Fundamental features of microbial cellulose utilization are examined at successively higher levels of aggregation encompassing the structure and composition of cellulosic biomass, taxonomic diversity, cellulase enzyme systems, molecular biology of cellulase enzymes, physiology of cellulolytic microorganisms, ecological aspects of cellulase-degrading communities, and rate-limiting factors in nature. The methodological basis for studying microbial cellulose utilization is considered relative to quantification of cells and enzymes in the presence of solid substrates as well as apparatus and analysis for cellulose-grown continuous cultures. Quantitative description of cellulose hydrolysis is addressed with respect to adsorption of cellulase enzymes, rates of enzymatic hydrolysis, bioenergetics of microbial cellulose utilization, kinetics of microbial cellulose utilization, and contrasting features compared to soluble substrate kinetics. A biological perspective on processing cellulosic biomass is presented, including features of pretreated substrates and alternative process configurations. Organism development is considered for "consolidated bioprocessing" (CBP), in which the production of cellulolytic enzymes, hydrolysis of biomass, and fermentation of resulting sugars to desired products occur in one step. Two organism development strategies for CBP are examined: (i) improve product yield and tolerance in microorganisms able to utilize cellulose, or (ii) express a heterologous system for cellulose hydrolysis and utilization in microorganisms that exhibit high product yield and tolerance. A concluding discussion identifies unresolved issues pertaining to microbial cellulose utilization, suggests approaches by which such issues might be resolved, and contrasts a microbially oriented cellulose hydrolysis paradigm to the more conventional enzymatically oriented paradigm in both fundamental and applied contexts.

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Microbial cellulose utilization: fundamentals and biotechnology.

That major flows of energy occur along detrital pathways in all ecosystems is a recent recognition. In freshwater ecosystems, detritus or dead organic matter (217) has two possible sources: autochthonous detritus generated within the ecosystem and allochthonous detritus generated externally. This review is concerned with the breakdown of vascular plant detritus whether autochthonous, from aquatic vascular plants, or allochthonous, derived from riparian trees and herbs. The importance to the energetics of streams of vascular plant material from riparian vegetation was recognized in early studies by Nelson & Scott (184), Egglishaw (85), and Minshall (175). Organic matter budgets for various streams have provided quantitative data to support these early observations (96, 132, 182, 254). However, many low-order streams that lack canopies of riparian vegetation may be dominated by autochthonous primary production of nonvascular plant origin. (72, 176). Theoretical models (256) predict increasing importance of autochthonous production by periphyton and aquatic vascular plants for middle-order streams but less importance of these sources in very large streams, mainly due to light limitation. The relative dominance of allochthonous vs autochthonous sources has been shown to vary between stream systems and with local conditions within streams (72, 178). While vascular plant leaves have received most attention in stream research, there is growing recognition that wood is also important. The direct contribution of wood to stream energy budgets is minimal because wood is resistant to breakdown (e.g. 8, 251). However, woody debris is indirectly important because it creates habitat for aquatic organisms (5), promotes

Vascular plant breakdown in freshwater ecosystems

Although it is well known that metabolism, feeding, and behaviour of lotic organisms is influenced by various flow characteristics, hydraulic variables usually are not accurately measured in lotic ecology studies. Using an approach we call "hydraulic stream ecology", we link organismic responses to a more comprehensive treatment of the physical environment. Since a unified analytical solution for all important hydraulic variables in running waters does not exist at the moment, we advocate a simpler view of the physical system. We demonstrate methods for estimating complex hydraulic key characteristics, like turbulence in the free flow, turbulence close to the stream bottom, and the force of flow prevailing at the bottom. Calculations of these complex key characteristics require measurement of simple hydraulic characteristics like mean velocity, water surface slope, depth, bottom roughness, kinematic viscosity, and density of the water. The hydraulic environment shows characteristic patterns within whole c...

Hydraulic Stream Ecology: Observed Patterns and Potential Applications

Life histories and annual production were determined for six species of net-spinning caddisflies in a headwater stream of the Tallulah River in north Georgia, USA. Five species in the family Hydropsychidae were univoltine, whereas the sixth, a member of the Philopotamidae, had at least two generations per year. Combined annual production, as determined by the Hynes method, was 1.0 g/m2 (ash-free dry mass). Seventy-five percent of the production was concentrated in the two largest species, Arctopsyche irrorata and Parapsyche cardis. The remaining production from highest to lowest percent, was contributed by Dolophilodes distinctus, Hydropsyche sparna, Diplectrona modesta, and Hydropsyche macleodi. Analysis of gut contents alone indicated that detritus was the most important food source. How- ever, food preference and food-specific ecological efficiencies were utilized to calculate the amount of production attributable to each major food category. Surprisingly, almost 80% of all caddisfly production was attributed to animal food, 13% to detritus, and 8% to algae. Actual annual consumption required to account for this production was 2.28 g/m2 animals, 2.54 g/m2 detritus, and 0.51 g/m2 algae. We attempt to quantify the role that net-spinning caddisflies play in the "spiralling" of seston in mountain streams. Our results show that the omnivorous caddisflies are not the major consumer of detritus and algae, and that they produce more detritus in their feces than they consume, thus ap- pearing to lower the food quality of the seston. Net-spinning caddisfly production in this mountain stream appears to be limited by the amount of high quality food available in the seston.

Trophic Basis of Production Among Net-Spinning Caddisflies in a Southern Appalachian Stream

The sustainable use of water resources requires clear guidelines for the management of diffuse pollution inputs to rivers. Without informed guidelines, management decisions are unlikely to deliver cost-effective improvements in the quality of rivers as required by current water policy. Here, we review the evidence available for deriving improved guidelines on the loading of fine sediment to rivers based on the impact on macro-invertebrates. The relationship between macro-invertebrates and fine sediments is poorly defined. Studies of the impacts of fine sediment on macro-invertebrates have been undertaken at various scales, which has an influence on the range of responses displayed and the reliability of the results obtained; results obtained from investigations at smaller scales may not manifest at the scale required to manage rivers and vice versa. Many of the identified effects of increased loading of fine sediment on macro-invertebrates occur as a consequence of deposition on the river bed, yet many current management guidelines are based on suspended sediment targets. On this basis, existing water quality guidelines for sediment management are unlikely to be appropriate.

The impact of fine sediment on macro-invertebrates

Some streams near Dorset in south-central Ontario suffer from acid precipitation via run-off and seepage from thin soils with little buffering capacity A spring-summer survey of eight headwater streams revealed some characteristics of their insect communities which could be correlated with pH The streams could be divided into three groups according to pH and community structure In the most acid group (annual pH range 43–48), Ephemeroptera were absent from two streams although mature Leptophlebia were collected just after spring thaw from the most acid one (pH 43–45) One of these three streams also lacked Plecoptera but the others had two or three genera, all shredders The second group of three streams (pH 50–63), with one exception, did support Ephemeroptera (3–4 genera) and Plecoptera (1–4 genera), most of the latter being shredders In all six of these acid streams, Trichoptera were more diverse and more dense than Ephemeroptera and Plecoptera; again, shredders were clearly dominant, especially the limnephilid caddisfly, Frenesia difficilis (Walker) These six streams also had similar chironomid communities (densities were an order of magnitude higher than other insects) Dominance by Chironomini and abundant Tanypodinae typified the most acid streams In contrast, the two streams in the third group (pH 53–67) had richer and more balanced communities in general with relatively fewer shredders (no Frenesia), more collectors, and fewer Chironomini and Tanypodinae As a field experiment showed that autumn-shed leaves decomposed more slowly in acid than in non-acid streams, summer-growing shredders may benefit from the pulse of acidity at snowmelt

A preliminary study of aquatic insect communities and leaf decomposition in acid streams near Dorset, Ontario

Features of hydropsychid larvae are described which allowed coexisting species in southern Ontario to be distinguished while in the 1st 3 instars; these young stages cannot usually be identified by existing taxonomic keys. Cheumatopsyche differed from Hydropsyche in having a long tapered seta on each antero-lateral corner of the pronotum. Species of Hydropsyche were distinguished according to the length and degree of tapering of the pronotal seta, by background color of head and thoracic sclerites, by round spots and oval patches on the dorsum of the head capsule, and by abdominal setae and scale hairs. After species had been differentiated, measurements of head widths showed that successive instars increased in size in a regular geometric progression (Dyar's Rule). The factor of increase was ca. 1.5 in all species. The use of Dyar's Rule is suggested as a taxonomic tool to associate young instars of coexisting hydropsychids with the more easily identified older instars.

Larval Identification and Instar Association in Some Species of Hydropsyche and Cheumatopsyche (Trichoptera: Hydropsychidae)

A plexiglass chamber 15.2 cm in diameter contains a circular stream channel 3.5 cm wide in which water is circulated by a fine stream of air bubbles. Even, uni-directional currents are achieved by having a spirally-ascending ceiling to the flowing-water channel. When pebbles and fine gravel are used as substrates, the stream is suitable for experiments or rearing programmes using hydropsychid caddisfly larvae (Trichoptera). Many units can be operated simultaneously for replicate experiments or for testing several different factors concurrently.

A miniature laboratory stream powered by air bubbles

Life histories and distribution of mayflies (Insecta: Ephemeroptera) were investigated in 11 streams in south central Ontario that ranged from highly acidic to circumneutral. At least 29 mayfly spe...

Life history and distribution of mayflies (Ephemeroptera) in some acid streams in south central Ontario, Canada

The life-history patterns of four Hydropsyche species (Trichoptera: Hydropsychidae) found in the Credit and Humber Rivers of southern Ontario were investigated through rearing studies, larval and adult collections, and analyses of densities and mortality of field populations of pupae Hydropsyche slossonae was univoltine but was probably capable of producing a second generation under favourable conditions at the warmest station at which it occurred Hydropsyche sparna was partially bivoltine at upstream stations and bivoltine at downstream stations At downstream stations, the common species were Hydropsyche bronta, which was trivoltine, and Hydropsyche morosa, which was bivoltine Hydropsyche sparna, H bronta and H morosa all exhibited a split-cohort development, in which not all of the summer-produced larvae completed development, pupated and emerged before the end of the growing season Overwintering populations consisted of young larvae that had hatched from eggs laid by adults of the previous generation Analysis of the temporal changes in the densities of living and dead pupae provided a reliable way to separate overwintering and spring- and summer-produced generations

Rosemary J. Mackay

Papers

A preliminary study of aquatic insect communities and leaf decomposition in acid streams near Dorset, Ontario

Larval Identification and Instar Association in Some Species of Hydropsyche and Cheumatopsyche (Trichoptera: Hydropsychidae)

A miniature laboratory stream powered by air bubbles

Life history and distribution of mayflies (Ephemeroptera) in some acid streams in south central Ontario, Canada

Variability in the life‐history patterns of four species of Hydropsyche (Trichoptera: Hydropsychidae) in southern Ontario streams