Johnson Matthey Technology Review - Volume 64, Issue 4, 2020

The main objective of this study was to evaluate the performance of a self-developed filler micro-embedded with Pseudomonas putida (P. putida) for toluene removal in a biofilter under various loading rates. The results show that the biofilter could reach 85% removal efficiency (RE) on the eighth day and remain above 90% RE when the empty bed residence time (EBRT) was 18 s and the inlet loading was not higher than 41.4 g m⁻³ h⁻¹. Moreover, the biofilter could tolerate substantial transient shock loadings. After two shut-down experiments, the removal efficiency could be restored to above 80% after a recovery period of three days and six days, respectively. Sequence analysis of the 16S rRNA gene of fillers in four operating periods revealed that the highly efficient bacterial colonies in fillers mainly included Firmicutes, Actinobacteria and Proteobacteria and that the abundance of Bacteroidetes increased significantly during the re-start period.

Generation of artificial metalloenzymes (ArMs) has gained much inspiration from the general understanding of natural metalloenzymes. Over the last decade, a multitude of methods generating transition metal-protein hybrids have been developed and many of these new-to-nature constructs catalyse reactions previously reserved for the realm of synthetic chemistry. This perspective will focus on ArMs incorporating 4d and 5d transition metals. It aims to summarise the significant advances made to date and asks whether there are chemical strategies, used in nature to optimise metal catalysts, that have yet to be fully recognised in the synthetic enzyme world, particularly whether artificial enzymes produced to date fully take advantage of the structural and energetic context provided by the protein. Further, the argument is put forward that, based on precedence, in the majority of naturally evolved metalloenzymes the direct coordination bonding between the metal and the protein scaffold is integral to catalysis. Therefore, the protein can attenuate metal activity by positioning ligand atoms in the form of amino acids, as well as making non-covalent contributions to catalysis, through intermolecular interactions that pre-organise substrates and stabilise transition states. This highlights the often neglected but crucial element of natural systems that is the energetic contribution towards activating metal centres through protein fold energy. Finally, general principles needed for a different approach to the formation of ArMs are set out, utilising direct coordination inspired by the activation of an organometallic cofactor upon protein binding. This methodology, observed in nature, delivers true interdependence between metal and protein. When combined with the ability to efficiently evolve enzymes, new problems in catalysis could be addressed in a faster and more specific manner than with simpler small molecule catalysts.

Cooling towers are industrial cooling units operating to dissipate heat. As with any surface in contact with aqueous systems, biofilm formation appears on the surface of heat exchangers. Although biofilm formation on plastic tower fill in wet cooling towers has been studied widely, no studies were found regarding biofilm formation on steel heat exchangers in closed-loop systems. In this study, heat exchangers were coated with nano-silica, which is known to reduce the formation of biofilm. Natural biofilm formation was monitored for six months. Biofouling was examined monthly using epifluorescence microscopy by assessing the numbers of live and dead bacteria. It was observed that the biofilm layer formed on the nano-silica coated heat exchanger surfaces was significantly lower than on the control surfaces. 3 log microbial reduction was recorded on coated surfaces in the first month. After six months, total biomass on control surfaces reached 1.28 × 10¹² cell cm⁻², while the biomass on nano-silica coated surfaces was 6.3 × 10⁴ cell cm⁻².

Shape-memory polymers (SMPs) enable the production of stimuli-responsive polymer-based materials with the ability to undergo a large recoverable deformation upon the application of an external stimulus. Academic and industrial research interest in the shape-memory effects (SMEs) of these SMP-based materials is growing for task-specific applications. This mini-review covers interesting aspects of SMP-based materials, their properties, how they may be investigated and highlights examples of the potential applications of these materials.

The purpose of this study was to devise an antibacterial treatment for footwear insock leathers. Orange oil-loaded chitosan microparticles were utilised for this purpose. Emulsion formulations with different ratios were prepared, and from these formulations microparticles were manufactured using a spray drying technique. Microparticles obtained in this way were applied to the insock leathers using a finishing process. Successful encapsulation was confirmed by ultraviolet-visible (UV-vis) spectrophotometry, Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) techniques. The microparticles exhibited highly spheroid shape with a size range of 3–5 μm. Microparticle encapsulation efficiencies ranged from 79.41% ± 3.36% to 86.60% ± 1.13%. After performing microbiological tests and in vitro release studies on the insock leathers, it was determined that the prepared microparticles are able to perform core material delivery. Also, successful microparticle application resulted in these leathers acquiring antibacterial properties. The products and process are biodegradable, nontoxic and biocompatible.

Oil fields harbour a wide variety of microorganisms with different metabolic capabilities. To examine the microbial ecology of petroleum reservoirs, a molecular-based approach was used to assess the composition of bacterial communities in produced water of Diyarbakır oil fields in Turkey. Denaturing gradient gel electrophoresis (DGGE) of polymerase chain reaction (PCR)-amplified 16S rRNA gene fragments was performed to characterise the bacterial community structure of produced water samples and to identify predominant community members after sequencing of separated DGGE bands. The majority of bacterial sequences retrieved from DGGE analysis of produced water samples belonged to unclassified bacteria (50%). Among the classified bacteria, Proteobacteria (29.2%), Firmicutes (8.3%), Bacteroidetes (8.3%) and Actinobacteria (4.2%) groups were identified. Pseudomonas was the dominant genus detected in the produced water samples. The results of this research provide, for the first time, insight into the complexity of microbial communities in the Diyarbakır oil reservoirs and their dominant constituents.

Since cave ecosystems have extraordinary environmental conditions, these ecosystems offer opportunities for microbiological studies. In this study, cultivable bacteria isolated from Parsık cave, Turkey, were investigated regarding enzyme profiles, antibiotic resistance and potential for production of antimicrobial agents. The metabolic properties of 321 bacterial isolates were determined. The most produced enzyme by the isolates was found to be tyrosine arylamidase. The enzymatic reactions of the bacteria showed that Parsık cave isolates have high aminopeptidase activity. The highest antibiotic resistance frequency of the isolates was 38.6% against ampicillin. While the isolates displayed variable inhibition rates against tested pathogenic microorganisms, they showed the highest inhibition against Candida albicans. The results show that the bacteria isolated from Parsık cave have potential for further studies related to biotechnological applications. The study findings contribute increased knowledge on metabolic peculiarities of bacteria isolated from cave ecosystems.

Antibacterial resistant bacteria are a significant problem in the hide or skin soaking process due to their destructive properties on finished leather. Lichens may be a solution to overcome this resistance problem. Enterococcus durans (99.86%) was isolated from soak liquor samples. For screening of possible antibacterial effects of lichen acetone extracts, six lichen species (Hypogymnia tubulosa,H. physodes,Evernia divaricata, Pseudevernia furfuracea, Parmelia sulcata and Usnea sp.) were examined by nine-fold dilution against E. durans.H. tubulosa,H. physodes and E. divaricata extracts showed antibacterial effects at the concentrations of 240 μg ml⁻¹, 120 μg ml⁻¹ and 60 μg ml⁻¹ whereas the extracts of P. furfuracea had an antibacterial effect at 240 μg ml⁻¹ and 120 μg ml⁻¹. On the other hand, P. sulcata had no antibacterial effect. The most successful lichen extract was determined to be Usnea sp. at the concentrations of 240 μg ml⁻¹, 120 μg ml⁻¹, 60 μg ml⁻¹, 30 μg ml⁻¹ and 15 μg ml⁻¹. In conclusion, lichen extracts seem to have potential antibacterial efficacies against E. durans.

Proteolytic and lipolytic extremely halophilic archaea found in curing salt may contaminate skins during the brine curing process and damage skin structure. In the present study, three proteolytic and lipolytic extremely halophilic archaea were isolated from deteriorated salted sheepskins and characterised using conventional and molecular methods. Each test strain (Haloarcula salaria AT1, Halobacterium salinarum 22T6, Haloarcula tradensis 7T3), a mixed culture of these strains and the mixed culture treated with 1.5 A direct current (DC) were used for brine curing processes of fresh sheepskins and examined during 47 days of storage to evaluate the degree of destruction wreaked by these microorganisms. Both organoleptic properties and scanning electron microscopy (SEM) images of sheepskins proved that each separate test strain and the mixed culture caused serious damage. However, the mixed culture of strains treated with electric current did not damage sheepskin structure. Therefore, we highly recommend sterilisation of brine using DC to prevent archaeal damage on cured hides and skins in the leather industry.

Heavy metal and antibiotic-resistant bacteria have potential for environmental bioremediation applications. Resistant bacteria were investigated in sediment and seawater samples taken from the Aegean Sea, Turkey, between 2011 and 2013. Bioindicator bacteria in seawater samples were tested using the membrane filtration technique. The spread plate technique and VITEK^® 2 Compact 30 micro identification system were used for heterotrophic aerobic bacteria in the samples. The minimum inhibition concentration method was used for heavy metal-resistant bacteria. Antibiotic-resistant bacteria were tested using the disk diffusion method. All bacteria isolated from sediment samples showed 100% resistance to rifampicin, sulfonamide, tetracycline and ampicillin. 98% of isolates were resistant against nitrofurantoin and oxytetracycline. Higher antibiotic and heavy metal resistance was recorded in bacteria isolated from sediment than seawater samples. The highest levels of bacterial metal resistance were recorded against copper (58.3%), zinc (33.8%), lead (32.1%), chromium (31%) and iron (25.2%). The results show that antibiotic and heavy metal resistance in bacteria from sediment and seawater can be observed as responses to environmental influences including pollution in marine areas.

The asymmetric reduction of C=C double bonds is a sought-after chemical transformation to obtain chiral molecules used in the synthesis of fine chemicals. Biocatalytic C=C double bond reduction is a particularly interesting transformation complementary to more established chemocatalytic methods. The enzymes capable of catalysing this reaction are called ene-reductases (ENEs). For the reaction to take place, ENEs need an electron withdrawing group (EWG) in conjugation with the double bond. Especially favourable EWGs are carbonyls and nitro groups; other EWGs, such as carboxylic acids, esters or nitriles, often give poor results. In this work, a substrate engineering strategy is proposed whereby a simple transformation of the carboxylic acid into a fluorinated ester or a cyclic imide allows to increase the ability of ENEs to reduce the conjugated double bond. Up to complete conversion of the substrates tested was observed with enzymes ENE-105 and *ENE-69.