Variations in bacterial community structures during geothermal water recharge-induced bioclogging

Rhamnolipid-induced alleviation of bioclogging in Managed Aquifer Recharge (MAR): Interactions with bacteria and porous media

The prevention and treatment of bioclogging is of great significance to the application of Managed Aquifer Recharge (MAR). This study investigated the alleviating effect of biosurfactant rhamnolipid (RL) on bioclogging by laboratory-scale percolation experiments. The results show that the addition of RL greatly reduced bioclogging. Compared with the group without RL, the relative hydraulic conductivity (K') of the 100 mg/L RL group increased 5 times at the end of the experiment (23 h), while the bacterial cell amount and extracellular polymeric substances (EPS) content on the sand column surface (0-2 cm) decreased by 60.8% and 85.7%, respectively. In addition, the richness and diversity of the microbial communities within the clogging matter decreased after the addition of RL. A variety of bacterial phyla were found, among which Proteobacteria were predominant in all groups. At the genus level, RL reduced the relative abundance of Acinetobacter, Bacillus, Klebsiella, and Pseudomonas. These microbes are known as strong adhesion, large size, and easy to form biofilms, therefore playing a critical role during MAR bioclogging. Moreover, RL changed the surface properties of bacteria and porous media, which results in the increase of electrostatic repulsion and decrease of hydrophobic interaction between them. Therefore, RL mediated the bacteria-porous media interaction to reduce biomass in porous media, thereby alleviating bioclogging. This study implies that RL's addition is an environmentally friendly and effective method to alleviate the bioclogging in MAR.

Petroleum spill bioremediation by an indigenous constructed bacterial consortium in marine environments

In the process of marine oil spill remediation, adding highly efficient oil degrading microorganisms can effectively promote oil degradation. However, in practice, the effect is far less than expected due to the inadaptability of microorganisms to the environment and their disadvantage in the competition with indigenous bacteria for nutrients. In this article, four strains of oil degrading bacteria were isolated from seawater in Jiaozhou Bay, China, where a crude oil pipeline explosion occurred seven years ago. Results of high-throughput sequencing, diesel degradation tests and surface activity tests indicated that Peseudomonas aeruginosa ZS1 was a highly efficient petroleum degrading bacterium with the ability to produce surface active substances. A diesel oil-degrading bacterial consortium (named SA) was constructed by ZS1 and another oil degrading bacteria by diesel degradation test. Degradation products analysis indicated that SA has a good ability to degrade short chain alkanes, especially n-alkanes (C₁₀-C₁₈). Community structure analysis showed that OTUs of Alcanivorax, Peseudomona, Ruegeria, Pseudophaeobacter, Hyphomonas and Thalassospira on genus level increased after the oil spill and remained stable throughout the recovery period. Most of these enriched microorganisms were related to known alkane and hydrocarbon degraders by the previous study. However, it is the first time to report that Pseudophaeobacter was enriched by using diesel as the sole carbon source. The results also indicated that ZS1 may have a dominant position in competition with indigenous bacteria. Oil pollution has an obvious selective effect on marine microorganisms. Although the oil degradation was promoted after SA injection, the recovery of microbial community structure took a longer time.

Microeukaryotic Community Shifting Along a Lentic-Lotic Continuum

As an important regulator of ecosystem functions in river systems, microeukaryotes play an important role in energy and material conversion, yet little is known about the shift along a lentic-lotic continuum. In this study, the 18S rRNA genes sequencing was used to identify the microeukaryotic communities at 82 sites along a lentic-lotic continuum with the aim of understanding the impact of upstream inlet river on microeukaryotic communities in Baiyang Lake (BYD) and its downstream. Our results showed that the upstream inlet river affected the diversity and community composition of microeukaryotes in BYD and downstream rivers, and environmental variables greatly affected the composition of microeukaryotic community. The community composition in BYD had lower variabilities. Co-occurrence network analysis revealed that the network was non-random and clearly parsed into three modules, and different modules were relatively more abundant to a particular area. As keystone taxa, some nodes of the upstream microeukaryotic network played an important role in structuring network and maintaining the stability of the ecosystem. In BYD and downstream, the microeukaryotic network was highly fragmented, and the loss of keystone taxa would have an adverse impact on the integrity and function of the microeukaryotic community. Microeukaryotes had strong tendencies to co-occur, which may contribute to the stability and resilience of microeukaryotic communities. Overall, these findings extend the current understanding of the diversity and community composition of microeukaryotic along a lentic-lotic continuum.