Influence of salinity on the degradation of xenobiotic compounds in rhizospheric mangrove soil

Unveiling bacterial consortium for xenobiotic biodegradation from Pichavaram mangrove forest soil: a metagenomic approach

Pichavaram mangrove forest was established as a wetland of International Importance by Article 2.1 in April 2022 by the Ministry of Environment, Forest and Climate Change, India. Even though it is a conserved site, xenobiotic agrochemical leaching on the forest land during monsoon is inevitable. These threaten the microbial diversity in the environment. Xenobiotic degradation is achieved using bacterial consortia already acclimatised to this environment. This study aims to identify the indigenous microbial consortia able to degrade xenobiotic compounds such as fluorobenzoate, furfural, and steroids. Pichavaram mangrove metagenomic dataset was obtained by shotgun sequencing of soil DNA and processed using the automated tool SqueezeMeta. Further, the DIAMOND database provided the taxonomical classification of the microbes in each contig. With reference to the KEGG database, the selected xenobiotic degradation pathways were confirmed in the dataset. Of 1,253,029 total contigs, 1332, 72 and 1262 were involved in fluorobenzoate, furfural and steroid degradation, respectively. This study identified that microbial consortia comprising Marinobacter, Methyloceanibacter and Vibrio natriegens/Gramella sp. can degrade fluorobenzoate. While Afipia, Nitrosopumilus sp., and Phototrophicus methaneseepsis favour the degradation of furfural compound. The steroid degradation pathway possessed a plethora of bacteria belonging to the phylum Proteobacteria.

Effect of salinity on genes involved in the stress response in mangrove soils

Mangroves are a challenging ecosystem for the microorganisms that inhabit them, considering they are subjected to stressful conditions such as high and fluctuating salinity. Metagenomic analysis of mangrove soils under contrasting salinity conditions was performed at the mouth of the Ranchera River to the Caribbean Sea in La Guajira, Colombia, using shotgun sequencing and the Illumina Hiseq 2500 platform. Functional gene analysis demonstrated that salinity could influence the abundance of microbial genes involved in osmoprotectant transport, DNA repair, heat shock proteins (HSP), and Quorum Sensing, among others. In total, 135 genes were discovered to be linked to 12 pathways. Thirty-four genes out of 10 pathways had statistical differences for a p-value and FDR < 0.05. UvrA and uvrB (nucleotide excision repair), groEL (HSP), and secA (bacterial secretion system) genes were the most abundant and were enriched by high salinity. The results of this study showed the prevalence of diverse genetic mechanisms that bacteria use as a response to survive in the challenging mangrove, as well as the presence of various genes that are recruited in order to maintain bacterial homeostasis under conditions of high salinity.

Comparative genomic analysis of Chryseobacterium species: deep insights into plant-growth-promoting and halotolerant capacities

Members of the genus Chryseobacterium have attracted great interest as beneficial bacteria that can promote plant growth and biocontrol. Given the recent risks of climate change, it is important to develop tolerance strategies for efficient applications of plant-beneficial bacteria in saline environments. However, the genetic determinants of plant-growth-promoting and halotolerance effects in Chryseobacterium have not yet been investigated at the genomic level. Here, a comparative genomic analysis was conducted with seven Chryseobacterium species. Phylogenetic and phylogenomic analyses revealed niche-specific evolutionary distances between soil and freshwater Chryseobacterium species, consistent with differences in genomic statistics, indicating that the freshwater bacteria have smaller genome sizes and fewer genes than the soil bacteria. Phosphorus- and zinc-cycling genes (required for nutrient acquisition in plants) were universally present in all species, whereas nitrification and sulphite reduction genes (required for nitrogen- and sulphur-cycling, respectively) were distributed only in soil bacteria. A pan-genome containing 6842 gene clusters was constructed, which reflected the general features of the core, accessory and unique genomes. Halotolerant species with an accessory genome shared a Kdp potassium transporter and biosynthetic pathways for branched-chain amino acids and the carotenoid lycopene, which are associated with countermeasures against salt stress. Protein-protein interaction network analysis was used to define the genetic determinants of Chryseobacterium salivictor NBC122 that reduce salt damage in bacteria and plants. Sixteen hub genes comprised the aromatic compound degradation and Por secretion systems, which are required to cope with complex stresses associated with saline environments. Horizontal gene transfer and CRISPR-Cas analyses indicated that C. salivictor NBC122 underwent more evolutionary events when interacting with different environments. These findings provide deep insights into genomic adaptation to dynamic interactions between plant-growth-promoting Chryseobacterium and salt stress.

Large-scale phylogenomics of aquatic bacteria reveal molecular mechanisms for adaptation to salinity

The crossing of environmental barriers poses major adaptive challenges. Rareness of freshwater-marine transitions separates the bacterial communities, but how these are related to brackish counterparts remains elusive, as do the molecular adaptations facilitating cross-biome transitions. We conducted large-scale phylogenomic analysis of freshwater, brackish, and marine quality-filtered metagenome-assembled genomes (11,248). Average nucleotide identity analyses showed that bacterial species rarely existed in multiple biomes. In contrast, distinct brackish basins cohosted numerous species, but their intraspecific population structures displayed clear signs of geographic separation. We further identified the most recent cross-biome transitions, which were rare, ancient, and most commonly directed toward the brackish biome. Transitions were accompanied by systematic changes in amino acid composition and isoelectric point distributions of inferred proteomes, which evolved over millions of years, as well as convergent gains or losses of specific gene functions. Therefore, adaptive challenges entailing proteome reorganization and specific changes in gene content constrains the cross-biome transitions, resulting in species-level separation between aquatic biomes.

Metagenomic and genomic characterization of heavy metal tolerance and resistance genes in the rhizosphere microbiome of Avicennia germinans in a semi-arid mangrove forest in the tropics

Mangroves are often exposed to heavy metals that accumulate in the food chain, generate toxicity to mangrove plants and affect microbial diversity. This study determined the abundance of genes associated with resistance and tolerance to heavy metals in the rhizosphere microbiome of Avicennia germinans from a semi-arid mangrove of La Guajira-Colombia by metagenomics and genomics approach. Twenty-eight genes associated with tolerance and 49 genes related to resistance to heavy metals were detected. Genes associated with tolerance and resistance to Cu, especially cusA and copA, were the most abundant. The highest number of genes for tolerance and resistance were for Zn and Co, respectively. The isolate Vibrio fluvialis showed the ability to tolerate Cu, Ni, Zn, and Cd. This work used a complementary approach of metagenomics and genomics to characterize the potential of mangrove microorganisms to tolerate and resist heavy metals and the influence of salinity on their abundance.

Biodegradation Pathway and Detoxification of β-cyfluthrin by the Bacterial Consortium and Its Bacterial Community Structure

In the process of microbial degradation of pyrethroid pesticides, the synergistic effect of the microbial community is more conducive to the complete degradation of toxic compounds than a single strain. At present, the degradation pathway of pyrethroids in a single strain has been well revealed, but the synergistic metabolism at the community level has not been well explained. This study elucidated the bacterial community succession, metabolic pathway, and phytotoxicity assessment during β-cyfluthrin biodegradation by a novel bacterial consortium enriched from contaminated soil. The results showed that the half-life of β-cyfluthrin at different initial concentrations of 0.25, 0.5, 0.75, and 1.0 mg mL^-1 were 4.16, 7.34, 12.81, and 22.73 days, respectively. Enterobacter was involved in β-cyfluthrin degradation metabolism in the initial stage, and other bacterial genera (Microbacterium, Ochrobactrum, Pseudomonas, Hyphomicrobiaceae, Achromobacter, etc.) significantly contribute to the degradation of intermediate metabolites in the later stages. Functional gene prediction and metabolite analysis showed that xenobiotic biodegradation and metabolism, especially benzoate degradation and metabolism by cytochrome P450 were the major means of β-cyfluthrin degradation. Further, two degradation pathways of β-cyfluthrin were proposed, which were mainly ester hydrolysis and oxidation to degrade β-cyfluthrin through the production of carboxylesterase and oxidoreductase. In addition, the inoculated bacterial consortium could degrade β-cyfluthrin residues in water and soil and reduce its phytotoxicity in Medicago sativa. Hence, this novel bacterial consortium has important application in the remediation environments polluted by β-cyfluthrin.

Genes associated with antibiotic tolerance and synthesis of antimicrobial compounds in a mangrove with contrasting salinities

Salinity and wastewater pollution in mangrove ecosystems can affect microorganisms and the abundance of genes involved in response to these stressors. This research aimed to identify genes associated with resistance and biosynthesis of antimicrobial compounds in mangrove soils subjected to contrasting salinities and wastewater pollution. Samples of rhizospheric soil were taken from a mangrove at the mouth of the Ranchería River in La Guajira, Colombia. A functional analysis was performed using Illumina HiSeq 2500 sequencing data obtained from total DNA extracted. Increased salt concentration influenced metabolic pathways and differential abundance of genes associated with the synthesis of antimicrobial compounds (e.g., rfbB/rffG, INO1/ISYNA1, rfbA/rffH, sat/met3, asd). Also, among 33 genes involved in intrinsic antibiotic resistance, 16 were significantly influenced by salinity (e.g., cusR/copR/silR, vgb, tolC). We concluded that salt stress tolerance and adaptive mechanisms could favor the biosynthesis of antimicrobial compounds in mangroves contaminated by sewage.

Comparing Sediment Microbiomes in Contaminated and Pristine Wetlands along the Coast of Yucatan

Microbial communities are important players in coastal sediments for the functioning of the ecosystem and the regulation of biogeochemical cycles. They also have great potential as indicators of environmental perturbations. To assess how microbial communities can change their composition and abundance along coastal areas, we analyzed the composition of the microbiome of four locations of the Yucatan Peninsula using 16S rRNA gene amplicon sequencing. To this end, sediment from two conserved (El Palmar and Bocas de Dzilam) and two contaminated locations (Sisal and Progreso) from the coast northwest of the Yucatan Peninsula in three different years, 2017, 2018 and 2019, were sampled and sequenced. Microbial communities were found to be significantly different between the locations. The most noticeable difference was the greater relative abundance of Planctomycetes present at the conserved locations, versus FBP group found with greater abundance in contaminated locations. In addition to the difference in taxonomic groups composition, there is a variation in evenness, which results in the samples of Bocas de Dzilam and Progreso being grouped separately from those obtained in El Palmar and Sisal. We also carry out the functional prediction of the metabolic capacities of the microbial communities analyzed, identifying differences in their functional profiles. Our results indicate that landscape of the coastal microbiome of Yucatan sediment shows changes along the coastline, reflecting the constant dynamics of coastal environments and their impact on microbial diversity.

Streptomyces sp. S501, a Marine Petroleum-Degrading Actinobacterium Isolated from Sediment of Yalujiang Estuary, Northern China, and Its Genome Annotation

Streptomyces sp. S501, which was isolated from the sediment of Yalujiang Estuary in China, was the first marine Streptomyces species discovered to act as an excellent petroleum degrader. We analyzed the effect of pH, temperature, and concentration of NH₄NO₃ on the petroleum degradation of strain S501, and the optimum biodegradation rate reached 63.02% under the condition of 2 g/L NH₄NO₃ addition at 30 °C and pH 8. The complete genome sequence of Streptomyces sp. S501 was determined by using the PacBio RSII platform, which contains a linear chromosome with 7,173,651 bp and a linear plasmid with 288,181 bp, with GC contents of 71.19% and 67.57%, respectively. The genome sequence suggests that Streptomyces sp. S501 has the ability to degrade several hazardous pollutants, as well as the ability to biosynthesize diverse secondary metabolites and enzymes. There are fifty annotated genes involved in oil component degradation, and there are three genes without known annotation information in Streptomyces sp. S501, which have high homology with genes encoding P450 family enzymes and should be novel genes involved in alkane degradation. This study provides useful genetic information for investigating the molecular mechanisms of marine Streptomyces, with biodegradation and application potential.