Inoculation with endophytic Bacillus megaterium H3 increases Cd phytostabilization and alleviates Cd toxicity to hybrid pennisetum in Cd-contaminated aquatic environments

Biofilm-overproducing Bacillus subtilis B12ΔYwcc decreases Cd uptake in Chinese cabbage through increasing Cd-immobilizing related gene abundance and root surface colonization

Biofilm-producing bacteria can decrease Cd uptake in vegetables, but mechanisms underlying this effect are poorly characterized. In this study, two mutant strains B12ΔYwcc and B12ΔSlrR were constructed from a biofilm-producing Bacillus subtilis strain B12. Then, the impacts of strain B12 and its high biofilm-producing mutant strain B12ΔYwcc and low biofilm-producing mutant strain B12ΔSlrR on Cd availability and uptake in Chinese cabbage and the related mechanisms were investigated in the Cd-polluted soil. Strain B12 and its mutants B12ΔYwcc and B12ΔSlrR increased the dry biomasses of edible tissues by 54%-130% compared with the controls. Strain B12 and its mutant B12ΔYwcc reduced the soil available Cd content by 36%-50% and root and edible tissue Cd contents by 23%-50% compared with the controls. Furthermore, the mutant strain B12ΔYwcc reduced the edible tissue Cd content by 40% and increased the polysaccharide content by 23%, invertase activity by 139%, and gene copies of the cumA by 4.5-fold, epsA by 7.1-fold, and cadA by 4.3-fold, which were involved in Cd adsorption in the rhizosphere soils, respectively, compared with strain B12. The polysaccharide content and cumA, epsA, and cadA gene copy numbers showed significantly reverse correlations with the available Cd content. Notably, the mutant strain B12ΔYwcc showed better ability to colonize the vegetable root surface than strain B12. These findings demonstrated that the biofilm-overproducing mutant strain B12ΔYwcc increased the polysaccharide production and Cd-immobilizing related cumA, epsA, and cadA gene copies, resulting in lower Cd availability and accumulation in Chinese cabbage in the Cd-polluted soil.

Effects of a compound microbial agent and plants on soil properties, enzyme activities, and bacterial composition of Pisha sandstone

The objective of this study was to investigate the effects of the microbial agent on the improvement of Pisha sandstone soil and find out an effective measure for the control of soil erosion in the Pisha sandstone area. Pisha sandstone containing the microbial agent composed of Bacillus halotolerans P75, Sinorhizobium meliloti D10, Bacillus megaterium H3, Bacillus subtilis HB01, and organic substrate was utilized to be the soil matrix for pot experiment, and then alfalfa, ryegrass, and caragana were planted, respectively. Effects of the microbial agent plus plants on the soil properties of Pisha sandstone were evaluated, and the results showed that the microbial agent plus plants significantly increased the organic matter content, alkali hydrolyzed nitrogen content, available phosphorus content, available potassium content, invertase activity, and urease activity. Meanwhile, inoculation with the microbial agent significantly promoted the growth of alfalfa, ryegrass, and caragana and also influenced the number of soil bacteria and the relative abundance of Proteobacteria, Bacteroidetes, Actinobacteria, and others. However, the effects of the microbial agent plus different plants on the soil properties and bacterial composition of Pisha sandstone were different, while the growth of different plants showed differences, suggesting that there was a different interaction between microbes and different plants in Pisha sandstone soil. In conclusion, the microbial agent plus plants could improve Pisha sandstone soil which could provide some theoretical and experimental references for soil erosion control in the Pisha sandstone area.

Effect of endophytic Bacillus megaterium colonization on structure strengthening, microbial community, chemical composition and stabilization properties of Hybrid Pennisetum

BACKGROUND

This study was conducted to analyze the effects of endophytic Bacillus megaterium (BM 18-2) colonization on structure strengthening, microbial community, chemical composition and stabilization properties of Hybrid Pennisetum.

RESULTS

The BM 18-2 had successfully colonized in the interior tissues in both leaf and stem of Hybrid Pennisetum. During ensiling, the levels of pH, acetic acid (AA), butyric acid (BA), propionic acid (PA), and the population of yeast and aerobic bacteria were significantly (P > 0.05) lower, while lactic acid bacteria (LAB) and lactic acid (LA) were significantly (P < 0.001) higher with the steps forward of ensiling in with BM 18-2 as compared to without BM 18-2 colonized of Hybrid Pennisetum. During the different ensiling days, at days 3, 6, 15, and 30, the genus Brevundimonas, Klebsiella, Lactococcus, Weissella, Enterobacter, Serratia, etc. population were significantly decreased, while genus Pediococcus acidilactici and Lactobacillus plantarum were significantly influenced in treated groups as compared to control. The genus Lactobacillus and Pediococcus were positively correlated with treatment groups.

CONCLUSIONS

It is concluded that the endophytic bacteria strain BM 18-2 significantly promoted growth characteristics and biomass yield before ensiling and after ensiling inoculated with or without Lactobacillus plantarum could improve the distinct changes of the undesirable microbial diversity, chemical composition, and stabilization properties in with BM 18-2 as compared to without BM 18-2 colonized Hybrid Pennisetum. © 2019 Society of Chemical Industry.

Endophytic Bacillus megaterium BM18-2 mutated for cadmium accumulation and improving plant growth in Hybrid Pennisetum

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The endophytic Bacillus megaterium isolated from Hybrid Pennisetum is promising isolate for Cd bioremediation.

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The mutated strain BM18-2 showed higher capacity to resist Cd until 70 μM and improving plant growth.

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Six different genes of BM18-2 are involved in Cd resistance mechanism.

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Hybrid Pennisetum inoculated with BM18-2 showed higher amount of growth and toleranc to Cd toxicity than uninoculated plants.

Hybrid Pennisetum (Pennisetum americanum × P. purpureum Schumach L.) is a tall and rapidly growing perennial C₄ bunch grass. It has been considered as a promising plant for phytoremediation of heavy metal-contaminated soil due to its high biomass, high resistance to environmental stress, pests and diseases. Heavy metal bioavailability level is the most important parameter for measurement of the phytoremediation efficiency. Endophytic bacteria were used to further enhance phytoremediation of heavy metals through bioaccumulation or bioabsorption process. In the present study, the endophytic Bacillus megaterium strain ‘BM18’ isolated from hybrid Pennisetum was screened under 10-70 μM cadmium (Cd) stress for Cd-resistant mutant colonies. And one such mutant colony‘BM18-2’ was obtained from the screen. Comparably, ‘BM18-2’ was more Cd-tolerant and had higher Cd removal ability than the original strain‘BM18’. The amount of IAA and ammonia production, and phosphate solubilization were 1.09, 1.23 and 1.24 times in ‘BM18-2’ than those of ‘BM18’, respectively. Full genome sequencing of these two strains revealed 6 different genes: BM18GM000901, BM18GM005669 and BM18GM005870 encoding heavy metal efflux pumps, BM18GM003487 and BM18GM005818 encoding transcriptional regulators for metal stress biosensor and BM18GM001335 encoding a replication protein. Inoculation with ‘BM18-2’ or ‘BM18’ both significantly reduced the toxic effect of Cd on hybrid Pennisetum, while the effect of ‘BM18-2’ on plant growth promotion in the presence of Cd was significantly better that of ‘BM18’. Therefore, the mutated strain ‘BM18-2’ could be used as a potential agent for Cd bioremediation, improving growth and Cd absorption of hybrid Pennisetum in Cd contaminated soil.

Increased biomass and quality and reduced heavy metal accumulation of edible tissues of vegetables in the presence of Cd-tolerant and immobilizing Bacillus megaterium H3

A Cd-resistant and immobilizing Bacillus megaterium H3 was characterized for its impact on the biomass and quality and heavy metal uptake of edible tissues of two vegetables (Brassica campestris L. var. Aijiaohuang and Brassica rapa L. var. Shanghaiqing) grown in heavy metal-polluted soil. The impact of strain H3 on the soil quality was also evaluated. The increase in the edible tissue biomass and the contents of soluble proteins and vitamin C of the vegetables inoculated with strain H3 ranged from 18% to 33%, 17% to 31%, and 15% to 19%, respectively, compared with the controls. Strain H3 significantly decreased the edible tissue Cd and Pb contents of the two greens (41-80%), DTPA-extractable Cd content (35-47%) of the rhizosphere soils, and Cd and Pb translocation factors (25-56%) of the greens compared with the controls. Moreover, strain H3 significantly increased the organic matter content (17-21%) and invertase activity (13-14%) of the rhizosphere soils compared with the controls. Our results demonstrated the increased edible tissue biomass and quality, decreased Cd and Pb uptake of the edible tissues, and improved soil quality in the presence of strain H3. The results also suggested an effective bacterial-enhanced technique for decreased metal uptake of greens and improved vegetable and soil qualities in the metal-contaminated soils.

Role of Streptomyces pactum in phytoremediation of trace elements by Brassica juncea in mine polluted soils

The industrial expansion, smelting, mining and agricultural practices have increased the release of toxic trace elements (TEs) in the environment and threaten living organisms. The microbe-assisted phytoremediation is environmentally safe and provide an effective approach to remediate TEs contaminated soils. A pot experiment was conducted to test the potential of an Actinomycete, subspecies Streptomyces pactum (Act12) along with medical stone compost (MSC) by growing Brassica juncea in smelter and mines polluted soils of Feng County (FC) and Tongguan (TG, China), respectively. Results showed that Zn (7, 28%), Pb (54, 21%), Cd (16, 17%) and Cu (8, 10%) uptake in shoot and root of Brassica juncea was pronounced in FC soil. Meanwhile, the Zn (40, 14%) and Pb (82, 15%) uptake in the shoot and root were also increased in TG soil. Shoot Cd uptake remained below detection, while Cu decreased by 52% in TG soil. The Cd and Cu root uptake were increased by 17% and 33%, respectively. Results showed that TEs uptake in shoot increased with increasing Act12 dose. Shoot/root dry biomass, chlorophyll and carotenoid content in Brassica juncea were significantly influenced by the application of Act12 in FC and TG soil. The antioxidant enzymatic activities (POD, PAL, PPO and CAT) in Brassica juncea implicated enhancement in the plant defense mechanism against the TEs induced stress in contaminated soils. The extraction potential of Brasssica was further evaluated by TF (translocation factor) and MEA (metal extraction amount). Based on our findings, further investigation of Act12 assisted phytoremediation of TEs in the smelter and mines polluted soil and hyperaccumulator species are suggested for future studies.