Abstract
This study was conducted to screen for pectinase production by Aspergillus niger isolated from soil samples collected from three different locations within Ahmadu Bello University, Zaria, namely; botanical garden, refuse dump and sheep pen sites. A total of fifteen (15) soil samples were collected from different locations and used for isolation by a cultural method. Isolates suspected to be Aspergillus niger were further identified by microscopic examination of the lactophenol cotton blue stained-preparation and slide culture technique. The isolates were then screened in a pectin-containing medium for their pectinase activity. The isolates were further subjected to pectinase production using citrus pectin as the substrate under submerged fermentation conditions. Seven (7) isolates were confirmed to be Aspergillus niger with percentage occurrence of 60% each from sheep pen (SP) and refuse dumpsites (RD), and 20% from the botanical garden (BG). Aspergillus niger RD3 produced the highest zone of pectin hydrolysis (53 ± 1.1 mm) while isolate RD5 produced the lowest (35 ± 3.1 mm). Under submerged fermentation conditions, Aspergillus niger SP5 had the highest pectinase activity of 2.92 U/mL while isolate RD4 had the lowest pectinase activity of 1.29 U/mL. Aspergillus niger can be readily isolated from various soil types with the highest frequency in soils from sheep pen and refuse dumpsites. All the Aspergillus niger isolates demonstrated the potential for pectinase production. The study reveals the potential of various Aspergillus niger isolates from different soil in the production of pectinase.
Highlights
Pectin is a polymeric material having carbohydrate group esterified with methanol
The percentage occurrence of the Aspergillus niger isolates in the three different soil samples is presented in Table 2 with soil samples from botanical garden having the least isolation rate of 20%, while soils from refuse dump and sheep pen sites had isolation rate of 60% each
Aspergillus niger are known to be ubiquitous in the soil, the observed differences in the percentage occurrence might be due to the richness in organic matter content of the humic soil from sheep pen and refuse dump sites, whereas botanical garden might have little organic matter as nutrient to the organism
Summary
Pectin is a polymeric material having carbohydrate group esterified with methanol It is an important component of plant cell wall with highest concentration in the middle lamella (Rohit et al, 2013). Pectinases consist of a mixture of complex enzymes that catalyzes the hydrolysis of pectin-containing substrates (Torimiro and Okonji, 2013) These enzymes are divided into three main classes that catalyzes depolymerization, demethylation and de-esterification reactions (Hatice and Filiz, 2016). Aspergillus niger are widely distributed geographically and have been observed in broad range of habitats because they can colonize wide variety of substances They are commonly found as saprophytes growing on dead leaves, stored grains, compost piles and other decaying vegetation. This study isolates Aspergillus niger from soil samples of different locations and screen isolates for pectin-degrading enzymes
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