Genetically modified indigenous Pseudomonas aeruginosa drove bacterial community to change positively toward microbial enhanced oil recovery applications.

AIMS: Microbial enhanced oil recovery (MEOR) is cost-effective and eco-friendly for oil exploitation. Genetically modified biosurfactants-producing high-yield strains are promising for ex-situ MEOR. However, can they survive and produce biosurfactants in petroleum reservoirs for in-situ MEOR? What is their effect on the native bacterial community? METHODS AND RESULTS: A genetically modified indigenous biosurfactants-producing strain Pseudomonas aeruginosa PrhlAB was bioaugmented in simulated reservoir environments. Pseudomonas aeruginosa PrhlAB could stably colonize in simulated reservoirs. Biosurfactants (200 mg l-1) were produced in simulated reservoirs after bio-augmenting strain PrhlAB. The surface tension of fluid was reduced to 32.1 mN m-1. Crude oil was emulsified with an emulsification index of 60.1%. Bio-augmenting strain PrhlAB stimulated the MEOR-related microbial activities. Hydrocarbon-degrading bacteria and biosurfactants-producing bacteria were activated, while the hydrogen sulfide-producing bacteria were inhibited. Bio-augmenting P. aeruginosa PrhlAB reduced the diversity of bacterial community, and gradually simplified the species composition. Bacteria with oil displacement potential became dominant genera, such as Shewanella, Pseudomonas, and Arcobacter. CONCLUSIONS: Culture-based and sequence-based analyses reveal that genetically modified biosurfactants-producing strain P. aeruginosa PrhlAB are promising for in-situ MEOR as well.

Enhanced chromium and nitrogen removal by constructing a biofilm reaction system based on denitrifying bacteria preferential colonization theory.

Understanding the developmental characteristics of microbial communities in biofilms is crucial for designing targeted functional microbial enhancements for the remediation of complex contamination scenarios. The strong prioritization effect of microorganisms confers the ability to colonize strains that arrive first dominantly. In this study, the auto-aggregating denitrifying bacterial Pseudomonas stutzeri strain YC-34, which has both nitrogen and chromium removal characteristics, was used as a biological material to form a stable biofilm system based on the principle of dominant colonization and biofortification. The effect of the biofilm system on nitrogen and chromium removal was characterized by measuring the changes in the quality of influent and effluent water. The pattern of biofilm changes was analyzed by measuring biofilm content and thickness and characterizing extracellular polymer substances (EPS). Further analysis of the biofilm microbiota characteristics and potential functions revealed the mechanism of strain YC-34 biofortified biofilm. The results revealed that the biofilm system formed could achieve 90.56% nitrate-nitrogen removal with an average initial nitrate-nitrogen concentration of 51.9 mg/L and 40% chromium removal with an average initial hexavalent chromium Cr(VI) concentration of 7.12 mg/L. The biofilm properties of the system were comparatively analyzed during the biofilm formation period, the fluctuation period of Cr(VI)-stressed water quality, and the stabilization period of Cr(VI)-stressed water quality. The biofilm system may be able to increase the structure of hydrogen bonds, the type of protein secondary structure, and the abundance of amino acid-like components in the EPS, which may confer biofilm tolerance to Cr(VI) stress and allow the system to maintain a stable biofilm structure. Furthermore, microbial characterization indicated an increase in microbial diversity in the face of chromium stress, with an increase in the abundance of nitrogen removal-associated functional microbiota and an increasing trend in the abundance of nitrogen transfer pathways. These results demonstrate that the biofilm system is stable in nitrogen and chromium removal. This bioaugmentation method may provide a new way for the remediation of heavy metal-polluted water bodies and also provides theoretical and application parameters for the popularization and application of biofilm systems.

Competitive bio-augmentation overcoming unusual direct inhibitor inefficacy in mainstream nitrite-oxidizing bacteria suppression: Unveiling the underpinnings in microbial and nitrogen metabolism aspects.

The long-stabilized mainstream partial nitritation/Anammox (PN/A) process continues to encounter significant challenges from nitrite-oxidizing bacteria (NOB). Therefore, this study aimed to determine an efficient, rapid, and easily implementable strategy for inhibiting NOB. A laboratory-scale reactor was operated continuously for 325 days, experiencing NOB outbreak in mainstream and recovery with simulated sidestream support. The results show that direct inhibitory strategies including intermittent aeration and approximately 35 mg/L free ammonia had unusual weak inhibitory effects on NOB activity. Subsequently, the exogenous Anammox from sidestream employed as a competitive bio-augmentation approach rapidly inhibited NOB dynamics. Evidence suggests that the damaged hydroxyapatite granules under low pH conditions might have contributed to NOB dominance by diminishing Anammox bacteria activity, thereby creating a substrate-rich environment favoring NOB survival. In contrast, the introduction of exogenous Candidatus Kuenenia facilitated the nitrogen removal efficiency from 32.5 % to over 80 %. This coincided with a decrease in the relative abundance of Nitrospira from 16.5 % to 2.7 % and NOB activity from 0.34 to 0.07 g N/(g mixed liquor volatile suspended solid)/d. Metagenomic analysis reveals a decrease in the functional potential of most nitrite transport proteins, coupled with a significant increase in eukaryotic-like serine/threonine-protein kinase involved in cellular regulation, during the Anammox activity recovery. This study's findings reveal the feasibility of the bio-augmentation based on substrate competition, wherein sidestream processes support the mainstream PN/A integration, offering significant potential for practical applications.

Dynamic pulse approach to enhancing mainstream Anammox process stability: Integrating sidestream support and tackling nitrite-oxidizing bacteria challenges.

Nitrite-oxidizing bacteria (NOB) seriously threaten the partial nitritation and Anammox (PN/A) process, hindering its mainstream application. Herein, a one-stage PN/A reactor was continuously operated for 245 days under nitrogen loading rate lifted from 0.4 g N/L/d to 0.6 g N/L/d and 0.8 g N/L/d with the nitrogen removal efficiency of 71 %, 64 %, and 41 %, respectively. Furthermore, the NOB species over time was identified as Nitrospira_sp._OLB3, exhibiting an increase of the relative abundance from 0.9 % to 4.3 %. The hydroxyapatite (HAP) granules gradually lost their microbiological function of Anammox bacteria then aged, leading to NOB dominance. Therefore, one "pulse therapy" was introduced and combined with "continuous enhancement" of Anammox sludge supported by sidestream to competitively limit the NOB dynamics. The treatment's effect persisted for around two months. The strategy that returning at least 50 % of the impaired HAP granular sludge to the sidestream for recultivation could fulfill the bottlenecks of mainstream PN/A.