Plant growth-promoting rhizobacteria (PGPR) are noticeably applied to enhance plant nutrient acquisition and improve plant growth and health. However, limited information is available on the compositional dynamics of rhizobacteria communities with PGPR inoculation. In this study, we investigated the effects of three PGPR strains, Stenotrophomonas rhizophila, Rhodobacter sphaeroides, and Bacillus amyloliquefaciens on the ecophysiological properties of Oilseed rape (Brassica napus L.), rhizosphere, and bulk soil; moreover, we assessed rhizobacterial community composition using high-throughput Illumina sequencing of 16S rRNA genes. Inoculation with S. rhizophila, R. sphaeroides, and B. amyloliquefaciens, significantly increased the plant total N (TN) (p < 0.01) content. R. sphaeroides and B. amyloliquefaciens selectively enhanced the growth of Pseudomonadacea and Flavobacteriaceae, whereas S. rhizophila could recruit diazotrophic rhizobacteria, members of Cyanobacteria and Actinobacteria, whose abundance was positively correlated with inoculation, and improved the transformation of organic nitrogen into inorganic nitrogen through the promotion of ammonification. Initial colonization by PGPR in the rhizosphere affected the rhizobacterial community composition throughout the plant life cycle. Network analysis indicated that PGPR had species-dependent effects on niche competition in the rhizosphere. These results provide a better understanding of PGPR-plant-rhizobacteria interactions, which is necessary to develop the application of PGPR.

Soil salinization poses a global threat to terrestrial ecosystems. Soil microorganisms, crucial for maintaining ecosystem services, are sensitive to changes in soil structure and properties, particularly salinity. In this study, contrasting dynamics within the rhizosphere and bulk soil were focused on exploring the effects of heightened salinity on soil microbial communities, evaluating the influences shaping their composition in saline environments. This study observed a general decrease in bacterial alpha diversity with increasing salinity, along with shifts in community structure in terms of taxa relative abundance. The size and stability of bacterial co-occurrence networks declined under salt stress, indicating functional and resilience losses. An increased proportion of heterogeneous selection in bacterial community assembly suggested salinity’s critical role in shaping bacterial communities. Stochasticity dominated fungal community assembly, suggesting their relatively lower sensitivity to soil salinity. However, bipartite network analysis revealed that fungi played a more significant role than bacteria in intensified microbial interactions in the rhizosphere under salinity stress compared to the bulk soil. Therefore, microbial cross-domain interactions might play a key role in bacterial resilience under salt stress in the rhizosphere.

Gold bioleaching mediated by iodide oxidizing bacteria (IOB) has been proposed as a sustainable alternative to conventional technologies such as cyanidation. This study evaluated the ability of two IOB sourced from a commercial culture collection, Roseovarius (R.) tolerans DSM 11457^T and R. mucosus DSM 17069^T, to bioleach gold from electronic waste (e-waste) (1030 ppm gold) and sulfidic gold ore concentrate (45 ppm gold) using one-step, two-step and spent medium leaching at 1% pulp density over 10 days. Two-step bioleaching of ore concentrate resulted in the highest gold leaching yields (approximately ~100% and 34% for R. tolerans and R. mucosus, respectively), followed by spent medium leaching and one-step leaching. The yields remained low for e-waste with both strains (maximum 0.93% and 1.6% for R. tolerans and R. mucosus, respectively) and decreased over time, likely due to the instability of the solubilized gold at relatively low redox potentials (<300 mV vs. Ag/AgCl). Another limiting factor may be the partial inhibition of bacterial growth in the presence of the ore concentrate and e-waste. Therefore, future studies should evaluate the pre-treatment of the ore concentrate and e-waste to remove inhibitory and oxidant consuming compounds before bioleaching with IOB to optimize leaching yields.

Iron is a vital element for plant and microbial growth; yet, the major portion of iron in soils is in the form of (oxi-)hydroxides with limited bioavailability, resulting in decreased crop yield quality. In response to iron deficiency, soil microorganisms produce siderophores that transform insoluble iron into a soluble form that plants and microorganisms can use. The abundance and activity of siderophore-producing bacteria (SPB) might be used as a biological assessment index for the fertility status of cultivated land. In order to achieve this goal, it is critical to investigate the influences of SPB on plant growth and soil quality. In this study, we performed a mixed-effect model meta-analysis on 342 research studies that compared plant growth with and without SPB. The findings revealed that SPB increased plant growth significantly (up to 30%). The stimulating effects on plants followed the sequences of pant weight, plant height, and germination rate.

The discovery of heterotrophic nitrification-aerobic denitrification (HN-AD) microorganisms has opened a new window for wastewater treatment. The underlying mechanism of HN-AD, however, is not fully understood because of the phylogenetic diversity of HN-AD microbes. The isolation and characterization of new HN-AD microorganisms are encouraging for furthering the understanding of this process. In this study, we found an Alphaproteobacteria isolate W30 from a historically polluted river in China through an HN-AD microbes screening process, which we identified as Pannonibacter sp. A potential HN-AD pathway for W30 was proposed based on N conversion analyses and the successful amplification of the entire denitrification gene series. The isolate exhibited high efficiency of aerobic inorganic nitrogen transformation, which accounted for 97.11% of NH₄⁺-N, 100% of NO₃⁻-N, and 99.98% of NO₂⁻-N removal with a maximum linear rate of 10.21 mg/L/h, 10.46 mg/L/h, and 10.77 mg/L/h, respectively. Assimilation rather than denitrification was the main mechanism for the environmental nitrogen depletion mediated by W30. The effect of environmental constraints on aerobic NO₃⁻-N removal were characterized, following a membrane bioreactor effluent test under an oxic condition. Compared to known Alphaproteobacterial HN-AD microbes, we showed that Pannonibacter sp. W30 could deplete nitrogen with no NO₂⁻-N or NO₃⁻-N accumulation in the HN-AD process. Therefore, the application of Pannonibacter sp. W30 has the potential for developing a felicitous HN-AD technology to treat N-laden wastewater at the full-scale level.

To enhance the degradability of poly(butylene adipate-co-terephthalate) (PBAT), reed fiber (RF) was blended with PBAT to create composite materials. In this study, a fifteen day degradation experiment was conducted using four different enzyme solutions containing lipase, cellulase, Proteinase K, and esterase, respectively. The degradation process of the sample films was analyzed using an analytical balance, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). The PBAT/RF composites exhibited an increased surface hydrophilicity, which enhanced their degradation capacity. Among all the enzymes tested, lipase had the most significant impact on the degradation rate. The weight loss of PBAT and PBAT/RF, caused by lipase, was approximately 5.63% and 8.17%, respectively. DSC analysis revealed an increase in the melting temperature and crystallinity over time, especially in the film containing reed fibers. FTIR results indicated a significant weakening of the ester bond peak in the samples. Moreover, this article describes a biodegradation study conducted for three months under controlled composting conditions of PBAT and PBAT/RF samples. The results showed that PBAT/RF degraded more easily in compost as compared to PBAT. The lag phase of PBAT/RF was observed to decrease by 23.8%, while the biodegradation rate exhibited an increase of 11.8% over a period of 91 days. SEM analysis demonstrated the formation of more cracks and pores on the surface of PBAT/RF composites during the degradation process. This leads to an increased contact area between the composites and microorganisms, thereby accelerating the degradation of PBAT/RF. This research is significant for preparing highly degradable PBAT composites and improving the application prospects of biodegradable green materials. PBAT/RF composites are devoted to replacing petroleum-based polymer materials with sustainable, natural materials in advanced applications such as constructional design, biomedical application, and eco-environmental packaging.