Exploring the relationship between bacterial genera and lipid metabolism in bovine rumen.

The rumen is characterised by a complex microbial ecosystem, which is particularly active in lipid metabolism. Several studies demonstrated a role of diet and breed on bacterial community profile, with the effect on metabolic pathways. Despite the knowledge achieved on metabolism and the bacterial profile, little is known about the relationship between individual bacteria and metabolic pathways. Therefore, a multivariate approach was used to search for possible relationships between bacteria and products of several pathways. The correlation between rumen bacterial community composition and rumen lipid metabolism was assessed in 40 beef steers (20 Maremmana and 20 Aubrac) reared with the same system and fed the same diet. A canonical discriminant analysis combined with a canonical correlation analysis (CCA) was performed to explore this correlation. The variables showing a Pearson correlation higher than 0.6 as absolute value and significant were retained for CCA considering the relationship of bacterial composition with several metabolic pathways. The results indicated that some bacterial genera could have significant impacts on the presence of several fatty acids. However, the relationship between genera and fatty acid changes according to the breed, demonstrating that the metabolic pathways change according to the host genetic background, related to breed evolution, although there is also an intra-breed genetic background which should not be ignored. In Maremmana, Succiniclasticum and Rikenellaceae_RC9_gut_group showed a high positive correlation with dimethylacetals (DMAs) DMAC13:0, DMAC14:0, DMAC14:0iso, DMAC15:0, DMAC15:0iso, and DMAC18:0. Prevotellaceae_UCG-003 correlates with C18:3c9c12c15 and C18:1t11, while Fibrobacter and Succiniclasticum correlate with C18:2c9t11 and Lachnospiraceae_NK3A20_group correlates with C18:1c12. Prevotellaceae_UCG-003, Ruminococcaceae_UCG-010, and Oribacterium showed a positive correlation with C13:0iso, and C17:0. Conversely, in Aubrac, Treponema_2 and Rikenellaceae_RC9_gut_group correlated with DMAC14:0iso, DMAC16:0iso, DMAC17:0iso, while Ruminococcaceae_UCG-010, Christensenellaceae_R-7_group and Ruminococcaceae_NK4A214_group correlated with DMAC18:1t11, DMAC14:0, DMAC18:1c12. Acetitomaculum correlated with C18:2c9c12, C18:1c12, C18:1c13, C18:1t12 and Lachnospiraceae_NK3A20_group with C18:1t6-8 and C18:1t9. Saccharofermentas, Ruminococcaceae_UCG-010 and Rikenellaceae_RC9_gut_group correlated with C18:2c9t11 while, Prevotellaceae_UCG-001 and Ruminococcus_1 correlated with C14:0iso, C15:0, C15:0iso, C17:0. Saccharofermentans, Rikenellaceae_RC9_gut_group, Ruminococcaceae_NK4A214_group, and Ruminococcaceae_UCG-010 correlated with C13:1c12 and C16:0iso. These results lead to hypothesise a possible association between several metabolic pathways and one or a few bacterial genera. If these associations are confirmed by further investigations that verify the causality of a bacterial genus with a particular metabolic process, it will be possible to deepen the knowledge on the activity of the rumen population in lipid metabolism. This approach appears to be a promising tool for uncovering the correlation between bacterial genera and products of rumen lipid metabolism.

Physical and metabolic interactions of Pseudomonas sp. strain JA5-B45 and Rhodococcus sp. strain F9-D79 during growth on crude oil and effect of a chemical surfactant on them.

Methods to enhance crude oil biodegradation by mixed bacterial cultures, for example, (bio)surfactant addition, are complicated by the diversity of microbial populations within a given culture. The physical and metabolic interactions between Rhodococcus sp. strain F9-D79 and Pseudomonas sp. strain JA5-B45 were examined during growth on Bow River crude oil. The effects of a nonionic chemical surfactant, Igepal CO-630 (nonylphenol ethoxylate), also were evaluated. Strain F9-D79 grew attached to the oil-water interface and produced a mycolic acid-containing capsule. Crude oil emulsification and surface activity were associated with the cellular fraction. Strain JA5-B45 grew in the aqueous phase and was unable to emulsify oil, but cell-free supernatants mediated kerosene-water emulsion formation. In coculture, stable emulsions were formed and strain JA5-B45 had an affinity for the capsule produced by strain F9-D79. Igepal CO-630 inhibited F9-D79 cells from adhering to the interface, and cells grew dispersed in the aqueous phase as 0.5-microm cocci rather than 2.5-microm rods. The surfactant increased total petroleum hydrocarbon removal by strain JA5-B45 from 4 to 22% and included both saturated compounds and aromatics. In coculture, TPH removal increased from 13 to 40% following surfactant addition. The culture pH normally increased from 7.0 to between 7.5 and 8.5, although addition of Igepal CO-630 to F9-D79 cultures resulted in a drop to pH 5.5. We suggest a dual role for the nonylphenol ethoxylate surfactant in the coculture: (i) to improve hydrocarbon uptake by strain JA5-B45 through emulsification and (ii) to prevent strain F9-D79 from adhering to the oil-water interface, indirectly increasing hydrocarbon availability. These varied effects on hydrocarbon biodegradation could explain some of the known diversity of surfactant effects.

Volatile hydrocarbon biodegradation by a mixed-bacterial culture during growth on crude oil.

Volatile hydrocarbon biodegradation by a mixed-bacterial culture during growth on Bow River crude oil was investigated using solid phase microextraction (SPME). Inoculum treatments were examined in relation to C(5)-C(11) hydrocarbon degradation. Up to 1600 mg/l biomass (dry weight) was tested without achieving significant volatile hydrocarbon partitioning and affecting analysis. Inoculum age rather than concentration had the most profound impact on biodegradation. When late log phase crude oil-grown inocula were used, C(5)-C(11) biodegradation reached 55-60%; methylcyclohexane and other branched compounds eluting before n-C(8) were recalcitrant. Increasing the late log inoculum concentration from 0.63 to 63 mg/l resulted in a twofold increase in degradation rate without improving the substrate range. Methylcyclohexane recalcitrance was correlated with reduced levels of hydrocarbon-degrading bacteria and volatile hydrocarbon evaporation from the inoculum flasks. A decreased lag phase prior to degradation was observed when using early stationary phase cultures as inocula and most compounds up to C(11), including methylcyclohexane, were biodegraded.

Community dynamics of a mixed-bacterial culture growing on petroleum hydrocarbons in batch culture.

The effects of various hydrocarbon substrates, and a chemical surfactant capable of enhancing crude-oil biodegradation, on the community structure of a mixed-bacterial inoculum were examined in batch culture. Of 1000 TSA-culturable isolates, 68.6% were identified at the genus level or better by phospholipid fatty acid analysis over 7-day time course experiments. Cultures were exposed to 20 g/L Bow River crude oil with and without 0.625 g/L Igepal CO-630 (a nonylphenol ethoxylate surfactant), 5 g/L saturates, 5 g/L aromatics, or 125 g/L refinery sludge. A group of six genera dominated the cultures: Acinetobacter, Alcaligenes, Ochrobactrum, Pseudomonas/Flavimonas, Stenotrophomonas, and Yersinia. Species from four of the genera were shown to be capable of hydrocarbon degradation, and counts of hydrocarbon degrading and total heterotrophic bacteria over time were nearly identical. Pseudomonas/Flavimonas and Stenotrophomonas normally dominated during the early portions of cultures, although the lag phase of Stenotrophomonas appears to have been increased by surfactant addition. Acinetobacter calcoaceticus was the most frequently isolated microorganism during exposure to the saturate fraction of crude oil. Regardless of substrate, the culture medium supported a greater variety of organisms during the latter portions of cultures. Understanding the community structure and dynamics of mixed bacterial cultures involved in treatment of heterogeneous waste substrates may assist in process development and optimization studies.

Influence of chemical surfactants on the biodegradation of crude oil by a mixed bacterial culture.

The effects of surfactant physicochemical properties, such as the hydrophile-lipophile balance (HLB) and molecular structure, on the biodegradation of 2% w/v Bow River crude oil by a mixed-bacterial culture were examined. Viable counts increased 4.6-fold and total petroleum hydrocarbon (TPH) biodegradation increased 57% in the presence of Igepal CO-630, a nonylphenol ethoxylate (HLB 13, 0.625 g/L). Only the nonylphenol ethoxylate with an HLB value of 13 substantially enhanced biodegradation. The surfactants from other chemical classes with HLB values of 13 (0.625 g/L) had no effect or were inhibitory. TPH biodegradation enhancement by Igepal CO-630 occurred at concentrations above the critical micelle concentration. When the effect of surfactant on individual oil fractions was examined, the biodegradation enhancement for the saturate and aromatic fractions was the same. In all cases, biodegradation resulted in increased resin and asphaltene concentrations. Optimal surfactant concentrations for TPH biodegradation reduced resin and asphaltene formation. Chemical surfactants have the potential to improve crude oil biodegradation in complex microbial systems, and surfactant selection should consider factors such as molecular structure, HLB, and surfactant concentration.