Selective cultivation of bacterial strains with lipolytic and hydrocarbon-oxidizing activity from bottom sediments of the Ob River, Western Siberia

Bacteria play a key role in biogeochemical cycles in natural and anthropogenic ecosystems. In river ecosystems, bacteria intensively colonize silt sediments. Microorganisms are essential for energy conversion, biogeochemical nutrient cycling, pollutant degradation, and biotransformation of organic matter; therefore, bottom sediments can be a source of metabolically diverse microorganisms, including those with promise for industrial biotechnologies. The aim of this work was to isolate and study pure cultures of microorganisms – producers of industrially important enzymes and decomposers of organic matter – from bottom sediments of the Ob River. Pork fat and diesel fuel were used as substrates to obtain enrichment and pure cultures for selective cultivation of bacteria with lipolytic and hydrocarbon-oxidizing activity. A total of 21 pure cultures were isolated. The phylogenetic position of the obtained bacterial isolates was determined based on the analysis of 16S rRNA gene sequences. The strains isolated on selective media belonged to representatives of the genera Pseudomonas and Aeromonas (Gammaproteobacteria), and the genus Microvirgula (Betaproteobacteria). The ability of strains to grow on culture media containing pork fat, olive oil and diesel fuel was analyzed. The lipolytic activity of the isolates was evidenced by cultivation on a diagnostic medium containing 1 % tributyrin. The phylogenetic and metabolic diversity of the cultivated non-pathogenic bacterial strains with lipolytic and oil-oxidizing activity revealed in the study indicates the biotechnological potential of the isolates. The most promising strains were M. aerodenitrificans sp. LM1 and P. lini sp. KGS5K3, which not only exhibited lipolytic activity on the diagnostic medium with tributyrin in a wide temperature range, but also utilized diesel fuel, pork fat and olive oil.

Two polyurethanases PueA and PueB are major extracellular lipases partly secreted by the mediation of their cognate ABC exporter AprDEF in Pseudomonas protegens Pf-5

Two polyurethanases PueA and PueB from Pseudomonas protegens Pf-5 have been reported to have hydrolytic activity against synthetic p-nitrophenyl palmitate of lipase substrate, and PueA may play a more effective role in this activity. However, it is still unknown whether PueA and PueB play similar parts in the lipase activity against natural acylglycerols and achieve the extracellular secretion via their cognate ABC exporter AprDEF. In this study, we investigated these questions through the construction of four markerless deletion mutants in Pf5139 (Δupp derivative of Pf-5), two heterologous co-expression strains and their three control strains in lipase-free Escherichia coli BL21(DE3), and detected their lipase activities by the tributyrin plate assay and the liquid culture assay. The results showed that PueA and PueB, classified as subfamily I.3 lipases, are major extracellular lipases involved in the uptake of oil in Pf-5, and PueA plays a leading role in extracellular lipase activity. In addition, the extracellular secretion of PueA and PueB can be partly mediated via AprDEF in Pf-5 and BL21(DE3). Finally, PueA and PueB are also able to achieve the extracellular secretion without the assistance of AprDEF in Pf-5 and BL21(DE3).

Optimization of an organic solvent-tolerant lipase production by Staphylococcus capitis SH6. Immobilization for biodiesel production and biodegradation of waste greases

Using the statistical approach, this work seeks to optimize the process parameters to boost the generation of an organic solvent-tolerant lipase by Staphylococcus capitis SH6. The main parameters influencing the enzyme production were identified by using Plackett-Burman's screening design. Among the test variables, only tryptone (25 g/L), malt extract (2.5 g/L), NaCl (10 g/L) and pH (7.0) contributed positively to enzyme production. Then, the crude lipase was immobilized by adsorption on CaCO₃ at pH 10. A maximum immobilization efficiency of 82% was obtained by incubating 280 mg of enzyme with CaCO₃ (1 g) during 30 min. The immobilized lipase was more stable toward organic solvents than the free enzyme. It retained about 90% of its original activity in the presence of ethanol and methanol. After that, the immobilized enzyme was used for biodiesel production by transesterification process between waste oil and methanol or ethanol during 24 h at 30 °C. Our results show that the lipase can be utilized efficiently in biodiesel industry. Likewise, we have demonstrated that the immobilized enzyme may be implicated in the biodegradability of waste grease; the maximum conversion yield into fatty acids obtained after 12 h at 30 °C, was 57%.

Stability and structure of Penicillium chrysogenum lipase in the presence of organic solvents

The present work describes the enzymatic properties of Penicillium chrysogenum lipase and its behavior in the presence of organic solvents. The temperature and pH optima of the purified lipase was found to be 55 °C and pH 8.0 respectively. The lipase displayed remarkable stability in both polar and non-polar solvents upto 50% (v/v) concentrations for 72 h. A structural perspective of the purified lipase in different organic solvents was gained by using circular dichroism and intrinsic fluorescence spectroscopy. The native lipase consisted of a predominant α-helix structure which was maintained in both polar and non-polar solvents with the exception of ethyl butyrate where the activity was decreased and the structure was disrupted. The quenching of fluorescence intensity in the presence of organic solvents indicated the transformation of the lipase microenviroment P. chrysogenum lipase offers an interesting system for understanding the solvent stability mechanisms which could be used for rationale designing of engineered lipase biocatalysts for application in organic synthesis in non-aqueous media.

Isolation and characterization of organic matter-degrading bacteria from coking wastewater treatment plant

As a step toward bioaugmentation of coking wastewater treatment 45 bacteria strains were isolated from the activated sludge of a coking wastewater treatment plant (WWTP). Three strains identified as Bacillus cereus, Pseudomonas synxantha, and Pseudomonas pseudoaligenes exhibited high dehydrogenase activity which indicates a strong ability to degrade organic matter. Subsequently all three strains showed high naphthalene degradation abilities. Naphthalene is a refractory compound often found in coking wastewater. For B. cereus and P. synxantha the maximum naphthalene removal rates were 60.4% and 79.8%, respectively, at an initial naphthalene concentration of 80 mg/L, temperature of 30 °C, pH of 7, a bacteria concentration of 15% (V/V), and shaking speed of 160 r/min. For P. pseudoaligenes, the maximum naphthalene removal rate was 77.4% under similar conditions but at 35 °C.

Autotransporter domain-dependent enzymatic analysis of a novel extremely thermostable carboxylesterase with high biodegradability towards pyrethroid pesticides

The EstPS1 gene, which encodes a novel carboxylesterase of Pseudomonas synxantha PS1 isolated from oil well-produced water, was cloned and sequenced. EstPS1 has an open reading frame of 1923 bp and encodes the 640-amino acid carboxylesterase (EstPS1), which contains an autotransporter (AT) domain (357–640 amino acids). Homology analysis revealed that EstPS1 shared the highest identity (88%) with EstA from Pseudomonas fluorescens A506 (NCBI database) and belonged to the carboxylesterase family (EC 3.1.1.1). The optimum pH and temperature of recombinant EstPS1 were found to be 8.0 and 60 °C, respectively. EstPS1 showed high thermostability, and the half-lives (T_1/2 thermal inactivation) at 60, 70, 80, 90, and 100 °C were 14 h, 2 h, 31 min, 10 min, and 1 min, respectively. To understand the role of the AT domain in carboxylesterase, AT domain-truncated carboxylesterase (EstPS1ΔAT) was generated. EstPS1ΔAT showed a clearly decreased secretion rate, owing to the AT domain strongly improved secretory expression in the heterogeneous system. EstPS1 degraded various pyrethroid pesticides, and hydrolysis efficiencies were dependent on the pyrethroid molecular structure. EstPS1 degraded all the tested pyrethroid pesticides and hydrolysed the p-nitrophenyl esters of medium-short-chain fatty acids, indicating that EstPS1 is an esterase with broad specificity.