Saccharification of macroalgal polysaccharides through prioritized cellulase producing bacteria

Abstract

Marine macroalgal cell wall is predominantly comprised of cellulose (polysaccharide) with the complex chain of glycosidic linkages. Bioethanol production from macroalgae entails breaking this complex chain into simple glucose molecule, which has been the major challenge faced by the industries. Cellulases have been preferred for hydrolysis of cellulose due to the absence of inhibitors affecting the subsequent fermentation process. Cellulose degrading bacteria were isolated from wide-ranging sources from marine habitats to herbivore residues and gastrointestinal region. The investigation reveals that Vibrio parahaemolyticus bacteria has higher hydrolytic capacity with salt tolerance up to 14% and 3.5% salinity is optimum for growth. Higher hydrolytic activity of 2.45 was recorded on carboxymethyl cellulose medium at 48 h and hydrolytic activity of 2.46 on Ulva intestinalis hydrolysate, 3.06 on Ulva lactuca hydrolysate at 72 h of incubation. Total activity of enzyme of 2.11 U/ml and specific activity of 6.05 U/mg were recorded at 24 h. Enzyme hydrolysis of macroalgal biomass; U. intestinalis and U. lactuca produced 135.9 mg/g and 107.6 mg/g of reducing sugar respectively. The study reveals that the enzyme extracted from salt tolerant Vibrio parahaemolyticus bacteria is suitable for optimal saccharification of seaweed polysaccharides towards biofuel production.

Bioethanol from macroalgae: Prospects and challenges

“…Utilization of red and brown seaweeds biomass for bioethanol production can lead to debate on hydrocolloid versus fuel affecting the existing multibillion hydrocolloid industry [89]. Therefore, for further processes of detoxification, enzyme hydrolysis and fermentation, two seaweeds Ulva lactuca and Enteromorpha intestinalis were selected as both the species satisfy the criteria of potential feedstock for bioethanol production such as; annual availability, carbohydrate rich biomass, producing higher reducing sugar concentration, ease of harvest by mechanical means, amenable to transplanting and reproducing prolifically in given environment [89].…”

“…However, limitation of dilute acid pretreatment is the formation of Hydroxymethyl furfurals (HMF) and Levulinic acid (LA) resulting from the degradation of sugars that inhibit the subsequent process (fermentation) in ethanol production [81,82]. These inhibitors are mitigated by neutralization process before fermentation [83,84] or by employing other sustainable alternatives such as biological pretreatment: enzyme hydrolysis [53,[85][86][87][88][89][90][91][92][93][94].…”

“…Commercial industrial enzymes are produced from aerobic fungi Trichoderma reesei, which produces over 100 g per liter of crude cellulase enzyme with higher specific activity, achieved by genetic engineered strains [101]. Most common enzymes employed for seaweed hydrolysis are commercial enzymes such as Cellulase, Celluclast 1.5 L, Viscozyme L, Novozyme 188, Termamyl 120 L, β-glucosidase, Multifect, Meicelase, Amyloglucosidase etc operated at pH 4.5-5.5 and temperature 35-55 � C, incubation time varies based on the algal feedstock [56,71,89,90,[102][103][104][105][106][107][108][109].…”

“…Studies emphasize on production of bioethanol from readily available carbohydrates of brown and red seaweeds, but utilization of red and brown seaweeds such as Kappaphycus, Gelidium, Gracilaria, Sargassum, and Laminaria have the likelihood to override the existing multi-billion dollar hydrocolloid industry [89]. This can be addressed in two ways: (i) utilization of cellulosic rich residue after hydrocolloid extraction, (ii) exploration of green seaweeds which are abundantly recorded from various estuaries and abandoned aquaculture ponds across maritime states in India [134].…”

“…Cellulose is a glucan present in green seaweeds, which can be easily hydrolysed by using enzyme and subsequently fermented to produce bioethanol. Green seaweeds are rich in cellulose content (>10%) [37,89,105] when compared to red and brown seaweed (2-10%).…”