Invadopodia are matrix-degrading membrane protrusions in invasive carcinoma cells. The mechanisms regulating invadopodium assembly and maturation are not understood. We have dissected the stages of invadopodium assembly and maturation and show that invadopodia use cortactin phosphorylation as a master switch during these processes. In particular, cortactin phosphorylation was found to regulate cofilin and Arp2/3 complex–dependent actin polymerization. Cortactin directly binds cofilin and inhibits its severing activity. Cortactin phosphorylation is required to release this inhibition so cofilin can sever actin filaments to create barbed ends at invadopodia to support Arp2/3-dependent actin polymerization. After barbed end formation, cortactin is dephosphorylated, which blocks cofilin severing activity thereby stabilizing invadopodia. These findings identify novel mechanisms for actin polymerization in the invadopodia of metastatic carcinoma cells and define four distinct stages of invadopodium assembly and maturation consisting of invadopodium precursor formation, actin polymerization, stabilization, and matrix degradation.

The effect of the tropical pasture grass Brachiaria brizantha on numbers of bacteria, fungi and degraders of alkanes, aromatics, cycloalkanes and crude oil in petroleum hydrocarbon contaminated and uncontaminated savannah soil was evaluated. Substrate induced soil respiration and soil pH were compared between planted and unplanted soil. B. brizantha had a mostly increasing effect on microbial numbers. As an exception, growth of bacteria was not or negatively affected. Microbial respiration and pH were always lower in planted than in unplanted soil. Low pH may result from enhanced oil degradation in planted soil leading to an accumulation of organic acids. A comparable stimulation of crude oil degraders and fungi in planted soil points to the importance of fungi. Since they tolerate lower pH values than bacteria, they are considered to play a central role in oil degradation. Given that the enhancement of crude oil degradation under the influence of B. brizantha could not clearly be correlated to microbial numbers and activity, other factors like oxygen availability, plant enzymes and synergistic degradation by microbial consortia have to be considered.

Determination of fertilizer levels in phytoremediation of petroleum hydrocarbons is a complex issue, since nutrient demands of the plant and of degrading microorganisms in the rhizosphere have to be considered In the present work, three fertilizer levels were tested in a greenhouse experiment with the aim of optimizing growth of the tropical pasture grass Brachiaria brizantha and enhance microbial degradation of heavy crude oil in soil Fertilizer was applied twice in a concentration of 200, 300, and 400 mg each of N, P, and K per kg soil before and after the first sampling (14 wk). The medium fertilizer concentration resulted in best root growth and highest absolute oil dissipation (18.4%) after 22 wk The highest concentration produced best shoot growth and highest relative oil dissipation after 14 wk (10.5% less than unplanted control). In general, degradation of total oil and grease was higher in planted than in unplanted soil, but differences diminished toward the end of the experiment. Next to fertiizer quantity, its composition is an important factor to be further studied, including the form of available nitrogen (N-NO3- vs. N-NH4+). Field trials are considered indispensable for further phytoremediation studies, since greenhouse experiments produce particular water and nutrient conditions.

Bioremediation represents one of the most promising, cost-effective, and safest technologies to be used for the restoration of crude oil contaminated soils. However, some previous studies have shown that bioremediation is less effective for heavy, low API gravity crude oils. INTEVEP and CHEVRON have independently conducted laboratory studies to evaluate the feasibility of using bioremediation technologies for crude oils (ranging from 9 to 320 API gravity) produced by MARAVEN in Venezuela The composition of the hydrocarbons in each crude oil was first characterized by Iatroscan, gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS) in order to better understand the potential relationship between API gravity, hydrocarbon composition, and biodegradability. Five percent (w/w) of each oil was applied to a Venezuelan loam soil and fertilizers and organic material (used as bulking agents to improve soil conditions such as moisture holding capacity, tilth, and texture) were added to the oily soil to optimize conditions for biodegradation. Abiotic controls (containing 2% v/w HgCl2 to ensure no microbial activity) and a positive control containing fertilizer, but no crude oil, were also prepared. Biodegradation was measured directly by monitoring the decreases in the percentages of saturated, aromatic, resins and asphaltene fractions via Iatroscan throughout the 4 month incubation time. The initial and final samples were also monitored for losses of total petroleum hydrocarbons by GC and polyaromatic hydrocarbons by GC/MS. Biodegradation was monitored indirectly by measuring the production of CO2, a final breakdown product of hydrocarbon metabolism. Higher microbial activity (c.a. CO2 evolution) was observed in the soil amended with light crude oils (120 mg C02/h/m2) than in soil amended with heavy crude oils (85 mg C02/h/m2). Iatroscan, GC, and GC/MS analyses confirmed that the light Venezuelan crude oils >300APl) were readily biodegraded. The biodegradation potential of each of the crude oils and recommendations for which oil types are most amenable to bioremediation technologies are presented.