Abstract

         Cyanobacteria reveal vast potential in varied industries for food, feed, fuel, fertilizer, medicine and combating pollution. In this mini-review, culturing and biotechnological applications of marine cyanobacteria such as biomass, pigments, nanoparticles, bioremediation, ESBL producers, antioxidants etc are assessed. Cyanobacteria are expected to be used in vegetating as well as oxygenating future newer habitations outside earth. Further, there are many potential applications of cyanobacteria yet to be discovered and requires more detailed studies to explore the versatility of cyanobacteria in eco-friendly way.

Introduction

         Marine cyanobacteria are one of the largest sub-groups of Gram-negative oxygenic photosynthetic prokaryotes, possessing chlorophyll a and phycopobiliproteins such as phycocyanin and phycoerythrin, which are responsible for the blue-green pigmentation predominant in this group. In general, cyanobacteria are morphologically diverse forms that exhibit different pigmentation (Fig.1). They reveal vast potential in varied industries for food, feed, fuel, fertilizer, medicine and combating pollution (Thajuddin and Subramanian, 2005). In this mini-review, culture and biotechnological applications of marine cyanobacteria are assessed. Cyanobacteria in general, can grow in all aquatic habitats such as freshwater; all types of marine environments including hypersaline salt pans; all types of soils; deserts; cave walls; hot springs; polar regions; on tree barks; on leaf surfaces; rocks; sewage; industrial effluents and other extreme environments (Singh et al., 2008; Thajuddin et al., 2014; Muthukumar et al., 2007; Vijayakumar et al., 2007). There are several reports on the diversity and distribution of cyanobacteria from marine habitats including brines in different parts of the world. Thajuddin and Subramanian (1992 and 1994) carried out a detailed survey of the marine cyanobacterial biodiversity on a continuous stretch of the eastern coasts of south India and adjoining islands.

         Cyanobacteria play vital roles in many environmental processes such as bioremediation, biodegradation, nutrient cycling, climate change etc. They can degrade toxic chemicals into environmentally safer compounds and remove heavy metals like Lead (Pb), Chromium (Cr) and Mercury (Hg) from waterbodies through bioaccumulation, which can be recovered later from their biomass (Uma and Subramanian, 1990). The bio-pigments produced by Cyanobacteria are used for food colouring and bio-labelling. It also offers many genetic and biotechnological applicastions such as primary and secondary metabolites, restriction enzymes, plant growth hormones and various other products (Thajuddin and Subramanian, 2005) (Fig.2).

         Marine cyanobacteria are known for their potential applications in the treatment of hazardous wastes. Some cyanobacteria have the capacity to change or tune up the extreme environmental conditions into lively dynamic ones. In a bioremediation study, Uma and Subramanian (1990) treated Ossein factory effluent with highly elevated calcium and chloride levels using the marine cyanobacteria Oscillatoria sp. BDU 10742, Aphanocapsa sp. BDU 16 along with a halophilic bacterium Halobacterium US 101. The treatment enabled the effluent to be used for the cultivation of Tilapia fishes with 100% survival and the fishes had reproduced with cyanobacteria as the only feed source. Effective degradation and metabolization of the recalcitrant melanoidin pigment (responsible for the dark brown colour) in distillery effluent was achieved using the marine cyanobacterium, Oscillatoria boryana BDU 92181 (Kalavati et al., 2001). The marine cyanobacterium Oscillatoria formosa NTDM02 was identified as a potential bioremediator for the decolourization of a textile dye Amido Black G200 and also for the treatment of raw textile dye effluent (Mubarakali et al., 2011). Oscillatoria brevis was reported to remove the organic and inorganic chemicals from the dye industry effluent along with the removal of its colour (Vijayakumar et al., 2005). Marine cyanobacteria Oscillatoria sp. NTMS01 and Phormidium sp. NTMS02 were reported to have the ability to remove harmful metals such as Lead and Chromium, making it a highly efficient bioremediator (Satheeshkumar et al., 2011; Rajeswari et al., 2012). Hypersaline cyanobacterium Phormidium tenue KMD33 was reported to remediate the paper mill effluent by significant reduction of colour, BOD and COD (Nagasathya and Thajuddin, 2008).

         The role of enzymes such as dioxygenase and peroxidases have been discussed and found to play an important role in cyanobacteria mediated degradation (Baldev et al., 2013). The dioxygenase enzyme system in Phormidium tenue was reported to degrade the harmful naphthalene to naphthoquinone and naphthalene-1,2-diol (Thajuddin and Subramanian, 2005; Singh et al., 2008). Further it also degraded anthracene into environment friendly products anthracene-1,2-dione, 8-hydroxy-anthracene-1,2-dione and 10-hydroxy-anthracene-1,2-dione (Satheeshkumar et al., 2009).

Fig.1: Morphologically diverse forms of cyanobacteria isolated from various ecosystem.

Fig. 2: Potential applications of marine cyanobacteria.

         The fact that cyanobacterial protein could well be utilized as a supplement or an alternative source of single cell protein has received worldwide attention. In particular, Anabaena and Nostoc are being consumed as food in Chile, Mexico, Peru and Philippines, while N. commune with high amount of fibre and moderate protein is a new dietary fibre source and can play an important physiological and nutritional role in human diet (Jeraci and Vansoest, 1986). A large number of marine nitrogen-fixing cyanobacteria have been tested for their nutritional value with the hybrid Tilapia fish fry; a majority were acceptable as single ingredient feeds. Very high growth rates of Tilapia fish using marine cyanobacteria with in-door and out-door cultures have been reported (Mitsui et al., 1983). In our earlier study, the marine cyanobacterium Phormidium valderianum BDU 30501 was shown to serve as a complete aquaculture feed source, based on the nutritional qualities and non-toxic nature with animal model experiments. A mass cultivation technology of this strain as pellet feed was developed and transferred to an industry for the commercial production (Thajuddin and Subramanian, 2005).

          Extended-spectrum β-lactamase (ESBL) producing bacteria pose a big challenge in clinical practices, warranting a new therapeutic strategy. In one of our study, methanolic extract of the marine cyanobacterium, Oscillatoria acuminata NTAPC05 was fractionated and the fractions were tested against ESBL producing bacteria Escherichia coli U655, Stenotrophomonas maltophilia B929 and Enterobacter asburiae B938. They were more efficient against these bacteria at a minimal concentration of 100 μg ml⁻¹ while Cephalosporin was needed at a minimal concentration of >125 μg ml⁻¹ to be effective (Parveez Ahamed et al., 2017). In addition, monogalactosyl-diacylglycerol containing a palmitoyl was reported for the first time as the active fraction and its bactericidal property against ESBL producers was determined. There is scope to develop analogues of this for therapeutic use against bacteremia caused by ESBL producers especially after surgery. Some of the marine microalgae were investigated for antibacterial activity against human pathogens. In general, microalgae having high growth, pH, CO₂ fixation, carbon content and biochemical diversity that pave the way for the pharmaceutical activity of these organisms and their potential health benefits (Dineshkumar et al., 2017).

          Emergence of extended antibiotic resistance among bacterial pathogens especially in aquaculture, leads to the failure of existing antibiotics to treat bacterial infections, causing extensive financial losses. Therefore, there is an urgent need to look for novel alternative treatment measures. Such an attempt has led to a growing interest in the discovery of novel anti-quorum sensing (anti-QS) compounds from natural sources to interrupt or hinder the Quorum Sensing signalling pathway in pathogenic bacteria. These anti-QS compounds are believed to provide complementary medicine for emerging bacterial infections by inhibiting the QS system. Santhakumari et al. (2016) reported the anti-Quorum sensing potential of the marine cyanobacterium Synechococcus sp. against emerging aquatic bacterial pathogens such as V. harveyi and V. vulnificus.

         Marine cyanobacteria play a versatile role in top-down as well as bottom up approaches in the field of nanobiotechnology, which includes synthesis and stabilization of nanoparticles (MubarakAli et al., 2011). Biomolecules in general and specially proteins are extracted from cyanobacteria play a key role in nanoparticle synthesis. C-phycoerythrin extracted from mairne cyanobacterium, Phormidium tenue NTDM05 was used in the synthesis and stabilization of CdS nanoparticles (MubarakAli et al., 2012). It has also been reported that Oscillatoria willei NTDM01 could play a significant role in the synthesis of silver nanoparticles (MubarakAli et al., 2011). A marine cyanobacterium, Phormidium sp. was used for the synthesis of triangular gold nanoparticles, in which nanoparticles synthesized intracellularly were less than 20 nm while extracellular production resulted in particles >100 nm in size (MubarakAli et al., 2013). Eventually, poly dispersed gold nanoparticles could be used for the biolabelling study.

Conclusion

         Cyanobacteria are not only value able for the industrial production of useful substances; treatment and recycling of several industrial effluents; CO₂ sequestration and pollution abatement but also play unique roles in element recycling; solar energy harnessing& fixation of atmospheric nitrogen. They can replace land intensive crop plants for animal and human nutrition for the ever-increasing population in the limited cultivable land area. They are expected to be used in vegetating as well as oxygenating future newer habitations outside earth. These significant gene pools must not be lost and culture collections in different climatic and geographic locations for ex-situ conservation should be established.

Acknowledgement

         Authors are thankful to Department of Biotechnology (DBT, Govt. of India) for sanctioning NRMC-F (BT/PR7005/PBD/26/357/26.03.15).

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