Regulation of colony morphology and biofilm formation in Shewanella algae.

Bacterial colony morphology can reflect different physiological stages such as virulence or biofilm formation. In this work we used transposon mutagenesis to identify genes that alter colony morphology and cause differential Congo Red (CR) and Brilliant Blue G (BBG) binding in Shewanella algae, a marine indigenous bacterium and occasional human pathogen. Microscopic analysis of colonies formed by the wild-type strain S. algae CECT 5071 and three transposon integration mutants representing the diversity of colony morphotypes showed production of biofilm extracellular polymeric substances (EPS) and distinctive morphological alterations. Electrophoretic and chemical analyses of extracted EPS showed differential patterns between strains, although the targets of CR and BBG binding remain to be identified. Galactose and galactosamine were the preponderant sugars in the colony biofilm EPS of S. algae. Surface-associated biofilm formation of transposon integration mutants was not directly correlated with a distinct colony morphotype. The hybrid sensor histidine kinase BarA abrogated surface-associated biofilm formation. Ectopic expression of the kinase and mutants in the phosphorelay cascade partially recovered biofilm formation. Altogether, this work provides the basic analysis to subsequently address the complex and intertwined networks regulating colony morphology and biofilm formation in this poorly understood species.

Bio-based films from wheat bran feruloylated arabinoxylan: Effect of extraction technique, acetylation and feruloylation.

This study demonstrates the potential of feruloylated arabinoxylan (AX) from wheat bran for the preparation of bioactive barrier films with antioxidant properties. We have comprehensively evaluated the influence of the structural features and chemical acetylation of feruloylated AX extracted by subcritical water on their film properties, in comparison with alkaline extracted AX and a reference wheat endosperm AX. The degree of substitution (DS) of AX had a large influence on film formation, higher DS yielded better thermal and mechanical properties. The barrier properties of AX films were significantly enhanced by external plasticization by sorbitol. Chemical acetylation significantly improved the thermal stability but not the mechanical or barrier properties of the films. The presence of bound ferulic acid in feruloylated AX films resulted in higher antioxidant activity compared to external addition of free ferulic acid, which demonstrates their potential use in active packaging applications for the preservation of oxygen-sensitive foodstuff.

Cascade extraction of proteins and feruloylated arabinoxylans from wheat bran.

A cascade process for the sequential recovery of proteins and feruloylated arabinoxylan from wheat bran is proposed, involving a protein isolation step, enzymatic destarching and subcritical water extraction. The protein isolation step combining lactic acid fermentation and cold alkaline extraction reduced the recalcitrance of wheat bran, thus improving the total yields of the subsequent subcritical water extraction. The time evolution of subcritical water extraction of feruloylated arabinoxylan was compared at two temperatures (160 °C and 180 °C). Longer residence times enhanced the purity of target feruloylated arabinoxylans, whereas higher temperatures resulted in faster extraction at the expense of significant molar mass reduction. The radical scavenging activity of the extracted feruloylated arabinoxylans was preserved after the initial protein isolation step. This study opens new possibilities for the cascade valorization of wheat bran into enriched protein and non-starch polysaccharide fractions, which show potential to be used as functional food ingredients.