Bioprocess optimisation for chitosan production by chitinolytic microorganisms.

Chitin-rich organic wastes in aquatic environments provide ecological niches for chitinolytic microorganisms capable of converting chitin into chitosan, a high-value biopolymer with applications in agriculture, biotechnology, and environmental management. Microbial chitosan production represents a sustainable alternative to conventional chemical extraction; however, its efficiency is strongly influenced by environmental and physicochemical process parameters. This study investigated the occurrence, chitinolytic potential, and chitosan-producing capacity of indigenous microorganisms isolated from freshwater and sediment samples in Minna, Niger State, Nigeria, and optimised production under controlled fermentation conditions. Physicochemical characteristics of water bodies were determined, followed by the isolation and characterisation of bacterial and fungal chitinolytic strains. Selected isolates were screened for chitinase activity and subjected to fermentation-based chitosan production. Process optimisation was performed using a five-factor central composite design to assess the effects of temperature, pH, glucose level (5-20 g L⁻¹), nitrogen source concentration (1-5 g L⁻¹), and incubation time, with response surface methodology applied for model development and interaction analysis. Low dissolved oxygen and moderate temperatures favoured chitinolytic genera, including Aspergillus, Bacillus, and Fusarium, with Aspergillus niger exhibiting the highest chitosan yield. Incubation time was the most significant factor (p < 0.001), while temperature, pH, and substrate concentration showed strong interaction effects. Initial batch fermentations yielded up to 0.20 g L⁻¹ chitosan from selected isolates, while response surface optimisation with Aspergillus niger increased production to 1.46 g L⁻¹ at 32.8 °C, pH 5.12, 15.3 g L⁻¹ glucose, 2.45 g L⁻¹ yeast extract, and 5.2 days incubation. The optimised product exhibited a high degree of deacetylation, indicating suitability for agricultural and environmental applications. These findings highlight inland aquatic ecosystems as valuable reservoirs of chitinolytic microorganisms and provide an optimised, environmentally benign framework for scalable microbial chitosan production.