Enzyme recruitment allows the biodegradation of recalcitrant branched hydrocarbons by Pseudomonas citronellolis

Experiments were carried out to construct pseudomonad strains capable of the biodegradation of certain recalcitrant branched hydrocarbons via a combination of alkane and citronellol degradative pathways. To promote the metabolism of the recalcitrant hydrocarbon 2,6-dimethyl-2-octene we transferred the OCT plasmid to Pseudomonas citronellolis, a pseudomonad containing the citronellol pathway. This extended the n-alkane substrate range of the organism, but did not permit utilization of the branched hydrocarbon even in the presence of a gratuitous inducer of the OCT plasmid. In a separate approach n-decane-utilizing (Dec+) mutants of P. citronellolis were selected and found to be constitutive for the expression of medium- to long-chain alkane oxidation. The Dec+ mutants were capable of degradation of 2,6-dimethyl-2-octene via the citronellol pathway as shown by (i) conversion of the hydrocarbon to citronellol, determined by gas-liquid chromatography-mass spectrometry, (ii) induction of geranyl-coenzyme A carboxylase, a key enzyme of the citronellol pathway, and (iii) demonstration of beta-decarboxymethylation of the hydrocarbon by whole cells. The Dec+ mutants had also acquired the capacity to metabolize other recalcitrant branched hydrocarbons such as 3,6-dimethyloctane and 2,6-dimethyldecane. These studies demonstrate how enzyme recruitment can provide a pathway for the biodegradation of otherwise recalcitrant branched hydrocarbons.     

Microbial growth on hydrocarbons: terminal branching inhibits biodegradation

A variety of octane-utilizing bacteria and fungi were screened for growth on some terminally branched dimethyloctane derivatives to explore the effects of iso- and anteiso-termini on the biodegradability of such hydrocarbons. Of 27 microbial strains tested, only 9 were found to use any of the branched hydrocarbons tested as a sole carbon source, and then only those hydrocarbons containing at least one iso-terminus were susceptible to degradation. Anteiso-or isopropenyl termini prevented biodegradation. None of the hydrocarbonoclastic yeasts tested was able to utilize branched-hydrocarbon growth sustrates. In the case of pseudomonads containing the OCT plasmid, whole-cell oxidation of n-octane was poorly induced by terminally branched dimethyloctanes. In the presence of a gratuitous inducer of the octane-oxidizing enzymes, the iso-branched 2,7-dimethyloctane was slowly oxidized by whole cells, whereas the anteiso-branched 3,6-dimethyloctane was not oxidized at all. This microbial sampling dramatically illustrated the deleterious effect of alkyl branching, especially anteiso-terminal branching, on the biodegradation of hydrocarbons.     

Alternate microbial strategies for the metabolism of a 3-methyl branched alkanoic acid

The branched alkanoic acid, 3-methylvaleric acid (3-MVA), was used to test the effect of a β-methyl branch on short chain alkanoic acid biodegradability by various bacteria. Most of the bacteria tested were able to usen-valeric acid as sole carbon source but were unable to assimilate 3-MVA. Three bacterial strains capable of growth on 3-MVA are described here because they exemplify metabolism of the branched compound via different strategies.Pseudomonas citronellolis used a β-methyl activation sequence involving CO₂ fixation, analogous to that seen in the isovalerate pathway. AMycobacterium sp. used an α-oxidation sequence to convert 3-MVA to 2-methyl-butyrate, which was then assimilated via part of the isoleucine pathway. AnArthrobacter sp. metabolized 3-MVA via ω-oxidation to produce 3-methylglutarate that was degraded through the 3-hydroxy-3-methylglutarate pathway.     

Subcellular localization of 3-methylcrotonyl-coenzyme A carboxylase in bovine kidney

The intracellular localization of 3-methylcrotonyl-CoA carboxylase (MCase), an enzyme of the leucine oxidative pathway, was studied in bovine kidney. Differential centrifugation of kidney homogenates demonstrated that the majority of the enzyme was associated with the mitochondrial and cytosolic fractions. Isopycnic centrifugation of the mitochondrial fraction demonstrated cofractionation of MCase with mitochondrial markers, but not with lysosomal markers, consistent with a mitochondrial location for the enzyme. Using different homogenization techniques and comparing the fractional extraction of MCase and mitochondrial and cytosolic marker enzymes, the appearance of MCase in the “cytosolic” fraction was shown to be due to mitochondrial damage. The intramitochondrial distribution of MCase was determined using a digitonin procedure, and indicated that the enzyme is associated with the inner mitochondrial membrane. Although a fraction of MCase (30–40%) was “solubilized” by homogenization of whole mitochondria, the remaining MCase (60–70%) was tightly associated with the mitochondrial membrane fraction. Release and “solubilization” of this latter fraction was achieved by polyethylene glycol treatment. The “solubilized” MCase was stabilized in a glycerol-containing buffer.     

Ecology of a typical West African Sudanian savannah rodent community

The small‐mammal community of a typical Sudanian savannah area of south‐eastern Senegal was studied by way of intensive sampling at the beginning (July) and at the end (November) of the rainy season. A total of 5931 trapnights and 200 pitfallnights yielded 767 small mammals, including 757 rodents of 12 species, as well as a few shrews and hedgehogs. Accumulation curve indicated that the rodent community was well sampled. Murine rodents were far more numerous than gerbilline rodents, and among them, Mastomys erythroleucus was the dominant species, being caught in high numbers in all habitats. Arvicanthis niloticus and Praomys daltoni were also abundant, followed by Mastomys natalensis and Gerbilliscus guineae. Abundances were high at the beginning of the rainy season when reproductive activity was low in all species. At the end of the rainy season, murine rodents were actively involved in reproduction, while gerbilline rodents were at their lowest density. Significant changes in relative abundance among habitats (including human dwellings) were observed between periods in some species, suggesting seasonal trends in habitat preferences. This may help species coexistence in this species‐rich rodent community, in an area likely to be submitted to significant habitat alterations in the years to come.     

High incidence of selenite-resistant bacteria from a site polluted with selenium

The level of selenium-resistant bacteria in water, algal mats, and sediment from Kesterson reservoir, Calif., a site with known selenium pollution, was compared with that in nearby Volta reservoir, a site with low selenium levels. A high percentage (greater than 50%) of all isolates from the Kesterson samples were resistant to 10 mM selenite. In contrast, only a small percentage of the Volta isolates were resistant to this level of selenite. The identity of some selenite-resistant isolates and MICs of selenite, selenate, arsenate, tellurite, and tellurate were determined.     

Fire history and composition of the subalpine forest of western Colorado during the Holocene

Pollen and plant macrofossils from the Keystone Ironbog are used to document changes in species composition and the dynamics of the subalpine forest in western Colorado over the past 8000 years. Modern pollen spectra (particularly pollen influx), plant macrofossils, observations on modern species composition, and quantified densities and mean basal areas of forest trees are used to interpret the paleoecology of the forest. From 8000 to 2600 years ago the fen was surrounded by a subalpine forest. However, unlike the modern subalpine forest where Abies lasiocarpa (Hooker) Nuttall is slighlty more abundant than Picea engelmannii (Parry) Engelmann, these Holocene forests had a greater dominance of P. engelmannii , perhaps reflecting a summer wet climate like that of the modern southern Rocky Mountains and Colorado Plateau. Mesic conditions promoted a dense understory of Sphagnum moss, forbs, grasses, and shrubs which periodically burned with long (centennial) return-interval and stand-replacing fires. Populus tremuloides Michaux was the dominant successional forest tree 8000–6400 and 4400–2600 years ago, with Picea engelmannii and Abies lasiocarpa becoming reestablished within a couple hundred years. A subalpine meadow or grassland covered the fen for about 2000 years between 6400 and 4400 years ago. Over the past 2600 years a stable, non-successional Pinus contorta (Douglas) spp latifolia (Engelmann) Critchfield forest grew around the fen. This forest stand had a relatively sparse understory. The persistence of Pinus contorta at this elevation (2920 m) probably reflects a shift to drier climatic conditions, perhaps coupled with a change in fire regime to relatively frequent (decadal) surface fires. Following fire Pinus contorta became reestablished at least within 200 years, but the subalpine Picea engelmannii-Abies lasiocarpa forest never regenerated at this elevation     

Diesel Biodegradation Capacities and Biosurfactant Production in Saline-Alkaline Conditions by Delftia sp NL1, Isolated from an Algerian Oilfield

Abstract

In this study, a diesel oil-degrading bacterium was isolated from an oilfield water injection (water-bearing formations, 1,205?m depth) in Algeria. The bacterial strain, designated NL1, was cultivated on diesel oil as sole carbon and energy sources. Molecular analyses of the 16S rRNA gene sequence (KY397882) placed NL1 strain closely related to distinct cultivated species of the Delftia genus. Optimal diesel oil biodegradation by Delftia sp NL1 strain occurred at pH 11, 40?°C, 2?M NaCl and initial hydrocarbon concentration of 5% (v/v) as sole carbon source. GC-MS analyses evidenced that strain Delftia sp NL1 was able to degrade more than 66.76% of diesel oil within only 7?days. On the other hand, and in the same conditions, biosurfactant production by Delftia sp NL1 was also evaluated evidencing high emulsifying capacity (E₂₄ = 81%), ability to lower the surface tension of growing media (with the value of 25.7?mN m^?1), and production of glycolipids (8.7?g L^?1) as biosurfactants. This research presents indigenous strain Delftia sp NL1 for diesel degradation and synthesis of biosurfactant in extreme conditions. In this sense, strain NL1 is a good candidate for possible in situ oil recovery and in wastewater treatment in refineries and oil terminals in petroleum industry.