Karakterisasi Isolat Bakteri Berpigmen Merah Menggunakan Spektrofotometer UV-Vis dan Potensi Aktivitas Antioksidannya

Abstract

Pigmen merah bakteri dihasilkan oleh prodigiosin maupun karotenoid pada bakteri fotosintetik dan non-fotosintetik sehingga tidak dapat dibedakan berdasarkan warna saja. Pigmen alami memiliki aktivitas antioksidan yang berperan menangkal radikal bebas penyebab penyakit degeneratif. Penelitian ini bertujuan membandingkan spektrum panjang gelombang serapan pigmen merah bakteri fotosintetik dan non-fotosintetik serta mengukur aktivitas antioksidannya. Tiga isolat (IRA5, IRA9 dari perairan laut; SR3 dari perairan danau) dikarakterisasi morfologi koloni secara makroskopik dan sel melalui pewarnaan Gram. Pigmen diekstraksi menggunakan aseton dengan lisis mekanik dan sentrifugasi 10.000xg, lalu dianalisis dengan spektrofotometer UV-Vis pada rentang 300–1000 nm terhadap ekstrak kasar pigmen, supernatan, dan kultur bakteri. Aktivitas antioksidan diuji dengan metode DPPH pada enam variasi konsentrasi (5–300 µg/mL) dan dianalisis menggunakan regresi linear ln konsentrasi terhadap persen inhibisi untuk memperoleh IC50. Ketiga isolat memiliki koloni berwarna merah, circular, tepian rata, elevasi convex, permukaan halus berlendir, dan sel batang pendek Gram negatif. Isolat IRA5 dan IRA9 menunjukkan puncak serapan 468– 532 nm mengindikasikan prodigiosin, sedangkan SR3 menunjukkan puncak serapan 463–531 nm (karotenoid) dan 800–870 nm (bakterioklorofil) khas bakteri fotosintetik anoksigenik. Nilai IC50 IRA5, IRA9, dan SR3 berturut-turut 196,60; 223,71; dan 196,04 µg/mL, dikategorikan lemah hingga sangat lemah dibandingkan asam askorbat (7,86 µg/mL).

Bacterial red pigments are produced by prodigiosin and carotenoids in photosynthetic and non-photosynthetic bacteria, so they cannot be distinguished based on color alone. Natural pigments have antioxidant activity that plays a role in warding off free radicals that cause degenerative diseases. This study aims to compare the absorption wavelength spectrum of red pigments of photosynthetic and non-photosynthetic bacteria and measure their antioxidant activity. Three isolates (IRA5, IRA9 from marine waters; SR3 from lake waters) were characterized by macroscopic colony morphology and cells through Gram staining. Pigments were extracted using acetone with mechanical lysis and centrifugation at 10,000×g, then analyzed with a UV-Vis spectrophotometer at a range of 300–1000 nm against crude pigment extracts, supernatants, and bacterial cultures. Antioxidant activity was tested by the DPPH method at six concentration variations (5–300 µg/mL) and analyzed using linear regression of ln concentration against the percentage of inhibition to obtain IC50. All three isolates had red, circular colonies with flat edges, convex elevations, smooth, slimy surfaces, and short, Gram-negative rods. Isolates IRA5 and IRA9 showed absorption peaks at 468–532 nm, indicating prodigiosin, while SR3 showed absorption peaks at 463–531 nm (carotenoids) and 800–870 nm (bacteriochlorophyll), typical of anoxygenic photosynthetic bacteria. The IC50 values of IRA5, IRA9, and SR3 were 196.60; 223.71; and 196.04 µg/mL, respectively, categorized as weak to very weak compared to ascorbic acid (7.86 µg/mL).