- Title
- Algae and bacteria interaction in wastewater and their biotechnological applications
- Creator
- Perera, Isiri Adhiwarie
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2021
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Excessive wastewater generation and their uncontrolled discharge into water bodies in recent years have been a serious concern worldwide. Hence, proper wastewater treatment is a necessity before discharging. However, conventional treatment methods have certain drawbacks such as high cost, intensive chemical usage, high energy demand and limited nutrient removal. Given these limitations, it is essential to consider the environmentally friendly wastewater treatment method with improved nutrient removal capacity thereby reducing eutrophication. Microalgae and bacteria abundantly present in aquatic systems coexist together, establishing the microalgal-bacterial consortium. However, their metabolic versatility and interspecies interactions, which could benefit treating wastewater, are poorly understood. Hence, this study focused on exploring their interactions, metabolites exchange and physiological changes as a comprehensive approach in understanding the microalgal-bacterial consortium for efficient use for treating wastewater and biotechnological applications. This study initially investigated five morphologically distinct microalgae for their ability in establishing consortia in Bold’s basal medium with a bacterial strain, Variovorax paradoxus IS1, all isolated from wastewaters. Tetradesmus obliquus IS2 or Coelastrella sp. IS3 with V. paradoxus IS1 as two species microalgal-bacterial consortia were selected to gain insight into their physiological changes. The observed changes in microalgal-bacterial co-cultures were the increase of pigments such as chlorophyll a, b and carotenoids (>1.2-fold), reduction of reactive oxygen species and increased lipid yield (>2-fold) compared to their mono-cultures. The distinct regulation of cellular metabolites such as sugars, amino acids, organic acids, and phytohormones was evident in the two microalgal–bacterial consortia. Hence, the selected microalgal strains, T. obliquus IS2 and Coelastrella sp. IS3 established efficient consortia with V. paradoxus IS1 by making the required physiological changes, including metabolomics. The bacterium V. paradoxus IS1 increased the specific growth rates of microalgal species significantly in the consortia by enhancing the uptake of nitrate (88‒99%) and phosphate (92‒95%) besides accumulating higher amounts of carbohydrates and proteins. The EPS, collected from the bacterial or microalgal cultures, contained numerous phytohormones, vitamins, polysaccharides and amino acids that are likely involved in interspecies interactions. The addition of EPS obtained from V. paradoxus IS1 to the culture medium doubled the growth of both the microalgal strains. The EPS collected from T. obliquus IS2 significantly increased the growth of V. paradoxus IS1. Still, there was no apparent change in bacterial growth when cultured in the presence of EPS from Coelastrella sp. IS3. These observations indicate that the interaction between V. paradoxus IS1 and T. obliquus IS2 was mutualism, while commensalism appeared between the bacterial strain and Coelastrella sp. IS3. Hence, present findings unveil the EPS-induced symbiotic interactions among the partners involved in microalgal–bacterial consortia. The role of extracellular metabolites investigated during mutualistic interactions in co-cultures of a microalga, Tetradesmus obliquus IS2 or Coelastrella sp. IS3, and a bacterium, Variovorax paradoxus IS1, grown with varying levels of NO3-N and NH4-N. Both NO3-N and NH4-N were added to modified Bold’s basal medium at 16:0, 12:4, 8:8; 4:12 and 0:16 molar ratios by keeping a final N:P ratio of 16:1. Mono-cultures of microalgae grown with nitrate showed enhanced growth (>2-fold), while the bacterial strain cultured with ammonium exhibited a >1.3-fold increase in growth. Co-culturing with nitrate and ammonium resulted in enhanced growth of microalgae (>1.7-fold) and the bacterium (>4.1-fold) as compared to the mono-cultures. Uptake of NO3-N, NH4-N and PO4-P by mono-cultures or co-cultures depended on the ratio of two inorganic nitrogen sources used. Partners in co-cultures grown with different ratios of nitrate and ammonium differentially released exudates enriched with organic acids, amino acids, and simple sugars. Thus, the present novel study demonstrates the release of exudates changed qualitatively and quantitatively, improving the mutualistic interactions in microalgal‒bacterial co-cultures. The results suggest that the variables such as inorganic nitrogen sources and extracellular metabolites released need to be considered while using co-cultures for practical bioremediation of wastewaters. This study demonstrated the phenotypic response in a co-culture involving a microalga, Tetradesmus obliquus IS2, and a bacterium, Variovorax paradoxus IS1, grown with varying concentrations of two inorganic nitrogen sources. Modified Bold’s basal medium was supplemented with 16:0, 12:4, 8:8; 4:12 and 0:16 molar ratios of NO3-N and NH4-N by keeping N:P ratio of 16:1. The observed morphological changes in microalga included an increase in granularity and a broad range of cell sizes under the influence of increased ammonium levels. Co-culturing in the presence of NO3-N alone or combination with NH4-N up to equimolar concentrations resulted in complete nitrogen uptake, increased growth in both the microbial strains and enhanced accumulation of carbohydrates, proteins and lipids. Total chlorophyll content in microalga was also significantly higher when it was grown as a co-culture with NO3-N and NH4-N up to a ratio of 1:1. Significant upregulation in the synthesis of amino acids and sugars and downregulation of organic acids were evident with higher ammonium uptake in the co-culture, indicating the regulation of carbon and nitrogen assimilation pathways and energy synthesis. The data suggest that the co-culture of strains IS1 and IS2 could be exploited for effluent treatment by considering the concentrations of inorganic sources, particularly ammonium, in the wastewaters. The interactions of Tetradesmus obliquus IS2‒Variovorax paradoxus IS1 co-culture and the native bacterial communities in wastewaters collected from dairy farm and poultry slaughterhouse were studied during effluent bioremediation. Co-culturing of the two microbial strains in non-sterile wastewaters alone resulted in significant removal of total N (>92%), PO4-P (>89%) and COD (>84%) as well as increased production of ROS and neutral lipids, indicating significant mutualistic interactions with native bacterial communities. Metagenomic data of the co-cultures in wastewaters revealed selective enrichment of Firmicutes and Actinobacteria, resulting in enhanced microalgal growth and nutrient removal. The findings of this novel study suggest that microalgal‒bacterial co-cultures mediate interspecies interactions among native bacterial communities in wastewaters and enhance bioremediation of effluents. Altogether, these investigations revealed microalgal–bacterial consortia partners release differential extracellular compounds varying with the environment and species, which induces the symbiotic association. The synergistic interaction in the co-culture, T. obliquus IS2 with V. paradoxus IS1, made them a promising microalgal-bacterial association for achieving higher microalgal biomass yield and nutrients removal in wastewater. Hence, studying their interactions would enable understanding the efficiency of microalgal-bacterial consortia, which could broadly be used in wastewater treatment and for the production of value-added metabolites.
- Subject
- wastewaters; microalgal–bacterial consortia; symbiotic interactions; nutrient removal; metabolites; extracellular polymeric substances
- Identifier
- http://hdl.handle.net/1959.13/1483264
- Identifier
- uon:51087
- Rights
- Copyright 2021 Isiri Adhiwarie Perera
- Language
- eng
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