弧菌在海洋有机碳循环中的重要作用

弧菌(Vibrio)属于变形菌门中的γ-变形菌纲,是一类兼具遗传多样性与生态多样性的异养细菌,广泛分布于海洋环境中,尤其是近岸区域.弧菌是这些生境中可培养细菌的优势类群,其占比可高达10%.弧菌的分布受各种环境因子的控制,尤其是温度、盐度和溶解有机碳.弧菌可以利用多种大分子有机化合物,包括几丁质(大多数弧菌可以参与其代谢)、褐藻胶和琼脂等.许多弧菌具有很短的复制时间(代时短至10min),可使它们在短时间内发展达到较高的生物量.尽管弧菌通常只占总微生物种群的一小部分(约占近岸水体总浮游细菌的1%),但已有研究表明,它们在各种富营养条件下(如发生藻类水华时增加的有机物以及来自撒哈拉沙漠沙尘暴沉降的铁离子)可爆发性繁殖.因此,弧菌可能对海洋(尤其边缘海区域)有机碳循环产生巨大的影响.在基因组学和相关研究领域的探索,将会在分子水平上揭示更多的关于弧菌介导的生物转化和再矿化机制.

Significance of Vibrio species in the marine organic carbon cycle-A review

The genus Vibrio,belonging to Gammaproteobacteria of the phylum Proteobacteria,is a genetically and ecologically diverse group of heterotrophic bacteria,that are ubiquitous in marine environments,especially in coastal areas.In particular,vibrios dominate,i.e.up to 10%of the readily culturable marine bacteria in these habitats.The distribution of Vibrio spp.is shaped by various environmental parameters,notably temperature,salinity and dissolved organic carbon.Vibriospp.may utilize a wide range of organic carbon compounds,including chitin(this may be metabolized by most Vibrio spp.),alginic acid and agar.Many Vibrio spp.have very short replication times(as short as～10 min),which could facilitate them developing into high biomass content albeit for relatively short durations.Although Vibriospp.usually comprise a minor portion(typically^1%of the total bacterioplankton in coastal waters)of the total microbial population,they have been shown to proliferate explosively in response to various nutrient pulses,e.g.,organic nutrients from algae blooms and iron from Saharan dust.Thus,Vibrio spp.may exert large impacts on marine organic carbon cycling especially in marginal seas.Genomics and related areas of investigation will reveal more about the molecular components and mechanisms involved in Vibrio-mediated biotransformation and remineralization processes.

Vibrioharveyi: a serious pathogen offish and invertebrates in mariculture

Vibrio harveyi,which belongs to family Vibrionaceae of class G cunmap rote obacte ria,includes the species V.car char iae and V.trachuri as its junior synonyms.The organism is a well-recognized and serious bacterial pathogen of marine fish and invertebrates,including penaeid shrimp,in aquaculture.Diseased fish may exhibit a range of lesions,including eye lesions/blindness,gastro-enteritis,muscle necrosis,skin ulcers,and tail rot disease.In shrimp,V.harveyi is regarded as the etiological agent of luminous vibriosis in which affected animals glow in the dark.There is a second condition of shrimp known as Bolitas negricans where the digestive tract is filled with spheres of sloughed-off tissue.It is recognized that the pathogenicity mechanisms of V.harveyi may be different in fish and penaeid shrimp.In shrimp,the pathogenicity mechanisms involved the endotoxin lipopolysaccharide,and extracellular proteases,and interaction with bacteriophages.In fish,the pathogenicity mechanisms involved extracellular hemolysin(encoded by duplicate hemolysin genes),which was identified as a phospholipase B and could inactivate fish cells by apoptosis,via the caspase activation pathway.V.harveyi may enter the so-called viable but nonculturable(VBNC)state,and resuscitation of the VBNC cells may be an important reason for vibriosis outbreaks in aquaculture.Disease control measures center on dietary supplements(including probiotics),nonspecific immunostimulants,and vaccines and to a lesser extent antibiotics and other antimicrobial compounds.

Viable but nonculturable bacteria and their resuscitation:implications for cultivating uncultured marine microorganisms

Culturing has been the cornerstone of microbiology since Robert Koch first successfully cultured bacteria in the late nineteenth century. However, even today, the majority of microorganisms in the marine environment remain uncultivated. There are various explanations for the inability to culture bacteria in the laboratory, including lack of essential nutrients, osmotic support or incubation conditions, low growth rate, development of micro-colonies, and the presence of senescent or viable but nonculturable (VBNC) cells. In the marine environment, many bacteria have been associated with dormancy, as typified by the VBNC state. VBNC refers to a state where bacteria are metabolically active, but are no longer culturable on routine growth media. It is apparently a unique survival strategy that has been adopted by many microorganisms in response to harsh environmental conditions and the bacterial cells in the VBNC state may regain culturability under favorable conditions. The resuscitation of VBNC cells may well be an important way to cultivate the otherwise uncultured microorganisms in marine environments. Many resuscitation stimuli that promote the restoration of culturability have so far been identified;these include sodium pyruvate, quorum sensing autoinducers, resuscitation-promoting factors Rpfs and YeaZ, and catalase. In this review, we focus on the issues associated with bacterial culturability, the diversity of bacteria entering the VBNC state, mechanisms of induction into the VBNC state, resuscitation factors of VBNC cells and implications of VBNC resuscitation stimuli for cultivating these otherwise uncultured microorganisms. Bringing important microorganisms into culture is still important in the era of high-throughput sequencing as their ecological functions in the marine environment can often only be known through isolation and cultivation.

Methods for the diagnosis of bacterial fish diseases

The diagnosis of bacterial fish diseases has progressed from traditional culture・dependent methods involving the recoveryof pathogens on agar-containing media and identification by examination of phenotypic traits. Newer approaches centreon culture-independent approaches. A problem with culturing is that it lacks sensitivity, tends to be slow, and its successdepends on the composition of the media and incubation conditions employed. In contrast, culture-independent methods,now centring on molecular methods, are highly specific and sensitive. This raises an important issue that detection of verylow numbers of bacterial cells does not necessarily imply the presence of clinical disease. Positivity could reflect backgroundpopulations of the pathogen that may be present in the aquatic environment.

Phylotype resolved spatial variation and association patterns of planktonic Thaumarchaeota in eastern Chinese marginal seas

The majority of marine ammonia oxidizers belong to Thaumarchaeota,a phylum of Archaea,which is distributed throughout the water column.Marine surface waters contain distinct thaumarchaeotal phylotypes compared to the deeper ocean,but spatial dynamics of the surface-associated lineages are largely unsolved.This study of 120 seawater samples from the eastern Chinese marginal seas identifed contrasting distribution and association patterns among thaumarchaeotal phylotypes across diferent dimensions.Horizontally,Nitrosopumilus-like and Nitrosopelagicus-like phylotypes dominated the surface water(3 m)of the Yellow Sea(YS)and East China Sea(ECS),respectively,along with increased abundance of total free-living Thaumarchaeota in ECS.Similar compositional changes were observed in the surface microlayer.The spatial heterogeneity of particle-attached Thaumarchaeota was less clear in surface microlayers than in surface waters.Vertically,the Nitrosopelagicus-like phylotype increased in abundance from surface to 90 m in ECS,which led to an increase in the proportion of Thaumarchaeota relative to total prokaryotes.This occurred mainly in the free-living fraction.These results indicate a clear size-fractionated niche partitioning,which is more pronounced at lower depths than in the surface water/surface microlayer.In addition,associations of Thaumarchaeota with other microbial taxa varied between phylotypes and size fractions.Our results show that a phylotype-resolved and size-fractionated spatial heterogeneity of the thaumarchaeotal community is present in surface oceanic waters and a vertical variation of the Nitrosopelagicus-like phylotype is present in shallow shelf waters.