Haliscomenobacter hydrossis and Type 0961...

Haliscomenobacter hydrossis is another Eikelboom type which can be taxonomically positioned in the order Chlamydobacterriales. The microorganism isolated from activated sludge by an author was characterized by other two authors as a sheathed bacterium with small cells O.35-O.45 micro-m in diameter and with real branching. Another distinguishing feature specified by two researchers is the formation of carotenoid pigments. While the presence of pigments was confirmed by other authors, the branching was not. According to Eikelboom, Haliscomenobacter hydrossis has small, "unbranched", straight filaments protruding from flocs like needles. An author described the activated sludge floc with Haliscomenobacter hydrossis filaments as "pins in a pincushion". Eikelboom's description of Haliscomenobacter hydrossis strongly resembles a filamentous microorganism often found in Czech activated sludge plants and described as Pelonema subtilissimum.

Haliscomenobacter hydrossis isolated from activated sludges is able to utiltic most readily biodegradable substrates. The growth of Haliscomenobacter hydrossis isolates from the Berlin-Ruhleben wastewater treatment plant was positively affected by an icreased concentration of calcium ions in the cultivation medium. Haliscomenobacter hydrossis is Gram negative, and the cells do not contain any volutine, sudanophilic and sulphur granules. Haliscomenobacter hydrossis is able to reduce nitrate to nitrite but the ability to perform a complete denitrification is not reported. The growth of Haliscomenobacter hydrossis is strongly limited by increased values of pH. Some authors described a case when Haliscomenobacter hydrossis could not compete with a mixed culture with the floc-forming bacterium Arthrobacter globiformis at pH values higher than 9.

The basic kinetic parameters (for glucose) which can be found in the literature for Haliscomenobacter hydrossis are as follows:

µmax (1 / day)	1.2 - 2.2
Ks (mg / L)	5
Y (mg / mg)	0.59
m (mg / mg . day)	0.48 - 0.5

Finally, a practical suggestion for microscopic observation. The trichomes of Haliscomenobacter hydrossis are so subtle that in a common microscope without phase contrast this microorganism can be easily overlooked, especially by untrained eyes.

Type 0961 is characterized by long straight filaments (under normal growth conditions, several hundred micrometers) with a diameter up to about 1.5 micrometers. The individual cells are rectangular and the trichomes can be covered by a slime coating, which is not considered a true sheath. A characteristic feature in phase contrast light is that the trichomes appear very transparent.

Some researchers examined the properties and behaviour of, among others, Type 0961 in a full - scale study at the Gold Bar wastewater treatment plant in Edmonton, Canada. According to their results, Type 0961 is an organotrophic microorganism requiring oxygen as an electron donor. They found that Type 0961 dominated the biocenosis of activated sludge at Gold Bar during periods of dry weather flow and increased wastewater strength, while this activity was not significant during wet weather flow. They also came to a very promising conclusion from their full - scale experiments with the hydraulic regime of aeration basins - the growth of Type 0961 was suppressed when a substrate concentration gradient was introduced and the degree of axial mixing in the experimental basin was decreased.

Experiments carried out by two researchers proved that Type 0961 significantly decreases its metabolic activity (measured as respiration rate) when it is exposed to alternating feed and fast cultivation conditions. In addition, Type 0961 responded to the prolonged period of starvation in the cultivation cycle with a change of morphology. The trichomes, initially longer than 500 micro - m, shortened and finally Type 0961 grew in the form of individual cells of approximately 5 micro - m in length.

They also measured the basic kinetic parameters of Type 0961. However, their figures look unrealistically high. Thus the values used by two authors for modelling the growth of Type 0961 seem to be more appropriate for readily biodegradable substrates. Those values (in COD units) are:

µmax (1 / day)	1.7
b (1 / day)	0.1
Ks	0.5
KDO	0.1
Y (mg / mg)	0.67