Some like it cold: understanding the survival strategies of psychrophiles

Much of the Earth's surface, both marine and terrestrial, is either periodically or permanently cold. Although habitats that are largely or continuously frozen are generally considered to be inhospitable to life, psychrophilic organisms have managed to survive in these environments. This is attributed to their innate adaptive capacity to cope with cold and its associated stresses. Here, we review the various environmental, physiological and molecular adaptations that psychrophilic microorganisms use to thrive under adverse conditions. We also discuss the impact of modern “omic” technologies in developing an improved understanding of these adaptations, highlighting recent work in this growing field.http://embor.embopress.org/content/15/5/508hb201

Methanogens, sulphate and heavy metals: a complex system

Anaerobic digestion (AD) is a well-established technology used for the treatment of wastes and wastewaters with high organic content. During AD organic matter is converted stepwise to methane-containing biogasa renewable energy carrier. Methane production occurs in the last AD step and relies on methanogens, which are rather sensitive to some contaminants commonly found in wastewaters (e.g. heavy metals), or easily outcompeted by other groups of microorganisms (e.g. sulphate reducing bacteria, SRB). This review gives an overview of previous research and pilot-scale studies that shed some light on the effects of sulphate and heavy metals on methanogenesis. Despite the numerous studies on this subject, comparison is not always possible due to differences in the experimental conditions used and parameters explained. An overview of the possible benefits of methanogens and SRB co-habitation is also covered. Small amounts of sulphide produced by SRB can precipitate with metals, neutralising the negative effects of sulphide accumulation and free heavy metals on methanogenesis. Knowledge on how to untangle and balance sulphate reduction and methanogenesis is crucial to take advantage of the potential for the utilisation of biogenic sulphide as a metal detoxification agent with minimal loss in methane production in anaerobic digesters.The research was financially supported by the People Program (Marie Curie Actions) of the European Union's Seventh Framework Programme FP7/2007-2013 under REA agreement 289193

Bacterial contribution to mitigation of iron and manganese in mangrove sediments

The Mandovi and Chapora are two tropical estuaries lying in close geographic proximity on the west coast of India. Seasonal changes in down core variation of Fe, Mn and Total Organic Carbon (TOC) in the mangrove sediments adjoining these estuaries were studied to assess their influence on some of the representative benthic bacteria belonging to heterotrophic and autotrophic groups. Heterotrophic bacteria (HB) cultured on different nutrient concentrations (0.01, 0.1 and 25) together with nitrifiers (NtB; representating autotroph) were chosen to assess the influence of the above-mentioned abiotic parameters on the former. The experimental site located along the Mandovi is under the influence of extensive ferromanganese ore mining, while the control site at Chapora is relatively free from such influences. Geoaccumulation index computed for Mandovi showed that sediments (0-10 cm) were 'uncontaminated to moderately contaminated' by Fe during the pre monsoon and monsoon seasons, while in the post monsoon season the 4-10 cm fraction was almost completely restored from contamination. Similar computations for Mn showed that in pre monsoon, sediments fell in the 'moderately contaminated' and 'moderately to strongly contaminated' categories, while in the monsoon and post monsoon seasons all the sections were 'Uncontaminated'. The difference observed in correlation between Fe and Mn with the various fractions of heterotrophs and nitrifiers indicated that though these two elements shared a similar chemistry in the environment, microbes involved in biogeochemical processes might prefer them differentially. The relationship between TOC and HB enumerated on 0.01 dilute nutrient agar remained at r = 0.50, p < 0.05 throughout the year. Hence, it could be apparently linked to their preferred concentration of organic carbon requirement. A relationship of r = 0.61, p < 0.01 between manganese concentration and heterotrophs recovered on different strengths of nutrient agar is suggestive of their response to the metal enrichment. They could thus contribute towards maintaining the level of Mn at par with reference levels at Chapora. A positive correlation between Mn with NtB (n = 10, p < 0.05, r = 0.58) at the experimental site during the non-monsoon months is suggestive of the latter's contribution to regulation of the metal concentration in the sediment probably through anaerobic nitrification at the expense of manganese. The study therefore supports our hypothesis that both autochthonous autotrophs and heterotrophs work in tandem to mitigate concentration of Mn and related metals in mangrove sediments

Assessment of viability in the bacterial standing stock of the Antarctic sea from the Indian side

During the austral summer, we examined the bacterial population along the cruise track extending from 70degrees S and 18degrees E to 30degrees S and 35degrees E. During the cruise, three distinct fractions of the bacterioplankton viz. total count, total direct viable and retrievable counts were simultaneously enumerated in these waters. In the stations south of the convergent region designated as section I the population ranged within 10(8-9) L-1 whereas in the north of the region designated as section 11 they were one order higher and ranged from 10(9-10) L-1. The percentage of viability in the region was high corresponding to the generally high chlorophyll and primary productivity encountered in the eastern Aghulas bank. The study substantiates the hypothesis that in the Antarctic, not only the bacterial standing stock but also the active population of bacterioplankton (ca. 50 %) are almost equal in abundance to those in the other oceanic or coastal regions. The viable fraction forms a hitherto unreported significant component of these waters. (C) 2001 Ifremer/CNRS/IRD/Editions scientifiques et medicales Elsevier SAS.Lors de la 13e expédition antarctique indienne, nous avons examiné les populations bactériennes le long d’une section s’étendant de 70° S et de 18° E à 30° S et 35° E. Trois fractions du bactérioplancton ont été dénombrées : la population totale, la population viable et le nombre de colonies. Au sud de la convergence (section I), les concentrations sont comprises entre 108 et 109 cellules par litre alors qu'au nord (section II), elles se situent entre 109–1010. Le pourcentage de viabilité est élevé dans cette dernière zone, également riche en chlorophylle et en production primaire (banc des Aiguilles). Cette étude confirme que les concentrations bactériennes et leur viabilité sont équivalentes dans l’océan Austral à ce qu’elles sont dans d’autres régions océaniques ou côtières de l’océan mondial. La partie viable représente une fraction significative, ce qui n’avait pas encore été mis en évidence

Anoxia over the western continental shelf of India: Bacterial indications of intrinsic nitrification feeding denitrification

Studies on the Arabian Sea coastal anoxia have been of immense interest, but despite its ecological significance there is sparse understanding of the microbes involved. Hence, observations were carried out off Goa (15°30′N, 72°40′E to 15°30′N, 72°59′E) to understand the processes that mediate the changes in various inorganic nitrogen species in the water column during anoxia. Water column chemistry showed a clear distinct oxic environment in the month of April and anoxic condition in October. Our study based on microbial signatures indicated that oxygen deficit appeared as a well-defined nucleus almost 40 km away from the coast during the oxic period (April) and spreads there after to the entire water column synchronizing with the water chemistry. Striking results of net changes in inorganic nitrogen species in nitrification blocked and unblocked experimental systems show that denitrification is the predominant process in the water column consuming available nitrate (∼0.5 μM) to near zero levels within ∼72 h of incubation. These observations have been supported by concomitant increase in nitrite concentration (∼4 μM). Similar studies on denitrification-blocked incubations, demonstrate the potential of nitrification to feed denitrification. Nitrification could contribute almost 4.5 μM to the total nitrate pool. It was found that the relation between ammonium and total dissolved inorganic nitrogen (DIN) pool (r = 0.98, p < 0.001, n = 122) was significant compared to the latter with nitrite and nitrate. The occurrence of high ammonium under low phosphate conditions corroborates our observations that ammonium does not appear to be locked under low oxygen regimes. It is suggested that ammonium actively produced by detrital breakdown (ammonification) is efficiently consumed through nitrification process. The three processes in concert viz. ammonification, nitrification and denitrification appear to operate in more temporal and spatial proximity than hitherto appreciated in these systems and this gives additional cues on the absence of measurable nitrate at surface waters, which was earlier attributed only to efficient algal uptake. Hence we hypothesize that the alarming nitrous oxide input into the atmosphere could be due to high productivity driven tighter nitrification–denitrification coupling, rather than denitrification driven by extraneous nitrat