Hydrocarbon Degradation and Microbial Survival Improvement in Response to γ-Polyglutamic Acid Application

Abstract

To improve the environmental sustainability of cleanup activities of contaminated sites there is a need to develop technologies that minimize soil and habitat disturbances. Cleanup technologies, such as bioremediation, are based on biological products and processes, and they are important for the future of our planet. We studied the potential of γ-poly glutamic acid (PGA) as a natural component of biofilm produced by Bacillus sp. to be used for the decomposition of petroleum products, such as heavy naphtha (N), lubricating oil (O), and grease (G). The study aimed to assess the impact of the use of different concentrations of PGA on the degradation process of various fractions of petroleum hydrocarbons (PH) and its effect on bacterial population growth in harsh conditions of PH contamination. In laboratory conditions, four treatments of PGA with each of the petroleum products (N, O, and G) were tested: PGA0 (reference), PGA1 (1% PGA), PGA1B (1% PGA with Bacillus licheniformis), and PGA10 (10% PGA). After 7, 28, 56, and 112 days of the experiment, the percentage yield extraction, hydrocarbon mass loss, geochemical ratios, pH, electrical conductivity, and microorganisms survival were determined. We observed an increase in PH removal, reflected as a higher amount of extraction yield (growing with time and reaching about 11% in G) and loss of hydrocarbon mass (about 4% in O and G) in all treatments of the PGA compared to the reference. The positive degradation impact was intensive until around day 60. The PH removal stimulation by PGA was also reflected by changes in the values of geochemical ratios, which indicated that the highest rate of degradation was at the initial stage of the process. In general, for the stimulation of PH removal, using a lower (1%) concentration of PGA resulted in better performance than a higher concentration (10%). The PH removal facilitated by PGA is related to the anionic homopoliamid structure of the molecule and its action as a surfactant, which leads to the formation of micelles and the gradual release of PH absorbed in the zeolite carrier. Moreover, the protective properties of PGA against the extinction of bacteria under high concentrations of PH were identified. Generally, the γ-PGA biopolymer helps to degrade the hydrocarbon pollutants and stabilize the environment suitable for microbial degraders development.

Oil-Contaminated Soil Remediation with Biodegradation by Autochthonous Microorganisms and Phytoremediation by Maize (Zea mays)

“…The Ambiogel ® (Ambioteco Sp. z o.o., Staszów, Poland) containing 5% of pure poly-γ-glutamic acid with varying molecular mass (2000–1000 kDa—30%; 1000–140 kDa—50%; 100 kDa–300 Da—15%; <300 Da—5%) was used as a γ-PGA additive [ 130 ]. The phytoremediation tests used seeds of maize ( Zea mays ) (Legutko, Poland) planted in pre-treated soil (after completing biodegradation tests using inoculation with biopreparations) in May 2022.…”

Evaluation of the Effectiveness of Bioaugmentation-Assisted Phytoremediation of Soils Contaminated with Petroleum Hydrocarbons Using Echinacea purpurea

“…Moreover, the use of γ-PGA as an additive to microbial consortia made it possible to provide the plant with a readily available source of carbon and energy, which further influenced biomass production. It is also worth noting that some literature sources report that γ-PGA can be considered a biosurfactant, which affects the diffusion of xenobiotics into the root [17,62,64,75]. Chromatographic analyses of the roots and shoots showed that extraction of aliphatic hydrocarbons from the soil to the root occurred most readily in systems 4 and 5, and 10 and 11.…”

“…More information about the microbial consortia used in the research is available in Supplementary Materials. A commercially available formulation of Ambiogel ® (Ambioteco, Staszów, Poland) containing 5% pure poly-γ-glutamic acid [64], whose impact on the efficiency of bioremediation has been confirmed in earlier studies, was used as an additive for microbial consortia. The phytoremediation process was carried out using seeds of Echinacea purpurea (Legutko, Poland), which were sown in each of the tested systems.…”