Algae and bacteria have coexisted ever since the early stages of evolution. This coevolution has revolutionized life on earth in many aspects. Algae and bacteria together influence ecosystems as ...varied as deep seas to lichens and represent all conceivable modes of interactions — from mutualism to parasitism. Several studies have shown that algae and bacteria synergistically affect each other's physiology and metabolism, a classic case being algae–roseobacter interaction. These interactions are ubiquitous and define the primary productivity in most ecosystems. In recent years, algae have received much attention for industrial exploitation but their interaction with bacteria is often considered a contamination during commercialization. A few recent studies have shown that bacteria not only enhance algal growth but also help in flocculation, both essential processes in algal biotechnology. Hence, there is a need to understand these interactions from an evolutionary and ecological standpoint, and integrate this understanding for industrial use. Here we reflect on the diversity of such relationships and their associated mechanisms, as well as the habitats that they mutually influence. This review also outlines the role of these interactions in key evolutionary events such as endosymbiosis, besides their ecological role in biogeochemical cycles. Finally, we focus on extending such studies on algal–bacterial interactions to various environmental and bio-technological applications.
This article summarizes several developed and industrial technologies for nitrate removal from drinking water, including physicochemical and biological techniques, with a focus on autotrophic nitrate ...removal. Approaches are primarily classified into separation-based and elimination-based methods according to the fate of the nitrate in water treatment. Biological denitrification as a cost-effective and promising method of biological nitrate elimination is reviewed in terms of its removal process, applicability, efficiency, and associated disadvantages. The various pathways during biological nitrate removal, including assimilatory and dissimilatory nitrate reduction, are also explained. A comparative study was carried out to provide a better understanding of the advantages and disadvantages of autotrophic and heterotrophic denitrification. Sulfur-based and hydrogen-based denitrifications, which are the most common autotrophic processes of nitrate removal, are reviewed with the aim of presenting the salient features of hydrogenotrophic denitrification along with some drawbacks of the technology and research areas in which it could be used but currently is not. The application of algae-based water treatment is also introduced as a nature-inspired approach that may broaden future horizons of nitrate removal technology.
Rhizobium plays the pivotal role in mutualistic interactions with plants and this study extends this mutualism to several species of green algae. Denaturing gradient gel electrophoresis (DGGE) and ...16S rRNA gene clone library experiments of Chlamydomonas reinhardtii, Chlorella vulgaris, Scenedesmus sp., and Botryococcus braunii revealed that the dominant phycosphere bacteria hosted by these green algae were Rhizobium, Mesorhizobium, and Shinella within Rhizobiales, Flavobacterium within Flavobacteriales, and Pseudomonas within Pseudomonadales. When Rhizobium sp., most prevalent and dominant bacterium isolated from C. vulgaris, was co-cultured with green algae, it promoted algal cell count by ∼72%. The qPCR analysis of 16S rRNA, Rhizobium specific rirA and rhtA genes, performed to understand the effect of green algae on growth of Rhizobium sp., showed a significant increase in copy numbers indicating sustained growth of Rhizobium upon co-culture with green algae. Likewise, growth rates of algae and Rhizobium increased by an average of ∼11% and ∼110%, respectively, confirming mutualistic interaction. Considering the presence of Rhizobium sp. in a variety of green algae, this must be a major mutualistic relationship among green algae and this ubiquitous association might serve as a model for elucidating the mutualistic mechanism between green algae and rhizobacter. This interaction could be also utilized in enhancing microalgal biomass, especially slow growing organisms like B. braunii, to augment their bioenergy productivity.
•Rhizobium is the most dominant phycosphere bacterium in all tested green algae.•Rhizobium sp., isolated from Chlorella vulgaris, enhances green algal growth.•All studied green algae enhance growth of Rhizobium sp.•Growth enhancement of slow growing algae offers promise for algal biotechnology.•This mutualism has both evolutionary importance and practical implications.
Various methods, including autoclaving, bead-beating, microwaves, sonication, and a 10% NaCl solution, were tested to identify the most effective cell disruption method. The total lipids from
...Botryococcus sp.,
Chlorella vulgaris, and
Scenedesmus sp. were extracted using a mixture of chloroform and methanol (1:1). The lipid contents from the three species were 5.4–11.9, 7.9–8.1, 10.0–28.6, 6.1–8.8, and 6.8–10.9
g
L
−1 when using autoclaving, bead-beating, microwaves, sonication, and a 10% NaCl solution, respectively.
Botryococcus sp. showed the highest oleic acid productivity at 5.7
mg
L
−1
d
−1 when the cells were disrupted using the microwave oven method. Thus, among the tested methods, the microwave oven method was identified as the most simple, easy, and effective for lipid extraction from microalgae.
Effects of photoperiod were investigated in lab-scale photobioreactors containing algal-bacterial consortia to reduce organic nutrients from municipal wastewater. Under three photoperiod conditions ...(12 h:12 h, 36 h:12 h, and 60 h:12 h dark–light cycles), nutrient removals and biomass productions were measured along with monitoring microbial population dynamics. After a batch operation for 12 days, 59–80% carbon, 35–88% nitrogen, and 43–89% phosphorus were removed from influents, respectively. In this study, carbon removal was related positively to the length of dark cycles, while nitrogen and phosphorus removals inversely. On the contrast, the highest microbial biomass in terms of chlorophyll a, dry cell weight, and algal/bacterial rRNA gene markers was produced under the 12 h:12 h dark–light cycle among the three photoperiods. The results showed 1) simultaneous growths between algae and bacteria in the microbial consortia and 2) efficient nitrogen and phosphorus removals along with high microbial biomass production under prolonged light conditions. Statistical analyses indicated that carbon removal was significantly related to the ratio of bacteria to algae in the microbial consortia along with prolonged dark conditions (p < 0.05). In addition, the ratio of nitrogen removal to phosphorus removal decreased significantly under prolonged dark conditions (p < 0.001). These results indicated that the photoperiod condition has remarkable impacts on adjusting nutrient removal, producing microbial biomass, and altering algal-bacterial population dynamics. Therefore, the control of photoperiod was suggested as an important operating parameter in the algal wastewater treatment.
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•Up to 80–89% of organic nutrients were removed from wastewater in photobioreactor.•Microbial biomass of algal-bacterial consortia ranged up to 0.7 g/L after 6 days.•Bacteria/algae ratio correlated positively with dark/light ratio in photoperiod.•Prolonged dark cycle fosters sCOD removal by increasing bacteria/algae ratio.•Prolonged light cycle facilitates TDN and TDP removals by increasing total biomass.
To select microalgae with a high biomass and lipid productivity,
Botryococcus braunii, Chlorella vulgaris, and
Scenedesmus sp. were cultivated with ambient air containing 10% CO
2 and flue gas. The ...biomass and lipid productivity for
Scenedesmus sp. with 10% CO
2 were 217.50 and 20.65
mg
L
−1
d
−1 (9% of biomass), while those for
B. braunii were 26.55 and 5.51
mg
L
−1
d
−1 (21% of biomass). With flue gas, the lipid productivity for
Scenedesmus sp. and
B. braunii was increased 1.9-fold (39.44
mg
L
−1
d
−1) and 3.7-fold (20.65
mg
L
−1
d
−1), respectively. Oleic acid, a main component of biodiesel, occupied 55% among the fatty acids in
B. braunii. Therefore, the present results suggested that
Scenedesmus sp. is appropriate for mitigating CO
2, due to its high biomass productivity and C-fixation ability, whereas
B. braunii is appropriate for producing biodiesel, due to its high lipid content and oleic acid proportion.
► Flocculation of axenic and xenic cultures of Chlorella vulgaris implicates bacteria. ► DGGE analysis indicates presence of five species of microalgae-associated bacteria. ► FACS treatment of xenic ...culture implicates three bacterial species in flocculation. ► Bacteria and its extracellular substances increase floc size. ► This study proves that bacteria play a major role in flocculation of microalgae.
Flocculation is most preferred method for harvesting microalgae, however, the role of bacteria in microalgal flocculation process is still unknown. This study proves that bacteria play a profound role in flocculating by increasing the floc size resulting in sedimentation of microalgae. A flocculating activity of 94% was achieved with xenic Chlorella vulgaris culture as compared to 2% achieved with axenic culture. Denaturing gradient gel electrophoresis (DGGE) analysis of 16S rRNA gene of xenic C. vulgaris culture revealed the presence of Flavobacterium sp., Terrimonas sp., Sphingobacterium sp., Rhizobium sp. and Hyphomonas sp. as microalgae-associated bacteria. However when Flavobacterium, Terrimonas, Sphingobacterium were eliminated by fluorescence activated cell sorter (FACS), flocculating activity reduced to 3%. Further studies with cell free extracts also suggest that bacterial extracellular substances might also have a role in enhancing flocculation. We conclude that the collective presence of certain bacteria is the determining factor in flocculation of C. vulgaris.
It is established that biodiversity determines productivity of natural ecosystems globally. We have proved that abiotic factors influenced biomass productivity in engineered ecosystems i.e. high rate ...algal ponds (HRAPs), previously. This study demonstrates that biotic factors, particularly microalgal diversity, play an essential role in maintaining stable biomass productivity in HRAP treating municipal wastewater by mutualistic adaptation to environmental factors. The current study examined data from the second year of a two-year study on HRAP treating municipal wastewater. Microalgal diversity, wastewater characteristics, treatment efficiency and several environmental and meteorological factors were documented. Multivariate statistical analyses reveal that microalgae in uncontrolled HRAPs adapt to adverse environmental conditions by fostering diversity. Subsequently, five dominant microalgal strains by biovolume were isolated, enriched, and optimum conditions for high biomass productivity were ascertained. These laboratory experiments revealed that different microalgal strains dominate in different conditions and a consortium of these diverse taxa help in sustaining the algae community from environmental and predatory pressures. Diversity, niche or seasonal partitioning and mutualistic growth are pertinent in microalgal cultivation or wastewater treatment. Therefore, enrichment of selective species would deprive the collective adaptive ability of the consortium and encourage system vulnerability especially in wastewater treatment.
Summary
Nannochloropsis species, unicellular industrial oleaginous microalgae, are model organisms for microalgal systems and synthetic biology. To facilitate community‐based annotation and mining of ...the rapidly accumulating functional genomics resources, we have initiated an international consortium and present a comprehensive multi‐omics resource database named Nannochloropsis Design and Synthesis (NanDeSyn; http://nandesyn.single‐cell.cn). Via the Tripal toolkit, it features user‐friendly interfaces hosting genomic resources with gene annotations and transcriptomic and proteomic data for six Nannochloropsis species, including two updated genomes of Nannochloropsis oceanica IMET1 and Nannochloropsis salina CCMP1776. Toolboxes for search, Blast, synteny view, enrichment analysis, metabolic pathway analysis, a genome browser, etc. are also included. In addition, functional validation of genes is indicated based on phenotypes of mutants and relevant bibliography. Furthermore, epigenomic resources are also incorporated, especially for sequencing of small RNAs including microRNAs and circular RNAs. Such comprehensive and integrated landscapes of Nannochloropsis genomics and epigenomics will promote and accelerate community efforts in systems and synthetic biology of these industrially important microalgae.
Significance Statement
Nannochloropsis species have emerged as model organisms for microalgal systems and synthetic biology, but a centralized portal to store, mine and disseminate the rapidly expanding multi‐omics datasets is lacking. Here, we initiate an international consortium and present a comprehensive resource database named Nannochloropsis Design and Synthesis (NanDeSyn; http://nandesyn.single‐cell.cn). NanDeSyn hosts genomic and epigenomic resources such as gene annotation, transcriptome, proteome, small RNA and mutant information, and provides tools for search, Blast, synteny view, enrichment analysis, metabolic pathway analysis and a genome browser.
This study demonstrates that ecologically engineered bacterial consortium could enhance microalgal biomass and lipid productivities through carbon exchange. Phycosphere bacterial diversity analysis ...in xenic Chlorella vulgaris (XCV) confirmed the presence of growth enhancing and inhibiting microorganisms. Co-cultivation of axenic C. vulgaris (ACV) with four different growth enhancing bacteria revealed a symbiotic relationship with each bacterium. An artificial microalgal-bacterial consortium (AMBC) constituting these four bacteria and ACV showed that the bacterial consortium exerted a statistically significant (P<0.05) growth enhancement on ACV. Moreover, AMBC had superior flocculation efficiency, lipid content and quality. Studies on carbon exchange revealed that bacteria in AMBC might utilize fixed organic carbon released by microalgae, and in return, supply inorganic and low molecular weight (LMW) organic carbon influencing algal growth and metabolism. Such exchanges, although species specific, have enormous significance in carbon cycle and can be exploitated by microalgal biotechnology industry.
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