Biosequestration of carbon dioxide using carbonic anhydrase from novel Streptomyces kunmingensis

The increase in the atmospheric concentrations of carbon dioxide due to anthropogenic interventions has led to several undesirable consequences, notably global warming and related changes. Avoidance of and/or removal of carbon dioxide will result in the reduction of global warming. Biosequestration of carbon by using carbonic anhydrase (CA) as biocatalyst is one of most effective approaches. In the present study, actinobacterial cultures isolated from bamboo (Bambusa vulgaris) rhizosphere were screened for the production of carbonic anhydrase enzyme. The strain BS19 which showed promising CA production was selected as the potential strain. Strain BS19 was identified as Streptomyces kunmingensis based on the phenotypic and molecular characteristics. In submerged fermentation, strain BS19 produced 214.21 IU/ml of CA enzyme. The molecular mass of the CA was determined as 45 ± 2 kDa. The production of CA was found to be optimal at pH 7.0 and at temperature of 28 °C. The full length periplasmic CA gene was successfully amplified from S. kunmingensis BS19. Biomimetic sequestration of carbon was detected and quantified through CaCO₃ precipitation method. Further, the CA of BS 19 was successfully used to mineralize CO₂ present in motorbike exhaust, which has a similar composition to that of flue gas. The well-defined rhombohedral calcite crystals formed in the mineral carbonation reaction was observed through SEM analysis. The findings of this study clearly indicated that Streptomyces kunmingensis BS19 isolated from bamboo rhizosphere is a promising candidate for the production of carbonic anhydrase which deserves the potential for CO₂ sequestration.

New Biocalcifying Marine Bacterial Strains Isolated from Calcareous Deposits and Immediate Surroundings

Marine bacterial biomineralisation by CaCO3 precipitation provides natural limestone structures, like beachrocks and stromatolites. Calcareous deposits can also be abiotically formed in seawater at the surface of steel grids under cathodic polarisation. In this work, we showed that this mineral-rich alkaline environment harbours bacteria belonging to different genera able to induce CaCO3 precipitation. We previously isolated 14 biocalcifying marine bacteria from electrochemically formed calcareous deposits and their immediate environment. By microscopy and µ-Raman spectroscopy, these bacterial strains were shown to produce calcite-type CaCO3. Identification by 16S rDNA sequencing provided between 98.5 and 100% identity with genera Pseudoalteromonas, Pseudidiomarina, Epibacterium, Virgibacillus, Planococcus, and Bhargavaea. All 14 strains produced carbonic anhydrase, and six were urease positive. Both proteins are major enzymes involved in the biocalcification process. However, this does not preclude that one or more other metabolisms could also be involved in the process. In the presence of urea, Virgibacillus halodenitrificans CD6 exhibited the most efficient precipitation of CaCO3. However, the urease pathway has the disadvantage of producing ammonia, a toxic molecule. We showed herein that different marine bacteria could induce CaCO3 precipitation without urea. These bacteria could then be used for eco-friendly applications, e.g., the formation of bio-cements to strengthen dikes and delay coastal erosion.

Trends, application and future prospectives of microbial carbonic anhydrase mediated carbonation process for CCUS

Growing industrialization and the desire for a better economy in countries has accelerated the emission of greenhouse gases (GHGs), by more than the buffering capacity of the earth's atmosphere. Among the various GHGs, carbon dioxide occupies the first position in the anthroposphere and has detrimental effects on the ecosystem. For decarbonization, several non-biological methods of carbon capture, utilization and storage (CCUS) have been in use for the past few decades, but they are suffering from narrow applicability. Recently, CO₂ emission and its disposal related problems have encouraged the implementation of bioprocessing to achieve a zero waste economy for a sustainable environment. Microbial carbonic anhydrase (CA) catalyses reversible CO₂ hydration and forms metal carbonates that mimic the natural phenomenon of weathering/carbonation and is gaining merit for CCUS. Thus, the diversity and specificity of CAs from different micro-organisms could be explored for CCUS. In the literature, more than 50 different microbial CAs have been explored for mineral carbonation. Further, microbial CAs can be engineered for the mineral carbonation process to develop new technology. CA driven carbonation is encouraging due to its large storage capacity and favourable chemistry, allowing site-specific sequestration and reusable product formation for other industries. Moreover, carbonation based CCUS holds five-fold more sequestration capacity over the next 100 years. Thus, it is an eco-friendly, feasible, viable option and believed to be the impending technology for CCUS. Here, we attempt to examine the distribution of various types of microbial CAs with their potential applications and future direction for carbon capture. Although there are few key challenges in bio-based technology, they need to be addressed in order to commercialize the technology.