than 0.9 g/l silver nitrate was over 90% and the minimum inhibition concentration of nanoparticles was determined against S. aureus, E. coli, P. aeruginosa, and A. baumannii ranging from 1.4 to 5.6 µg/ml.ConclusionWe found that the bacteria residing in the gold mine have a high capacity for the synthesis of spherical and high stable silver nanoparticles with a strong antibacterial effect.

Non-caloric artificial sweeteners exhibit antimicrobial activity against bacteria and promote bacterial evolution of antibiotic tolerance

Non-caloric artificial sweeteners are being widely used as safe table sugar substitutes with highly intensive sweetness but low calories. Previous studies have suggested that some of the sweeteners can alter the gut microbiota composition and promote horizontal transfer of antibiotic resistance genes across bacterial genera. However, little is known about whether these sweeteners could show antibiotic-like antimicrobial activity against bacteria, especially gut relevant bacteria. Whether they could affect evolutional trajectory of antibiotic resistance or tolerance in bacteria is also not clear yet. Here we investigated four commonly used artificial sweeteners (saccharin, sucralose, aspartame, and acesulfame potassium) against both Gram-negative (Escherichia coli and Klebsiella pneumoniae) and positive (Bacillus subtilis) strains. Results show that all four sweeteners exhibit antimicrobial effects on these strains. The antimicrobial mechanism is due to increased reactive oxygen species (ROS) and cell envelope damage. Compared to sucrose and glucose, the treatment of artificial sweeteners stimulates bacterial efflux pumps and promotes bacterial evolution of antibiotic tolerance. Collectively, our finding provides insights into roles of artificial sweeteners in the emergence of antibiotic tolerance and calls for a re-evaluation of risks due to their intensive usage.

In vitro Sequestration of Molecular and Mass Spectra Characterized Metallophilic Cadmium Tolerant Bacteria for Sustainable Agriculture.

Due to industrialization, the contamination of toxic metals in soils is currently one of the major concerns to scientists worldwide. The presence of high concentrations of heavy metals including cadmium in the environment is mainly attributed to human activities. Being a highly toxic metal, cadmium can enter plant cell transporters usually used for the uptake of essential cations, such as iron, calcium, and zinc. This study deals with the appraisement of response and tolerance shown by various bacteria in varied cadmium concentrations (100–1,000 ppm). The optical density (OD) of the isolates was measured to determine the minimum inhibitory concentration (MIC) of cadmium. Isolated bacteria have been identified using 16S rRNA gene sequence and Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). Among the 72 isolates, 07 (Bacillus pumilus, Enterobacter kobei, Klebsiella pneumonia, Pseudomonas mandelii, Pseudomonas putida, Pseudomonas avellanae, and Staphylococcus equorum), isolates had efficacy for cadmium tolerance and showed sequestration potential at varying MIC. Furthermore, K. pneumonia was observed to have the highest (900 ppm) tolerance for cadmium and the lowest (600 ppm) was shown by E. kobei. Besides, K. pneumonia showed the highest (75.2%) sequestration potential while the least (52.4%) potential was observed for P. putida. These cadmium tolerant species can be implemented in contaminated environments for detoxification and elimination of cadmium from these agricultural fields. Graphical

The Diverse Indigenous Bacterial Community in the Rudna Mine Does Not Cause Dissolution of Copper from Kupferschiefer in Oxic Conditions

Blasting and fracking of rock in mines exposes fresh rock surfaces to the local water and microbial communities. This may lead to leaching of metals from the rock by chemical or biological means and can cause acidification of the water system in the mine, i.e., acid rock drainage (ARD). Failure to prevent leakage of metal contaminated mine water may be harmful for the environment, especially to the local groundwater. In the Rudna mine, Poland, an in situ bioleaching pilot test at approximately 1 km depth was performed in the H2020 BIOMOre project (Grant Agreement #642456). After the leaching stage, different methods for irreversible inhibition of acidophilic iron oxidizing microorganisms used for reoxidation of reduced iron in the leaching solution were tested and were shown to be effective. However, the potential of the natural mine water microbial communities to cause leaching of copper or acidification of the mine waters has not been tested. In this study, we set up a microcosm experiment simulating the exposure of freshly fractionated Kupferschiefer sandstone or black schist to two different chloride-rich water types in the Rudna mine. The pH of the microcosms water was measured over time. At the end of an 18-week incubation, the bacterial community was examined by high throughput sequencing and qPCR, and the presence of copper tolerant heterotrophic bacteria was tested by cultivation. The dissolution of copper into the chloride rich microcosm water was measured. The pH in the microcosms did not decrease over the time of incubation. The sandstone increased the number of bacteria in the microcosms with one or over two orders of magnitude compared to the original water. The bacterial communities in the two tested mine waters were diverse and similar despite the difference in salinity. The bacterial diversity was high but changed in the less saline water during the incubation. There was a high content of sulphate reducing bacteria in the original mine waters and in the microcosms, and their number increased during the incubation. No acidophilic iron oxidizers were detected, but in the microcosms containing the less saline water low numbers of Cu tolerant bacteria were detected. Copper to a concentration of up to 939 mg L−1 was leached from the rock also in the microbe-free negative controls, which was up to 2.4 times that leached in the biotic microcosms, indicating that the leaching was also abiotic, not only caused by bacteria.

Transient Antibiotic Tolerance Triggered by Nutrient Shifts From Gluconeogenic Carbon Sources to Fatty Acid.

Nutrient shifts from glycolytic-to-gluconeogenic carbon sources can create large sub-populations of extremely antibiotic tolerant bacteria, called persisters. Positive feedback in Escherichia coli central metabolism was believed to play a key role in the formation of persister cells. To examine whether positive feedback in nutrient transport can also support high persistence to β-lactams, we performed nutrient shifts for E. coli from gluconeogenic carbon sources to fatty acid (FA). We observed tri-phasic antibiotic killing kinetics characterized by a transient period of high antibiotic tolerance, followed by rapid killing then a slower persister-killing phase. The duration of transient tolerance (3–44 h) varies with pre-shift carbon source and correlates strongly with the time needed to accumulate the FA degradation enzyme FadD after the shift. Additionally, FadD accumulation time and thus transient tolerance time can be reduced by induction of the glyoxylate bypass prior to switching, highlighting that two interacting feedback loops simultaneously control the length of transient tolerance. Our results demonstrate that nutrient switches along with positive feedback are not sufficient to trigger persistence in a majority of the population but instead triggers only a temporary tolerance. Additionally, our results demonstrate that the pre-shift metabolic state determines the duration of transient tolerance and that supplying glyoxylate can facilitate antibiotic killing of bacteria.

Biodegradation of crude oil by a moderately haloalkaliphilic Acinetobacter strain

Bioremediation of crude oil (or petroleum) pollution in the saline-alkali environment is challenging due to the lack of halotolerant and alkali tolerant oil-degrading bacteria. It is shown here that a newly isolated Acinetobacter strain D2 able to degrade crude oil was moderately haloalkaliphilic. Physiological characterization showed that the optimal crude oil degradation conditions for D2 strain occurred at pH = 9 and NaCl concentration of 2% w/v. Moreover, D2 can tolerate pH 11 and NaCl concentration of 8% w/v. Kinetic analysis indicated that crude oil (0.2% and 0.5% w/v) biodegradation by D2 followed the first-order kinetic model, with the k constant estimated as 0.089–0.111 d−1 and the half-life period of petroleum degradation as 6.24–7.79 d. The results of the gas chromatographic analysis revealed that strain D2 could degrade most saturated hydrocarbons, with higher removal efficiencies for shorter-chain alkanes. Strain D2 can also remove aromatic hydrocarbons with an average efficiency of 33.4%. Combined, these results demonstrated that a moderately haloalkaliphilic Acinetobacter strain can be a suitable candidate for bioremediation of oil-contaminated saline soil and oilfield produced water.

Pre-culturing soil microbial inoculum in plant residues enhanced the resilience of tolerant bacteria and bioneutralization efficacy in alkaline bauxite residues

Bioneutralization of alkaline bauxite residues (BR) may be achieved through in situ organic acids produced from fermentative decomposition of carbohydrates-rich organic matters (e.g., plant residues), which are driven by organophilic and heterotrophic prokaryotes tolerant of extremely saline and alkaline conditions. The present study investigated if the resilience of tolerant prokaryotes in soil microbial inoculums could be improved by pre-culturing them in carbohydrate-rich plant residues, leading to enhanced bioneutralization efficacy in strongly alkaline BR. In a 2-week microcosm experiment with BR (pH ~ 10.5), it was found that the resilience of prokaryotic communities and their functional modules and bioneutralization efficacy were significantly boosted in BR admixed with plant residues (i.e., SM: sugarcane mulch, LH: Lucerne hay) pre-cultured with soil microbial inoculum. The results showed that 10–20% of the initially inoculated soil prokaryotic features were recovered in treatments with pre-cultured plant residues. Besides, the enriched diverse prokaryotes formed highly clustered networks in the amended BR. These modules actively drove C and N mineralization and sustained 0.8–2.0 units of pH reduction, despite the buffering effects of alkaline minerals in BR solid phase. In contrast, soil microbial inoculation cultured in the growth medium lost >99% of the original prokaryotic features in soil inoculums, resulting in merely 0.2–0.7 unit pH reduction in the treated BR. Therefore, pre-culturing soil inoculum in plant residues would be preferred as an integral system to treat BR for effective bioneutralization.

Biodegradation of insecticides by gut bacteria isolated from stored grain beetles and its implication in host insecticide resistance

Stored grain pests have developed widespread resistance to currently available grain protectants. Although symbiotic microbes played an important role in insecticide resistance of insect hosts, it has not been reported in stored grain pests. In this study, five gut bacteria were excised from adult Sitophilus oryzae (L.) (Coleoptera: Curculionidae), Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae), and Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae). These bacteria can degrade malathion, pirimiphos-methyl, and deltamethrin and utilize these insecticides as the carbon source in vitro. When treated with 0.5–10 mg/kg of malathion, pirimiphos-methyl and 0.3–0.75 mg/kg of deltamethrin, gnotobiotic reinoculation of a given bacterial strain significantly enhanced survival rates of its hosts. The significance of gut bacteria in host insecticide tolerance was insecticide dosage-dependent. Furthermore, the in vitro insecticide biodegradability of gut bacteria was not completely consistent with their in vivo performance in host insecticide resistance. This suggests that there may be other physiological processes responsible for host insecticide tolerance mediated by symbiotic bacteria except for direct degradation of insecticides. These results provide insight into insecticide resistance management of stored grain pests and further study of the association between gut bacteria and insecticide resistance.

Effect of LDPE and biodegradable PBAT primary microplastics on bacterial community after four months of soil incubation

Biodegradable plastics would be gradually degraded by microbes after being used and discarded, forming biodegradable microplastics (BMPs). It is however not clear if it, like conventional microplastics, can affect the original soil ecological balance. In this study, the non-degradable LDPE (low density polyethylene) was used as the reference primary microplastic, and the BMP PBAT (polyadipate/butylene terephthalate) was used as the test object. The effects of the amount of PBAT on soil physical-chemical properties, bacterial community were investigated using high throughput sequencing. The results showed that when the highest amount of PBAT applied was up to 250 times higher than the normal application amount, resulted in a certain dose-effect, and a higher amount of PBAT would reduce the content of NO3--N and TP. The lower amount of PBAT relatively increased the diversity of soil bacterial communities, and the relative abundance of the unique Azotobacter increased with increasing PBAT amount. The abundance of bacterial community in soil with different PBAT amounts was significantly correlated with the soil’s physical-chemical properties. In addition, Mesorhizobium, TM7a and Azotobacter were observed to be highly tolerant bacteria in PBAT containing soil which can be actively explored to study the biodegradation of BMPs PBAT.