Nelda L. Olivera

Enhancement of hydrocarbon wastebiodegradation by addition of a biosurfactantfrom Bacillus subtilis O9

A non-sterile biosurfactant preparation (surfactin)was obtained from a 24-h culture of Bacillussubtilis O9 grown on sucrose and used to study itseffect on the biodegradation of hydrocarbon wastes byan indigenous microbial community at theErlenmeyer-flask scale. Crude biosurfactant was addedto the cultures to obtain concentrations above andbelow the critical micelle concentration (CMC). Lowerconcentration affected neither biodegradation normicrobial growth. Higher concentration gave highercell concentrations. Biodegradation of aliphatichydrocarbons increased from 20.9 to 35.5% and in thecase of aromatic hydrocarbons from nil to 41%,compared to the culture without biosurfactant. Theenhancement effect of biosurfactant addition was morenoticeable in the case of long chain alkanes. Pristaneand phytane isoprenoids were degraded to the sameextent as n-C17 and n-C18 alkanes and, consequently,no decrease in the ratios n-C17/pri and n-C18/phy wasobserved. Rapid production of surfactin crudepreparation could make it practical for bioremediationof ship bilge wastes.

Isolation and characterization of biosurfactant-producing Alcanivorax strains: hydrocarbon accession strategies and alkane hydroxylase gene analysis.

Biosurfactant-producing bacteria belonging to the genera Alcanivorax, Cobetia and Halomonas were isolated from marine sediments with a history of hydrocarbon exposure (Aristizábal and Gravina Peninsulas, Argentina). Two Alcanivorax isolates were found to form naturally occurring consortia with strains closely related to Pseudomonas putida and Microbacterium esteraromaticum. Alkane hydroxylase gene analysis in these two Alcanivorax strains resulted in the identification of two novel alkB genes, showing 86% and 60% deduced amino acid sequence identity with those of Alcanivorax sp. A-11-3 and Alcanivorax dieselolei P40, respectively. In addition, a gene homologous to alkB2 from Alcanivorax borkumensis was present in one of the strains. The consortium formed by this strain, Alcanivorax sp. PA2 (98.9% 16S rRNA gene sequence identity with A. borkumensis SK2(T)) and P. putida PA1 was characterized in detail. These strains form cell aggregates when growing as mixed culture, though only PA2 was responsible for biosurfactant activity. During exponential growth phase of PA2, cells showed high hydrophobicity and adherence to hydrocarbon droplets. Biosurfactant production was only detectable at late growth and stationary phases, suggesting that it is not involved in initiating oil degradation and that direct interfacial adhesion is the main hydrocarbon accession mode of PA2. This strain could be useful for biotechnological applications due to its biosurfactant production, catabolic and aggregation properties.

Biosurfactant-enhanced degradation of residual hydrocarbons from ship bilge wastes

The use of Bacillus subtilis O9 biosurfactant (surfactin) and of bioaugmentation to improve the treatment of residual hydrocarbons from ship bilge wastes was studied. A biodegradation experiment was conducted in aquaria placed outdoors under non-aseptic conditions. Three treatments were examined: culture medium plus bilge wastes, bioaugmentation with microorganisms from bilge wastes, and bioaugmentation plus biosurfactant. Samples were analyzed for viable counts, aliphatic and aromatic hydrocarbon concentrations, n-C17/pristane and n-C18/phytane ratios. While the addition of biosurfactant stimulated hydrocarbon degradation, bioaugmentation did not produce any remarkable effect. At day 10, the remaining percentages of aliphatic and aromatic hydrocarbons in aquaria, which received biosurfactant, were 6.8 and 7.2, respectively, while it took 20 days to reach comparable results with the other treatments. The biosurfactant did not affect the preferential biodegradation of n-C17/pristane and n-C18/phytane. This biosurfactant, which can be produced in a relatively simple and inexpensive process, is a promising alternative in the optimization of hydrocarbon waste treatment. Journal of Industrial Microbiology & Biotechnology (2000) 25, 70–73.

Alkane biodegradation by a microbial community from contaminated sediments in Patagonia, Argentina

Biodegradation of a mix of normal alkanes (decane, dodecane, tetradecane, hexadecane, octadecane and eicosane) was studied in batch cultures after inoculating with microbial communities from pristine and hydrocarbon contaminated sediments. Analysis showed that the community from polluted sediments reduced the concentrations of all alkanes to < 5 mg l−1 after a 240-h incubation period (< 5% initial concentration), while the control community only degraded 5–10% of them. The hydrocarbon adapted community showed a lag phase of 48 h, in which no alkane biodegradation was found, followed by a 96-h growth period and a stationary phase from that moment, whereas the control community grew poorly. Isolated strains were mainly Gram-negative, motile and non-glucose fermenter rods. Based on these results, it could be concluded that the hydrocarbon adaptation of microorganisms led to an increase in alkane biodegradation. This capacity could be useful to improve biodegradation of hydrocarbon regional wastes.

Bioprospection of marine microorganisms: biotechnological applications and methods

Environmental microorganisms constitute an almost inexhaustible reserve of genetic and functional diversity, accumulated during millions of years of adaptive evolution to various selective pressures. In particular, the extent of microbial biodiversity in marine habitats seems to grow larger as new techniques emerge to measure it. This has resulted in novel and more complex approaches for the screening of molecules and activities of biotechnological interest in these environments. In this review, we explore the different partially overlapping biotechnological fields that make use of microorganisms and we describe the different marine habitats that are particularly attractive for bioprospection. In addition, we review the methodological approaches currently used for microbial bioprospection, from the traditional cultivation techniques to state of the art metagenomic approaches, with emphasis in the marine environment.

Isolation, identification and antimicrobial activity of lactic acid bacteria from the Bahía Blanca Estuary

This study analyzed the biodiversity of lactic acid bacteria present in the Bahia Blanca Estuary and their antimicrobial activity against pathogens associate...

Characterization of indigenous Rhodococcus sp. 602, a strain able to accumulate triacylglycerides from naphthyl compounds under nitrogen-starved conditions

An indigenous bacterium (strain 602) isolated in this study from a polluted soil sample collected in Patagonia (Argentina) was investigated in relation to its metabolic responses under unbalanced growth conditions. This strain was identified as Rhodococcus sp. by molecular analyses. Strain 602 showed the ability to degrade a wide range of compounds and to synthesize triacylglycerols under nitrogen-limiting conditions. Cells were also able to accumulate triacylglycerols during cultivation on naphthalene and naphthyl-1-dodecanoate. Triacylglycerols produced by resting cells in the presence of naphthyl-1-dodecanoate contained only short-chain length fatty acids (from C(8) to C(12)), suggesting an initial attack of the substrate by an esterase releasing 1-naphthol and dodecanoic acid, which was subsequently degraded by beta-oxidation. On the other hand, naphthalene seemed to be degraded by a mono-oxygenase yielding 1-naphthol, which was then transformed to 4-hydroxy-1-tetralone and to other possible metabolic intermediates. On the basis of the results obtained, a pathway involved in the metabolism of both aromatic compounds under nitrogen starvation by strain 602 is proposed. The results also demonstrated that Rhodococcus sp. 602 maintains its metabolic activity even in the absence of a nitrogen source. Intracellular triacylglycerols may help cells to maintain their catabolic activities under these growth-restricting conditions.

Antibacterial properties of water-soluble gold(I) N-heterocyclic carbene complexes

The antibacterial properties of water-soluble gold(I) complexes [1-methyl-3-(3-sulfonatopropyl)imidazol-2-ylidene]gold(I) chloride (C1), [1-mesityl-3-(3-sulfonatopropyl)imidazol-2-ylidene]gold(I) chloride (C2), [1-(2,6-diisopropylphenyl)-3-(3-sulfonatopropyl)imidazol-2-ylidene]gold(I) chloride (C3) and [1,3-bis(2,6-diisopropyl-4-sodiumsulfonatophenyl)imidazol-2-ylidene]gold(I) chloride (C4) and the respective ligands were assessed by agar diffusion and broth macrodilution methods against Gram-positives Staphylococcus aureus, Enterococcus faecalis and Micrococcus luteus and the Gram-negative bacteria Yersinia ruckeri, Pseudomonas aeruginosa and Escherichia coli. Viability after treatments was determined by direct plate count. The bactericidal activity displayed by C1 and C3 was comparable to that of AgNO3.

Do soil enzymes respond to long-term grazing in an arid ecosystem?

Background and aimsOur objective was to assess the effects of long-term continuous grazing on soil enzyme activities in relation to shifts in plant litter attributes and soil resources in an arid ecosystem, considering both spatial and temporal variations.MethodsWe randomly extracted soil samples with the respective litter cover at 5 modal size plant-covered patches (PCP) and the nearest inter-canopy areas (IC) at Patagonian Monte sites with low, medium and high grazing intensity in winter and summer from 2007 to 2009. We analyzed enzyme activities (dehydrogenase, ß-glucosidase, protease, alkaline and acid phosphatase), microbial biomass-C, organic-C, total soil-N, and moisture in soil and mass and quality in plant litter. We assessed faeces density and plant cover in the field.Results and conclusionsGrazing led to reduced grass cover, decreasing plant litter mass with increasing soluble phenolics, and reduced phosphatases, ß-glucosidase and microbial biomass-C at PCP. A localized nutrient input from animal excreta seems to promote microbial biomass-C, alkaline phosphatase and dehydrogenase activities but only at IC from the site with high grazing intensity. Plant heterogeneous distribution, plant litter quantity and quality, nutrient inputs from grazers and seasonal variation in soil moisture, also affecting soil resources and microbial biomass, modulate soil enzyme responses to long-term grazing in the arid Patagonian Monte.

Newly isolated Bacillus sp. G51 from Patagonian wool produces an enzyme combination suitable for felt-resist treatments of organic wool

Bacteria from Patagonian Merino wool were isolated to assess their wool-keratinolytic activity and potential for felt-resist treatments. Strains from Bacillus, Exiguobacterium, Deinococcus, and Micrococcus produced wool-degrading enzymes. Bacillus sp. G51 showed the highest wool-keratinolytic activity. LC-MS/MS analysis revealed that G51 secreted two serine proteases belonging to the peptidase family S8 (MEROPS) and a metalloprotease associated with Bacillolysin, along with other enzymes (γ-glutamyltranspeptidase and dihydrolipoyl dehydrogenases) that could be involved in reduction of keratin disulfide bonds. Optimum pH and temperature of G51 proteolytic activity were 9 and 60 °C, respectively. More than 80% of activity was retained in H2O2, Triton X-100, Tween 20, Lipocol OXO650, Teridol B, and β-mercaptoethanol. Treatment of wool top with G51 enzyme extract caused a decrease in wool felting tendency without significant weight loss (<1.5%). Sparse work has so far been performed to investigate suitable keratinases for the organic wool sector. This eco-friendly treatment based on a new enzyme combination produced by a wild bacterium has potential for meeting the demands of organic wool processing which bans the use of hazardous chemicals and genetic engineering.