淡水湖渔场沉积物中产胶原蛋白酶菌株的筛选及发酵优化

【背景】胶原蛋白酶能够高效降解水不溶性的胶原蛋白,在各行业中都有着广泛的应用。淡水湖渔场中大部分动物残骸中的胶原蛋白都会沉降到沉积物中,因而其生态环境中应含有丰富的产胶原蛋白酶菌株。【目的】以环洞庭湖水系淡水湖渔场沉积物为样品,筛选产胶原蛋白酶菌株,并对其中一株产酶量和生物安全性均高的菌株进行鉴定及发酵产酶条件的初步研究,以期为胶原蛋白和胶原蛋白酶的工业生产及应用奠定基础。【方法】采用稀释涂布平板法和点种法筛选产胶原蛋白酶菌株,通过茚三酮显色法测定发酵液胶原蛋白酶酶活,并结合16S rRNA基因序列比对和系统发育分析确定产酶菌株的种类。采用滤纸片扩散法检测菌株抗生素敏感性和溶血性,用溴甲酚紫显色法检测菌株氨基酸脱羧酶活性,硝酸还原酶活性测定用试剂盒,通过单因素试验法和正交试验法进行菌株产胶原蛋白酶发酵条件的优化。【结果】从环洞庭湖水系中的4个淡水湖渔场的表层沉积物中共筛选分离得到113株产胶原蛋白酶菌株,并从中挑选一株来自东湖沉积物的产酶量和生物安全性均高的菌株,该菌株为Exiguobacterium属细菌,命名为Exiguobacterium sp. DJ1。菌株DJ1的最佳产酶条件...     

海洋低温几丁质酶菌株筛选、鉴定及酶谱分析

以胶体几丁质为唯一碳源,从大连渤海湾的底泥样品中分离到1株高产低温几丁质酶的海洋细菌,命名为DL-06。由菌株的形态特征结合16S rDNA系统发育分析,初步确定该菌株属于交替假单胞菌(Pseudoalteromonas sp. DL-06)。该菌株经30 h摇瓶发酵后测定粗酶液几丁质酶酶活为9.184 U/mL,最适反应温度为15 ℃,60 ℃孵育1 h仍保持50%以上的酶活性,表明该低温酶具有一定热稳定性。经SDS-PAGE及酶谱分析,该菌株能够产生至少3种以上不同分子质量的几丁质酶组分。Pseudoalteromonas sp. DL-06产几丁质酶在低温下高活性与热稳定特点,使其具有潜在的工业应用价值。     

产蛋白酶细菌Bs3210菌株产酶条件的研究

在对我国地带性土壤中产蛋白酶细菌生态分布的研究基础上,获得了一株产酶活力达到1945单位/ml的野生菌株。经鉴定为枯草芽孢杆菌(Bacillus subtnis)、对该菌的产酶条件进行了比较系统的研究。结果表明,王米粉和豆饼粉是该菌良好的碳源和氮源。而有机酸和无机盐对产酶有抑制作用。     

WHS3菌株产几丁质酶对棉铃虫HaSNPV的增效作用

WHS3 (Serratia marcescens)菌是一株几丁质酶的高产菌株,在诱导培养基中几丁质 酶的产量可达84.4μg/mL.通过对中国棉铃虫进行的生物测定表明WHS3菌所产的几丁质酶 (A3)能有效地提高HaSNPV的毒力20%～70%, LT50、LT90比对照组缩短天数最高可达1.1d、1.3d.     

多重耐药铜绿假单胞菌产ESBLs酶与高产AmpC酶情况及药物敏感性研究

目的探讨多重耐药铜绿假单胞菌产超广谱β-内酰胺酶(ESBLs酶)与高产头孢菌素酶(Amp C酶)情况及药物敏感性。方法收集我院各病区提供的多重耐药铜绿假单胞菌菌株共128株,无重复菌株,检测产ESBLs酶、Amp C酶情况同时进行药物敏感性分析。结果 128株铜绿假单胞菌共检测出产酶菌株98株,占总菌株数的76.56%,其中单产ESBLs酶菌株25株、单产Amp C酶菌株58株、同时产ESBLs酶与Amp C酶菌株15株、不产酶菌株30株;大多数抗菌素对产酶铜绿假单胞菌不敏感,特别是同时产ESBLs酶与Amp C酶菌株几乎所有抗菌素均不敏感,而对于不产酶铜绿假单胞菌大多数抗菌素均较为敏感。结论多重耐药铜绿假单胞菌产酶菌株较多,抗菌药物敏感性差,临床应该根据药敏结果合理使用抗菌素,减少和控制细菌耐药的发生。     

一株高效降解纤维素菌株的筛选及其产酶能力研究

目的筛选并鉴定一种产纤维素酶能力较高的菌株,为纤维素的高效利用贮备菌源。方法用羧甲基纤维素钠(CMC-Na)平板筛选产纤维素酶菌株,通过LB培养基对其进行纯化,16SrDNA基因序列分析其分类地位,3,5-二硝基水杨酸法(DNS)测定其产酶能力。结果分离纯化得到的产纤维素酶菌株(S1)为芽胞杆菌属(Bacillus genus)的短小芽胞菌,在最佳产酶条件下产酶含量达到1 204U/mL,产纤维素酶能力与里氏木霉(Trichoderma reesei)相当,但其产酶速率较里氏木霉低。结论 S1是一株产纤维素酶能力较高的菌株,产酶条件温和,初步鉴定为一种新种,具有较高研究及应用价值。     

从新疆吉木乃地区冬季泌乳双峰驼中培养的细菌多样性及产酸、产酶活效果

[目的]本研究拟通过可培养获得驼源细菌,分析菌种分布规律,获得产酸、产酶特性的菌株资源,为驼源益生细菌的开发和利用提供资源和技术支撑。[方法]采用稀释法筛选新疆吉木乃地区冬季养殖双峰泌乳骆驼驼乳、唾液及直肠粪便中的细菌,通过16S rRNA基因序列分析对菌株进行鉴定;透明圈法对产酸和产酶的菌株进行初筛,并对菌株产有机酸能力及产淀粉酶、纤维素酶和蛋白酶活力进行复筛。[结果]共培养出63株细菌菌株,经分子鉴定得知,从驼粪中分离的35株菌以嗜冷杆菌属和不动杆菌属为主;驼乳中分离出的21株菌以假单胞菌属和明串珠菌属为优势菌属;唾液中分离纯化出7株,主要为芽孢杆菌属;平板初筛得到产酸菌共有11株,1株粪源肠膜明串珠菌(Leuconostoc mesenteroides) 2F11M乳酸产量最高,达到3.93 mg/mL;1株奶源乳酸明串珠菌(Leuconostoc lactis) 2N5M乙酸产量最高,达到12.73 mg/mL;1株粪源蒙氏肠球菌(Enterococcus mundtii) 2F17M丙酸产量最高,达到10.36 mg/mL;根据初筛产透明圈,产酶菌株主要分离自驼粪和驼奶,其中产淀粉酶的菌株17株,产纤维素酶的菌株10株,产蛋白酶的菌株15株;1株奶源的贝莱斯芽孢杆菌(Bacillus velezensis) Nai1的淀粉酶活性最高,为509.07 μg/(min·mL),1株粪源鲁氏不动杆菌(Acinetobacter lwoffii) 2F5N的纤维素酶活性最高,为156.87 μg/(min·mL),1株奶源枯草芽孢杆菌(Bacillus subtilis) 2N2N产蛋白酶活性最高,为3.59 μmol/(min·mL)。[结论]从新疆泌乳双峰骆驼中筛选出了多种产酸、产酶菌株,且活力都较好,具有制备微生态制剂的潜力。     

天山1号冰川底部沉积层产β-半乳糖苷酶低温菌株的系统发育分析及生理多样性

[目的]通过对天山1号冰川底部沉积层冻土中细菌的分离和产β-半乳糖苷酶低温菌株的筛选,了解天山冻土微生物的物种多样性,并对产β-半乳糖苷酶低温菌株的系统发育和生理多样性进行分析.[方法]以乳糖为主要碳源,X-Gal为显色剂,分离筛选出产低温β-半乳糖苷酶菌株.对细菌常规生理生化实验、最适生长温度、耐盐性、药物敏感性进行测定.根据16S rRNA基因序列初步确定产β-半乳糖苷酶低温菌种的系统进化地位,并采用BOX-PCR指纹图谱技术对16S rRNA基因高度同源性的菌株进一步区分.[结果]分离到90株可培养低温菌中25株可产β-半乳糖苷酶,其中76％为革兰氏阳性菌.依据生长温度,产酶菌株80％为嗜冷菌,20％为耐冷菌.在系统发育上,产酶菌株隶属于4个类群,其中肠球菌属(Enterococcus)占26％,短波单胞菌属(Brevundimonas)占22％,假单胞菌属(Pseudomonas)占13％.[结论]天山1号冰川底部沉积层冻土中产β-半乳糖苷酶的低温细菌具有比较丰富的物种和生理多样性.     

产几丁质酶菌株SWCH-6的筛选、鉴定及其产酶条件的优化研究

从汕头海湾养殖区域的海底沉积物中分离到1株几丁质酶活性较高的菌株,命名为SWCH-6,根据菌株的形态特征、生理生化特征和16S Rdna序列,确定该菌株为嗜水气单胞茵(Aeromonas hydrophlilla).采用单因素优化方法结合正交实验,得到菌株SWCH-6产几丁质酶的最佳发酵条件:胶体几丁质25.0g/L,胰蛋白胨10.0g/L,陈海水1.0L, Ph 8.5,32℃,150 r/min培养72h;在该条件下酶活力达0.39U/Ml.此外,菌株所产几丁质酶的最适催化Ph 5.0;最适催化温度为40℃;Cu2、Fe3及表面活性剂Tween-80能增强该酶的催化活性;Zn2 、Mn2 及表面活性剂SDS、洗衣粉对该酶的催化活性有抑制作用,与其它几丁质酶存在着一些不同.     

阴沟肠杆菌产AmpC酶菌和非产酶菌的耐药性研究

目的：探讨阴沟肠杆菌分布特征及产AmpC酶菌和非AmpC酶菌的耐药性。方法：对临床分离的158株阴沟肠杆菌分布科室、感染部位及对16种抗生素耐药性进行分析,并通过酶粗提物头孢西丁三维试验结合PCR法检测AmpC酶。结果：标本来源主要为患者的痰液、尿液、创口分泌物等,科室以重症监护室为多,感染部位以呼吸道为主,耐药性较高的抗生素为头孢西丁、头孢噻肟、头孢曲松等,158株阴沟肠杆菌中产AmpC酶菌株共33株,产AmpC酶阳性率占总菌株数20．9％,产AmpC酶菌株对各种抗生素的耐药率比不产AmpC酶的明显增高。结论：阴沟肠杆菌的耐药与产AmpC酶有关,治疗首选亚胺培南。     

Anaerobic methane oxidation potential and bacteria in freshwater lakes: Seasonal changes and the influence of trophic status

Nitrite-dependent anaerobic methane oxidation (n-damo), mainly carried out by n-damo bacteria, is an important pathway for mitigating methane emission from freshwater lakes. Although n-damo bacteria have been detected in a variety of freshwater lakes, their potential and distribution, and associated environmental factors, remain unclear. Therefore, the current study investigated the potential and distribution of anaerobic methanotrophs in sediments from Erhai Lake and Dianchi Lake, two adjacent freshwater lakes in the Yunnan Plateau with different trophic status. Both lakes showed active anaerobic methane oxidation potential and harbored a high density of n-damo bacteria. Based on the n-damo pmoA gene, sediment n-damo bacterial communities mainly consisted of Candidatus Methylomirabils oxyfera and Candidatus Methylomirabils sinica, as well as novel n-damo organisms. Sediment anaerobic methane oxidation potential and the n-damo bacterial community showed notable differences among seasons and between lakes. The environmental variables associated with lake trophic status (e.g. total nitrogen, ammonia nitrogen, nitrate nitrogen, and total organic carbon) might have significant impacts on the anaerobic methane oxidation potential, as well as the abundance and community structure of n-damo bacteria. Therefore, trophic status could determine the n-damo process in freshwater lake sediment.     

Community Structure of Bacteria Associated with Sheaths of Freshwater and Brackish Thioploca Species

Bacterial communities associated with sheaths of Thioploca spp. from two freshwater lakes (Lake Biwa, Japan, and Lake Constance, Germany) and one brackish lake (Lake Ogawara, Japan) were analyzed with denaturing gradient gel electrophoresis (DGGE) of 16S rRNA gene fragments. The comparison between the DGGE band patterns of bulk sediment and Thioploca filaments of Lake Biwa suggested the presence of specific bacterial communities associated with Thioploca sheaths. As members of sheath-associated communities, bacteria belonging to Bacteroidetes were detected from the samples of both freshwater lakes. A DGGE band from Thioploca of Lake Biwa, belonging to candidate division OP8, was quite closely related to another DGGE band detected from that of Lake Constance. In contrast to the case of freshwater lakes, no bacterium of Bacteroidetes or OP8 was detected from Thioploca of Lake Ogawara. However, two DGGE bands from Lake Ogawara, belonging to Chloroflexi, were quite closely related to a DGGE band from Lake Constance. Two DGGE bands obtained from Lake Biwa were closely related to phylogenetically distant dissimilatory Fe(III)-reducing bacteria. Cloning analyses for a dissimilatory sulfite reductase gene were performed on the same samples used for DGGE analysis. The results of the analyses suggest that sheaths of freshwater/brackish Thioploca have little ecological significance for the majority of sulfate reducers.     

Anaerobic Oxalate Degradation: Widespread Natural Occurrence in Aquatic Sediments

Significant concentrations of oxalate (dissolved plus particulate) were present in sediments taken from a diversity of aquatic environments, ranging from 0.1 to 0.7 mmol/liter of sediment. These included pelagic and littoral sediments from two freshwater lakes (Searsville Lake, Calif., and Lake Tahoe, Calif.), a hypersaline, meromictic, alkaline lake (Big Soda Lake, Nev.), and a South San Francisco Bay mud flat and salt marsh. The oxalate concentration of several plant species which are potential detrital inputs to these aquatic sediments ranged from 0.1 to 5.0% (wt/wt). In experiments with litter bags, the oxalate content of Myriophyllum sp. samples buried in freshwater littoral sediments decreased to 7% of the original value in 175 days. This suggests that plant detritus is a potential source of the oxalate within these sediments. [¹⁴C]oxalic acid was anaerobically degraded to ¹⁴CO₂ in all sediment types tested, with higher rates evident in littoral sediments than in the pelagic sediments of the lakes studied. The turnover time of the added [¹⁴C]oxalate was less than 1 day in Searsville Lake littoral sediments. The total sediment oxalate concentration did not vary significantly between littoral and pelagic sediments and therefore did not appear to be controlling the rate of oxalate degradation. However, depth profiles of [¹⁴C]oxalate mineralization and dissolved oxalate concentration were closely correlated in freshwater littoral sediments; both were greatest in the surface sediments (0 to 5 cm) and decreased with depth. The dissolved oxalate concentration (9.1 μmol/liter of sediment) was only 3% of the total extractable oxalate (277 μmol/liter of sediment) at the sediment surface. These results suggest that anaerobic oxalate degradation is a widespread phenomenon in aquatic sediments and may be limited by the dissolved oxalate concentration within these sediments.     

Diversity of Carbon Monoxide-Oxidizing Bacteria in Five Lakes on the Qinghai-Tibet Plateau,China

Carbon monoxide-oxidizing (COX) bacteria play an important role in controlling the flux of carbon monoxide among natural reservoirs, and thus studying their diversity in natural environments is of great significance to understanding the carbon cycle. In this study, the COX bacterial diversity was investigated in five lakes (Erhai Lake, Gahai Lake1, Gahai Lake2, Xiaochaidan Lake, Lake Chaka) on the Qinghai-Tibet Plateau and its correlation with environmental variables of the lakes was explored. Phylogenetic analyses showed that the CO-oxidizers were dominated by Proteobacteria and Actinobacteria in the Qinghai-Tibet Plateau lakes, and their relative abundance varied with salinity: in the freshwater Erhai Lake, the COX bacteria in the water were dominated by the Betaproteobacteria, in contrast to the Actinobacteridae dominance in the sediment; in the saline and hypersaline lakes of Gahai Lake1, Gahai Lake2 and Xiaochaidan Lake, alphaproteobacterial COX bacteria were dominant in the water, whereas Actinobacteridae and alphaproteobacterial COX bacteria were dominant in the sediment. In the hypersaline Lake Chaka, an unknown COX bacterial clade and alphaproteobacterial COX bacteria were dominant in the water and sediment, respectively. Statistical analyses showed that salinity, pH, and major ions (e.g., K⁺, Na⁺, Ca²⁺, Mg²⁺, SO₄ ^2-, and Cl^-) were important factors affecting the COX bacterial community compositions in the investigated lakes. Overall, our results provided insights into the COX bacterial diversity in Qinghai-Tibetan lakes.     

Diversity of Freshwater <Emphasis Type="Italic">Thioploca</Emphasis> Species and Their Specific Association with Filamentous Bacteria of the Phylum <Emphasis Type="Italic">Chloroflexi</Emphasis>

Phylogenetic diversity among filamentous sulfur-oxidizing bacteria of the genus Thioploca inhabiting freshwater/brackish environments was analyzed in detail. The 16S rRNA gene sequence of Thioploca found in a freshwater lake in Japan, Lake Okotanpe, was identical to that of Thioploca from Lake Ogawara, a brackish lake. The samples of the two lakes could be differentiated by the sequences of their 23S rRNA genes and 16S–23S rRNA internal transcribed spacer (ITS) regions. The 23S rRNA-based phylogenetic relationships between Thioploca samples from four lakes (Lake Okotanpe, Lake Ogawara, Lake Biwa, and Lake Constance) were similar to those based on the 16S rRNA gene sequences. In addition, multiple types of the ITS sequences were obtained from Thioploca inhabiting Lake Okotanpe and Lake Constance. Variations within respective Thioploca populations were also observed in the analysis of the soxB gene, involved in sulfur oxidation. As major members of the sheath-associated microbial community, bacteria of the phylum Chloroflexi were consistently detected in the samples from different lakes. Fluorescence in situ hybridization revealed that they were filamentous and abundantly distributed within the sheaths of Thioploca.     

Abundance and Diversity of Sulfur-Oxidizing Bacteria along a Salinity Gradient in Four Qinghai-Tibetan Lakes,China

Sulfur-oxidizing bacteria (SOB) play important roles in the sulfur cycle and are widespread in a number of environments, but their occurrence and relationship to geochemical conditions in (hyper)saline lakes are still poorly understood. In this study, the abundance and diversity of SOB populations were investigated in four Qinghai-Tibetan lakes (Erhai Lake, Gahai Lake 1, Gahai Lake 2 and Xiaochaidan Lake) by using quantitative polymerase chain reaction (qPCR) and soxB gene- (encoding sulfate thiohydrolase) based phylogenectic analyses. qPCR analyses showed that in the studied lakes, the total bacterial 16S rRNA and soxB gene abundances in the sediments were distinctly higher than in the overlying waters. The 16S rRNA gene abundance in the waters ranged 5.27 × 10⁶–6.09 × 10⁸ copies per mL and 7.39 × 10¹⁰–2.9 × 10¹¹ copies per gram sediment. The soxB gene abundance in the waters ranged from 1.88 × 10⁴ to 5.21 × 10⁵ per mL and 4.73 × 10⁶–2.65 × 10⁷ copies per gram sediment. The soxB gene in the waters of the two hypersaline lakes (Gahai Lake 2 and Xiaochaidan Lake) was more abundant (2.97 × 10⁵ and 5.21 × 10⁵ copies per mL) than that in the two low-salinity lakes (1.88 × 10⁴ and 3.36 × 10⁴ copies per mL). Phylogenetic analysis showed that Alpha- and Betaproteobacteria were dominant SOB in the investigated lakes, and the composition of proteobacterial subgroups varied with salinity: in freshwater Erhai Lake and low-salinity Gahai Lake 1, the SOB populations were dominated by the Betaproteobacteria, whereas in hypersaline Lake Gahai 2 and Xiaochaidan Lake, the SOB populations were dominated by Alphaproteobacteria. Overall, salinity played a key role in controlling the diversity and distribution of SOB populations in the investigated Qinghai-Tibetan lakes.     

Microbial diversity in lake sediments detected by PCR-DGGE

In this study, PCR-denaturing gradient gel electrophoresis (DGGE) was applied to analyze the microbial communities in lake sediments from Lake Xuanwu, Lake Mochou in Nanjing and Lake Taihu in Wuxi. Sediment samples from seven locations in three lakes were collected and their genomic DNAs were extracted. The DNA yields of the sediments of Lake Xuanwu and Lake Mochou were high (10 μg/g), while that of sediments in Lake Taihu was relatively low. After DNA purification, the 16S rDNA genes (V3 to V5 region) were amplified and the amplified DNA fragments were separated by parallel DGGE. The DGGE profiles showed that there were five common bands in all the lake sediment samples indicating that there were similarities among the populations of microorganisms in all the lake sediments. The DGGE profiles of Lake Xuanwu and Lake Mochou were similar and about 20 types of microorganisms were identified in the sediment samples of both lakes. These results suggest that the sediment samples of these two city lakes (Xuanwu, Mochou) have similar microbial communities. However, the DGGE profiles of sediment samples in Lake Taihu were significantly different from these two lakes. Furthermore, the DGGE profiles of sediment samples in different locations in Lake Taihu were also different, suggesting that the microbial communities in Lake Taihu are more diversified than those in Lake Xuanwu and Lake Mochou. The differences in microbial diversity may be caused by the different environmental conditions, such as redox potential, pH, and the concentrations of organic matters. Seven major bands of 16S rDNA genes fragments from the DGGE profiles of sediment samples were further re-amplified and sequenced. The results of sequencing analysis indicate that five sequences shared 99%–100% homology with known sequences (Bacillus and Brevibacillus, uncultured bacteria), while the other two sequences shared 93%–96% homology with known sequences (Acinetobacter, and Bacillus). The study shows that the PCR-DGGE technique combined with sequence analysis is a feasible and efficient method for the determination of microbial communities in sediment samples. __________ Translated from Acta Ecologica Sinica, 2006, 26(11): 3610–3616 [译自: 生态学报]     

Abundance and diversity of iron reducing bacteria communities in the sediments of a heavily polluted freshwater lake

Iron reduction mediated by Fe(III)-reducing bacteria (FeRB) occurs in aqueous environments and plays an essential role in removing contaminates in polluted freshwater lakes. Two model FeRB species, Shewanella and Geobacter, have been intensively studied because of their functions in bioremediation, iron reduction, and bioelectricity production. However, the abundance and community diversity of Shewanella and Geobacter in eutrophic freshwater lakes remain largely unknown. In this work, the distribution, abundance and biodiversity of Shewanella, Geobacter and other FeRB in the sediments of a heavily polluted lake, Chaohu Lake, China, across four successive seasons were investigated. Shewanella, Geobacter, and other FeRB were found to be widely distributed in the sediment of this heavily eutrophic lake. Geobacter was abundant with at least one order of magnitude more than Shewanella in cold seasons. Three Shewanella-related operational taxonomic units were detected and sixty one Geobacter-related operational taxonomic units were grouped into three phylogenetic clades. Thiobacillus, Desulfuromonas and Geobacter were identified as the main members of FeRB in the lake sediments. Interestingly, nutrients like carbon, nitrogen, and phosphorus were found to be the key factors governing the abundance and diversity of FeRB. Total FeRB, as well as Geobacter and Shewanella, were more abundant in the heavily eutrophic zone than those in the lightly eutrophic zone. The abundance and diversity of FeRB in the sediments of freshwater lakes were highly related with the degree of eutrophication, which imply that FeRB might have a great potential in alleviating the eutrophication and contamination in aqueous environments.

     

Molecular Existence and Diversity of Nitrite-Dependent Anaerobic Methane Oxidizing (n-Damo) Bacteria in the Lakes of Badain of the Gobi Desert

Nitrite-dependent anaerobic methane oxidation (n-damo) process, mediated by Candidatus Methylomirabilis oxyfera of the candidate phylum NC10, was discovered recently which plays an important role in coupling the global nitrogen and carbon cycles. However, the distribution and diversity of this new anaerobic methane-oxidizing microorganism have not been investigated in desert lakes yet. The present study successfully retrieved n-damo bacterial 16S rRNA and pmoA gene sequences using PCR technique from lakes in Badain Jaran Desert of China. Phylogenetic analyses showed that n-damo bacteria widely occurred in brine and freshwater lakes on the desert with high diversity, including both sediment and water samples. The results of quantitative PCR indicated that the abundance of the 16S rRNA gene in lake sediments varied from 1.12?±?0.68?×?10⁵ to 1.64?±?0.70?×?10⁵ copies g^?1 (dry weight), while that in water samples per milliliter was generally one order of magnitude lower than sediments. Correlation analyses suggested that n-damo bacterial abundance and diversity strongly depended on salinity. In lake sediments, the distribution, abundance, and diversity of n-damo bacteria were significantly associated with depth due to the concentration gradient of the NO_x^- and ammonium. This study provided new insights into both the n-damo community patterns and its interaction with ambient environmental factors in the desert lake ecosystem.     

Mesozooplankton of the Kosi Bay lakes,South Africa

The Kosi coastal lake system, a chain of four interconnected basins, is located in the subtropical north-eastern corner of South Africa. Little information is available on zooplankton of the system and the main aim of this study is to report on zooplankton samples collected during 2002 and 2003. The set of samples consists of seasonal, subsurface mesozooplankton samples that were collected during nighttime in each of the lakes. A well-developed salinity gradient was evident along the interconnected lakes in the subsurface water during all seasons, ranging from freshwater in the upper lake Amanzamnyama to a maximum of 22 recorded in Lake Makhawulani. The zooplankton community structures of the lakes reflected the salinity gradient of the system, with some coastal marine taxa recorded in the lakes closer to the mouth and only freshwater taxa recorded in Lake Amanzamnyama. Mesozooplankton diversity and abundance were relatively low compared to other estuarine systems along the eastern coast of South Africa. The dominant taxa were calanoid copepods Acartiella natalensis and Pseudodiaptomus stuhlmanni and the mysid Mesopodopsis africana in the lower lakes, whereas cyclopoids Mesocyclops sp. and Thermocyclops sp. dominated the freshwater lake Amanzamnyama.