Bioremediasi Aluminium Oleh Bacillus subtilis ATCC 6633 dan Dampaknya Terhadap Respons Fisiologis Oreochromis niloticus

Abstract

Pencemaran aluminium di perairan berpotensi menurunkan kualitas lingkungan budidaya dan mengganggu kondisi fisiologis organisme akuatik. Aluminium terlarut dapat menyebabkan gangguan respirasi, osmoregulasi, perubahan hematologi, kerusakan jaringan, dan peningkatan mortalitas ikan. Salah satu pendekatan yang dapat digunakan untuk mengurangi toksisitas aluminium adalah bioremediasi menggunakan bakteri. Bacillus subtilis ATCC 6633 diketahui memiliki kemampuan adaptasi terhadap lingkungan tercemar dan berpotensi digunakan dalam proses biosorpsi logam. Namun, informasi mengenai efektivitas B. subtilis ATCC 6633 dalam menurunkan aluminium terlarut serta kaitannya dengan kondisi fisiologis ikan budidaya masih terbatas. Penelitian ini bertujuan mengevaluasi kemampuan B. subtilis ATCC 6633 dalam menurunkan konsentrasi aluminium terlarut serta dampaknya terhadap kualitas air, tingkat kelangsungan hidup, dan respons fisiologis ikan nila (Oreochromis niloticus). Penelitian terdiri atas uji toksisitas akut aluminium, uji resistensi dan bioremediasi bakteri, serta uji pemeliharaan ikan menggunakan kombinasi perlakuan aluminium dan bakteri. Penelitian utama menggunakan rancangan acak lengkap dengan empat perlakuan, yaitu kontrol (K), B. subtilis ATCC 6633 106 CFU/mL (B), aluminium 7,85 mg/L (Al), dan kombinasi aluminium 7,85 mg/L dengan B. subtilis ATCC 6633 106 CFU/mL (AB), masing-masing dengan tiga ulangan. Parameter yang diamati meliputi tingkat kelangsungan hidup ikan, kualitas air, kepadatan bakteri, konsentrasi aluminium terlarut, hematologi, dan histologi insang. Hasil penelitian menunjukkan bahwa nilai LC50-96 jam aluminium terhadap O. niloticus sebesar 7,847 mg/L dengan selang kepercayaan 95% sebesar 7,585–8,124 mg/L. B. subtilis ATCC 6633 mampu tumbuh pada media yang mengandung aluminium hingga konsentrasi 100 mg/L. Pada uji bioremediasi, perlakuan kombinasi aluminium dan B. subtilis menunjukkan penurunan konsentrasi aluminium terlarut hingga 70,32% selama 96 jam pengamatan. Keberadaan aluminium pada fraksi pelet setelah sentrifugasi menunjukkan adanya perpindahan aluminium dari fase terlarut ke biomassa bakteri yang mengarah pada mekanisme biosorpsi. Paparan aluminium menurunkan tingkat kelangsungan hidup ikan nila dibandingkan kontrol, sedangkan perlakuan kombinasi aluminium dan B. subtilis menunjukkan tingkat kelangsungan hidup yang lebih tinggi dibandingkan perlakuan aluminium tanpa bakteri. Parameter kualitas air selama penelitian masih berada pada kisaran toleransi O. niloticus, meskipun perlakuan aluminium menunjukkan nilai alkalinitas yang lebih rendah dibandingkan perlakuan lainnya. Paparan aluminium juga menyebabkan perubahan parameter hematologi berupa penurunan eritrosit dan perubahan leukosit dibandingkan kontrol. Pada akhir pengamatan, perlakuan kombinasi aluminium dan B. subtilis menunjukkan respons hematologi yang lebih baik dibandingkan perlakuan aluminium tanpa bakteri, meskipun pemulihan fisiologis belum sepenuhnya terjadi selama periode pengamatan. Penurunan konsentrasi aluminium terlarut pada perlakuan kombinasi aluminium dan B. subtilis menunjukkan bahwa keberadaan bakteri tidak hanya berperan dalam memperbaiki kondisi media pemeliharaan, tetapi juga berkontribusi terhadap pengurangan tekanan toksik pada ikan. Meskipun demikian, respons fisiologis ikan belum sepenuhnya kembali mendekati kondisi kontrol selama periode pengamatan 96 jam. Kondisi tersebut mengindikasikan bahwa pemulihan fisiologis ikan berlangsung lebih lambat dibandingkan penurunan konsentrasi aluminium di media. Dengan demikian, efektivitas bioremediasi aluminium tidak hanya ditentukan oleh kemampuan bakteri dalam menurunkan logam terlarut, tetapi juga oleh durasi pemaparan dan kemampuan organisme dalam melakukan pemulihan fisiologis setelah mengalami stres akibat logam. Pengamatan histologi insang menunjukkan bahwa paparan aluminium menyebabkan kerusakan jaringan berupa fusi lamela, pemendekan lamela sekunder, dan infiltrasi sel inflamasi. Tingkat kerusakan jaringan pada perlakuan kombinasi aluminium dan B. subtilis lebih rendah dibandingkan perlakuan aluminium tanpa bakteri. Secara keseluruhan, penelitian ini menunjukkan bahwa B. subtilis ATCC 6633 berpotensi dikembangkan sebagai agen bioremediasi aluminium pada sistem akuakultur terkontrol melalui kemampuannya dalam menurunkan konsentrasi aluminium terlarut dan mengurangi dampak toksik aluminium terhadap ikan nila, meskipun pemulihan fisiologis ikan belum berlangsung sepenuhnya dalam periode pengamatan 96 jam.

Aluminium contamination in aquatic environments may reduce water quality and disrupt the physiological condition of aquatic organisms. Dissolved aluminium can cause respiratory and osmoregulatory disturbances, hematological alterations, tissue damage, and increased fish mortality. One approach that may reduce aluminium toxicity is bacterial bioremediation. Bacillus subtilis ATCC 6633 is known to possess adaptability to contaminated environments and potential application in heavy metal biosorption. However, information regarding the effectiveness of B. subtilis ATCC 6633 in reducing dissolved aluminium and its relationship with fish physiological condition remains limited. Therefore, this study was conducted to evaluate the ability of B. subtilis ATCC 6633 to reduce dissolved aluminium concentration and its effects on water quality, survival rate, and physiological responses of Nile tilapia (Oreochromis niloticus). The study consisted of acute aluminium toxicity testing, bacterial resistance and bioremediation testing, and fish exposure experiments using combinations of aluminium and bacterial treatments. The main experiment employed a completely randomized design with four treatments: control (K), B. subtilis ATCC 6633 at 106 CFU/mL (B), aluminium at 7,85 mg/L (Al), and a combination of aluminium 7,85 mg/L with B. subtilis ATCC 6633 at 106 CFU/mL (AB), each with three replicates. Observed parameters included fish survival rate, water quality, bacterial density, dissolved aluminium concentration, hematology, and gill histology. The results showed that the LC50-96 hours value of aluminium against O. niloticus was 7,847 mg/L with a 95% confidence interval of 7,585–8,124 mg/L. B. subtilis ATCC 6633 was able to grow in media containing aluminium up to 100 mg/L. In the bioremediation test, the combined aluminium and B. subtilis treatment reduced dissolved aluminium concentration by 70,32% during the 96 hours observation period. The presence of aluminium in the pellet fraction after centrifugation indicated the transfer of aluminium from the dissolved phase into bacterial biomass through mechanisms associated with biosorption. Aluminium exposure reduced fish survival rate compared with the control treatment, whereas the combined aluminium and B. subtilis treatment resulted in a higher survival rate than aluminium treatment without bacteria. Water quality parameters remained within the tolerance range for O. niloticus, although aluminium treatment showed lower alkalinity values compared with other treatments. Aluminium exposure also caused hematological alterations, including decreased erythrocyte counts and changes in leukocyte counts compared with the control. At the end of the observation period, the combined aluminium and B. subtilis treatment showed better hematological responses than aluminium treatment without bacteria, although complete physiological recovery had not yet occurred during the observation period. The reduction of dissolved aluminium concentration in the combined aluminium and B. subtilis treatment indicates that the presence of bacteria not only contributed to improving the culture media condition, but also played a role in reducing toxic stress in fish. However, the physiological responses of fish had not fully returned to conditions comparable with the control treatment during the 96 hours observation period. This condition suggests that physiological recovery in fish occurred more slowly than the reduction of dissolved aluminium concentration in the media. Therefore, the effectiveness of aluminium bioremediation was not only determined by the bacterial ability to reduce dissolved metal concentration, but also by the duration of exposure and the ability of organisms to recover physiologically after experiencing heavy metal-induced stress. Histological observations showed that aluminium exposure caused tissue damage, including lamellar fusion, shortening of secondary lamellae, and inflammatory cell infiltration. The degree of tissue damage in the combined aluminium and B. subtilis treatment was lower than that in aluminium-only treatment. Overall, this study demonstrated that B. subtilis ATCC 6633 has potential to be developed as an aluminium bioremediation agent in controlled aquaculture systems through its ability to reduce dissolved aluminium concentration and alleviate aluminium toxic effects on Nile tilapia, although physiological recovery had not fully occurred during the 96 hours observation period.