Starting with a brief history of solid-state fermentation (SSF), major aspects of SSF are reviewed, which include factors affecting SSF, biomass, fermentors, modeling, industrial microbial enzymes, organic acids, secondary metabolites, and bioremediation. Physico-chemical and environmental factors such as inoculum type, moisture and water activity, pH, temperature, substrate, particle size, aeration and agitation, nutritional factors, and oxygen and carbon dioxide affecting SSF are reviewed. The advantages of SSF over Submerged Fermentation (SmF) are indicated, and the different types of fermentors used in SSF described. The economic feasibilities of adopting SSF technology in the commercial production of industrial enzymes such as amylases, cellulases, xylanase, proteases, phytases, lipases, etc., organic acids such as citric acid and lactic acid, and secondary metabolites such as gibberellic acid, ergot alkaloids, and antibiotics such as penicillin, cyclosporin, cephamycin and tetracyclines are highlighted. The relevance of applying SSF technology in the production of mycotoxins, biofuels, and biocontrol agents is discussed, and the need for adopting SSF technology in bioremediation of toxic compounds, biological detoxication of agro-industrial residues, and biotransformation of agro-products and residues is emphasized.

Solid-State Fermentation Systems—An Overview

Production of fungal xylanases

Production of Aspergillus terreus xylanase in solid-state cultures: application of the Plackett–Burman experimental design to evaluate nutritional requirements

Filamentous fungi have been widely used to produce hydrolytic enzymes for industrial applications, including xylanases, whose levels in fungi are generally much higher than those in yeast and bacteria. We evaluated the influence of carbon sources, nitrogen sources, and moisture content on xylanase production by Penicillium canescens 10-10c in solid-state fermentation. Among agricultural wastes tested (wheat bran, untreated wheat straw, treated wheat straw, beet pulp, and soja meal), untreated wheat straw gave the highest production of xylanase. Optimal initial moisture content for xylanase production was 83%. The addition of 0.4 g of xylan or easily metabolizable sugar, such as glucose and xylose, at a concentration of 2 % to wheat straw enhanced xylanase production. In solid-state fermentation, even at high concentrations of glucose or xylose (10%), catabolic repression was minimized compared to the effect observed in liquid culture. Yeast extract was the best nitrogen source among the nitrogen sources investigated: peptone, ammonium nitrate, sodium nitrate, ammonium chloride, and ammonium sulfate. A combination of yeast extract and peptone as nitrogen sources led to the best xylanase production.

Xylanase production by Penicillium canescens 10-10c in solid-state fermentation.

Silicosis — Continued Silicosis is a chronic lung disease associated with the inhalation and pulmonary deposition of dust that contains crystalline silica. Through the Sentinel Event Notification System for Occupational Risks (SENSOR)* program, CDC's National Institute for Occupational Safety and Health (NIOSH) is assessing practical models for implementing state-based surveillance of silicosis and linking follow-up intervention activities to surveillance reports. From 1989 through 1992, the Ohio Department of Health (ODH) SENSOR program identified silicosis cases through reports of Bureau of Workers' Compensation (BWC) claims, physician reports, and death certificates. The addition in 1993 of hospital discharge reports as an ascertainment source resulted in a substantial increase in the number of silicosis case reports identified annually (Table 1). This report describes the investigation of a case of occupational silicosis in Ohio and summarizes the impact of hospital-based reporting on surveillance for silicosis in Case Report In September 1991, a case report † was sent to ODH by an infectious disease specialist who was treating a 55-year-old sandblaster with advanced silicosis and an associated Mycobacterium kansasii infection § (2). In January 1992, NIOSH and ODH conducted a joint investigation at the worker's place of employment—a metal preparation shop—to evaluate current levels of exposure to respirable crystalline silica and to screen co-workers for silicosis. The investigation detected excessive exposures to respirable crystalline silica (2–5). Chest radiology revealed radiographic abnormalities consistent with pneumoconiosis in four of 16 current and former workers *SENSOR is a program of cooperative agreements with state health departments to develop surveillance and intervention strategies for selected occupational conditions. The National Institute for Occupational Safety and Health currently supports SENSOR silicosis programs in seven states and Wisconsin). † Case reports should be submitted for persons with a physician's provisional diagnosis of silicosis, a chest radiograph interpreted as consistent with silicosis, or pathologic findings consistent with silicosis (1).

Current trends in

Maximum xylanase production byChaetomiumcellulolyticum was obtained in the culture supernatant after 30 h of growth at 37°C in basal medium containing 1% xylan at pH maintained between 6.5 and 7.5. Addition of 0.05% Tween 80 to the medium increased the enzyme production considerably. Xylanase production was found to be growth associated. The optimal conditions for enzymatic hydrolysis of xylan were found to be pH 6.0 and 50°C. During enzymatic hydrolysis, xylose, xylobiose and other xylooligosaccharides were liberated from xylan. The pH values for xylanase production and for xylan hydrolysis were closely related to the utilization of hemicelluloses of aspen wood for fungal protein production by this organism as reported in our earlier work.

Xylanase of Chaetomium cellulolyticum: its nature of production and hydrolytic potential

Chaetomium
cellulolyticum was able to produce xylanases on all the three lignocelluloses: wheat straw, corn stover and aspen wood. Wheat straw was the best. Solid state fermentation of lignocelluloses gave higher yields of xylanases than liquid state fermentation, but it took longer time of incubation.

D. S. Chahal

Papers

Xylanase of Chaetomium cellulolyticum: its nature of production and hydrolytic potential

Production of xylanases by Chaetomium cellulolyticum during growth on lignocelluloses.