Bioremediation, which has several advantages over traditional methods, represents an alternative means of dealing with heavy metal pollution. We screened for microorganisms showing heavy metal tolerance in polluted mangrove soils. A novel yeast, Geotrichum sp. CS-67, was discovered and tested for tolerance of Cu²⁺, Zn²⁺, and Ni²⁺. Zn²⁺ was the most efficiently sequestered by Geotrichum sp. CS-67 followed by Ni²⁺ and Cu²⁺. Zn²⁺ and Ni²⁺ were actively taken up into the cell, while Cu²⁺ was adsorbed to the cell wall. We used RNA-Seq to show that a large number of genes involved in the physiological and biochemical processing of heavy metals were differentially expressed in this yeast when it was subjected to Zn²⁺ and Ni²⁺ stress. From this panel, we selected the SED1, GDI1 and ZRT1 genes for validation by qRT-PCR and discovered that, during Zn²⁺ and Ni²⁺ stress, SED1 and GDI1 were upregulated, while ZRT1 was downregulated, which was consistent with the RNA-Seq results and the biochemical function of these genes. In conclusion, the novel yeast Geotrichum sp. CS-67 has a marked ability to accumulate heavy metal ions, making it of great interest as a possible microbial agent for heavy metal pollution remediation in the future.

The structure of sedimentary bacterial communities in mangroves depends on environmental factors such as pH, salinity, organic matter content, and metal pollution. To investigate the effect of heavy metal pollution on such communities, core samples of sediments from four sites in three distinct mangrove reserves (Golden Bay Mangrove Reserve in Beihai, Guangxi province (GXJHW), Shankou Mangrove Reserve in Hepu, Guangxi province (GXSK), and MaiPo mangrove in Hong Kong (MPCT and MPFQ)) in South China were analyzed for physicochemical properties, multiple chemical forms of metals, and vertical bacterial diversity. Sedimentary bacterial communities varied greatly among the different sampling sites, with biodiversity decreasing in the order of GXSK, GXJHW, MPFQ, and MPCT. Proteobacteria was the dominant phylum, followed by Chloroflexi, across all four sampling sites. Multivariate statistical analysis of the effect of environmental factors on the sedimentary bacterial communities found that total carbon was the only physicochemical factor with a significant influence at all four sites. The correlations between environmental factors and bacterial structure were weak for the two sites in Guangxi province, but strong at MPCT in Hong Kong where environmental factors were almost all significantly negatively correlated with bacterial diversity. Variance partitioning analysis revealed that physicochemical properties and chemical forms of metals could explain most of the changes in bacterial diversity. Overall, we observed that heavy metal forms were more important than total metal content in influencing the sedimentary bacterial diversity in mangroves, consistent with the more bioavailable metal species having the greatest effect.

Introduction: Mangroves are a unique ecosystem, but are often affected by heavy metal pollution. Bacterial communities in mangrove sediments usually respond to heavy-metal pollution stress by expressing specific heavy-metal resistance genes (HMRGs).Methods: Multivariate statistics were performed on Metagenomics as well as environmental data to evaluated the effects of Cu addition on the sedimentary bacterial community structure.Results and discussion: Using metagenomics technology, we found that the Shannon andChao1 indices of natural sediments were significantly higher than in sediments with artificially added Cu. Addition of Cu significantly altered bacterial community structure and diversity at the phylum, class and order levels in sediments. The relative abundance of HMRGs in Cuadded sediments was lower than that in natural sediments. Environmental factors that affect bacterial communities also affect HMRGs. However, the contribution of heavy-metal pollution to the change in HMRG abundance was much lower than its contribution to the change in the bacterial community, indicating that the relationship between HMRG abundance and heavy-metal pollution is complex and needs to be comprehensively studied.

With increasing concerns of the environmental problems associated with current fungicide application, investigation of alternative, environmentally compatible biopesticides for plant disease management is needed. A total of 113 strains associated with Acanthus ilicifolius Linn in the Maipo Reserve, Hong Kong, were isolated and identified. In vitro assay with crude extracts of bacterial fermentation cultures identified ∼26% of the isolates producing antimicrobial compounds against a variety of agriculturally important phytopathogens. Selected crude extracts with inhibition to Colletotrichum fructicola and Magnaporthe oryzae growth significantly suppressed anthracnose and rice blast development in pear fruits and rice plants, respectively, when applied at 50 μg ml⁻¹. Furthermore, 10 of 14 selected crude extracts with good antimicrobial activities had no significant differences in toxicity to the genus Chlorella compared with the control when used at 25 μg ml⁻¹, whereas Amistar Top and Mancozeb completely killed the alga under the same concentration. These data illustrate the potential of natural products from mangrove rhizosphere bacteria in future agricultural application.

Host defense peptides (HDPs) are components of plant defensive barriers that resist microbial infection. Members of the Snakin/GASA protein family in plants have functions of regulating plant growth, defense, and bacteriostasis. Most mangrove plants grow in coastal zones. In order to survive in harsh environments, mangrove plants have evolved complex adaptations against microbes. In this study, Snakin/GASA family members were identified and analyzed in the genomes of three mangrove species. Twenty-seven, thirteen, and nine candidate Snakin/GASA family members were found in Avicennia marina, Kandelia obovata, and Aegiceras corniculatum, respectively. These Snakin/GASA family members were identified and categorized into three subfamilies via phylogenetic analysis. The genes coding for the Snakin/GASA family members were unevenly distributed on chromosomes. Collinearity and conservative motif analyses showed that the Snakin/GASA family members in K. obovata and A. corniculatum underwent multiple gene duplication events. Snakin/GASA family member expression in normal leaves and leaves infected with pathogenic microorganisms of the three mangrove species was verified using real-time quantitative polymerase chain reaction. The expression of KoGASA3 and 4, AcGASA5 and 10, and AmGASA1, 4, 5, 15, 18, and 23 increased after microbial infection. This study provides a research basis for the verification of HDPs from mangrove plants and suggests directions for the development and utilization of marine biological antimicrobial peptides.

To explore the characteristics of overland flow resistance under the condition of sparse vegetative stem coverage and improve the basic theoretical research of overland flow, the resistance characteristics of overland flow were systematically investigated under four slope gradients (S), seven flow discharges (Q), and six degrees of vegetation coverage (Cr). The results show that the Manning roughness coefficient (n) changes with the ratio of water depth to vegetation height (h/hv) while the Reynolds number (Re), Froude number (Fr), and slope (S) are closely related to vegetation coverage. Meanwhile, h/hv, Re, and Cr have strong positive correlations with n, while Fr and S have strong negative correlations with n. Through data regression analysis, a power function relationship between n and hydraulic parameters was observed and sensitivity analysis was performed. It was concluded that the relationship between n and h/hv, Re, Cr, Q, and S shows the same law; in particular, for sparse stem vegetation coverage, Cr is the dominant factor affecting overland flow resistance under zero slope condition, while Cr is no longer the first dominant factor affecting overland flow resistance under non-zero slope condition. In the relationship between n and Fr, Cr has the least effect on overland flow resistance. This indicates that when Manning roughness coefficient is correlated with different hydraulic parameters, the same vegetation coverage has different effects on overland flow resistance. Therefore, it is necessary to study overland flow resistance under the condition of sparse stalk vegetation coverage.