Biochar has caught great attention over the last decade with the loose and porous structure, and carbon stability provides suitable living conditions for the growth and activity of microorganisms. This review provided a comprehensive summary of biochar immobilization microbe (BIM) in water and soil decontamination. Firstly, the bacterial immobilization techniques including adsorption, entrapping, and covalence methods were exhibited. Secondly, the applications of BIM in water and soil environmental remediation were introduced, mainly including the treatment of organic pollutants, heavy metals, and N/P, among which the most frequently immobilized microorganism was Bacillus. Then, the mechanisms of adsorption, redox, and degradation were analyzed. Finally, pertinent questions for future research of BIM technology were proposed. The purpose of this paper is to provide useful background information for the selection of better biochar fixation microorganisms for water and soil remediation. 

Immobilization of microbes on biochar for water and soil remediation: A review.

Camelina [(Camelina sativa (L.) Crantz], an oilseed species of Brassicaceae, does not have approved herbicides for weed control, which limits its expansion as a commercial crop. To evaluate agronomic traits and ecosystem services of non-transgenic cultivars of sulfonylurea-resistant camelina and canola (Brassica napus L.), a field study was conducted near Fargo, North Dakota. Two replicated locations (NDSU and NW22) were set up in a randomized complete block design including four blocks of camelina, canola, and fallow per location. Camelina and canola were seeded (18 May) at 4.9 and 2.9 kg ha−1, respectively, using 19-cm row spacing. Data was collected mid- and late-season (29 June and 22 July 2020 respectively) for crop and weed stem count (no. m−2), biomass dry matter (kg m−2), and nutrient (N, P, K, S) content (kg ha−1), as-well-as final season (7 August) seed yield (kg ha−1) for camelina and canola treated with and without sulfonylurea. Using Prefer 90 (NIS) at 0.25% v/v, camelina was treated with thifensulfuron at 6.3 g a.i. ha−1, and canola was treated with thifensulfuron at 10.5 g a.i. ha−1 and tribenuron at 5.3 g a.i. ha−1. Sulfonylurea-resistant camelina and canola reduced late-season dry weight biomass of weeds by >75% and ≥60%, respectively, compared with fallow plots. Application of sulfonylurea herbicides to camelina or canola prior to mid-season analyses was not a significant factor (p ≤ 0.05) for reducing weed pressure and generally had little impact on altering crop biomass, seed yield, and nutrient retention. However, in some cases, herbicide treatment had an additive effect of reducing weed pressure over that of camelina or canola alone. Depending on the rotational cropping system, sulfonylurea-resistant camelina and canola should provide additional options for integrated weed management approaches and reducing nutrient leaching in the upper Midwest and northern Great Plains of the USA.

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Weed Pressure, Nutrient Content, and Seed Yield in Field Grown Sulfonylurea-Resistant Camelina sativa and Brassica napus

In this study, the effects of the immobilized bacterial mixture (IM-FN) of Arthrobacter sp. NJ-1 and Klebsiella variicola strain FH-1 using sodium alginate-CaCl2 on the degradation of atrazine were investigated. The results showed that the optimal ratio of three types of carrier materials (i.e., rice straw powder, rice husk, and wheat bran) was 1:1:1 with the highest adsorption capacity for atrazine (i.e., 3774.47 mg/kg) obtained at 30°C. On day 9, the degradation efficiency of atrazine (50 mg/L) reached 98.23% with cell concentration of 1.6 × 108  cfu/ml at pH 9 and 30°C. The Box–Behnken method was used to further optimize the culture conditions for the degradation of atrazine by the immobilized bacterial mixture. The IM-FN could be reused for 2–3 times with the degradation efficiency of atrazine maintained at 73.0% after being stored for 80 days at 25°C. The population dynamics of IM-FN was explored with the total soil DNA samples specifically analyzed by real-time PCR. In 7 days, the copy numbers of both PydC and estD genes in the IM-FN were significantly higher than those of bacterial suspensions in the soil. Compared with bacterial suspensions, the IM-FN significantly accelerated the degradation of atrazine (20 mg/kg) in soil with the half-life shortened from 19.80 to 7.96 days. The plant heights of two atrazine-sensitive crops (wheat and soybean) were increased by 14.99 and 64.74%, respectively, in the soil restored by immobilized bacterial mixture, indicating that the IM-FN significantly reduced the phytotoxicity of atrazine on the plants. Our study evidently demonstrated that the IM-FN could significantly increase the degradation of atrazine, providing a potentially effective bioremediation technique for the treatment of atrazine-polluted soil environment and providing experimental support for the wide application of immobilized microorganism technology in agriculture.

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Immobilization of bacterial mixture of Klebsiella variicola FH-1 and Arthrobacter sp. NJ-1 enhances the bioremediation of atrazine-polluted soil environments

Bacillus mojavensis D50, a biocontrol strain, is used to prevent and treat the fungal plant pathogen Botrytis cinerea. Bacillus mojavensis D50’s biofilms can affect its colonization; thus, the effects of different metal ions and culture conditions on biofilm formation were determined in this study. The results of medium optimization showed that Ca2+ had the best ability to promote biofilm formation. The optimal medium composition for the formation of biofilms contained tryptone (10 g/L), CaCl2 (5.14 g/L), and yeast extract (5.0 g/L), and the optimal fermentation conditions included pH 7, a temperature of 31.4 °C, and a culture time of 51.8 h. We found that the antifungal activity and abilities to form biofilms and colonize roots were improved after optimization. In addition, the levels of expression of the genes luxS, SinR, FlhA, and tasA were up-regulated by 37.56-, 2.87-, 12.46-, and 6.22-fold, respectively. The soil enzymatic activities which related biocontrol-related enzymes were the highest when the soil was treated by strain D50 after optimization. In vivo biocontrol assays indicated that the biocontrol effect of strain D50 after optimization was improved.

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Adding Metal Ions to the Bacillus mojavensis D50 Promotes Biofilm Formation and Improves Ability of Biocontrol

Serratia ureilytica HNU47 was originally isolated from rhizosphere soil of stock in a continuous cropping tomato-planting field, which has excellent antagonistic ability against Ralstonia solanacearum. Here, we sequenced the genome of HNU47 to gain insights into the underlying basis of its antagonistic activity. Results of phylogenetic analysis of the whole genomic sequence demonstrated that HNU47 belongs to S. ureilytica. Through antiSMASH analysis, 10 secondary metabolite biosynthesis gene clusters were predicted. There were only two gene clusters with similarity higher than 95% with known compounds’ gene clusters and the similarities of the other eight gene clusters were lower than 30%, including three gene clusters with no homology. In addition, biocontrol experiments confirmed that HNU47 could decrease the incidence of bacterial wilt caused by R. solanacearum on tomato. These findings support the potential of developing S. ureilytica HNU47 as a biocontrol agent against R. solanacearum by producing some unknown active compounds. The genome sequence reported here is also useful for revealing the modulation mechanisms underlying biosynthesis of active compounds. 

Genome Sequence Resource of <i>Serratia ureilytica</i> HNU47: A Strain with Biocontrol Potential Against Bacterial Wilt Pathogen <i>Ralstonia solanacearum</i>

Microbial degradation is one of the effective methods to remove thifensulfuron-methyl (TSM) in soil and water environments. In this study, a high-efficiency TSM degrading strain Serratia marcecens N80 was used. The abandoned fungus substrate was converted to biochars at various pyrolysis temperatures (300, 450 and 600 °C). Biochar made at 600 °C (BC600) showed the best TSM adsorption capacity, while strain N80 adsorption efficiency reached the maximum up to 81.08%. Therefore, BC600, polyvinyl alcohol (PVA), and sodium alginate (SA) were chosen to establish an immobilized system for strain N80. The immobilized N80 beads (IN80) showed significantly improved reusability and storage stability. Under the optimal condition (pH 7.0, 35 °C, 1.5 × 10 8  cfu/mL), TSM (50 mg/L) degradation rates by free N80 and IN80 were 83.47 and 89.37% within 48 h, respectively. Free N80 and IN80 accelerated TSM degradation in soil, reducing its half-life to 6.13 d and 4.36 d, respectively. However, immobilized material beads (IM) slightly delayed the soil TSM degradation. TSM activated catalase and dehydrogenase but inhibited invertase and urease. IN80 treatment accelerated the recovery of invertase and urease. Moreover, IN80 accelerated the recovery of bacterial and fungal populations; the beneficial genera inhibited by TSM such as Sphingomonas, Lysobacter, Massilia, Rhodanobacter, and Gemmatimonas also increased to varying degrees. Meanwhile, IN80 showed an excellent inhibitory effect on pathogenic fungi (Fusarium and Alternaria), while increased the relative abundance of Mortierella, and the soil resistance to diseases. This study offers a potential in situ remediation strategy to improve the quality of the soil environment.

Yulin Wu

Papers

Degradation characteristics and soil remediation of thifensulfuron-methyl by immobilized Serratia marcecens N80 beads