The biotechnological potential of the Chloroflexota phylum.

In the next decades, the increasing material and energetic demand to support population growth and higher standards of living will amplify the current pressures on ecosystems and will call for greater investments in infrastructures and modern technologies. A valid approach to overcome such future challenges is the employment of sustainable bio-based technologies that explore the metabolic richness of microorganisms. Collectively, the metabolic capabilities of Chloroflexota, spanning aerobic and anaerobic conditions, thermophilic adaptability, anoxygenic photosynthesis, and utilization of toxic compounds as electron acceptors, underscore the phylum's resilience and ecological significance. These diverse metabolic strategies, driven by the interplay between temperature, oxygen availability, and energy metabolism, exemplify the complex adaptations that enabled Chloroflexota to colonize a wide range of ecological niches. In demonstrating the metabolic richness of the Chloroflexota phylum, specific members exemplify the diverse capabilities of these microorganisms: Chloroflexus aurantiacus showcases adaptability through its thermophilic and phototrophic growth, whereas members of the Anaerolineae class are known for their role in the degradation of complex organic compounds, contributing significantly to the carbon cycle in anaerobic environments, highlighting the phylum's potential for biotechnological exploitation in varying environmental conditions. In this context, the metabolic diversity of Chloroflexota must be considered a promising asset for a large range of applications. Currently, this bacterial phylum is organized into eight classes possessing different metabolic strategies to survive and thrive in a wide variety of extreme environments. This review correlates the ecological role of Chloroflexota in such environments with the potential application of their metabolisms in biotechnological approaches.

Microbial selection strategies for polyhydroxyalkanoates production from crude glycerol: Effect of OLR and cycle length.

Crude glycerol from biodiesel manufacture can be used as carbon source for microbial fermentations. The production of polyhydroxyalkanoates by manipulating the Sequencing Batch Reactor (SBR) selection stage of microbial mixed cultures (MMC) using high organic loading rates (OLR, 50CmM/day) and different cycles lengths (6, 12 and 24h) were optimized. Batch-production of polyhydroxybutyrate (PHB) presented an accumulation capacity in the high range (0.44g/g) after 3 pulses of 50CmM, with a final content of 59% PHB/wt., for the culture selected with 50CmM/day and a 24h cycle length. These values were in the range to those obtained with pure cultures and higher than the ones for MMC. With this strategy three main advantages in terms of the PHA production can be considered: utilization of a real waste without the resort to pure microbial cultures and a pre-fermentation step, consolidating the role of MMC in the valorisation of complex wastes/by-products.

Bio-oil upgrading strategies to improve PHA production from selected aerobic mixed cultures.

Recent research on polyhydroxyalkanoates (PHAs) has focused on developing cost-effective production processes using low-value or industrial waste/surplus as substrate. One of such substrates is the liquid fraction resulting from pyrolysis processes, bio-oil. In this study, valorisation of bio-oil through PHA production was investigated. The impact of the complex bio-oil matrix on PHA production by an enriched mixed culture was examined. The performance of the direct utilization of pure bio-oil was compared with the utilization of three defined substrates contained in this bio-oil: acetate, glucose and xylose. When compared with acetate, bio-oil revealed lower capacity for polymer production as a result of a lower polymer yield on substrate and a lower PHA cell content. Two strategies for bio-oil upgrade were performed, anaerobic fermentation and vacuum distillation, and the resulting liquid streams were tested for polymer production. The first one was enriched in volatile fatty acids and the second one mainly on phenolic and long-chain fatty acids. PHA accumulation assays using the upgraded bio-oils attained polymer yields on substrate similar or higher than the one achieved with acetate, although with a lower PHA content. The capacity to use the enriched fractions for polymer production has yet to be optimized. The anaerobic digestion of bio-oil could also open-up the possibility to use the fermented bio-oil directly in the enrichment process of the mixed culture. This would increase the selective pressure toward an optimized PHA accumulating culture selection.