Temporal and spatial variability in the phytoplankton community of Myall Lakes,Australia, and influences of salinity

The variability in the phytoplankton communities of the Myall Lakes, a series of four interconnected coastal lakes on the lower north coast of New South Wales, was studied between 1999 and 2002. There was considerable spatial variability across the lake system. Bombah Broadwater experienced blooms of Anabaena in 1999 and early 2000, but these were replaced from late 2000 onwards by Chroococcus and a variety of eukaryotic taxa, particularly flagellates and diatoms. In comparison, the phytoplankton community of Myall Lake was dominated for much of the study period by Chroococcus, Merismopedia and chlorophyte taxa. The sites located midway between these two main lakes represent an ecotone, with elements of the phytoplanktonic flora of both main lakes being present. Changes in phytoplankton community composition in Bombah Broadwater occurred fairly frequently. In contrast, the phytoplankton community in Myall Lake changed little during the course of the study and can be considered as being at long-term equilibrium. The reasons for this lie in the morphology and hydrology of the lake system, which in turn create gradients in a number of physico-chemical water quality attributes. Bombah Broadwater is influenced by episodic and stochastic freshwater inflows from the upper Myall River catchment, and in times of drought by saline marine incursions via the lower Myall River. Myall Lake however represents a cul-de-sac, with only a small hydraulic connection to the remainder of the lake system. As it has little input from its small catchment, the limnological conditions within this lake remain relatively constant for long periods of time. Although no patterns of seasonal succession were discernable in any of the lakes, some longer-term (annual) changes did occur, and certain taxa displayed enhanced growth in summer. Salinity was found to be an important factor in determining phytoplankton community composition and abundance. Canonical Correspondence Analysis of phytoplankton and environmental data for all sites combined, showed ammonia, total nitrogen and salinity (measured as electrical conductivity) to have the most influence on the phytoplankton community composition and abundance. Anabaena growth was positively related to ammonia concentration and negatively related to conductivity.     

Circulation and the nutrient budget in Myall Lakes

A two-dimensional model is used to study transport of material within Myall Lakes and is coupled to the ocean using a one-dimensional model of Lower Myall River. Runoff from the catchment is calculated from water levels and compares favourably with rainfall assuming an average runoff yield of 28% and a runoff coefficient of 47% for events above the 90th percentile. Most of the runoff enters Bombah Broadwater which is also the only basin connected to the ocean. Intermittent runoff events rapidly displace water from Bombah Broadwater into Boolambayte Lake and from Boolambayte Lake into Myall Lake. Displaced water is mixed within basins by wind-driven circulation within the time scale that levels fall as water drains from the lakes to the ocean. Only 7% of the nutrient load entering Bombah Broadwater becomes resident Myall Lake. About 40% of the nutrient load entering Boolambayte Lake becomes resident in Myall Lake. Median time scales for loss of conservative material entering each basin with the runoff are: 140 days for Bombah Broadwater, 118 days for Boolambayte Lake, and 535 days for Myall Lake. Salinity fluctuates greatly in Bombah Broadwater but is stable in Myall Lake. Material loss from Bombah Broadwater is characterized by many time scales associated with runoff from the catchment and low-frequency changes in ocean water level. Comparison of observed distributions of total nitrogen with simulations indicates that there are sources of total nitrogen in Boolambayte Lake and Myall Lake and sinks of total nitrogen in Bombah Broadwater. There appear to be sinks of total phosphorus throughout the Myall Lakes.     

Ecological description of the sodium chloride mineral springs in the Kirenga River basin and the upper reaches of the Lena River: 1. General characteristics of the springs and their hydrofauna

The aquatic microecosystems and their environment have been studied in 12 mineral springs located in the Cis-Baikal Depression and in the basin of the upper reaches of the Lena River (Eastern Siberia). The hydrochemical characteristics of the springs, originating from the Cambrian salt deposits, are given. Their total mineralization varies from 1.1 to 123.0 g/L and the water is sodium chloride. The soils formed under the influence of the mineral waters (“para-soils”) are described. The data on the composition and quantitative abundance of aquatic fauna are presented. Six types of macroinvertebrate communities are described. The communities where Turbellaria, Gastropoda, and Psychodidae dominate are recorded in weakly mineralized waters (<3 g/L). The communities where Chironomidae dominate are found in waters characterized both by low and high (up to 28 g/L) salinity. In springs with a water salinity of 2.5–11 g/L, communities characterized by the dominance and high biomass of amphipods Gammarus lacustris Sars. are formed. A unique type of community where Ephydridae larvae dominate (>97% of the biomass) is described for the concentrated brines in Ust’-Kutskii spring. Halophilic species of crustaceans are recorded in the meiofauna. The presence of Foraminifera (marine organisms) in the two studied springs attracts specific interest.     

The effects of land use and cultural development on the Lake Ontario ecosystem since 1750

Lake Ontario is the lowest in the chain of five Great Lakes which form part of the boundary between Canada and the United States. Although European exploration began as early as 1615, it was not until the mid-18th Century that permanent settlement began in the Great Lakes basin. Construction of the Erie Canal which links Buffalo with New York via the Hudson River, and its branch to Oswego, strengthened ties between settlements around the lower Great Lakes (lakes Erie and Ontario) and rapidly growing populations along the Atlantic seaboard. The coming of railroads greatly expanded these ties, and provided a direct link between Canadian settlements and the port of Montreal. Over the past 200 years, successive waves of immigrants entered the region, particularly from Europe.Cultural development has resulted in a wide range of environmental impacts throughout the Great Lakes basin. Impacts have been particularly severe in Lake Ontario. Major changes in water quality and the structure of biological communities have resulted from forest clearance, agricultural expansion, intensive fishing, industrial and urban development, and lake level control. Introductions of exotic species, inputs of nutrient and toxic contaminants, and the effects of climatic variation and modification of microclimates have all interacted such that it is often impossible to establish singular cause and effect. The effects of cultural impact became most severe during the early 1970s and prompted strong support for the International Great Lakes Water Quality Agreement (1972) between Canada and the United States. In response to this agreement and subsequent revisions, contaminant loadings have been greatly reduced. Present water quality is generally good in Lake Ontario although some persistent toxic substances remain a problem. Programs to restock the lake have also provided major benefits. Although much further work remains, Lake Ontario is undoubtedly a good example of successful large scale remedial actions.     

Metabolic and molecular characterization of bacterial community associated to Patagonian Chilean oligotrophic-lakes of quaternary glacial origin

The Patagonian Lakes have particular environmental conditions with or without intermittent disturbances. The study of the microorganisms present in aquatic ecosystems has increased notably because they can be used as micro-scale bioindicators of, among others, anthropogenic pollution and climatic change. The aim of the work was to compare the composition of the bacterial communities associated with sediments of three Patagonian Lakes with different geomorphologic patterns and disturbances. The lake sediments were characterized by molecular techniques, physiology profiles and physico-chemical analyses. The metabolic and physiological profiles of the microbial community demonstrated that non-impacted Tranquilo Lake is statistically different to impacted Bertrand and Plomo Lakes. Similar results were detected by DGGE profiles. FISH results demonstrated that betaproteobacteria showed the highest count in the Tranquilo Lake while gammaproteobacteria showed the highest counts in the Bertrand and Plomo Lakes, indicating that their sediments are highly dystrophic. The results demonstrate differences in the metabolic activity and structural and functional composition of bacterial communities of the studied lakes, which have different geomorphological patterns due to disturbances such as volcanic activity and the climatic change.     

Nutrient and phytoplankton responses to a flood event in a series of interconnected coastal lakes: Myall Lakes Australia

Myall Lakes is a large brackish coastal lake on the east coast of Australia that was considered pristine until the occurrence of blue-green algal blooms in 1999. The temporal and spatial extent of chemical and biological changes to the water column of Myall Lakes was studied intensively after a rain event in 2002. Water quality profiles (T, EC, pH, DO), turbidity (secchi), nutrients (TN, NO _x , NH₄ ⁺, DON, TP, FRP, DOP, Si), and phytoplankton (chl a and cell counts) were measured at nine sites on eight occasions immediately after the rain event. Freshwater inflows affected a large area of the lake. Greatest changes were seen in areas close to the mouth of the upper Myall River which is the largest freshwater input to the lakes. Here, greatly elevated concentrations of NO _x , TP, and FRP (up to two orders of magnitude higher than background) were recorded immediately after the rain event but persisted for only 2 to 8 days. Slightly elevated concentrations of TP and NO _x were seen in inflows from the smaller Boolambayte Creek. Stratification was associated with bottom water anoxia and release of ammonia from the sediments. Identification of the sources of nutrient species delivered from different parts of the catchment, combined with studies of nutrient loads can assist managers to develop effective nutrient reduction strategies to reduce the incidence of blue-green algal blooms in Myall Lakes.     

Spatial and temporal patterns of sediment and nutrient accumulation in shallow lakes of the Upper St. Johns River Basin,Florida

We used paleolimnological methods to investigate spatial and temporal patterns of bulk sediment and nutrient (C, N, P) accumulation in Lakes Hell ‘n’ Blazes (A = 154 ha, zmax = 240 cm), Sawgrass (A = 195 ha, zmax = 157 cm) and Washington (A = 1766 ha, zmax = 322 cm), in the Upper St. Johns River Basin, Florida. The study was designed to evaluate long-term changes in sedimentation and nutrient storage in the basin, and was one component of a larger project addressing flood control, wetland restoration, and water quality improvement. These three study lakes are wide, shallow waterbodies in the upper reaches of the St. Johns River channel. Sediment mapping indicates soft, organic deposits are distributed uniformly throughout Lakes Hell ‘n’ Blazes and Sawgrass. In contrast, much of Lake Washington is characterized by sandy bottom, and organic sediment is largely restricted to the north end of the lake. Lakes Hell ‘n’ Blazes and Sawgrass are effective sediment traps because dense submersed macrophytes and their associated epiphytes reduce flow velocity, intercept suspended particles, and utilize dissolved nutrients. Abundant Hydrilla, combined with short fetch, prevents resuspension and downstream transport of sediments. Larger Lake Washington is probably wind-mixed and resuspended organic sediments are redeposited to downstream sites. 210Pb-dated sediment cores show that organic sediment accumulation began in all three lakes before 1900, but that bulk sediment and nutrient accumulation rates have generally increased since then. The increases are probably attributable, in part, to anthropogenic activities including 1) hydrologic modifications that reduced flow rates in the channel, 2) discharge of nutrient-rich waters from urban, agricultural and ranching areas, and, 3) introduction and periodic herbicide treatment of the exotic macrophytes Eichhornia and Hydrilla.     

Plankton community structure and size spectra in the Georgian Bay and North Channel ecosystems

Patterns in the size distribution and taxonomic composition of phytoplankton and zooplankton communities for 1974 in Georgian Bay and the North Channel are described. The Diatomeae predominate the phytoplankton in both areas. Copepods, particularly Calanoida, comprise the greatest fraction of the zooplankton biomass. Normalized plankton biomass spectra for both ecosystems are typical of those found in Lake Superior and offshore Lake Huron. The plankton communities of Georgian Bay and the North Channel are thus similar to the most oligotrophic of the Laurentian Great Lakes.     

Comparative metagenomics of toxic freshwater cyanobacteria bloom communities on two continents

Toxic cyanobacterial blooms have persisted in freshwater systems around the world for centuries and appear to be globally increasing in frequency and severity. Toxins produced by bloom-associated cyanobacteria can have drastic impacts on the ecosystem and surrounding communities, and bloom biomass can disrupt aquatic food webs and act as a driver for hypoxia. Little is currently known regarding the genomic content of the Microcystis strains that form blooms or the companion heterotrophic community associated with bloom events. To address these issues, we examined the bloom-associated microbial communities in single samples from Lake Erie (North America), Lake Tai (Taihu, China), and Grand Lakes St. Marys (OH, USA) using comparative metagenomics. Together the Cyanobacteria and Proteobacteria comprised >90% of each bloom bacterial community sample, although the dominant phylum varied between systems. Relative to the existing Microcystis aeruginosa NIES 843 genome, sequences from Lake Erie and Taihu revealed a number of metagenomic islands that were absent in the environmental samples. Moreover, despite variation in the phylogenetic assignments of bloom-associated organisms, the functional potential of bloom members remained relatively constant between systems. This pattern was particularly noticeable in the genomic contribution of nitrogen assimilation genes. In Taihu, the genetic elements associated with the assimilation and metabolism of nitrogen were predominantly associated with Proteobacteria, while these functions in the North American lakes were primarily contributed to by the Cyanobacteria. Our observations build on an emerging body of metagenomic surveys describing the functional potential of microbial communities as more highly conserved than that of their phylogenetic makeup within natural systems.     

Amazon fish bacterial communities show structural convergence along widespread hydrochemical gradients

The world's richest freshwater fish community thrives in gradients of contrasting environments in Amazonia, ranging from ion‐poor acidic black waters, to ion‐rich circumneutral white waters. These hydrochemical gradients structure Amazonian fish assemblages via ecological speciation events. Fish bacterial communities contain an important genetic heritage essential for their hosts' survival and are also involved in adaptive divergence via niche adaptation processes, but the extent to which they evolve in response to hydrochemical gradients in Amazonia is unknown. Here we investigated bacterial communities (gut and skin mucus) of two ecologically and phylogenetically divergent host species (Mesonauta festivus and Serrasalmus rhombeus) distributed throughout these hydrochemical gradients. The goal was to characterize intra‐ and interspecific Amazonian fish microbiome variations across multiple scales. Using a 16S metabarcoding approach, we investigated the microbiota of 43 wild M. festivus, 32 S. rhombeus and seven water samples, collected at seven sampling sites encompassing both water colours. Taxonomical structures of bacterial communities from both host species were significantly correlated to the environmental continua of magnesium, sodium, dissolved organic carbon, calcium, dissolved O₂, pH, potassium, hardness and chloride. Analysis of discriminating features in community structures across multiple scales demonstrated intra‐ and interspecific structural parallelisms in the response to the hydrochemical gradients. Together, these parallelisms suggest the action of selection on bacterial community structures along Amazonian hydrochemical gradients. Functional approaches along with reciprocal transplant experiments will provide further insights on the potential contribution of Amazonian fish microbiomes in host adaptation and ecological speciation events.     

高营养级捕食者在浅水湖泊沿岸带与敞水区能量耦合的维持作用

研究利用保安湖沿岸带与敞水区两种生境中高营养级捕食者(达氏鲌与红鳍原鲌)的碳(δ13C)、氮(δ15N)稳定同位素数据,通过稳定同位素质量平衡混合模型、非度量多维尺度分析(NMDS)等方法,分析了两种生境中鲌类食物来源的差异.结果表明,两种生境中鲌类食物来源基本一致,且食物来源较为广泛,包括沿岸带饵料鱼类、敞水区饵料鱼...     

Decomposition of dominant submerged macrophytes: implications for nutrient release in Myall Lake, NSW, Australia

Breakdown and nutrient dynamics of submerged macrophytes were studied in Myall Lake, Australia. Mass loss of Myriophyllum sulsagineum was the lowest (64.90%) among the studied macrophytes during the 322 days followed by charophytes (60.79%), whereas Najas marina and Vallisneria gigantea lost 91.15 and 86.02% of their respective initial mass during that time. The overall exponential breakdown rates of Najas marina and Vallisneria gigantea were similar, with k-values of 0.24 and 0.23 day⁻¹, respectively. These rates were significantly higher than the break down rates of charophytes (0.007 day⁻¹) and M. sulsagineum (0.008 day⁻¹). During growth phase, water column depicted lower nutrient concentrations while during decay period, significant increase in water column nutrients resulted. Release of nutrients from decomposing macrophytes and incorporation of these nutrients into sedimentary phase as well as uptake of nutrients by the growing macrophytes, can present a considerable cycling pathway of nutrients in Myall lake system. The results of this study suggest that different submerged macrophytes may differ appreciably in quality and may exhibit different decomposition rates, patterns and nutrient dynamics in aquatic ecosystems in general, and Myall lakes in particular.     

The effects of heavy metals pollution of the upper Arkansas River on the distribution of aquatic macroinvertebrates

Water quality, types, and diversity of aquatic macroinvertebrates show that heavy metal pollution of the upper Arkansas River is presently moderately severe and conditions for aquatic life are generally poor, particularly in the Leadville area. A 2 year study was done on a 30 km section of the upper Arkansas River, Colorado, to determine the effects of heavy metals pollution on the distribution of the aquatic macroinvertebrates. Physical and chemical water parameters were measured, and aquatic macroinvertebrates were collected. The major sources of heavy metal-laden inflows are Leadville Drain, California Gulch, and a number of intermittent flows entering the Arkansas River between Lake Fork and Lake Creek. Important freshening flows are Tennessee Creek, Lake Fork (containing Halfmoon Creek), and Lake Creek.     

Microhabitat variability of macrobenthic organisms within tidal creek systems

The historical development of the hydroseral vegetation of three humic lakes was studied. We applied a combination of methods to reconstruct the past vegetation (plant macroscopic remains, peat decomposition, sediment chemistry and radiocarbon dating). The contemporary environment of these lakes was assessed by vegetation and water chemistry analyses. The oldest foreshore sediments were formed 13075–12700 cal BP (Lake Suchar VI), 10115–9670 cal BP (Lake Suchar III) and 8747–8479 cal BP (Lake Widne). The differences in contemporary vegetation are reflected in the subfossil plant assemblages. From the beginning, poor fens and bogs occurred beside Lake Suchar III, moderately rich and poor fens were developed at Lake Suchar VI, while reedswamps and moderately rich fens occurred at Lake Widne. The foreshore vegetation changed over time but only within a restricted range, specific for each lake corresponding to the hydrochemical differences between the lakes. Lakes are classified as humic if some features are combined, such as the specific vegetation and water parameters. However, over the past few decades escalating climatic and anthropogenic changes could transform the character of these water bodies. The application of multidisciplinary methods permitted comparison of the development of three apparently similar lakes and identification of significant ecological differences.     

Phytoplankton Community Composition in the Tri‐Lakes Area of Central Wisconsin,USA

Tri‐Lakes (Upper and Lower Camelot, Sherwood, Arrowhead) in Adams County, WI, USA are man‐made impoundments draining substantial agricultural lands and surrounded by considerable shoreline residential development. The planktonic algal community, as sampled from June to November 2000, was sparse‐to‐moderately dense, fairly diverse (69 genera from six divisions basin‐wide), and unremarkable in taxonomic composition. All sites sampled displayed the general algal successional trends expected from northern‐temperate, mildly eutrophic waters. These included sparse but taxonomically diverse communities in the spring; a late spring pulse of diatoms; a late summer pulse of green algae; and a steadily increasing component of Cyanobacteria leading to their community dominance by the end of the growing season. Upper Lake Camelot (55 genera) best represented this pattern. Lower Lake Camelot (53 genera) had a large green algal pulse but only a small diatom pulse. Lake Sherwood was the most taxonomically diverse body (63 genera) and had the most extreme pulses of diatoms and greens. Lake Arrowhead had the lowest taxonomic diversity (39 genera), was the most dominated by Cyanobacteria, and had only minor pulses of diatoms and greens. The algal communities indicate a mesotrophic to slightly eutrophic lake status. Continued agricultural and residential inputs of fertilizers and pesticides will likely exacerbate the cyanobacterial dominance leading to further reductions in aquatic health and aesthetic values. Previous chemical treatment and macrophyte removal have achieved limited success, and might have altered algal community dynamics. Remediation approaches that might improve water quality include: reducing upstream inputs via sediment traps or lagoons; reducing in‐lake nutrients via sediment removal; reducing residential inputs via improved septic/sanitation systems; and shoreline vegetation filter strips.     

Mechanisms affecting biomass and distribution of charophytes and <Emphasis Type="Italic">Najas marina</Emphasis> in Myall Lake,New South Wales,Australia

Two years of measurements are explored with a view to formulating an ecosystem model for Myall Lake. Stable physical characteristics, low catchment loads, low light attenuation, flat-bottomed hypsometry, and soft gyttja substrate allow stable charophyte biomass throughout the year in Myall Lake. Chara fibrosa dominates the total biomass and is abundant over the depth range 0.5–4 m. Nitella hyalina is found over the same depth range but has diminished biomass at depths greater than 2 m due to increased incidence of zero-biomass samples at depths greater than 1.5 m. Upper bounds for biomass densities were estimated for charophytes. Najas marina has great seasonal variability and meadows can have very high biomass in waters 1.5–2.7 m deep. High biomass of Najas marina is associated with low biomass of Nitella hyalina and may be a factor determining how the biomass of Nitella hyalina is distributed with respect to depth. Patchiness of Najas marina is particularly high. Temperature and light can support two growing seasons for Najas marina but mechanical disturbance is often high in spring and high biomass was only observed in late autumn during the present study. Less than 5% of the present-day production of submerged macrophytes would have been required to produce organic material of the gyttja over a 1,000-year period. The spatial distributions of gyttja and the dominant macrophytes are consistent with wind patterns. Down-lake limits on the distributions of charophytes and Najas marina are related to a gradient in the coefficient of light attenuation that is, in turn, related to proximity to the bulk of the catchment load.     

青藏高原四县水生植物群落调查

青海省玛多县,达日县,甘肃省久治县和四川省阿坝县地处黄河上游,是高原水生植物分布的重要地区之一。此区有水生植物群落９个,它们是篦齿眼子菜群落,钝叶菹草群落,帕米尔眼子菜群落,圆叶碱毛茛群落,草群落,黄花水毛茛群落,看麦娘群落,曲轴黑三棱群落和西伯利亚蓼群落。     

Functional Groups and Activities of Bacteria in a Highly Acidic Volcanic Mountain Stream and Lake in Patagonia,Argentina

Acidic volcanic waters are naturally occurring extreme habitats that are subject of worldwide geochemical research but have been little investigated with respect to their biology. To fill this gap, the microbial ecology of a volcanic acidic river (pH approximately equal to 0-1.6), Rio Agrio, and the recipient lake Caviahue in Patagonia, Argentina, was studied. Water and sediment samples were investigated for Fe(II), Fe(III), methane, bacterial abundances, biomass, and activities (oxygen consumption, iron oxidation and reduction). The extremely acidic river showed a strong gradient of microbial life with increasing values downstream and few signs of life near the source. Only sulfide-oxidizing and fermentative bacteria could be cultured from the upper part of Rio Agrio. However, in the lower part of the system, microbial biomass and oxygen penetration and consumption in the sediment were comparable to non-extreme aquatic habitats. To characterize similarities and differences of chemically similar natural and man-made acidic waters, our findings were compared to those from acidic mining lakes in Germany. In the lower part of the river and the lake, numbers of iron and sulfur bacteria and total biomass in sediments were comparable to those known from acidic mining lakes. Bacterial abundance in water samples was also very similar for both types of acidic water (around 10(5) mL(-1)). In contrast, Fe(II) oxidation and Fe(III) reduction potentials appeared to be lower despite higher biogenic oxygen consumption and higher photosynthetic activity at the sediment-water interface. Surprisingly, methanogenesis was detected in the presence of high sulfate concentrations in the profundal sediment of Lake Caviahue. In addition to supplementing microbiological knowledge on acidic volcanic waters, our study provides a new view of these extreme sites in the general context of aquatic habitats.     

Distribution and abundance of young fish in the St. Clair River and associated waters,Ontario

Fish larvae were sampled in 1986 in the St. Clair River, and adjacent waters. Species richness (9 taxa as larvae; 4 others as juveniles) and abundance was lowest in the river, where many larvae (e.g., burbot, rainbow smelt, and yellow perch) were in transit from Lake Huron. The most abundant, and localized, species was gizzard shad, which reached a peak mean density of 4600 larvae 100 m^-3 in an agricultural canal. Adjacent waters contribute greatly to the fish communities of the river and adjoining Lakes Huron and Erie, especially in terms of the number and quantity of forage species.     

Novel N4 Bacteriophages Prevail in the Cold Biosphere

Coliphage N4 is a lytic bacteriophage discovered nearly half a century ago, and it was considered to be a “genetic orphan” until very recently, when several additional N4-like phages were discovered to infect nonenteric bacterial hosts. Interest in this genus of phages is stimulated by their unique genetic features and propagation strategies. To better understand the ecology of N4-like phages, we investigated the diversity and geographic patterns of N4-like phages by examining 56 Chesapeake Bay viral communities, using a PCR-clone library approach targeting a diagnostic N4-like DNA polymerase gene. Many new lineages of N4-like phages were found in the bay, and their genotypes shift from the lower to the upper bay. Interestingly, signature sequences of N4-like phages were recovered only from winter month samples, when water temperatures were below 4°C. An analysis of existing metagenomic libraries from various aquatic environments supports the hypothesis that N4-like phages are most prolific in colder waters. In particular, a high number of N4-like phages were detected in Organic Lake, Antarctica, a cold and hypersaline system. The prevalence of N4-like phages in the cold biosphere suggests these viruses possess yet-to-be-determined mechanisms that facilitate lytic infections under cold conditions.