Expert Opinion on Environmental BiologyISSN: 2325-9655

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Editorial, Expert Opin Environ Biol Vol: 1 Issue: 1

How do Microbes Enhance the Carrying Capacity of their Habitats?

Esperanza Martínez-Romero*
Centro de Ciencias Genómicas, Mexico
Corresponding author : Esperanza Martínez-Romero
Centro de Ciencias Genómicas, Cuernavaca, UNAM, Mexico
E-mail: [email protected]
Received: July 20, 2012 Accepted: July 23, 2012 Published: July 25, 2012
Citation: Martínez-Romero E (2012) How do Microbes Enhance the Carrying Capacity of their Habitats? Expert Opin Environ Biol 1:1. doi:10.4172/2325-9655.1000e103

Abstract

How do Microbes Enhance the Carrying Capacity of their Habitats?

A new era in Environmental Biology is emerging from genomic, metagenomic, transcriptomic, metatranscriptomic, proteomic, metabolomic, secretomic, stable isotope probing and nanospectroscopy analyses. These approaches are providing and will provide a wealth of molecular information beyond biodiversity studies (culture-dependent or -independent).To accommodate and understand such data, new theories and concepts are needed

Keywords:

A new era in Environmental Biology is emerging from genomic, metagenomic, transcriptomic, metatranscriptomic, proteomic, metabolomic, secretomic, stable isotope probing and nanospectroscopy analyses. These approaches are providing and will provide a wealth of molecular information beyond biodiversity studies (culture-dependent or -independent). To accommodate and understand such data, new theories and concepts are needed [1]. A relevant question in Environmental Biology is: How many organisms may a habitat support? Other questions are: What are the limiting resources? Do community members trade or compete for resources? For many years scientists have asked what the carrying capacity of humans on Earth is. The same question may be asked for other living organisms in the ocean, a sea, a country, a geographical region or an animal or plant tissue or organ.
In this editorial I will present some ideas on the carrying capacity of microbial habitats. The carrying capacity is the maximal load in population size that a habitat may support.

Beneficial Bacteria or Fungi Increase the Carrying Capacity of their Hosts to the Microbe Benefit

Many diverse examples support this, though they have not been considered under this perspective that proposes a novel and unifying view of symbionts.
Nitrogen-fixing bacteria increase the carrying capacity of their host plants. If plants grow more with the provided nitrogen (N) then they could return more nutrients to the bacteria. Remarkably bacteria in nodules may attain large population sizes, around 1012. Large numbers of nodules are found in healthy plants. N fixation is considered an ecological service as N is limiting in many natural habitats [2]. Nitrogen-fixing bacteria may be used as biofertilizers and it is worth noting that N chemical fertilizers have been recognized as a detonator of human population [3]. Fertilizers have increased the carrying capacity of humans on Earth, the same strategy (increase of the carrying capacity by N fertilization to plants) seems to have been used by bacteria for their own benefit for several million years.
In comparison to nodules, less bacteria are found at the rhizophere (around109 per g of wet tissue), in xylem vessels (around 103 per g of wet tissue), apoplasts or in seeds (around 102 per seed), indicating that their loading capacity is smaller than that of nodules. Leaves have heterogeneous bacterial populations and nutrients are scarce except in some spots [4]. Xylem is one of the poorest nutrient sources in plants [5].
Phosphate solubilizing bacteria and phosphate transporting mycorrhiza, by making phosphate available [6], increase the carrying capacity of plants. Besides N, the next limiting nutrient in many environments is phosphorus.
Vitamin producing bacteria stimulate host growth and development and for this they are also capable of increasing the loading capacity of their insect and mammal hosts. Endosymbiotic bacteria some of them found in bacteriomes and associated fungi in insects provide their hosts with essential amino acids, vitamins, lipids or other substances that promote host growth [7].
Hormone producing bacteria stimulate root or shoot growth in plants. Many (if not most) plant associated bacteria produce plant hormones or regulators that enhance plant growth [8].
Contrary to beneficial microbes, pathogens seem to overexploit and exceed the carrying capacity of their hosts. Bacteria and fungi that inhibit plant pathogens are capable of producing antimicrobials in plants and promote plant heath [8], a seemingly consequence would be an increased carrying capacity of plants. However, not all non-pathogenic associated microbes may contribute to increase host carrying capacity, those that do not contribute and benefit from the host have been designated cheaters. Rhizobial cheaters in plant symbiosis have been studied [9].
Bacteria differentiation into discrete sequence lineages may have the consequence of an increased carrying capacity in a single habitat.
Discrete sequence lineages have been evidenced in many environmental bacterial species and “reflect presumably some fundamental properties of the microbial world” [10]. If bacteria differentiate to efficiently use different resources in a single habitat then they may attain larger population numbers and compete less. Multiple species in a microbial community may be maintained on the same basis. This hypothesis remains to be tested with different microbial species.
Biased rhizopheres [11], from genetically manipulated plants that produce a particular substance in their roots, increase the loading carrying capacity selectively for some bacteria. Prebiotics (nutrients given to humans to promote beneficial bacteria in the digestive tract) may also have the same effects as the biased rhizospheres. Guts may contain 1013-1014 bacteria [12] and little is known on the species or strain capabilities to profit from different nutrients. It has been said that obese people have a different gut microbiota in comparison to that from thin people with a different ratio of Firmicutes to Bacteroidetes [13]. Do obese people have a different carrying capacity in their guts? It would seem so. Do obese people have a larger number of different species within the Firmicutes (the phyla with the enlarged proportion in obese people)? And does this correlate with larger nutrient extracting abilities?

Conclusion

The carrying capacity of any habitat seems to be limited and due to this, humans and microbes have developed mechanisms to increase the carrying capacity of their habitats in different ways. The carrying capacity of habitats and the microbial tricks to increase it may explain to a good extent the microbe life in natural conditions. In cases where humans and bacteria have over passed their habitat carrying capacity the consequences are negative. Accurate methods and theoretical models are needed to estimate the carrying capacity of different habitats including countries, cities and living organisms.

Acknowledgement

To Conacyt 2249-5 and PAPIIT IN205412 for financial support. To Julio Martínez for technicial support.

References

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  9. Oono R, Anderson CG, Denison RF 2011 Failure to fix nitrogen by non-reproductive symbiotic rhizobia triggers host sanctions that reduce fitness of their reproductive clonemates Proc Biol Sci. 278: 2698-2703.

  10. Konstantinidis, KT (2011) Metagenomic insights into bacterial species. In: Handbook of  Molecular Microbial Ecology II: Metagenomics in Different Habitats. Frans J. de Bruijn (Editor) John Wiley & Sons, Inc. Hoboken, New Jersey, USA.

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  13. Turnbaugh PJ, Ley RE, Mahowald MA, Magrini V, Mardis ER, et al. (2006) An obesity-associated gut microbiome with increased capacity for energy harvest. Nature. 444: 1027-1031

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