Chlamydomonas reinhardtii and Microbacterium forte sp. nov., a mutualistic association that favors sustainable hydrogen production

Optimization of hydrogen production using a coculture of Chlamydomonas reinhardtii and activated sludge bacteria

The production of biophotolytic hydrogen (H2) relies on the effective management of oxygen (O2) levels. Coculturing bacteria with microalgae helps mitigate the excess O2 produced by algal cells. After depleting O2, the bacteria activate the enzyme hydrogenase in microalgae, leading to H2 production. In this study, Chlamydomonas reinhardtii was cocultured with indigenous bacteria from activated sludge at varying algae-to-bacteria ratios (1:1, 1:1.5, 1:2, 1:2.5, and 1:3 v/v), with an illumination intensity of 2.8 mmol/m2/s (31 × 103 lux). The 1:1.5 v/v ratio yielded the highest H2 volume (1162 mL/L) and the highest O2 concentration (153.2 mL/L) over a 6-day period. Production of all gaseous components ceased for all ratios as the pH dropped below 4 due to acetate accumulation, and the concentration of acetate reached approximately 1 g/L by the end of each experiment. Gas composition analysis after the first day of coculture revealed that H2, CO2, N2, and O2 constituted 25%-46%, 20%-40%, 5%-30%, and 1%-10% of the total gas volume, respectively. Glucose (10 g/L) was introduced as an external carbon source for all cultures. After 6 days, the coculture maintained a high total organic carbon (TOC) level of 3.1 g/L, whereas the initial TOC ranged between 3.9 and 4.3 g/L. The findings illustrated a significant correlation between H2 production, acetate accumulation levels, and O2 consumption. The algae-activated sludge coculture method substantially enhanced H2 production compared with previously published methods employing only one or two types of bacterial cultures, underscoring its potential for more efficient biophotolytic H2 production.

Quantitative assessment, molecular docking and novel metabolic pathways reveal the interaction mechanisms between norfloxacin biodegradation and environmental implications

Norfloxacin (NOR) is widely used in medicine and animal husbandry, but its accumulation in the environment poses a substantial threat to ecological and human health. Traditional physical, chemical, and rudimentary biological methods often fall short in mitigating NOR contamination, necessitating innovative biological approaches. This study proposes an engineered bacterial consortium found in marine sediment as a strategy to enhance NOR degradation through inter-strain co-metabolism of diverse substrates. Strategically supplementing the engineered bacterial consortium with exogenous carbon sources and metal ions boosted the activity of key degradation enzymes like laccase, manganese peroxidase, and dehydrogenase. Iron and amino acids demonstrated synergistic effects, resulting in a remarkable 70.8% reduction in NOR levels. The innovative application of molecular docking elucidated enzyme interactions with NOR, uncovering potential biodegradation mechanisms. Quantitative assessment reinforced the efficiency of NOR degradation within the engineered bacterial consortium. Four metabolic routes are herein proposed: acetylation, defluorination, ring scission, and hydroxylation. Notably, this study discloses distinctive, co-operative metabolic pathways for NOR degradation within the specific microbial community. These findings provide new ways of understanding and investigating the bioremediation potential of NOR contaminants, which may lead to the development of more sustainable and effective environmental management strategies.

Exchange or Eliminate: The Secrets of Algal-Bacterial Relationships

Algae and bacteria have co-occurred and coevolved in common habitats for hundreds of millions of years, fostering specific associations and interactions such as mutualism or antagonism. These interactions are shaped through exchanges of primary and secondary metabolites provided by one of the partners. Metabolites, such as N-sources or vitamins, can be beneficial to the partner and they may be assimilated through chemotaxis towards the partner producing these metabolites. Other metabolites, especially many natural products synthesized by bacteria, can act as toxins and damage or kill the partner. For instance, the green microalga Chlamydomonas reinhardtii establishes a mutualistic partnership with a Methylobacterium, in stark contrast to its antagonistic relationship with the toxin producing Pseudomonas protegens. In other cases, as with a coccolithophore haptophyte alga and a Phaeobacter bacterium, the same alga and bacterium can even be subject to both processes, depending on the secreted bacterial and algal metabolites. Some bacteria also influence algal morphology by producing specific metabolites and micronutrients, as is observed in some macroalgae. This review focuses on algal-bacterial interactions with micro- and macroalgal models from marine, freshwater, and terrestrial environments and summarizes the advances in the field. It also highlights the effects of temperature on these interactions as it is presently known.