Abstract

Spirulina platensis is a filamentous, alkaliphilic cyanobacterium of considerable nutritional, pharmaceutical, and industrial value, and biotechnological interest in its cultivation has intensified in response to growing demand for natural, sustainably produced antimicrobial and functional ingredients. Optimizing the cultivation of S. platensis, enhancing its antibacterial activity, and realizing its commercial potential. The physicochemical determinants of growth, principally initial medium pH, light intensity, incubation temperature, and nutrient composition, are examined, together with the use of alternative substrates such as wastewater for cost-effective, sustainable biomass production. The extraction and characterization of antibacterial bioactive constituents, including phycocyanin, phenolic compounds, flavonoids, and antimicrobial peptides, are reviewed in relation to solvent polarity and the differential susceptibility of Gram-positive and Gram-negative bacteria. The commercial applications of optimized S. platensis biomass across the pharmaceutical, nutraceutical, cosmetic, food-preservation, and animal-feed sectors are also considered. The review methodology, comprising a structured search of major scientific databases, is described, and the synthesized findings are consolidated into five comparative tables. The review concludes that the rational manipulation of readily controllable cultivation parameters constitutes a scalable, evidence-based strategy for enhancing both the yield and the functional bioactivity of S. platensis biomass, and it identifies priority directions for future research, including factorial optimization designs, strain improvement, and pilot-scale validation.

Introduction

1.1 Taxonomy, Morphology, and Natural Habitat of Spirulina platensis

Spirulina platensis, taxonomically situated within the genus Arthrospira and more recently reclassified under Limnospira, is a multicellular, filamentous cyanobacterium characterized by a helically coiled trichome morphology and a distinctive blue-green pigmentation (Sinetova et al., 2024). The organism occurs naturally in alkaline, saline lakes across tropical and subtropical regions, where it has adapted physiologically to high pH, high irradiance, and elevated temperature, a set of environmental adaptations that has direct bearing on the cultivation conditions required for its efficient large-scale production (Spínola et al., 2024). Its long history of natural occurrence in such extreme alkaline environments, together with an equally long history of traditional human consumption, underlies its present-day recognition as a safe and well-characterized biotechnological organism.

The taxonomic revisions affecting the organism, whereby the names Spirulina, Arthrospira, and Limnospira have variously been applied to what is now recognized as a single biological entity, reflect an evolving understanding of cyanobacterial systematics rather than any change in the organism's underlying biology or industrial relevance (Sinetova et al., 2024). For consistency with the majority of the applied biotechnological literature reviewed here, and in keeping with the terminology most widely used in the antibacterial and cultivation-optimization studies discussed in subsequent sections, the name Spirulina platensis is retained throughout this review.

1.2 Nutritional and Industrial Importance of Spirulina platensis

S. platensis biomass is distinguished by an exceptionally high protein content, frequently exceeding sixty percent of dry weight, together with a rich complement of vitamins, essential fatty acids, and pigments, including the phycobiliprotein phycocyanin, chlorophyll a, and carotenoids (Grosshagauer et al., 2020). These attributes have established Spirulina as one of the most commercially significant microalgae worldwide, marketed extensively as a dietary supplement and functional food ingredient (Lafarga et al., 2020). The expanding global market for natural, minimally processed nutritional and functional ingredients has, in turn, created strong commercial incentives for research directed at improving both the yield and the bioactive quality of cultivated biomass.

The scalability of Spirulina cultivation, achievable in open raceway ponds as well as in closed photobioreactor systems, further distinguishes the organism from many other microalgae of comparable nutritional interest, since it permits production to be matched to a wide range of climatic and economic contexts (Soni et al., 2017). This operational flexibility, combined with a comparatively short doubling time under favourable conditions, has supported the establishment of commercial Spirulina production facilities across multiple continents, providing the industrial foundation upon which the biotechnological optimization strategies reviewed in this article are ultimately intended to be applied.

1.3 Cyanobacterial Secondary Metabolites and Antibacterial Potential

Beyond its established nutritional value, S. platensis synthesizes a diverse array of secondary metabolites with demonstrated antibacterial activity, including phenolic acids, flavonoids, polysaccharides, and bioactive peptides (Ilieva et al., 2024). The mounting global concern surrounding antibiotic resistance has intensified scientific and commercial interest in natural, multi-target antimicrobial agents of this kind, since their combined mode of action across several molecular targets is considered less liable to elicit the emergence of resistant bacterial strains than single-target synthetic antibiotics (Gheda & Ismail, 2020). This has positioned Spirulina-derived extracts as promising candidates for pharmaceutical, food-preservation, and cosmetic antimicrobial applications.

The antibacterial potential of cyanobacterial secondary metabolites is further reinforced by the ecological role that many of these compounds are believed to play in the natural environment, where they may confer a competitive advantage against co-occurring bacterial populations.

1.4 Biotechnological Strategies for Cultivation Enhancement

A substantial body of biotechnological research has sought to enhance the productivity and functional quality of S. platensis biomass through the systematic manipulation of cultivation conditions, including medium composition, pH, light regime, and temperature, as well as through the use of alternative, cost-effective substrates such as agro-industrial or municipal wastewater (Zhai et al., 2017). These strategies exploit the organism's well-defined physiological optima to achieve simultaneous improvements in biomass yield and bioactive constituent content, offering a practical alternative to genetic modification or costly synthetic medium supplementation (Molazadeh et al., 2019).

Complementary strategies reviewed in this article include the selection and screening of robust production strains, the optimization of downstream extraction procedures to maximize the recovery of antibacterial constituents, and the coupling of cultivation with wastewater bioremediation or carbon dioxide biofixation to improve overall process sustainability. Considered together, these approaches illustrate the breadth of the biotechnological toolkit currently available for enhancing the commercial value of S. platensis biomass, extending well beyond the manipulation of cultivation parameters alone.

1.5 Scope and Structure of the Review

The biotechnological optimization of S. platensis cultivation, the mechanisms and characterization of its antibacterial activity, and the commercial applications of the resulting biomass. The review is organized into four thematic sections addressing, respectively, the optimization of physicochemical cultivation parameters, the use of alternative nutrient media and substrates, the extraction and characterization of antibacterial bioactive compounds, and the commercial and industrial applications of Spirulina biomass. A structured review methodology is subsequently described, followed by a synthesis of conclusions and a discussion of priority directions for future research.

In adopting this four-part thematic structure, the review is intended to trace a coherent narrative arc from the fundamental biology and cultivation requirements of S. platensis, through the mechanistic basis of its antibacterial activity, to the applied commercial contexts in which that activity, together with the organism's broader nutritional profile, may ultimately be exploited. This structure is designed to be of practical value both to researchers seeking to identify gaps in the existing cultivation-optimization literature and to industry stakeholders evaluating the commercial feasibility of Spirulina-based antimicrobial products.

Conclusion

This review has synthesized the peer-reviewed literature published between 2015 and 2024 concerning the biotechnological optimization of Spirulina platensis cultivation and the enhancement of its antibacterial activity and commercial potential. The evidence reviewed consistently indicates that the systematic manipulation of readily controllable physicochemical parameters, principally initial medium pH, light intensity, and incubation temperature, produces substantial and reproducible enhancements in biomass yield, with reported optimum values converging within relatively narrow ranges across independent studies. Alternative, low-cost cultivation substrates, particularly wastewater streams, have been shown to support comparable or enhanced biomass productivity while simultaneously achieving nutrient bioremediation, offering a commercially and environmentally attractive complement to conventional synthetic media. The antibacterial activity of S. platensis extracts, most consistently and potently expressed in methanolic extracts, has been attributed to a range of bioactive constituents including phycocyanin, phenolic compounds, flavonoids, and antibacterial peptides, which appear to act synergistically to produce broad-spectrum, predominantly bactericidal activity against both Gram-positive and Gram-negative bacteria. This bioactivity, together with the organism's established nutritional value and favourable safety profile, underpins a diverse and expanding range of commercial applications across the pharmaceutical, nutraceutical, cosmetic, food-preservation, and animal-feed sectors. Taken together, the reviewed literature supports the conclusion that biotechnological cultivation optimization represents a scientifically well-substantiated and commercially viable strategy for enhancing the value of S. platensis biomass, warranting continued investment in both fundamental and applied research.

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2025