Halophilic archaea are unique microorganisms adapted to survive under high salt conditions and biomolecules produced by them may possess unusual properties. Haloarchaeal metabolites are stable at high salt and temperature conditions that are useful for industrial applications. Proteins and enzymes of this group of archaea are functional under salt concentrations at which bacterial counterparts fail to be active. Such properties makes haloarchaeal enzymes suitable for salt-based applications and their use under dehydrating conditions. For example, bacteriorhodopsin or the purple membrane protein present in halophilic archaea has the most recognizable applications in photoelectric devices, artificial retinas, holograms etc. Haloarchaea are also useful for bioremediation of polluted hypersaline areas. Polyhydroxyalkanoates and exopolysccharides produced by these microorganisms are biodegradable and have the potential to replace commercial non-degradable plastics and polymers. Moreover, halophilic archaea have excellent potential to be used as drug delivery systems and for nanobiotechnology by virtue of their gas vesicles and S-layer glycoproteins. Despite of possible applications of halophilic archaea, laboratory-to-industrial transition of these potential candidates is yet to be established.

Thirteen halophilic archaea were isolated from Kandla and Bhayander salt pans. These isolates were grouped into three different genera based on morphological and biochemical characterization, polar lipid analysis, Amplified 16S rDNA restriction analysis (ARDRA) and 16S rDNA sequence analysis. Biochemical characterization suggested the ability of isolates to produce protease, amylase and poly-hydroxybutyrate (PHB) indicating their biotechnological potential. The isolates were further screened for the amount of extracellular protease produced. sp. SP1(1) showed significant protease production compared to other isolates. Protease producing ability of the isolate was influenced by several factors such as NaCl concentration, type of protein source, metal ions and surfactants, and presence of amino acid supplements in the production medium. Soybean flour, FeCl and dicotylsulfosuccinate were found to increase protease production by 2.36, 1.54 and 1.26 folds, respectively compared to production in basal medium. Effect of organic solvents used in paints (n-decane, n-undecane and n-dodecane) was also investigated on protease production by the isolate. Protease production by sp. SP1(1) was enhanced by 1.2 folds in presence of n-decane compared to control. Furthermore, the ability of isolate to hydrolyse fish protein was investigated using three different edible fishes (Pomfret, Flat fish and Seer fish) as sole protein source. Pomfret was found to be a good protein source for protease production by the isolate. These results revealed that sp. SP1(1) may have potential for paint-based antifouling coating preparations and fish sauce preparation by virtue of its extracellular protease.

Samples were collected from different undisturbed areas along the coast of Gujarat like Okha, Diu, Veraval, and Somnath. A total of 68 marine isolates were obtained out of which 53 were associated with various marine macroorganisms like sponges, gastropods, and algae, whereas 15 were free living. Quorum‐quenching ability of all the isolates was tested against Chromobacterium violaceum MK by co‐culture technique as a way to simultaneously detect signal‐degrading as well as nondegrading quorum‐sensing inhibitors. Nineteen macroorganism‐associated bacteria and eight free‐living bacteria were found to possess quorum‐sensing inhibitory activity against C. violaceum MK without affecting its growth. Isolate OA22 from grape alga and OA10 from purple sponge (Haliclona sp.) were found to possess the highest C6‐HSL degradation activity and extracellular non‐N‐acyl‐homoserine lactone degrading QSI activity, respectively. OA22 was also found to degrade 3‐oxo‐C12 homoserine lactone. Acid recovery of both the C6‐ and C12‐HSL after degradation by OA22 indicated the presence of lactonase enzyme in the isolate. Cell‐free supernatant of OA10 was extracted with ethyl acetate to obtain the quorum‐quenching compound. Pigment inhibition in C. violaceum MK treated with OA10 extract was demonstrated in various ways and was indicative of QSI activity of the extract without degradation of the quorum‐sensing signaling molecule. The isolates OA22 and OA10 were identified as Desemzia incerta and Bacillus sp., respectively, by 16S ribosomal DNA sequence analysis.

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