Abstract. Alyousif NA, Al-Tamimi WH, Al-sahib MAA. 2022. Evaluation of the effect of various nutritional and environmental factors on biosurfactant production by Staphylococcus epidermidis. Biodiversitas 23: 3533-3538. Biosurfactants are biological surface-active compounds synthesized mainly by hydrocarbon-utilizing bacteria. The properties of biosurfactants make them promising compounds for the application in various fields. The current study evaluated the effect of various nutritional and environmental factors on biosurfactants produced by Staphylococcus epidermidis. This bacterium, for first time in world was isolated from oilfield reservoir in the current study and identified by 16S rDNA sequencing and considered biosurfactant producer according to screening tests. Several factors were evaluated in the current study to assess the optimal conditions for producing the biosurfactant. The results demonstrated that the best carbon source was olive oil with 2% concentration and glutamic acid was the best nitrogen source with 0.2% concentration. The study demonstrated that the best biosurfactant production was recorded at incubation time of 5 days with a 3% inoculum size. Further study is required to determine the chemical structure of produced biosurfactants and to evaluate the potential application of biosurfactants in various fields, therefore constituting a stimulus for future studies.

Abstract. Alshami HGA, Al-Tamimi WH, Hateet RR. 2022. Screening for extracellular synthesis of silver nanoparticles by bacteria isolated from Al-Halfaya oil field reservoirs in Missan province, Iraq. Biodiversitas 23: 3462-3470. Microorganisms that live in deep environments are thought to be adapted to the conditions of these environments and possess enzymatic systems that can be useful in scientific and commercial applications. The study aimed to isolate, identify, and screening of silver nanoparticles (AgNPs)-producing bacteria from five samples of produced water of the Al-Halfaya oil field reservoirs in Missan governorate, Iraq. The results revealed a total of 22 bacterial isolates were isolated and identified by morphological features and amplification of the 16S rDNA gene. The isolates are belonging to nine species, including Bacillus cereus strain DBA1.1, Bacillus thuringiensis strain MSP51, Neobacillus drentensis strain ROA042, Enterococcus faecalis strain 2674, Exiguobacterium mexicanum strain AB201, Klebsiella quasipneumoniae strain KP18-31, Klebsiella quasipneumoniae subsp. similipneumoniae strain 2437, Klebsiella pneumoniae strain IOB-L, and Acinetobacter lwoffii strain K34. The Gram-positive bacteria were the most dominant (55.56%), and the most frequent isolate was Klebsiella quasipneumoniae strain KP18-31 (63.64%). Six species out of nine species were recognized as AgNPs producing bacteria and B. cereus strain DBA1 was the best and most potent isolate in the synthesis of AgNPs. The phylogenetic tree was constructed depending on 16S rDNA gene sequences to determine the evolutionary relationship among the isolated bacteria.

Abstract. Alshami HGA, Al-Tamimi WH, Hateet RR. 2023. The antioxidant potential of copper oxide nanoparticles synthesized from a new bacterial strain. Biodiversitas 24: 2666-2673. Copper oxide nanoparticles (CuONPs) have recently gained much attention due to their potential in various fields. The present study aimed to screen nine bacterial strains (Klebsiella quasipneumoniae KP18-31, K. pneumoniae IOB-L, K. quasipneumoniae subsp. similipneumoniae 2437, Bacillus cereus DBA1, B. thuringiensis MSP51, Neobacillus drentensis ROA042, Enterococcus faecalis 2674, Exiguobacterium mexicanum AB201, and Acinetobacter lwoffii K34) isolated from produced water of oil field reservoirs for their ability to biosynthesize CuONPs, as well as characterize and evaluate the antioxidant potential of the manufactured CuONPs. Biosynthesized CuONPs were characterized using XRD, TEM, AFM, and zeta potential analysis. In addition, the DPPH method was used to analyze the antioxidant activity of CuONPs. The results revealed that five of the nine isolates could synthesize CuONPs. B. thuringiensis MSP5 was the best and most productive among them, and it was used for the first time in this present study as an oil field bacteria for the biosynthesis of CuONPs. The results showed that CuONPs have a spherical shape with an average size of 20, 33, and 75 nm based on XRD, TEM, and AFM analysis, respectively. The zeta potential value of the synthesized CuONPs was -12.4 mV. The antioxidant results demonstrated that CuONPs have a remarkable scavenging activity with an IC50 value of 141.68 ?g/mL. This study concluded that CuONPs were excellent free radical scavengers.