Periodic harvesting of microalgae from calcium alginate hydrogels for sustained high-density production

Effect of nutrients deficiency on biofilm formation and single cell protein production with a purple non-sulphur bacteria enriched culture

Purple non-sulphur bacteria (PNSB) are of interest for biorefinery applications to create biomolecules, but their production cost is expensive due to substrate and biomass separation costs. This research has utilized fuel synthesis wastewater (FSW) as a low-cost carbon-rich substrate to produce single-cell protein (SCP) and examines PNSB biofilm formation using this substrate to achieve a more efficient biomass-liquid separation. In this study, PNSB were grown in Ca, Mg, S, P, and N-deficient media using green shade as biofilm support material. Among these nutrient conditions, only N-deficient and control (nutrient-sufficient) conditions showed biofilm formation. Although total biomass growth of the control was 1.5 times that of the N-deficient condition and highest overall, the total biofilm-biomass in the N-deficient condition was 2.5 times greater than the control, comprising 49% of total biomass produced. Total protein content was similar between these four biomass samples, ranging from 35.0 ± 0.2% to 37.2 ± 0.0%. The highest protein content of 44.7 ± 1.3% occurred in the Mg-deficient condition (suspended biomass only) but suffered from a low growth rate. Overall, nutrient sufficient conditions are optimal for overall protein productivity and dominated by suspended growth, but where fixed growth systems are desired for cost-effective harvesting, N-deficient conditions provide an effective means to maximize biofilm production without sacrificing protein content.

Engineering consortia by polymeric microbial swarmbots

Synthetic microbial consortia represent a new frontier for synthetic biology given that they can solve more complex problems than monocultures. However, most attempts to co-cultivate these artificial communities fail because of the winner-takes-all in nutrients competition. In soil, multiple species can coexist with a spatial organization. Inspired by nature, here we show that an engineered spatial segregation method can assemble stable consortia with both flexibility and precision. We create microbial swarmbot consortia (MSBC) by encapsulating subpopulations with polymeric microcapsules. The crosslinked structure of microcapsules fences microbes, but allows the transport of small molecules and proteins. MSBC method enables the assembly of various synthetic communities and the precise control over the subpopulations. These capabilities can readily modulate the division of labor and communication. Our work integrates the synthetic biology and material science to offer insights into consortia assembly and serve as foundation to diverse applications from biomanufacturing to engineered photosynthesis.

Material biosynthesis, mechanism regulation and resource recycling of biomass and high-value substances from wastewater treatment by photosynthetic bacteria: A review

The environmental-friendly and economic benefits generated from photosynthetic bacteria (PSB) wastewater treatment have attracted significant attention. This process of resource recovery can produce PSB biomass and high-value substances including single cell protein, Coenzyme Q₁₀, polyhydroxyalkanoates (PHA), 5-aminolevulinic acid, carotenoids, bacteriocin, and polyhydroxy chain alkyl esters, etc. for application in various fields, such as agriculture, medical treatment, chemical, animal husbandry and food industry while treating wastewaters. The main contents of this review are summarized as follows: physiological characteristics, mechanism and application of PSB and potential of single cell protein (SCP) production are described; PSB wastewater treatment technology, including procedures and characteristics, typical cases, influencing factors and bioresource recovery by membrane bioreactor are detailed systematically. The future development of PSB-based resource recovery and wastewater treatment are also provided, particularly concerning PSB-membrane reactor (MBR) process, regulation of biosynthesis mechanism of high-value substances and downstream separation and purification technology. This will provide a promising and new alternative for wastewater treatment recycling.

Application of purple phototrophic bacteria in a biofilm photobioreactor for single cell protein production: Biofilm vs suspended growth

Single cell protein (SCP), has been proposed as alternative to effectively upgrade and recycle organics and nutrients from wastewater. Biomass recovery is a critical issue, and recovery as a biofilm is effective in comparison with sedimentation of suspended biomass. This study aims to determine the applicability of purple phototrophic bacteria (PPB) biofilm on infra-red irradiated, submerged surfaces for the treatment of pre-settled red meat processing wastewater, and SCP generation. PPB removed up to 66% of COD and 42% of TN and TP during batch operation with total areal productivities between 15 and 20 gVS m^-2 d^-1 achieved. More than 60% of the total biomass grew attached (as biofilm) with the remainder being suspended. The biofilm can be harvested at around 160 gTS L^-1 with high protein (>96 g L^-1) and low ash contents (>4.0% compared to >30% in the wastewater). The compositions of attached and suspended biomass differed significantly, where the suspended fraction resembled the wastewater composition (e.g. in terms of inert components). The PPB community was similar in the suspended and biofilm fractions while the biofilm had higher relative abundance of PPB representatives (57% vs 43%). A consistent product composition is highly relevant for the manufacturer and ultimately determines the value as feed, feed additive, or supplement.

Heterologous expression of mlrA in a photoautotrophic host - Engineering cyanobacteria to degrade microcystins

In this report, we establish proof-of-principle demonstrating for the first time genetic engineering of a photoautotrophic microorganism for bioremediation of naturally occurring cyanotoxins. In model cyanobacterium Synechocystis sp. PCC 6803 we have heterologously expressed Sphingopyxis sp. USTB-05 microcystinase (MlrA) bearing a 23 amino acid N-terminus secretion peptide from native Synechocystis sp. PCC 6803 PilA (sll1694). The resultant whole cell biocatalyst displayed about 3 times higher activity against microcystin-LR compared to a native MlrA host (Sphingomonas sp. ACM 3962), normalized for optical density. In addition, MlrA activity was found to be almost entirely located in the cyanobacterial cytosolic fraction, despite the presence of the secretion tag, with crude cellular extracts showing MlrA activity comparable to extracts from MlrA expressing E. coli. Furthermore, despite approximately 9.4-fold higher initial MlrA activity of a whole cell E. coli biocatalyst, utilization of a photoautotrophic chassis resulted in prolonged stability of MlrA activity when cultured under semi-natural conditions (using lake water), with the heterologous MlrA biocatalytic activity of the E. coli culture disappearing after 4 days, while the cyanobacterial host displayed activity (3% of initial activity) after 9 days. In addition, the cyanobacterial cell density was maintained over the duration of this experiment while the cell density of the E. coli culture rapidly declined. Lastly, failure to establish a stable cyanobacterial isolate expressing native MlrA (without the N-terminus tag) via the strong cpcB560 promoter draws attention to the use of peptide tags to positively modulate expression of potentially toxic proteins.