Chemistry Reference
In-Depth Information
Various types of microorganisms are found around the mangrove habitats. For example,
diverse cyanobacterial communities reside on leaf, root litter, live roots, and often form
extensive mats on the surrounding sediments; many of these communities are capable of
fixing atmospheric nitrogen. Many genera widespread in these habitats including
Oscillatoria
,
Lyngbya
,
Phormidium
and
Microcoleus
are, and as heterocystous genera,
Scytonema
is common in some areas [76]. The filamentous cyanobacterium
Microcoleus
sp.was
isolated and inoculated on to young mangrove seedlings. Such cyanobacterial filaments
colonize the roots of mangrove by gradual production of biofilm [77]. Also, bacteria may
influence the mangrove ecosystem directly; they contribute inevitably in the recycling of
nutrients [78]. Many potential bacteria were isolated from mangrove ecosystem such as
nitrogen-fixers, phosphate solubilizers, photosynthetic anoxygenic sulfur bacteria,
methanogenic and methane oxidizing bacteria, which are involved in efficient nutrient
recycling [79]. Also bacteria and fungi that either produce antibiotics [80, 81] or resistant to
antibiotics were isolated from mangrove ecosystem [82, 83].
4.2. Halophytes
Salt-tolerant microorganisms can grow in habitats containing high concentrations of salts.
The natural environments for salt-tolerant microbes may be similar to those of the
halophytic angiosperms. The chemical analysis of the materials excreted by the epidermal
glands of halophytes revealed the presence of mineral elements and some organic
compounds, such substances might be a source of nutrition to the microorganisms living on
the plant body [84]. A study on the desert plants of Egypt [85] indicated that the fungal
species inhabiting the surface of senescent leaves of the succulent halophyte
Zygophyllum
album
L. appeared to be adapted to stressful conditions of their microhabitats, namely high
convective heat, dry conditions and high salt content of their leachates. In the study of [84]
on some halophyte species growing at the Qatar North East coast showed that the total
bacterial count in the rhizosphere was higher than in the non-rhizosphere soil. Moreover,
the bacterial counts in the soil supporting the plant species of the coastal zone were higher
than those in the soil of the inland zones. Also, Gram- positive cocci predominated in the
isolates from rhizosphere and non-rhizosphere soil, and the isolates with white colonies
color predominated in the rhizosphere than from phyllosphere since low colonization of
bacterial cells were found on the aerial parts that have high contents of mineral ions due to
the activity of salt glands in most Halophytes. Also, the bacterial counts were higher on the
green parts of the plant than on the senescent parts, since the latter might have accumulated
high concentrations of mineral ions as a mechanism to exclude salt to the aged parts of the
plants compared to the growing ones. Moreover, the phyllosphere of the green and
senescing parts were characterized by the predominance of Gram-positive bacilli and by the
low percentage of isolates producing colored colonies. The general conclusion that can
drawn from various published studies that soil environment and phyllosphere of
halophytes support the growth of bacteria which seemed to have various mechanisms to
deal with the harsh environments like salt marshes and sabkhas. In fact, bacteria are the
most abundant inhabitants of the phyllosphere and the most colonists of leaves. On the
other hand, the bacterial flora of the above ground differs substantially from that at the
