Predicting the minimum liquid surface tension activity of pseudomonads expressing biosurfactants

Bacteria produce a variety of biosurfactants capable of significantly reducing liquid (aqueous) surface tension (γ) with a range of biological roles and biotechnological uses. In order to determine the lowest achievable surface tension (γMin), we tested a diverse collection of Pseudomonas-like isolates from contaminated soil and activated sludge, and identified those expressing biosurfactants by drop-collapse assay. Liquid surface tension reducing ability was quantitatively determined by tensiometry, with 57 isolates found to significantly lower culture supernatant surface tensions to 24.5 – 49.1 mN m−1. Differences in biosurfactant behaviour determined by foaming, emulsion and oil-displacement assays, was also observed amongst isolates producing surface tensions of 25 – 27 mN m−1, suggesting that a range of structurally-diverse biosurfactants were being expressed. Individual distribution identification (IDI) analysis was used to identify the theoretical probability distribution that best fitted the surface tension data, which predicted a γMin of 24.24 mN m−1. This was in agreement with predictions based on earlier work of published mixed–bacterial spp. data, suggesting a fundamental limit to the ability of bacterial biosurfactants to reduce surface tensions in aqueous systems. This implies a biological restriction on the synthesis and export of these agents or a physical-chemical restriction on their functioning once produced

Strategies for administration of biosurfactants-producing pseudomonads in closed hydroponic systems

Zoospore-producing oomycetes are major plant pathogens of particular concern in hydroponic systems. Compared with pesticides, biocontrol using antagonistic microorganisms is a sustainable approach to control oomycetes. Previous research has demonstrated that biosurfactants and biosurfactant-producing microorganisms are potentially useful components of a sustainable biocontrol strategy. In this study three ways of supplying a biosurfactant-producing strain to a recirculating hydroponic cultivation system infected with a zoospore-producing plant pathogen were evaluated. The strain P. koreensis 2.74 was added as washed cells, in its spent KB broth or in a minimal medium adapted from the nutrient solution, and compared with control treatments. A significant reduction in disease with up to 50% was achieved when a high concentration of washed cells was added weekly to the plant cultivation system. The disease suppression obtained through addition of washed cells equalled the effect achieved when the purified biosurfactant was used. Phytotoxicity was observed when the spent broth was included in the treatment

Production of biosurfactant by locally isolated bacteria from petrochemical waste

Ten bacterial strains previously isolated from petrochemical wastes were selected for the screening of biosurfactant producer(s), via four different methods; (i) surface tension measurements, (ii) blood hemolysis test, (iii) drop-collapsing test, and (iv) bacterial adherence to hydrocarbon (BATH) test. Two isolates coded AB-Cr1 and ETL-Cr1 identified as Actinobacillus sp. and Aeromonas sp., respectively were chosen to be the best candidates for biosurfactant production. Biosurfactant productions by both isolates were found to be growth-associated in all conditions tested. Biosurfactant production in glucose/crude oil medium (7.18-8.26 g/L) was found similar to that observed in crude oil-free medium (6.33-8.76 g/L). The production of biosurfactant was also studied in a fermentor using isolate AB-Cr1, as a factor of temperature, initial glucose concentration, pH and initial nitrogen concentration. The highest production of 12.45 g/L was obtained with AB-Cr1 grown in medium (pH 7) supplemented with 25mM NH4NO3 as nitrogen source and 3mM glucose as carbon source, incubated at 37°C under non-pH controlled strategy. TLC and FTIR characterization of crude biosurfactant produced by both isolates in medium supplemented or not with crude oil indicated the presence of lipoprotein and non-aromatic glycolipid types of biosurfactant. GC-MS analysis of fatty acid metyl esters indicated the presence of pentadecanoic acid in crude biosurfactant from both isolates as well as octadecanoic and heptadecanoic acid in the biosurfactant produced by AB-Cr1 and ETL-Cr1, respectively. The CMC of the biosurfactant produced in the presence and absence of crude oil were approximately (g/L) 1.0 and 0.1 for ABCr1, and 1.2 and 0.2 for ETL-Cr1, respectively. The biosurfactants were found capable of producing a relatively stable emulsion with hydrocarbon at pH 10. It was also found stable at various pHs (3.0-13.0 and 5.0-9.0) for AB-Cr1 and ETL-Cr1, respectively and thermostable for 1 hour at 100°C, based on the value of surface tensio

Ionic behavior assessment of surface-active compounds from corn steep liquor by exchange resins

Depending on their ionic nature, biosurfactants can be classified as nonionic, anionic, cationic, or amphoteric. The ionic behavior of biosurfactants is an important characteristic that dictates their use in industrial applications. In this work, a biosurfactant extract obtained from corn steep liquor was subjected to anionic or cationic resins, in order to study the ionic behavior under different operational conditions using response surface methodology. The independent variables included in the study are the dilution of biosurfactant solution, the amount of cationic or anionic resin, and the extraction time, whereas the dependent variables studied consisted of the surface tension of biosurfactant aqueous solution, after contacting with anionic or cationic resin. The results showed that biosurfactant extracted from corn steep liquor is amphoteric, since both resins were able to entrap this biosurfactant, making it particularly suited for use in personal care preparations for sensitive skin.Peer ReviewedPostprint (author's final draft

Characterization of CMR5c and CMR12a, novel fluorescent Pseudomonas strains from the cocoyam rhizosphere with biocontrol activity

Aim: To screen for novel antagonistic Pseudomonas strains producing both phenazines and biosurfactants that are as effective as Pseudomonas aeruginosa PNA1 in the biocontrol of cocoyam root rot caused by Pythium myriotylum. Material and Results: Forty pseudomonads were isolated from the rhizosphere of healthy white and red cocoyam plants appearing in natural, heavily infested fields in Cameroon. In vitro tests demonstrated that Py. myriotylum antagonists could be retrieved from the red cocoyam rhizosphere. Except for one isolate, all antagonistic isolates produced phenazines. Results from whole-cell protein profiling showed that the antagonistic isolates are different from other isolated pseudomonads, while BOX-PCR revealed high genomic similarity among them. 16S rDNA sequencing of two representative strains within this group of antagonists confirmed their relatively low similarity with validly described Pseudomonas species. These antagonists are thus provisionally labelled as unidentified Pseudomonas strains. Among the antagonists, Pseudomonas CMR5c and CMR12a were selected because of their combined production of phenazines and biosurfactants. For strain CMR5c also, production of pyrrolnitrin and pyoluteorin was demonstrated. Both CMR5c and CMR12a showed excellent in vivo biocontrol activity against Py. myriotylum to a similar level as Ps. aeruginosa PNA1. Conclusion: Pseudomonas CMR5c and CMR12a were identified as novel and promising biocontrol agents of Py. myriotylum on cocoyam, producing an arsenal of antagonistic metabolites. Significance and Impact of the Study: Present study reports the identification of two newly isolated fluorescent Pseudomonas strains that can replace the opportunistic human pathogen Ps. aeruginosa PNA1 in the biocontrol of cocoyam root rot and could be taken into account for the suppression of many plant pathogens

Liquid membrane extraction lipopeptides

Liquid membrane extraction lipopeptide

Weak and saturable protein-surfactant interactions in the denaturation of apo-α-lactalbumin by acidic and lactonic sophorolipid

Biosurfactants are of growing interest as sustainable alternatives to fossil-fuel-derived chemical surfactants, particularly for the detergent industry. To realize this potential, it is necessary to understand how they affect proteins which they may encounter in their applications. However, knowledge of such interactions is limited. Here, we present a study of the interactions between the model protein apo-alpha-lactalbumin (apo-aLA) and the biosurfactant sophorolipid (SL) produced by the yeast Starmerella bombicola. SL occurs both as an acidic and a lactonic form; the lactonic form (lactSL) is sparingly soluble and has a lower critical micelle concentration (cmc) than the acidic form [non-acetylated acidic sophorolipid (acidSL)]. We show that acidSL affects apo-aLA in a similar way to the related glycolipid biosurfactant rhamnolipid (RL), with the important difference that RL is also active below the cmc in contrast to acidSL. Using isothermal titration calorimetry data, we show that acidSL has weak and saturable interactions with apo-aLA at low concentrations; due to the relatively low cmc of acidSL (which means that the monomer concentration is limited to ca. 0-1 mM SL), it is only possible to observe interactions with monomeric acidSL at high apo-aLA concentrations. However, the denaturation kinetics of apo-aLA in the presence of acidSL are consistent with a collaboration between monomeric and micellar surfactant species, similar to RL and non-ionic or zwitterionic surfactants. Inclusion of diacetylated lactonic sophorolipid (lactSL) as mixed micelles with acidSL lowers the cmc and this effectively reduces the rate of unfolding, emphasizing that SL like other biosurfactants is a gentle anionic surfactant. Our data highlight the potential of these biosurfactants for future use in the detergent and pharmaceutical industry

Lipopeptide overproduction by cell immobilization on iron-enriched light polymer particles

The study concerns surfactin and/or fengycin batch production by immobilized cells of Bacillus subtilis ATCC 21332. Light carriers designed for a three phase inverse fluidized bed biofilm reactor (TPFIBR) were used. With respect to the biofilm reactor development, a new support based on iron grafting onto polypropylene foams has been proposed. A suspension solid-state grafting process was applied to graft ferric acetylacetonate onto polypropylene (PP) foams with a density of 0.3–0.7 g/cm3. The iron contents grafted onto PP increased with the reaction time and then it tended to level off. The iron contents at 7.5 and 10 h are 0.74 and 0.75 wt%, respectively. It was specified that the equilibrium was reached at 7.5 h. Influence of particles on lipopeptide production was analyzed in two kinds of experiments: preliminary colonization step of particles, followed by production step in modified culture medium (named in this work colonization step) or direct addition of pellets in culturemedium (named production step). All PP+ iron pellets promoted biomass enhancement. The production yield was modified for all types of PP supports, containing respectively 0, 0.35 and 0.75% of iron. The immobilized cultures produced 2.09–4.3 times more biosurfactants than planktonic cells. In production experiments addition of carriers seemed tomodify the ratio between surfactin and fengycin with an enhancement of the fengycin production. The highest concentration of fengycin was obtained with addition of pellets containing 0.35% of iron