Burkholderia thailandensis as a microbial cell factory for the bioconversion of used cooking oil to polyhydroxyalkanoates and rhamnolipids.

The present work assessed the feasibility of used cooking oil as a low cost carbon source for rhamnolipid biosurfactant production employing the strain Burkholderia thailandensis. According to the results, B. thailandensis was able to produce rhamnolipids up to 2.2 g/L, with the dominant congener being the di-rhamnolipid Rha-Rha-C14-C14. Rhamnolipids had the ability to reduce the surface tension to 37.7 mN/m and the interfacial tension against benzene and oleic acid to 4.2 and 1.5 mN/m, while emulsification index against kerosene reached up to 64%. The ability of B. thailandensis to accumulate intracellular biopolymers, in the form of polyhydroxyalkanoates (PHA), was also monitored. Polyhydroxybutyrate (PHB) was accumulated simultaneously and consisted of up to 60% of the cell dry weight. PHB was further characterized in terms of its molecular weight and thermal properties. This is the first study reporting the simultaneous production of polyhydroxyalkanoates and rhamnolipids by the non-pathogen rhamnolipid producer B. thailandensis.

Biotransformation of volatile fatty acids to polyhydroxyalkanoates by employing mixed microbial consortia: The effect of pH and carbon source.

Mixed microbial cultures that undergo successful enrichment, following eco-biotechnological approaches, to form a community dominant in polyhydroxyalkanoates (PHA) forming bacteria, represent an attractive economic alternative towards the production of those biopolymers. In the present study, an enriched mixed culture was investigated for the production of PHA at different initial pH values under non-controlled conditions in order to minimize process control and operational costs. Short-chain fatty acids were provided as PHA precursors and they were tested as sole carbon sources and as mixtures under nitrogen deficiency. By the obtained kinetic and stoichiometric parameters it was shown that at an initial pH value of 6.90 PHA production was favored. Butyrate was characterized as the preferred carbon source, whereas simultaneous feeding led to increased rates and yields when butyrate and acetate were present.

Polyhydroxyalkanoates from Pseudomonas sp. using synthetic and olive mill wastewater under limiting conditions.

The present study aimed at investigating the ability of bacteria isolated from an enriched mixed culture to produce polyhydroxyalkanoates (PHAs) and examining the effect of nitrogen and dual nitrogen-oxygen limitation on PHAs production, by using both synthetic and olive mill wastewater (OMW). PHAs production was performed through batch experiments using both the enriched culture and the isolated strains (belonging to the genus of Pseudomonas) aiming to compare PHAs accumulation capacity, yields and rates. The use of enriched culture and synthetic wastewater under nitrogen limitation resulted in the highest PHA accumulation, i.e. 64.4%gPHAs/g of cell dry mass (CDM). However, when OMW was used, PHAs accumulation significantly decreased, i.e. 8.8%gPHAs/g CDM. The same trend was followed by the isolated strains, nevertheless, their ability to synthesize PHAs was lower. Although, dual nitrogen-oxygen limitation generally slowed down PHAs biosynthesis, in certain strains PHAs production was positively affected.

Microbial bio-based plastics from olive-mill wastewater: Generation and properties of polyhydroxyalkanoates from mixed cultures in a two-stage pilot scale system.

The operational efficiency of a two stage pilot scale system for polyhydroxyalkanoates (PHAs) production from three phase olive oil mill wastewater (OMW) was investigated in this study. A mixed anaerobic, acidogenic culture derived from a municipal wastewater treatment plant, was used in the first stage, aiming to the acidification of OMW. The effluent of the first bioreactor that was operated in continuous mode, was collected in a sedimentation tank in which partial removal of the suspended solids was taking place, and was then forwarded to an aerobic reactor, operated in sequential batch mode under nutrient limitation. In the second stage an enriched culture of Pseudomonas sp. was used as initial inoculum for the production of PHAs from the acidified waste. Clarification of the acidified waste, using aluminium sulphate which causes flocculation and precipitation of solids, was also performed, and its effect on the composition of the acidified waste as well as on the yields and properties of PHAs was investigated. It was shown that clarification had no significant qualitative or quantitative effect on the primary carbon sources, i.e. short chain fatty acids and residual sugars, but only on the values of total suspended solids and total chemical oxygen demand of the acidified waste. The type and thermal characteristics of the produced PHAs were also similar for both types of feed. However the clarification of the waste seemed to have a positive impact on final PHAs yield, measured as gPHAs/100g of VSS, which reached up to 25%. Analysis of the final products via nuclear magnetic resonance spectroscopy revealed the existence of 3-hydroxybutyrate (3HB) and 3-hydroxyoctanoate (HO) units, leading to the conclusion that the polymer could be either a blend of P3HB and P3HO homopolymers or/and the 3HB-co-3HO co-polymer, an unusual polymer occurring in nature with advanced properties.

Exploitation of olive oil mill wastewater for combined biohydrogen and biopolymers production.

The present study aimed to the investigation of the feasibility of the combined biohydrogen and biopolymers production from OMW (Olive oil Mill Wastewater), using a two stage system. H(2) and volatile fatty acids (VFAs) were produced via anaerobic fermentation and subsequently the acidified wastewater was used as substrate for aerobic biodegradable polymer production. Two different bioreactors, one of CSTR type and a SBR were used for the anaerobic and the aerobic process respectively. The anaerobic reactor was operated at different hydraulic retention times (HRTs) with OMW, diluted 1:4 (v/v) with tap water, as feed. The main VFAs produced were acetate, butyrate and propionate, in different ratios depending on the HRT. Valerate, isovalerate and isobutyrate were also detected in small quantities. Selective effluents of the acidogenic/hydrogen producing reactor were subsequently used as feed for the aerobic reactor. The aerobic reactor was inoculated with an enriched PHAs producing bacteria culture, and was operated in sequential cycles of nitrogen offer (growth phase) and nitrogen limitation (PHAs accumulation phase). The operational program of the SBR was determined according to the results from batch test, and its performance was evaluated for a period of 100 days. During the accumulation phase butyrate was consumed preferably, indicating that the dominant PHA produced is polyhydroxybutyrate. The higher yield of PHAs observed was 8.94% (w/w) of dry biomass weight.