Engineering of a silica encapsulation platform for hydrocarbon degradation using Pseudomonas sp. NCIB 9816‐4

Abstract

Industrial application of encapsulated bacteria for biodegradation of hydrocarbons in water requires mechanically stable materials. A silica gel encapsulation method was optimized for Pseudomonas sp. NCIB 9816-4, a bacterium that degrades more than 100 aromatic hydrocarbons. The design process focused on three aspects: (i) mechanical property enhancement; (ii) gel cytocompatibility; and (iii) reduction of the diffusion barrier in the gel. Mechanical testing indicated that the compressive strength at failure (σf ) and elastic modulus (E) changed linearly with the amount of silicon alkoxide used in the gel composition. Measurement of naphthalene biodegradation by encapsulated cells indicated that the gel maintained cytocompatibility at lower levels of alkoxide. However, significant loss in activity was observed due to methanol formation during hydrolysis at high alkoxide concentrations, as measured by FTIR spectroscopy. The silica gel with the highest amount of alkoxide (without toxicity from methanol) had a biodegradation rate of 285 ± 42 nmol/L-s, σf = 652 ± 88 kPa, and E = 15.8 ± 2.0 MPa. Biodegradation was sustained for 1 month before it dropped below 20% of the initial rate. In order to improve the diffusion through the gel, polyvinyl alcohol (PVA) was used as a porogen and resulted in a 48 ± 19% enhancement in biodegradation, but it impacted the mechanical properties negatively. This is the first report studying how the silica composition affects biodegradation of naphthalene by Pseudomonas sp. NCIB 9816-4 and establishes a foundation for future studies of aromatic hydrocarbon biodegradation for industrial application.

Signal Disruption Leads to Changes in Bacterial Community Population

“…Silica encapsulation is a method of choice for entrapping enzymes or cells due to their compatibility with biological molecules, mechanical properties, durability, stability, cost, and easy synthesis. Silica gels have been previously used to encapsulate bioreactive bacteria for bioremediation (Reátegui et al, 2012; Aukema et al, 2014; Sakkos et al, 2016, 2017). While most encapsulated bacteria may remain viable through the process of making the gels (Benson et al, 2018), it is likely to be unnecessary in this study, since the lactonase Sso Pox is a metalloenzyme that only requires a water molecule as the nucleophile for the hydrolytic reaction (Elias et al, 2008).…”

“…In order to determine the effects of AHL degradation in the context of a complex microbial community, we used a silica gel, bead-based, bioencapsulation technique. Silica is a cytocompatible material in which bacteria or their enzymes can be physically confined, retained within the matrix, and protected from the environment (Reátegui et al, 2012; Mutlu et al, 2013, 2015; Aukema et al, 2014; Sakkos et al, 2016, 2017). Here, we used encapsulated Escherichia coli cells overexpressing the lactonase Sso Pox W263I to produce enzymatically active beads.…”

Silica ecosystem for synergistic biotransformation

“…3d). Dissolved oxygen in water at room temperature (260 μM) can be utilized to transform approximately 15% of a saturated (246 μM) naphthalene solution into CO 2 (based on 7.5 moles of O 2 per mole of naphthalene as previously reporte25). This suggests that some partial transformation of naphthalene to intermediate species occurred without complete transformation.…”

Enhanced Carbofuran Degradation Using Immobilized and Free Cells of Enterobacter sp. Isolated from Soil

“…The presence of heavy metals in polluted areas is one of the main limiting factors for bioremediation because several organisms might not tolerate high concentrations of metals; therefore, their ability to degrade pollutants might reduce due to the effect of metals [ 31 ], and consequently, the need to assess the effect of heavy metals on the biodegradation of organic compounds. Many researchers reported the effects of heavy metal on the microbial growth; yet, there is very limited information concerning their effects on the degradation of pesticides [ 22 , 32 ].…”