Bioprospection and selection of bacteria isolated from environments contaminated with petrochemical residues for application in bioremediation

The use of microorganisms with hydrocarbon degrading capability and biosurfactant producers have emerged as an alternative for sustainable treatment of environmental passives. In this study 45 bacteria were isolated from samples contaminated with petrochemical residues, from which 21 were obtained from Landfarming soil contaminated with oily sludge, 11 were obtained from petrochemical industry effluents and 13 were originated directly from oily sludge. The metabolization capability of different carbon sources, growth capacity and tolerance, biosurfactant production and enzymes detection were determined. A preliminary selection carried out through the analysis of capability for degrading hydrocarbons showed that 22% of the isolates were able to degrade all carbon sources employed. On the other hand, in 36% of the isolates, the degradation of the oily sludge started within 18–48 h. Those isolates were considered as the most efficient ones. Twenty isolates, identified based on partial sequencing of the 16S rRNA gene, were pre-selected. These isolates showed ability for growing in a medium containing 1% of oily sludge as the sole carbon source, tolerance in a medium containing up to 30% of oily sludge, ability for biosurfactant production, and expression of enzymes involved in degradation of aliphatic and aromatic compounds. Five bacteria, identified as Stenotrophomonas acidaminiphila BB5, Bacillus megaterium BB6, Bacillus cibi, Pseudomonas aeruginosa, and Bacillus cereus BS20 were shown to be promising for use as inoculum in bioremediation processes (bioaugmentation) of areas contaminated with petrochemical residues since they can use oily sludge as the sole carbon source and produce biosurfactants.     

Biodegradation potential of oily sludge by pure and mixed bacterial cultures

The biodegradation capacity of aliphatic and aromatic hydrocarbons of petrochemical oily sludge in liquid medium by a bacterial consortium and five pure bacterial cultures was analyzed. Three bacteria isolated from petrochemical oily sludge, identified as Stenotrophomonas acidaminiphila, Bacillus megaterium and Bacillus cibi, and two bacteria isolated from a soil contaminated by petrochemical waste, identified as Pseudomonas aeruginosa and Bacillus cereus demonstrated efficiency in oily sludge degradation when cultivated during 40 days. The bacterial consortium demonstrated an excellent oily sludge degradation capacity, reducing 90.7% of the aliphatic fraction and 51.8% of the aromatic fraction, as well as biosurfactant production capacity, achieving 39.4% reduction of surface tension of the culture medium and an emulsifying activity of 55.1%. The results indicated that the bacterial consortium has potential to be applied in bioremediation of petrochemical oily sludge contaminated environments, favoring the reduction of environmental passives and increasing industrial productivity.     

16S rDNA sequence analysis of culturable marine biofilm forming bacteria from a ship's hull

Marine bacteria from the hull of a ship in the form of biofilms or microfouling were isolated, cultured, and identified by phylogenetic analysis using 16S rDNA sequences. With an average length of 946 bp, all the 16 sequences were classified using the Ribosomal database project (RDP) and were submitted to the National Center for Biotechnology Information. Phylogenetic analysis using 16S rDNA sequences indicated that the 16 strains belonged to the Firmicutes (IK-MB6 Exiguobacterium aurantiacum, IK-MB7 Exiguobacterium arabatum, IK-MB8 Exiguobacterium arabatum, IK-MB9 Jeotgalibacillus alimentarius, IK-MB10 Bacillus megaterium, IK-MB11 Bacillus pumilus, IK-MB12 Bacillus pumilus, IK-MB13 Bacillus pumilus, IK-MB14 Bacillus megaterium), High GC, Gram-positive bacteria (IK-MB2 Micrococcus luteus, IK-MB5 Micrococcus luteus, IK-MB16 Arthrobacter mysorens), G-Proteobacteria (IK-MB3 Halomonas aquamarina, IK-MB15 Halotalea alkalilenta), CFB group bacteria (IK-MB1 Myroides odoratimimus), and Enterobacteria (IK-MB4 Proteus mirabilis). Among the 16 strains, representatives of the Firmicutes were dominant (56.25%) compared to the high GC, Gram-positive bacteria (18.75%), G-Proteobacteria (12.5%), CFB group bacteria (6.25%), and Enterobacteria (6.25%). Analysis revealed that majority of marine species found in marine biofilm are of anthropogenic origin.     

Alleviating salt stress in tomato seedlings using Arthrobacter and Bacillus megaterium isolated from the rhizosphere of wild plants grown on saline–alkaline lands

Salt-induced soil degradation is common in farmlands and limits the growth and development of numerous crop plants in the world. In this study, we isolated salt-tolerant bacteria from the rhizosphere of Tamarix chinensis, Suaeda salsa and Zoysia sinica, which are common wild plants grown on a saline–alkaline land, to test these bacteria's efficiency in alleviating salt stress in tomato plants. We screened out seven strains (TF1–7) that are efficient in reducing salt stress in tomato seedlings. The sequence data of 16S rRNA genes showed that these strains belong to Arthrobacter and Bacillus megaterium. All strains could hydrolyze casein and solubilize phosphate, and showed at least one plant growth promotion (PGP)-related gene, indicating their potential in promoting plant growth. The Arthrobacter strains TF1 and TF7 and the Bacillus megaterium strain TF2 and TF3 could produce indole acetic acid under salt stress, further demonstrating their PGP potential. Tomato seed germination, seedling length, vigor index, and plant fresh and dry weight were enhanced by inoculation of Arthrobacter and B. megaterium strains under salt stress. Our results demonstrated that salt-tolerant bacteria isolated from the rhizosphere of wild plants grown on saline–alkaline lands could be used for alleviating salt stress in crop plants.     

Effect of Carbon Source on the Antimicrobial Activity of the Air Flora

Summary In an attempt to screen for air flora producing new potent antimicrobial substances, Bacillus megaterium NB-3, Bacillus cereus NB-4, Bacillus cereus NB-5, Bacillus subtilis NB-6 and Bacillus circulans NB-7, were isolated and were found to be antagonistic to bacteria and/or fungi. Production of antimicrobial substances by the bacterial strains was greatly influenced by variation of carbon sources. Glycerol strongly enhanced the antimicrobial activity of strains NB-3 and NB-6, whereas glucose increased the antimicrobial activity of strains NB-4 and NB-5. The maximum antibiotic yield of NB-7 was achieved with fructose as a carbon source. Starch (Bacillus megaterium NB-3), maltose (Bacillus cereus NB-5), glycerol (Bacillus circulans NB-7), arabinose, ribose (Bacillus cereus NB-4) and arabinose, fructose, glucose, ribose and sucrose (Bacillus subtilis NB-6) repressed the production of antimicrobial substances by the respective bacterial strains.     

Taxonomic diversity of aerobic organotrophic bacteria from clean vietnamese soils and their capacity for oxidation of petroleum hydrocarbons

The dominant species and abundance of the cultured aerobic organotrophic bacteria were determined in the clean soils of the Republic of Vietnam. The total number of organotrophs varied from 2.0 × 10⁵ to 5.8 × 10⁸ CFU/g soil. A considerable fraction of the bacterial population (1.1 × 10⁵–9.5 × 10⁶ CFU/g soil) was able to utilize petroleum hydrocarbons as the sole carbon and energy source. Most of the organisms obtained in pure cultures were gram-positive bacteria; over 70% were hydrocarbon-oxidizing organisms. Analysis of 16S rRNA gene sequences resulted in tentative determination of the taxonomic position of 22 strains, with 12 belonging to the Firmicutes, 4, to the Proteobacteria, and 6 to the Actinobacteria. The most common bacteria capable of hydrocarbon oxidation belonged to the genera Acinetobacter, Bacillus, Brevibacillus, Chromobacterium, Cupriavidus, Gordonia, Microbacterium, Mycobacterium, and Rhodococcus. Some of the isolated Bacillus and Staphylococcus strains, as well as one Pseudomonas and one Sinomonas strain, did not utilize hydrocarbons. Gram-positive degraders, especially members of the order Actinomycetales, which exhibited high hydrocarbon-oxidizing activity, gained competitive advantage in the presence of hydrocarbons. This microbial group probably plays an important role in hydrocarbon degradation in tropical soils. Thus, Vietnamese soils, which had no history of petroleum contamination, support numerically significant and taxonomically diverse populations of h ydrocarbon-oxidizing bacteria.     

Stimulation of Plant Growth and Drought Tolerance by Native Microorganisms (AM Fungi and Bacteria) from Dry Environments: Mechanisms Related to Bacterial Effectiveness

In this study we tested whether rhizosphere microorganisms can increase drought tolerance to plants growing under water-limitation conditions. Three indigenous bacterial strains isolated from droughted soil and identified as Pseudomonas putida, Pseudomonas sp., and Bacillus megaterium were able to stimulate plant growth under dry conditions. When the bacteria were grown in axenic culture at increasing osmotic stress caused by polyethylene glycol (PEG) levels (from 0 to 60%) they showed osmotic tolerance and only Pseudomonas sp. decreased indol acetic acid (IAA) production concomitantly with an increase of osmotic stress (PEG) in the medium. P. putida and B. megaterium exhibited the highest osmotic tolerance and both strains also showed increased proline content, involved in osmotic cellular adaptation, as much as increased osmotic stress caused by NaCl supply. These bacteria seem to have developed mechanisms to cope with drought stress. The increase in IAA production by P. putida and B. megaterium at a PEG concentration of 60% is an indication of bacterial resistance to drought. Their inoculation increased shoot and root biomass and water content under drought conditions. Bacterial IAA production under stressed conditions may explain their effectiveness in promoting plant growth and shoot water content increasing plant drought tolerance. B. megaterium was the most efficient bacteria under drought (in successive harvests) either applied alone or associated with the autochthonous arbuscular mycorrhizal fungi Glomus coronatum, Glomus constrictum or Glomus claroideum. B. megaterium colonized the rhizosphere and endorhizosphere zone. We can say, therefore, that microbial activities of adapted strains represent a positive effect on plant development under drought conditions.     

Biosynthesis of Amino Acids from Hydrocarbons

Nine strains of bacteria, capable of synthesising amino acids from hydrocarbons, have been identified. Pseudomonas arvilla, Ps. fluorescens and Micrococcus ureae, previously reported as hydrocarbons assimilators, were found capable of synthesising amino acids. Pseudomonas taetrolens, Bacillus cereus var. mycoides, Bacillus subtilis and Bacillus sphaericus also synthesised amino acids from hydrocarbons.     

Diversity and bioactive potential of endospore-forming bacteria cultured from the marine sponge Haliclona simulans

Aims: Despite the frequent isolation of endospore‐formers from marine sponges, little is known about the diversity and characterization of individual isolates. The main aims of this study were to isolate and characterize the spore‐forming bacteria from the marine sponge Haliclona simulans and to examine their potential as a source for bioactive compounds. Methods and Results: A bank of presumptive aerobic spore‐forming bacteria was isolated from the marine sponge H. simulans. These represented c. 1% of the total culturable bacterial population. A subgroup of thirty isolates was characterized using morphological, phenotypical and phylogenetic analysis. A large diversity of endospore‐forming bacteria was present, with the thirty isolates being distributed through a variety of Bacillus and Paenibacillus species. These included ubiquitous species, such as B. subtilis, B. pumilus, B. licheniformis and B. cereus group, as well as species that are typically associated with marine habitats, such as B. aquimaris, B. algicola and B. hwajinpoensis. Two strains carried the aiiA gene that encodes a lactonase known to be able to disrupt quorum‐sensing mechanisms, and various isolates demonstrated protease activity and antimicrobial activity against different pathogenic indicator strains, including Clostridium perfringens, Bacillus cereus and Listeria monocytogenes. Conclusions: The marine sponge H. simulans harbours a diverse collection of endospore‐forming bacteria, which produce proteases and antibiotics. This diversity appears to be overlooked by culture‐dependent and culture‐independent methods that do not specifically target sporeformers. Significance and Impact of Study: Marine sponges are an as yet largely untapped and poorly understood source of endospore‐forming bacterial diversity with potential biotechnological, biopharmaceutical and probiotic applications. These results also indicate the importance of combining different methodologies for the comprehensive characterization of complex microbial populations such as those found in marine sponges.     

Characterization of Acetanilide Herbicides Degrading Bacteria Isolated from Tea Garden Soil

Three different green manures were added to the tea garden soils separately and incubated for 40 days. After, incubation, acetanilide herbicides alachlor and metolachlor were spiked into the soils, separately, followed by the isolation of bacteria in each soil at designed intervals. Several bacterial strains were isolated from the soils and identified as Bacillus silvestris, B. niacini, B. pseudomycoides, B. cereus, B. thuringiensis, B. simplex, B. megaterium, and two other Bacillus sp. (Met1 and Met2). Three unique strains with different morphologies were chosen for further investigation. They were B. megaterium, B. niacini, and B. silvestris. The isolated herbicide-degrading bacteria showed optimal performance among three incubation temperatures of 30°C and the best activity in the 10 to 50 μg/ml concentration of the herbicide. Each bacterial strain was able to degrade more than one kind of test herbicides. After incubation for 119 days, B. cereus showed the highest activity to degrade alachlor and propachlor, and B. thuringiensis to degrade metolachlor.     

土壤中可编码乌头酸异构酶的芽胞杆菌菌株筛选及鉴定

【目的】以芽胞杆菌(Bacillus)为筛选对象,分离土壤中可编码乌头酸异构酶(aconitate isomerase,AI)的革兰氏阳性(Gram positive,G+)菌株,以丰富对AI分布的科学认识,为其生物学功能研究奠定理论与材料基础。【方法】采用土样高温预处理法、含反式乌头酸(trans-aconitic acid,TAA)唯一碳源的ACO固体平板培养法,结合16S rDNA基因序列同源性分析,筛选能够编码AI的芽胞杆菌目的菌株。【结果】共分离得到22株能够利用TAA碳源的细菌菌株,成功鉴定了其中的16株,分别为巨大芽胞杆菌(Bacillus megaterium) 2株,阿氏芽胞杆菌(Bacillus aryabhattai) 7株,短小芽胞杆菌(Bacillus pumilus) 1株,未鉴定到种的芽胞杆菌(Bacillus sp.) 6株;且它们所含AI编码基因与已知AI基因在序列上存在差异。【结论】首次证明可编码AI的芽胞杆菌细菌种类具有多样性,暗示G+细菌广泛编码AI的可能性,更新了AI几乎只在G–细菌中分布的观点,为后续深入挖掘AI基因及其生物学功能研究提供更多可用微生物资源。     

Antimicrobial activity of <Emphasis Type="Italic">Bacillus megaterium</Emphasis> strains

A bacterial strain with a high level of antimicrobial activity was isolated from soil and identified as Bacillus megaterium. Production of antibiotics by nine strains of this species from the collection of the State Research Institute for Genetics and Selection of Industrial Microorganisms was investigated. In submerged cultures, nine out of ten B. megaterium strains were found to produce antibacterial antibiotics differing in their spectra of action. Physicochemical characteristics of five compounds were described. Three of them belonged to peptide antibiotics. All five compounds were active against the methicillin-resistant strain Staphylococcus aureus INA 00761. Three of them were shown to be the previously undescribed compounds. Antibiotics produced by various B. megaterium strains were also active against the Leuconostoc mesenteroides VKPM B-4177 strain resistant to glycopeptide antibiotics and against gram-negative bacteria Pseudomonas aeruginosa ATCC 27853 and Escherichia coli ATCC 25922.     

Enhanced Hydrocarbons Degradation in the Rhizosphere of Mangrove Plants by a Halophilic Bacillus Subtilis Subtilis Strain

Sulaibikhat Embayment is a severely contaminated coastline in the State of Kuwait. The contaminating pollutants include hydrocarbons, heavy metals, and suspended particles. The objective of this study is to assess the ability of mangroves planted in the Sulaibikhat Embayment to enhance hydrocarbons degradation by the activities of rhizospheric hydrocarbon degrading bacteria (HDB). Accordingly, samples were collected from the rhizosphere of selected mangrove plants and from sediments in the same location but away from mangrove marshes. The samples were analyzed chemically and microbiologically before being enriched with a mixture of hydrocarbon compounds (HC) to isolate HDB.

A number of halophilic HDB were isolated from mangroves rhizosphere and the surrounding sediments such as Pseudomonas balearica, Microbacterium barkeri and Gordonia soli. On the other hand, Bacillus velezensis and Bacillus subtilis subtilis were both isolated only from mangroves rhizosphere. Among the isolated HDB, Bacillus subtilis subtilis was distinguished with its high degradation rates of the tested HC including poly aromatic hydrocarbons. According to our knowledge, this is the first Bacillus subtilis HC-degrading strain that was isolated from Kuwait Bay and from mangroves rhizosphere.     

Simultaneous hydrocarbon biodegradation and biosurfactant production by oilfield-selected bacteria

Aims: To study the bacterial diversity associated with hydrocarbon biodegradation potentiality and biosurfactant production of Tunisian oilfields bacteria. Methods and Results: Eight Tunisian hydrocarbonoclastic oilfields bacteria have been isolated and selected for further characterization studies. Phylogenetic analysis revealed that three thermophilic strains belonged to the genera Geobacillus, Bacillus and Brevibacillus, and that five mesophilic strains belonged to the genera Pseudomonas, Lysinibacillus, Achromobacter and Halomonas. The bacterial strains were cultivated on crude oil as sole carbon and energy sources, in the presence of different NaCl concentrations (1, 5 and 10%, w/v), and at 37 or 55°C. The hydrocarbon biodegradation potential of each strain was quantified by GC–MS. Strain C450R, phylogenetically related to the species Pseudomonas aeruginosa, showed the maximum crude oil degradation potentiality. During the growth of strain C450R on crude oil (2%, v/v), the emulsifying activity (E24) and glycoside content increased and reached values of 77 and 1·33 g l^?1, respectively. In addition, the surface tension (ST) decreased from 68 to 35·1 mN m^?1, suggesting the production of a rhamnolipid biosurfactant. Crude biosurfactant had been partially purified and characterized. It showed interest stability against temperature and salinity increasing and important emulsifying activity against oils and hydrocarbons. Conclusions: The results of this study showed the presence of diverse aerobic bacteria in Tunisian oilfields including mesophilic, thermophilic and halotolerant strains with interesting aliphatic hydrocarbon degradation potentiality, mainly for the most biosurfactant produced strains. Significance and Impact of the Study: It may be suggested that the bacterial isolates are suitable candidates for practical field application for effective in situ bioremediation of hydrocarbon‐contaminated sites.     

Atrazine degradation by aerobic microorganisms isolated from the rhizosphere of sweet flag (Acorus calamus L.)

In presented study the capability of microorganisms isolated from the rhizosphere of sweet flag (Acorus calamus) to the atrazine degradation was assessed. Following isolation of the microorganisms counts of psychrophilic bacteria, mesophilic bacteria and fungi were determined. Isolated microorganisms were screened in terms of their ability to decompose a triazine herbicide, atrazine. Our results demonstrate that within the rhizosphere of sweet flag there were 3.8 × 10⁷ cfu of psychrophilic bacteria, 1.8 × 10⁷ cfu of mesophilic bacteria, and 6 × 10⁵ cfu of fungi per 1 g of dry root mass. These microorganisms were represented by more than 20 different strains, and at the first step these strains were grown for 5 days in the presence of atrazine at a concentration of 5 mg/l. In terms of the effect of this trial culture, the bacteria reduced the level of atrazine by an average of about 2–20%, but the average level of reduction by fungi was in the range 18–60%. The most active strains involved in atrazine reduction were then selected and identified. These strains were classified as Stenotrophomonas maltophilia, Bacillus licheniformis, Bacillus megaterium, Rahnella aquatilis (three strains), Umbelopsis isabellina, Volutella ciliata and Botrytis cinerea. Culturing of the microorganisms for a longer time resulted in high atrazine degradation level. The highest degradation level was observed at atrazine concentrations of 5 mg/l for S. maltophilia (83.5% after 15 days of culture) and for Botrytis sp. (82% after 21 days of culture). Our results indicate that microorganisms of the sweet flag rhizosphere can play an important role in the bioremediation of atrazine-contaminated sites.     

BACTERIAL INFLUENCE UPON GROWTH AND HYDROCARBON PRODUCTION OF THE GREEN ALGA BOTRYOCOCCUS BRAUNII1

Batch cultures of the hydrocarbon-rich alga Botryococcus braunii, Kütz. (axenic strains, non-axenic strains, associations with selected microorganisms) were examined with regard to total biomass and hydrocarbons at the onset of the stationary phase. Pronounced variations, related to the origin of the strains and to growth conditions, were observed with axenic cultures. It also appeared that the presence of microorganisms is not essential for high hydrocarbon production. Nevertheless, numerous bacteria were shown to exert considerable influence, antagonistic or beneficial, on B. braunii growth yield and hydrocarbon production. Such effects were strongly dependent on the species involved and on culture conditions. The presence of various microorganisms can influence not only the quantity of hydrocarbons produced, but also their level in the algal biomass and their relative abundance. However, their chemical structure is not affected. Intricate relationships were observed in B. braunii-bacteria systems and numerous factors (including, in some cultures, large positive effects due to bacterially produced CO₂) were implicated. Accordingly, specific associations should provide appropriate conditions for renewable hydrocarbon production via B. braunii large scale cultures.     

Enhanced Biodegradation of Anthracene by Bacillus Cereus Strain JMG-01 Isolated from Hydrocarbon Contaminated Soils

The present study displays the biodegradation capacities of native bacteria toward polycyclic aromatic hydrocarbons with particular emphasis to anthracene. A total of 23 bacterial strains were isolated from hydrocarbon-contaminated sites of Guwahati city, using anthracene as the carbon source. Among all these isolates, one Gram-positive strain (JMG-01) was selected as an efficient anthracene degrader, based on its maximum growth ability in anthracene enriched medium (100 ppm–700 ppm). At 500 ppm concentration, strain JMG-01 showed the maximum growth rate with 98% of anthracene degradation within 21 days of observation. The strain also demonstrated its potentiality by utilizing naphthalene and higher molecular hydrocarbons like pyrene, and benzo(a)pyrene at 500 ppm. The morphological, biochemical and molecular characterization identified the strain as Bacillus cereus. Surface morphology of the biomass, captured by Atomic Force Microscope, showed a distinctive modification, during the process of degradation. Study revealed that the effect of hydrocarbon exhibited the alteration, which concurrently enhanced the metabolic activity. Further, Gas chromatography-mass spectrometer analysis elucidates the possible metabolic pathway of anthracene degradation, depending on the intermediate metabolites produced. The finding thus suggests the essence of Bacillus cereus strain JMG-01 in enhanced anthracene degradation along the utilization of other hydrocarbons.     

Cropping as a Phytoremediation Practice for Oily Desert Soil with Reference to Crop Safety as Food

Broad beans (Vicia faba)could tolerate up to 10% (w)w) crude oil in desert soil (sand), therefore, the potential of this crop for cleaning oily desert soil via rhizosphere technology was investigated. The amounts of hydrocarbons recovered from oily desert soil samples supporting V. faba plants were less than the amounts extracted from uncultivated oily soil samples. Excised fresh V. faba roots with their intact rhizospheres resulted in the attenuation of n-octadecane, phenanthrene, and crude oil when shaken into sterile desert soil extract containing these hydrocarbons. The amounts of hydrocarbons eliminated were greater with roots of plants previously raised in oily soil than with roots of plants raised in clean soil. Similar hydrocarbon attenuation effects were recorded when, instead of excised roots, whole plants were used with their roots submerged in the hydrocarbon containing soil extract. The various parts of plants raised in oily desert soil contained more linolenic acid in their total lipids than did the same parts of plants raised in clean desert soil. This was much more pronounced for the roots than for shoots and seeds. The hydrocarbons of roots and shoots of V. faba plants were not as affected by oil pollution as were those of seeds, in which the proportions of very long chain hydrocarbons increased with increasing oil concentration in the soil. Those hydrocarbons are not recommended for human and animal nutrition.     

Antibacterial activity of different degree of hydrolysis of palm kernel expeller peptides against spore-forming and non-spore-forming bacteria

Aims: The goal of this study was to determine inhibitory effect of palm kernel expeller (PKE) peptides of different degree of hydrolysis (DH %) against spore‐forming bacteria Bacillus cereus, Bacillus circulans, Bacillus coagulans, Bacillus licheniformis, Bacillus megaterium, Bacillus pumilus, Bacillus stearothermophillus, Bacillus subtilis, Bacillus thuringiensis, Clostridium perfringens; and non‐spore‐forming bacteria Escherichia coli, Lisinibacillus sphaericus, Listeria monocytogenes, Pseudomonas aeruginosa, Salmonella Typhimurium and Staphylococcus aureus. Methods and Results: A range of DH % (50–100) of PKE peptides was prepared using alcalase, and hydrolysis conditions were determined using response surface methodology (RSM). The influence of pH (6·5–10·5), temperature (35–65°C), enzyme/substrate ratio (1–5%) and substrate concentration (1–2%) were studied on the response of the DH. The antibacterial activity of different DH % of PKE peptides was tested by using disc diffusion assay and micro‐broth dilution assay. According to the minimum inhibitory concentration (MIC) test on each of the PKE peptides of different DH %, the 70 DH % PKE peptide showed greater inhibitory effect compared to the 100 DH % PKE peptide against B. cereus, B. coagulans, B. megaterium, B. pumilus, B. stearothermophillus, B. subtilis, B. thuringiensis, Cl. perfringens, Lisinibacillus sphaericus and L. monocytogenes. Conclusions: The 70 DH % PKE peptides exhibited greatest overall antibacterial effect of the various peptides of PKE evaluated. Further research is needed to determine the mode of action of PKE peptides. Significance and Impact of the Study: Palm kernel expeller peptides, a natural plant product, effectively inhibited the growth of spore‐forming and non‐spore‐forming Gram‐positive bacteria. Potentially, PKE peptides could be used in food preservation and developed as antibacterial agent in the pharmaceutical industry.     

Production of Oil-Releasing Compounds by Microorganisms from the Daqing Oil Field,China

Twenty pure cultures isolated from formation waters of the Daqing oil field were studied with respect to their capacity to produce surface-active compounds in media with individual hydrocarbons, lower alcohols, and fatty acids. Aerobic saprotrophic bacteria belonging to the genera Bacillus, Brevibacillus, Rhodococcus, Dietzia, Kocuria, Gordonia, Cellulomonas, Clavibacter, Pseudomonas, and Acinetobacter decreased the surface tension of cultivation media from 55–63 to 28–44 mN/m. Strains of Bacillus cereus, Rhodococcus ruber, andBacillus licheniformis produced biosurfactants most actively. Bacteria of the genera Rhodococcus, Dietzia, Kocuria, and Gordonia produced exopolysaccharides in media with hydrocarbons. Culture liquids of the strains of R. ruberand B. licheniformis exhibited an oil-releasing effect. Thus, the Daqing oil field is inhabited by aerobic bacteria capable of producing effective oil-releasing agents.